Grosz & Sidner (1986)

7/17/2019 Grosz & Sidner (1986)

http://slidepdf.com/reader/full/grosz-sidner-1986 1/30

A T T E N T I O N , I N T E N T I O N S , A N D T H E S T R U C T U R E O F D I S C O U R S E

B a r b a r a J . G r o s z

A r t i f i c i a l I n t e l l i g e n c e C e n t e r a n d

C e n t e r f o r t h e S t u d y o f L a n g u a g e a n d I n f o r m a t i o n

S R I I n t e r n at i o n a l

M e n l o P a r k, C A 9 4 0 2 5

C a n d a c e L . S i d n e r

B B N L a b o r a t o r i e s I n c .

C a m b r i d g e , M A 0 2 2 3 8

I n t h i s p a p e r w e e x p l o r e a n e w t h e o r y o f d i s c o u r s e s t r u c t u r e t h a t s t r e s s e s t h e r o l e o f p u r p o s e a n d

p r o c e s s i n g i n d i s c o u r se . I n t h is t h e o r y , d i s c o u r s e s t r u c t u r e i s c o m p o s e d o f t h r e e s e p a r a t e b u t i n t e r r e -

l a t e d c o m p o n e n t s : t h e s t r u c t u r e o f t h e s e q u e n c e o f u t t e r a n c e s ( c a l l e d t h e l i n g u i s t i c s t r u c t u r e ) , a s t r u c -

t u r e o f p u r p o s e s ( c a l l e d t h e i n t e n t i o n a l s t r u c t u r e ) , a n d t h e s t a t e o f f o c u s o f a t t e n t i o n ( c a l l e d t h e

at ten t ion a l s ta te ) . T h e l i n g u i s t i c s t r u c t u r e c o n s i s t s o f s e g m e n t s o f t h e d i s c o u r s e i n t o w h i c h t h e u t t e r -

a n c e s n a t u r a l ly a g g r e g a t e . T h e i n t e n t io n a l s t r u c t u r e c a p t u r e s t h e d i s c o u r s e - r e l e v a n t p u r p o s e s ,

e x p r e s s e d i n e a c h o f t h e l in g u is t ic s e g m e n t s a s w e ll a s r e l a t io n s h i p s a m o n g t h e m . T h e a t t e n t i o n a l s t a t e

i s a n a b s t r a c t i o n o f t h e f o c u s o f a t t e n t i o n o f t h e p a r t i c i p a n t s a s t h e d i s c o u r s e u n f o ld s . T h e a t t e n t i o n a l

s t a t e , b e i n g d y n a m i c , r e c o r d s t h e o b j e c t s , p r o p e r t i e s , a n d r e l a t i o n s t h a t a r e s a l i e n t a t e a c h p o i n t o f t h e

d i s c o u r s e . T h e d i s t i n c ti o n a m o n g t h e s e c o m p o n e n t s i s e s s e n t i a l t o p r o v i d e a n a d e q u a t e e x p l a n a t i o n o f

s u c h d i s c o u r s e p h e n o m e n a a s c u e p h r a s e s , r e f e r r i n g e x p r e s s i o n s , a n d i n t e r r u p t i o n s .

T h e t h e o r y o f attent ion , in tent ion , a n d a g g r e g a t i o n o f u t t e r a n c e s i s i l l u s t r a t e d i n t h e p a p e r w i t h a

n u m b e r o f e x a m p l e d i s c o u r se s . V a r i o u s p r o p e r t i e s o f d is c o u r s e a r e d e s c r i b e d , a n d e x p l a n a t i o n s f o r t h e

b e h a v i o r o f c u e p h r a s e s , r e f e r r i n g e x p r e s s i o n s , a n d i n t e r r u p t i o n s a r e e x p l o r e d .

T h i s t h e o r y p r o v i d e s a f r a m e w o r k f o r d e s c r i bi n g t h e p r o c e s s i n g o f u t t e r a n c e s i n a d i s c o u rs e .

D i s c o u r s e p r o c e s s i n g r e q u i r e s r e c o g n i z i n g h o w t h e u t t e r a n c e s o f t h e d i s c o u r s e a g g r e g a t e i n t o s e g m e n t s ,

r e c o g n i z in g t h e i n t e n t i o n s e x p r e s s e d i n t h e d i s c o u r s e a n d t h e r e l a t i o n s h ip s a m o n g i n te n t i o n s , a n d t r a c k -

i n g t h e d i s c o u rs e t h r o u g h t h e o p e r a t i o n o f t h e m e c h a n i s m s a s s o c i a t e d w i t h a t t e n t i o n a l s t a t e . T h i s

p r o c e s s i n g d e s c r i p t i o n s p e c i f i e s i n t h e s e r e c o g n i t i o n t a s k s t h e r o l e o f i n f o r m a t i o n f r o m t h e d i s c o u r s e

a n d f r o m t h e p a r t i c i p a n t s ' k n o w l e d g e o f t h e d o m a i n .

1 INTRODUCTION

p a p e r p r e s e n t s t h e b a si c e l e m e n t s o f a c o m p u t a -

t h a t s i m p f if i e s a n d

w o r k . B y s p e c i fy i n g t h e b a s i c

u t t e r a n c e i n t h e d i s c o u rs e m u s t b e r e l a te d .

A n a c c o u n t o f d i s c o u r s e s t r u c t u r e i s c l o s e l y r e l a t e d t o

t w o q u e s t i on s : W h a t i n d i v i d u a t e s a d i s c o u r s e ? W h a t

m a k e s i t c o h e r e n t ? T h a t i s , f a c e d w i t h a s e q u e n c e o f

u t t e ra n c e s , h o w d o e s o n e k n o w w h e t h e r t h e y c o n s t it u t e a

s i n gl e d i sc o u r s e , s e v e r a l ( p e r h a p s i n t e r l e a v e d ) d i s c o u r s e s ,

o r n o n e ? A s w e d e v e l o p i t, t h e t h e o r y o f d i s c o u rs e s t r u c -

t u r e w i l l b e s e e n t o b e i n t i m a t e l y c o n n e c t e d w i t h t w o

n o n l i ng u i s ti c n o ti o n s : i n t e n t io n a n d a t t e n t io n . A t t e n t i o n

i s a n e s s e n t i a l f a c t o r i n e x p l i c a t i n g t h e p r o c e s s i n g o f

u t t e r a n c e s i n d i s c o u r se . I n t e n t i o n s p l a y a p r i m a r y r o l e i n

e x p l a i n i n g d i s c o u r s e s t r u c t u r e , d e f i n i n g d i s c o u r s e c o h e r -

e n c e , a n d p r o v i d i n g a c o h e r e n t c o n c e p t u a l i z a t i o n o f t h e

t e r m d i s c o u r s e i t s e l f .

h t 1 9 8 6 b y t h e A s s o c i a t i o n f o r C o m p u t a t i o n a l L i n g u i s t i c s. P e r m i s s i o n t o c o p y w i t h o u t f e e a l l o r p a r t o f t h i s m a t e r i a l is g r a n t e d p r o v i d e d t h a t

CL r e f e r e n c e a n d t h i s c o p y r i g h t n o t i c e a r e in c l u d e d o n t h e f i rs t p a ge . T o c o p y

e s a f e e a n d / o r s p e c if i c p e r m i s s io n .

0 3 6 2 - 6 1 3 X / 8 6 / 0 3 0 1 7 5 - 2 0 4 5 0 3 . 0 0

n a l L i n g ui s ti c s , V o l u m e 1 2 , N u m b e r 3 , ~ l u l y - S e pt e m b e r 1 9 8 6 1 7 5

7/17/2019 Grosz & Sidner (1986)


B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f Dis

T h e t h e o r y i s a f u r t h e r d e v e l o p m e n t a n d i n t e g r a t i o n o f

t w o l i n e s o f r e s e a r c h : w o r k o n f o c u s i n g i n d i s c o u r s e

( G r o s z 1 9 7 8a , 1 9 7 8 b , 1 9 8 1 ) a n d m o r e r e c e n t w o r k o n

i n t e n t i o n r e c o g n i t i o n i n d i s c o u r s e ( S i d n e r a n d I s r a e l

1 9 8 1 ; S i d n e r 1 9 8 3; 1 9 8 5 ; A l l e n 1 9 8 3 , L i t m a n 1 9 8 5 ;

P o l l a c k 1 9 8 6 ) . O u r g o a l h a s b e e n t o g e n e r a l i z e t h e s e

c o n s t r u c t s p r o p e r l y t o a w i d e r a n g e o f d i s c o u r s e t y p e s .

G r o s z ( 1 9 7 8 a ) d e m o n s t r a t e d t h a t t he n o t i o n s o f fo c u s in g

a n d t a s k s t r u c t u r e a r e n e c e s s a r y f o r u n d e r s t a n d i n g a n d

p r o d u c i n g t a s k - o r i e n t e d d i a l og u e . O n e o f t h e m a i n

g e n e r a l i z a t i o n s o f p r e v i o u s w o r k w i l l b e t o s h o w t h a t

d i s c o u r s e s a r e g e n e ra l l y i n s o m e s e n s e t a s k - o r i e n t e d ,

b u t th e ki n d s o f t a s k s t h a t c a n b e e n g a g e d in a r e q u i t e

v a r i e d - s o m e a r e p h y s i c a l, s o m e m e n t a l , o t h e r s l i n g u is -

t ic . C o n s e q u e n t l y , t he t e r m t a s k i s m i s l e a d i n g ; w e

t h e r e f o r e w i l l u s e t h e m o r e g e n e r a l t e r m i n o l o g y o f

in tent ions

( e .g . , w h e n s p e a k i n g o f d i s c o ur s e p u r p o s e s ) f o r

m o s t o f w h a t w e s a y .

O u r m a i n t h e s i s is th a t t h e s t r u c t u r e o f a n y d i s c o u r s e i s

a c o m p o s i t e o f t h r e e d i s t in c t b u t i n t e r a c t i n g c o m p o n e n t s :

• t h e s t r u c t u r e o f t h e a c t u a l s e q u e n c e o f u t t e r a n c e s i n t h e

d i s c o u r s e ;

• a s t r u c t u r e o f i n t e n t i o n s ;

• a n a t t e n t i o n a l s t a t e .

T h e d i s t i n c t io n a m o n g t h e s e c o m p o n e n t s i s e s s e n t i a l t o

a n e x p l a n a t i o n o f i n t e r r u p t i o n s ( s e e S e c t i o n 5 ) , a s w e l l a s

t o e x p l a n a t i o n s o f t h e u s e o f c e r t a i n t y p e s o f r e f e r r i n g

e x p r e s s i o n s ( s e e S e c t i o n 4 . 2 ) a n d v a r i o u s o t h e r

e x p r e s s i o n s t h a t a f f e c t d i s c o u r s e s e g m e n t a t i o n a n d s t r u c -

t u r e ( s e e S e c t i o n 6 ) . M o s t r e l a t e d w o r k o n d is c o u r s e

s t r u c t u r e ( in c l u d in g R e i c h m a n - A d a r 1 9 8 4 , L i n d e 1 9 7 9 ,

L i n d e a n d G o g u e n 1 9 7 8 , C o h e n 1 9 8 3 ) f a i ls t o d i s ti n -

g u i s h a m o n g s o m e ( o r , i n s o m e c a s e s , a l l ) o f t h e s e

c o m p o n e n t s . A s a r e s u lt , s i g n if i c a n t g e n e r a l i z a t i o n s a r e

l o s t , a n d t h e c o m p u t a t i o n a l m e c h a n i s m s p r o p o s e d a r e

m o r e c o m p l e x t h a n n e c e s s a r y . B y c a r e f u l l y d i s t in g u i s h -

i n g t h e s e c o m p o n e n t s , w e a r e a b l e t o a c c o u n t f o r s i g n i f -

i c a n t o b s e r v a t i o n s i n t h i s r e l a t e d w o r k w h i l e s i m p l i f y i n g

b o t h t h e e x p l a n a t i on s g i v e n a n d c o m p u t a t i o n a l m e c h -

a n i s m s u s e d .

I n a d d i t i o n t o e x p l i c a t i n g t h e s e l i n g u i s t i c p h e n o m e n a ,

t h e t h e o r y p r o v i d e s a n o v e r a l l f r a m e w o r k w i t h i n w h i c h t o

a n s w e r q u e s t i o n s a b o u t t h e r e l e v a n c e o f v a r i o u s

s e g m e n t s o f d i s c o u r s e t o o n e a n o t h e r a n d t o t h e o v e r a l l

p u r p o s e s o f t h e d i s c o u r s e p a r t i c i p a n t s . V a r i o u s p r o p e r -

t i e s o f t h e i n te n t i o n a l c o m p o n e n t h a v e i m p l i c a t i o n s fo r

r e s e a r c h i n n a t u r a l - l a n g u a g e p r o c e s s i n g in g e n e r a l . I n

p a r t i c u l a r , t h e i n t e n t i o n s t h a t u n d e r l i e d i s c o u r s e a r e s o

d i v e r s e t h a t a p p r o a c h e s t o d i s c o u r s e c o h e r e n c e b a s e d o n

s e l e c t in g d i s c o u r s e r e l a t i o n s h i p s f r o m a f i x e d s e t o f a l t e r -

n a t i v e r h e t o r i c a l p a t t e r n s ( e .g . , H o b b s 1 9 7 9 , M a n n a n d

T h o m p s o n 1 9 8 3 , R e i c h m a n 1 9 8 1 ) a r e u n li k e l y t o s u f f ic e .

T h e i n t e n t i o n a l s t r u c t u r e i n t r o d u c e d i n th i s p a p e r

d e p e n d s i n s t e a d o n a s m a l l n u m b e r o f s t r u c t u r a l r e l a t i o n s

t h a t c a n h o l d b e t w e e n i n t e n t i o n s . T h i s s tu d y a l s o r e v e a l s

s e v e r a l p r o b l e m s t h a t m u s t b e c o n f r o n t e d i n e x p a n d i n g

s p e e c h - a c t - r e l a t e d t h e o r i e s ( e . g . , A l l e n a n d P e r r a u l t

1 9 8 0, C o h e n a n d L e v e s q u e 1 9 8 0 , A l l e n 1 9 8 3 ) f r o m

c o v e r a g e o f i n d i v i d u a l u t t e r a n c e s t o c o v e r a g e o f e x t e

s e q u e n c e s o f u t t e r a n c e s i n d is c o u r s e .

A l t h o u g h a d e f i n it i o n o f d i s c o u r s e m u s t a w a i t f u

d e v e l o p m e n t o f t h e t h e o r y p r e s e n t e d i n th is p a p e r ,

p r o p e r t ie s o f th e p h e n o m e n a w e w a n t t o e x p la i n m u

s p e c i f i e d n o w . I n p a r t i c u l a r , w e t a k e a d i sc o u r s e t o

p i e c e o f l a n g u a g e b e h a v i o r t h a t t y p i c a l l y i n v o l v e s m

p l e u t t e r a n c e s a n d m u l t i pl e p a r t i c i p a n t s . A d is c o

m a y b e p r o d u c e d b y o n e o r m o r e o f t h e s e p a r t i c ip a n

s p e a k e r s o r w r i te r s ; t h e a u d i e n c e m a y c o m p r i s e o n

m o r e o f t h e p a r t i c i p a n t s a s h e a r e r s o r r e a d e r s . B e c

i n m u l t i - p a r t y c o n v e r s a t i o n s m o r e t h a n o n e p a r t i c

m a y s p e a k ( o r w r i te ) d i f f e r e n t u t t e r a n c e s w i t h

s e g m e n t , t h e t e r m s s p e a k e r a n d h e a r e r d o n o t d i f f

t i a t e t h e u n i q u e r o l e s t h a t t h e p a r t i c i p a n t s m a i n t a i n

s e g m e n t o f a c o n v e r s a t i o n . W e w il l t h e r e f o r e u s

t e r m s i n i t i a t i n g

conversat ional part ic ipant

( I C P ) a n d

conversat ional part ic ipant s) OCP ) t o d i s t i n g u i s h t h e

a t o r o f a d i s c o u r s e s e g m e n t f r o m i t s o t h e r p a r t i c i p

T h e I C P s p e a k s ( o r w r i t e s ) t h e f i r s t u t t e r a n c e

s e g m e n t , b u t a n O C P m a y b e t h e s p e a k e r o f s o m e s u

q u e n t u t t e r a n c e s . B y s p e a k i n g o f I C P s a n d O C P s , w

h i g h li g h t t h e p u r p o s i v e a s p e c t o f d i s c o u r s e . W e w i

t h e t e r m s speaker a n d hearer o n l y w h e n t h e p a r t i

s p e a k i n g / h e a r i n g a c t i v i t y i s i m p o r t a n t f o r t h e p o i n t

m a d e .

I n m o s t o f t h i s p a p e r , w e w i l l b e c o n c e r n e d

d e v e l o p i n g a n a b s t r a c t m o d e l o f d i s c o u r s e s t r u c t u r

p a r t i c u la r , t h e d e f i n i t i o n s o f t h e c o m p o n e n t s w i l l a b s

a w a y f r o m t h e d e t a i ls o f t h e d i s c o u r s e p a r t i c i p

W h e t h e r o n e c o n s t r u c t s a c o m p u t e r s y s t e m t h a t

p a r t i c i p a t e i n a d i s c o u r s e ( i . e . , o n e t h a t is a l a n g

u s e r ) o r d e f i n e s a p s y c h o l o g i c a l t h e o r y o f l a n g u a g e

t h e t a s k w i ll r e q u ir e t h e a p p r o p r i a t e p r o j e c t i o n o f

a b s t r a c t m o d e l o n t o p r o p e r t i e s o f a l a n g u a g e u s e r ,

s p e c i f i c a t i o n o f a d d i t io n a l d e t a i l s ( e . g ., s p e c i f y i n g m

r y f o r li n g ui s ti c s t r u c t u r e , m e a n s f o r e n c o d i n g a t t e n t

s t a t e , a n d a p p r o p r i a t e r e p r e s e n t a t i o n s o f i n t e n t

s t r u c t u r e ) . W e d o , h o w e v e r , a d d r e s s o u r s e l v e s d i r e c

c e r t a i n p r o c e s s i n g i s s u e s t h a t a r e e s s e n t i a l t o t h e c o

t a t i o n a l v a l i d i ty o f t h e [ a b s t r a c t ] m o d e l a n d t o i t s u t

t i o n f o r a l a n g u a g e - p r o c e s s i n g s y s t e m o r p s y c h o l o

t h e o r y .

F i n a l ly , i t i s i m p o r t a n t t o n o t e t h a t a l t h o u g h d i s c

mean ing

i s a s i g n i f i c a n t , u n s o l v e d p r o b l e m , w e w i l

a d d r e s s i t i n t h is p a p e r . A n a d e q u a t e t h e o r y o f d i s c

m e a n i n g n e e d s t o r e s t a t l e a s t p a r t i a l l y o n a n a d e q

t h e o r y o f d i s c o u r s e s t r u c t u re . O u r c o n c e r n i s w i t h p r

i n g t h e l a t t e r .

T h e n e x t s e c t i o n e x a m i n e s t h e b a s i c t h e o r

d i s c o u r s e s tr u c t u r e a n d p r e s e n t s a n o v e r v i e w o f e a

t h e c o m p o n e n t s o f d is c o u r s e s t r u c t u r e . S e c t i o

a n a l y z e s t w o s a m p l e d i s c o u r s e s - a w r i t t e n t e x t a

f r a g m e n t o f t a s k - o r i e n t e d d i al o g ue - f r o m t h e p e r

t i v e o f t h e t h e o r y b e i n g d e v e l o p e d ; t h e s e t w o e x a m

a r e a l s o u s e d t o i l l u s t r a t e v a r i o u s p o i n t s i n t h e r e m a

o f t h e p a p e r . S e c t i o n 4 i n v e s t i g a t e s v a r i o u s p r o c e

176

C o m p u t a t i o n a l L i n g u i s t i c s , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r

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J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e

e s t h a t th e t h e o r y r a i s e s. T h e f o l l o w i n g t w o s e c t i o n s

e o f th e d i s c o u r s e s t r u c t u re c o m p o n e n t s

S e c t i o n 7 d e s c r i b e s th e g e n e r a l i z a t i o n

e l t o d i s c o u r s e - l e v e l i n t e n t io n s , e s t a b -

t h e o r y .

2 T H E B A S IC T H E O R Y

a l i n g u is t i c s tr u c t u r e , a n i n t e n t i o n a l s t r u c -

a n d a n a t t e n t i o n a l s ta t e . T h e s e t h r e e c o n s t i t u e n t s

a d i s c o u rs e . U t t e r a n c e s - t h e a c t u a l s a y i n g

a r e t h e l i n g u is t i c s t r u c t u r e ' s b a s i c e l e m e n t s . I n t e n t i o n s

s t r u c tu r e . A t t e n t i o n a l s t a t e c o n t a i n s in f o r m a t i o n

h a t a r e m o s t s a l i e n t a t a n y g i v e n : p o i n t . I t is

a n t s ; i t s e r v e s t o s u m m a r i z e i n f o r m a t i o n f r o m

T o g e t h e r t h e t h r e e c o n s t i t u e n t s o f d i sc o u r s e s t r u c t u r e

t h e i n f o r m a t i o n n e e d e d b y t h e C P s t o d e t e r m i n e

i n e s s e n c e , e n a b l i n g t h e m t o f i g u r e o u t w h y i t

d a n d w h a t i t m e a n s . T h e c o n t e x t p r o v i d e d b y

a n a d d i t io n a l p u r p o s e : n a m e l y , i t f u r n i s h e s

2.1 LINGUI STIC STRUCTU RE

f i rs t c o m p o n e n t o f d is c o u r s e s t r u c t u r e i s t h e s t r u c -

1 J u s t a s t h e w o r d s i n a s i n g le s e n t e n c e f o r m

y a g g r e g a t e d i n t o d is c o u rs e s e g m e n ts . T h e u t t e r -

a r r o l e s w i t h r e s p e c t t o t h a t s e g m e n t . I n a d d i t i o n ,

r e s p e c t t o t h e o v e r a l l d i s c o u rs e . A l t h o u g h

m a y b e i n t h e s a m e d i s c o u r s e

T h e f a c t o r i n g o f d i s c o u r s e s i n to s e g m e n t s h a s b e e n

o b s e r v e d a c r o s s a w i d e r a n g e o f d i s c o u r s e t y p e s . G r o s z

( 1 9 7 8 a ) s h o w e d t h is f o r t a s k - o r i e n t e d d i a l o g ue s . L i n d e

( 1 9 7 9 ) f o u n d i t va l i d f o r d e s c r i p t i o n s o f a p a r t m e n t s ;

L i n d e a n d G o g u e n ( 1 9 7 8 ) d e s c r i b e s u c h s t r u c t u r i n g i n

t h e W a t e r g a t e t ra n s c ri p ts . R e i c h m a n - A d a r ( 1 9 8 4 )

o b s e r v e d i t i n i n f o r m a l d e b a t e s , e x p l a n a t i o n s , a n d t h e r a -

p e u t i c d i s c o u r se . C o h e n ( 1 9 8 3 ) f o u n d s im i l a r s t r u c t u r e s

i n e s s a y s i n r h e t o r i c a l t e x ts . P o l a n y i a n d S c h a ( 1 9 8 6 )

d i s c u s s t h i s f e a t u r e o f n a r r a t i v e s .

A l t h o u g h d i f f e r e n t r e s e a r c h e r s w i t h d i f f e r e n t t h e o r i e s

h a v e e x a m i n e d a v a r i e t y o f d is c o u r s e t y p e s a n d f o u n d

d i s c o u r s e - l e v e l s e g m e n t a t i o n , t h e r e h a s b e e n v e r y l i tt le

i n v e s t i g a ti o n o f t h e e x t e n t o f a g r e e m e n t a b o u t w h e r e t h e

s e g m e n t b o u n d a r i e s li e. T h e r e h a v e b e e n n o p s y c h o l o g -

i c a l s t u d i e s o f t h e c o n s i s t e n c y o f r e c o g n i t i o n o f s e c t i o n

b o u n d a ri e s . H o w e v e r , M a n n ( M a n n e t a l. 1 9 75 ) a s k e d

s e v e r a l p e o p l e t o s e g m e n t a s e t o f d ia l o g u e s . H e h a s

r e p o r t e d [ p e r s o n a l c o m m u n i c a t i o n ] t h a t h i s s u b j e c t s

s e g m e n t e d t h e d i s c o u r se s a p p r o x i m a t e l y t h e s a m e ; t h e i r

d i s a g r e e m e n t s w e r e a b o u t u t t e r a n c e s a t t h e b o u n d a r i e s o f

s e g m e n t s . 2 S e v e r a l s t u d i e s o f s p o n t a n e o u s l y p r o d u c e d

d i s c o u r s e s p r o v i d e a d d i t i o n a l e v i d e n c e o f t h e e x i s t e n c e o f

s e g m e n t b o u n d a r i e s , a s w e l l a s s u g g e s t in g s o m e o f t h e

l i ng u i st i c c u e s a v a i l a b le f o r d e t e c t i n g b o u n d a r i e s . C h a f e

( 1 9 7 9 , 1 9 8 0 ) f o u n d d i f f e r e n c e s i n p a u s e l e n g t h s a t

s e g m e n t b o u n d a ri e s . B u t t e r w o r t h ( 1 9 7 5 ) f o u n d s p e e c h

r a t e d i f f e r e n c e s t h a t c o r r e l a t e d w i t h s e g m e n t s ; s p e e c h

r a t e i s s l o w e r a t s t a r t o f a s e g m e n t t h a n t o w a r d t h e e n d .

T h e l i n g u i s t i c s t r u c t u r e c o n s i s t s o f t h e d i s c o u r s e

s e g m e n t s a n d a n e m b e d d i n g r e l a t i o n s h i p t h a t c a n h o l d

b e t w e e n t h e m . A s w e d i s c u s s i n S e c t i o n s 2 . 2 a n d 5 , t h e

e m b e d d i n g r e l a t i o n s h i p s a r e a s u r f a c e r e f l e c t i o n o f

r e l a t i on s h i p s a m o n g e l e m e n t s o f t h e i n t e n t i o n a l s t r u c tu r e .

I t i s i m p o r t a n t t o r e c o g n i z e t h a t t h e l i n g u i s ti c s t r u c t u r e i s

n o t s t r ic t l y d e c o m p o s i t i o n a l . A n i n d i v id u a l s e g m e n t m a y

i n c lu d e a c o m b i n a t i o n o f s u b s e g m e n t s a n d u t t e r a n c e s

o n l y i n th a t s e g m e n t ( a n d n o t m e m b e r s o f a n y o f i t s

e m b e d d e d s u b s e g m e n t s ) . B o t h o f t h e e x a m p l e s i n S e c ti o n

3 e x h i b i t s u c h n o n s t r i c t d e c o m p o s i t i o n a l i t y . B e c a u s e t h e

l i n g u i s t i c s t r u c t u r e i s n o t s t r i c t l y d e c o m p o s i t i o n a l , v a r i o u s

p r o p e r t i e s o f t h e d i s c o u r s e ( m o s t n o t a b l y t h e i n t e n t i o n a l

s t r u c t u r e ) a r e f u n c t i o n s o f p r o p e r t i e s o f i n d i v i du a l u t t e r -

a n c e s a n d p r o p e r t i e s o f s e g m e n t s .

T h e r e i s a t w o - w a y i n t e r a c t i o n b e t w e e n t h e d i s c o u r s e

s e g m e n t s t r u c t u r e a n d t h e u t t e r a n c e s c o n s t i t u t i n g t h e

d i s c o u r se : l in g u is t ic e x p r e s s i o n s c a n b e u s e d t o c o n v e y

i n f o r m a t i o n a b o u t t h e d i s c o u r s e s t r u c t u r e ; c o n v e r s e l y ,

t h e d i s c o u r s e s t r u c t u r e c o n s t r a i n s t h e i n t e r p r e t a t i o n o f

e x p r e s s i o n s ( a n d h e n c e a f f e c t s w h a t a s p e a k e r s a y s a n d

h o w a h e a r e r w i l l i n t e r p r e t w h a t i s s a i d ). N o t s u r p r i s i n g -

l y , l i n g u i s t i c e x p r e s s i o n s a r e a m o n g t h e p r i m a r y i n d i c a -

t o r s o f d i s c o u r s e s e g m e n t b o u n d a r i e s . T h e e x p l ic i t u s e o f

c e r t a i n w o r d s a n d p h r a s e s ( e . g . ,

in the f i rs t p lace)

a n d

m o r e s u b t l e c u e s , s u c h a s i n t o n a t i o n o r c h a n g e s i n t e n s e

a n d a s p e c t , a r e i n c l u d e d i n t h e r e p e r t o i r e o f l i n g u i s t i c

d e v i c e s t h a t f u n c t i o n , w h o l l y o r i n p a r t , t o i n d i c a t e t h e s e

1986 177

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Barbara J . Grosz and Candace L . S idner At tent ion , In tent ions , and the S tructure of Disc

boundaries (Grosz 1978a, Reichman-Adar 1984, Cohen

1983, Polanyi and Scha 1983, Hirschberg and Pierre-

humbert 1986). Reichm an (1981) discusses some words

that function in this way and coined the term

c l u e w o r d s .

We will use the term

c u e p h r a s e s

to generalize on her

observation as well as many others because each one of

these devices cue the hearer to some change in the

discourse structure.

As discussed in Section 6, these linguistic boundary

markers can be divided according to whether they explic-

itly indicate changes in the intentional structure or in the

attentional state of the discourse. The differential use of

these linguistic markers provides one piece of evidence

for considering these two components to be distinct.

Because these linguistic devices function explicitly as

indicators of discourse structure, it becomes clear that

they are best seen as providing information at the

discourse level, and not at the sentence level; hence,

certain kinds of questions (e.g., about their contribution

to the truth conditions of an individual sentence) do not

make sense. For example, in the utterance

I nc iden ta l l y ,

Jane swims every day ,

the

inc iden ta l l y

indicates an inter-

ruption of the main flow of discourse rather than affect-

ing in any way the meaning of

Jane swims every day .

Jane's swimming every day could hardly be fortuitous.

Just as linguistic devices affect structure, so the

discourse segmentation affects the interpretation of

linguistic expressions in a discourse. Refe rrin g

expressions provide the primary example of this effect. 3

The segmentation of discourse constrains the use of

referring expressions by delineating certain points at

which there is a significant change in what entities

(objects, properties, or relations) are being discussed.

For example, there are different constraints on the use of

pronouns and reduced definite-noun phrases within a

segment than across segment boundaries. While

discourse segmentation is obviously not the only factor

governing the use of referring expressions, it is an impor-

tant one.

2.2 INTENTIONAL STRUCTUR E

A rather straightforward property of discourses, namely,

that they (or, more accurately, those who participate in

them) have an overall purpose, turns out to play a funda-

mental role in the theory of discourse structure. In

particular, some of the purposes that underlie discourses,

and their component segments, provide the means of

individuating discourses and of distinguishing discourses

that are cohere nt from those that are not. These

purposes also make it possible to determine when a

sequence of utterances comprises more than one

discourse.

Although typically the participants in a discourse may

have more than one aim in participating in the discourse

(e.g., a story may entertain its listeners as well as

describe an event; an argument may establish a person's

brilliance as well as convince someone that a claim or

allegation is true), we distinguish one of these purp

as foundational to the discourse. We will refer to it as

d i s c o u r s e p u r p o s e (DP). From an intuitive perspective

discourse purpose is the intention that underlies enga

in the particular discourse. This intention provides

the reason a discourse (a linguistic act), rather than s

other action, is being performed and the reason

particular content of this discourse is being conv

rather than some other information. For each of

discourse segments, we can also single out one inten

- t h e d i sc o u r s e s e g m e n t p u r po s e

(DSP). Fr om an intu

standpoint, the DSP specifies how this segment con

utes to achieving the overall discourse purpose.

assumption that there are single such intentions wi

the end prove too strong. However, this assump

allows us to describe the basic theory more clearly.

must leave to future research (and a subsequent pa

the exploration and discussion of the complications

result from relaxing this assumption.

Typically, an ICP will have a num ber of differ ent k

of intentions that lead to initiating a discourse. One

might include intentions to speak in a certain languag

to utter certain words. Anot her might include intent

to amuse or to impress. The kinds of intentions that

serve as discourse purposes or discourse segm

purposes are distinguished from other intentions by

fact that they are intended to be recognized (cf. A

and Perrault 1980, Sidner 1985), whereas o

intentions are private; that is, the recognition of the

or DSP is

essent ial

to its achieving its intended ef

Discourse purposes and discourse segment purp

share this property with certain utterance-level intent

that Grice (1969) uses in defining utterance mea

(see Section 7).

It is important to distinguish intentions that

intended to be recognized from other kinds of intent

that are associated with discourse. Intentio ns that

intended to be recognized achieve their intended e

only if the intention is recognized. For exampl

compliment achieves its intended effect only if the in

tion to compliment is recognized; in contrast, a scream

boo

typically achieves its intended effect (scaring

hearer) without the hearer having to recognize the sp

er's intention.

Some intention that is private and not intended to

recognized may be the primary motivation for an IC

begin a discourse. For example, the ICP may inten

impress someone or may plan to teach someone.

neither case is the ICP's intention necessarily intende

be recognized. Quite the opposite may be true in

case of impressing, as the ICP may not want the OC

be aware of his intention. When teaching, the ICP

not care whether the OCP knows the ICP is teaching

or her. Thus, the intention that motivates the IC

engage in a discourse may be private. By contrast,

discourse segment purpose is always intended to

recognized.

178 C o m p u t a t i o n a l L i n g u i s t i c s , V o l u m e 12 , N u m b e r 3 , J u l y - S e p t e m b e r

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B a r b a r a J . G r o s z a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e

DPs and DSPs are basically the same sorts of

intentions. If an intention is a DP, then its satisfaction is a

main purpose of the discourse, whereas if it is a DSP,

then its satisfaction contributes to the satisfaction of the

DP. The following are some of the types of intentions

that could serve as DP/DSPs, followed by one example of

each type.

1. Intend that some agent intend to perfor m some phys-

ical task. Examp le: I n t e n d t h a t R u t h i n t e n d to f i x t h e

f l a t t ir e .

2. Intend that some agent believe some fact. Example:

I n t e n d t h a t R u t h b e l ie v e t h e c a m p f i r e h a s s t ar t e d.

3. Intend that some agent believe that one fact supports

another. Example:

l n t e n d t h a t R u t h b e l i e v e t h e s m e l l

o f s m o k e p r o v i d e s e v i d e n c e t h a t t h e c a m p f i r e i s s t a rt e d .

4. Intend that some agent intend to identify an object

(existing physical object, imaginary object, plan,

event, event sequence). Example: I n t e n d t h a t R u t h

in t en d t o i d en t i f y m y b i c yc l e .

5. Intend that some agent know some property of an

object. Example:

I n t e n d t h a t R u t h k n o w t h a t m y b ic y -

c l e h a s a f l a t t ir e .

We have identified two structural relations that play

an important role in discourse structure: dominance and

s a t i s f a c t i o n - p r e c e d e n c e . An action that satisfies one

intention, say DSP1, may be intended to provide part of

the satisfact ion of anothe r, say DSP2. Whe n this is the

case, we will say that DSP1 c o n t r i b u t e s t o DSP2;

conversely, we will say that DSP2 d o m i n a t e s DSP1 ( o r

DSP2 D O M DSP1). The dominance relation invokes a

partial ordering on DSPs that we will refer to as the domi-

nance h ie r a r c h y . For some discourses, including task-or-

iented ones, the order in which the DSPs are satisfied

may be significant, as well as being intended to be recog-

nized. We will say that DSP1 satisfaction- precedes DSP2

(or, DSP1

S P

DSP2) whenever DSP1 must be satisfied

bef ore DSP2. 4

Any of the intentions on the preceding list could be

either a DP or a DSP. Furt her more , a given instance o f

any one of them could contribute to another, or to a

different, instance of the same type. For example, the

intention that someone intend to identify some object

might dominate several intentions that she or he know

some property of that object; likewise, the intention to

get someone to believe some fact might dominate a

number of contributing intentions that that person

believe other facts.

As the above list makes clear, the range of intentions

that can serve as discourse, or discourse segment,

purposes is open- ended (cf. Wittgenstein 1953: para-

graph 23), much like the range of intentions that underlie

more general purposeful action. There is no finite list of

discourse purposes, as there is, say, of syntactic catego-

ries. It remains an unresolved research question whether

there is a finite description of the open-ended set of such

intentions. However, even if there were finite

descriptions, there would still be no finite list of

intentions from which to choose. Thus, a theor y of

discourse structure cannot depend on choosing the

DP/DSPs from a fixed list (cf. Reichman-Adar 1984,

Schank et al. 1982, Mann and Thompson 1983), nor on

the particulars of individual intentions. Althoug h the

particulars of individual intentions, like a wide range of

common sense knowledge, are crucial to understanding

any discourse, such particulars cannot serve as the basis

for

d e t e r m i n i n g

discourse structure.

What is essential for discourse structure is that such

intentions bear certain kinds of structural relationships to

one another. Since the CPs can never know the whole

set of intentions that,might serve as DP/DSPs, what they

must recognize is the relevant structural relationships

among intentions. Although there is an infinite numbe r

of intentions, there are only a small number of relations

relevant to discourse structure that can hold between

them.

In this paper we distinguish between the

d e t e r m i n a t i o n

of the DSP and the

rec o g n i t i o n

of it. We use the term

d e t e r m i n a t i o n

to refer to a semantic-like notion, namely,

the complete specification of what is int ende d by whom;

we use the term recognition to refer to a processing

notion, namely, the processing that leads a discourse

participant to identify what the intention is. These are

obviously related concepts; the same information that

determines a DSP may be used by an OCP to recognize it.

However, some questions are relevant to only one of

them. For example, the question of when the informa-

tion becomes available is not relevant to determination

but is crucial to recognition. An analogous distinction

has been drawn with respect to sentence structure; the

parse tree (determination) is differentiated from the pars-

ing process (recognition) that produces the tree.

2 .3 A T T E N T I O N A L S T A T E

The third component of discourse structure, the atten-

tional state, is an abstraction of the participants' focus of

attention as their discourse unfolds. The attentional state

is a property of the discourse itself, not of the discourse

participants. It is inherently dynamic, recording the

objects, properties, and relations that are salient at each

point in the discourse. The attentional state is modeled

by a set of f o c u s s p a c e s ; changes in attentional state are

modeled by a set of transition rules that specify the

conditions for adding and deleting spaces. We call the

collection of focus spaces available at any one time the

f o c u s i n g s t r u c t u r e and the process of manipulating spaces

f o c u s i n g .

The focusing process associates a focus space with

each discourse segment; this space contains those entities

that are salient - either because they have been

mentioned explicitly in the segment or because they

became salient in the process of producing or compre-

hending the utterances in the segmfnt (as in the original

work on focusing: Gros z 1978a). The focus space also

includes the DSP; the inclusion of the purpose reflects the

C o m p u t a t i o n a l

Ling u is ti cs , V o lu me 1 2 , N u mb er 3 , J u ly - S ep tem b er 1 98 6 1 7 9

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Bar bar a

J . G r o s z

a n d C a n d a e e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s

f a c t t h a t t h e C P s a r e f o c u s e d n o t o n l y o n w h a t t h e y a r e

t a l k in g a b o u t , b u t a l s o o n w h y t h e y a r e t a l k in g a b o u t i t.

T o u n d e r s t a n d t h e a t t e n t i on a l s t a t e c o m p o n e n t o f

d i s c o u r s e s t r u c t u r e , i t i s i m p o r t a n t n o t t o c o n f u s e i t w i t h

t w o o t h e r c o n c e p t s . F i r s t, t h e a t te n t i o n a l s t a t e c o m p o -

n e n t i s n o t e q u i v a l e n t t o c o g n i t i v e s t a t e , b u t i s o n l y o n e

o f i t s c o m p o n e n t s . C o g n i t i v e s t a t e i s a r i c h e r s t r u c t u r e ,

o n e t h a t i n c l u d e s a t l e a s t t h e k n o w l e d g e , b e l i e f s , d e s i r e s ,

a n d i n t e n t i o n s o f a n a g e n t , a s w e l l a s th e c o g n i t i v e c o r r e - '

l a t e s o f t h e a t t e n t i o n a l s t a t e a s m o d e l e d i n t h i s p a p e r .

S e c o n d , a l t h o u g h e a c h f o c u s s p a c e c o n t a i n s a D S P , t h e

f o c u s s t r u c t u r e d o e s not i n c l u d e t h e i n t e n t i o n a l s t r u c t u r e

a s a w h o l e .

F i g u r e 1 i l l u s t r a t e s h o w t h e f o c u s i n g s t r u c t u r e , i n a d d i -

t i o n t o m o d e l i n g a t t e n t i o n a l s t a t e , s e r v e s d u ri n g p r o c e s s -

i n g t o c o o r d i n a t e t h e l i n g u i s t i c a n d i n t e n t i o n a l s t r u c t u r e s .

T h e d i s c o u r s e s e g m e n t s ( t o t h e l e f t o f t h e f i g u r e ) a r e t i e d

t o f o c u s s p a c e s ( d r a w n v e r t i c a ll y d o w n t h e m i d d l e o f t h e

f i g u re ) . T h e f o c u s i n g s t r u c t u r e i s a s t a c k . I n f o r m a t i o n i n

l o w e r s p a c e s i s us u a l ly a c c e s s i b l e f r o m h i g h e r o n e s ( b u t

l e s s s o t h a n t h e i n f o r m a t i o n i n t h e h i g h e r s p a c e s ) ; w e u s e

a l i n e w i t h i n t e r s e c t i n g h a s h m a r k s t o d e n o t e w h e n t h i s i s

n o t t h e c a se . S u b s c r i p t e d t e r m s a r e u s e d t o i n d i c a t e t he

r e l e v a n t c o n t e n t s o f t h e f o c u s s p a c e s b e c a u s e t h e s p a c e s

c o n t a i n r e p r e s e n t a t i o n s o f e n t i t i e s ( i .e . , o b j e c t s , p r o p e r -

t i e s , a n d r e l a t i o n s ) a n d n o t l i n g u i s t i c e x p r e s s i o n s .

P a r t o n e o f F i g u r e 1 s h o w s t h e s t a t e o f f o c u s i n g w h e n

d i s c o u r s e s e g m e n t D S 2 i s b e i n g p r o c e s s e d . S e g m e n t D S1

g a v e r i s e t o F S 1 a n d h a d a s i t s d i s c o u r s e p u r p o s e D S P I .

T h e p r o p e r t i e s , o b j e c t s , r e l a t i o n s , a n d p u r p o s e r e p r e s -

e n t e d i n F S 1 a r e a c c e s s i b l e b u t l e s s s a l i e n t t h a n t h o s e i n

F S 2 . D S 2 y i e l d s a f o c u s s p a c e t h a t i s s t a c k e d r e l a t i v e t o

F S l b e c a u s e D S P 1 o f D S l d o m i n a t e s D S 2 ' s D SP , D S P2 . As

a r e s u lt o f t h e r e l a t i o n s h ip b e t w e e n F S1 a n d F S 2 , r e d u c e d

n o u n p h r a s e s w i l l b e i n t e r p r e t e d d i f f e r e n t l y i n D S 2 t h a n

i n D S 1. F o r e x a m p l e , i f s o m e r e d b a l l s e x i s t i n t h e w o r l d

o n e o f w h i c h i s r e p r e s e n t e d i n D S 2 a n d a n o t h e r i n F S 1 ,

t h e n the red ball u s e d i n D S 2 w i l l b e u n d e r s t o o d t o m e a n

t h e p a r t i c u l a r r e d b a l l t h a t i s r e p r e s e n t e d i n D S 2 . I f ,

h o w e v e r , t h e r e i s a l s o a g r e e n t r u c k ( i n t h e w o r l d ) a n d i t

i s r e p r e s e n t e d o n l y i n F S 1 ,

the green truck

u t t e r e d i n D S 2

w i ll b e u n d e r s t o o d a s r e f e r r i n g t o t h a t g r e e n t r u c k .

P a r t t w o o f F i g u r e 1 s h o w s t h e s t a t e o f fo c u s i n g w h e n

s e g m e n t D S3 is b e i n g p ro c e s s e d . F S 2 h a s b e e n p o p p e d

f r o m t h e s t a c k a n d F S 3 h a s b e e n p u s h e d o n t o i t b e c a u s e

t h e D S P o f D S 3 , D S P3 , is d o m i n a t e d s o l e l y b y D S P 1, n o t

b y D S P 2. I n t h i s e x a m p l e , t h e i n t e n t i o n a l s t r u c t u r e

i n c lu d e s o n l y d o m i n a n c e r e l a t io n s h i p s , a l th o u g h , i t m a y ,

i n g e n e r a l , a l s o i n c l u d e s a t i s f a c t i o n - p r e c e d e n c e r e l a t i o n -

sh ip s .

T h e s t a c k i n g o f f o c u s s p a c e s r e f l e c t s t h e r e l a t i v e s a l i -

e n c e o f t h e e n t i t i e s i n e a c h s p a c e d u r i n g t h e c o r r e s p o n d -

i n g s e g m e n t ' s p o r t i o n o f t h e d i s c o u r se . T h e s t a c k

r e l a t i o n s h i p s a r i s e f r o m t h e w a y s i n w h i c h t h e v a r i o u s

D S P s r e l a t e ; i n f o r m a t i o n a b o u t s u c h r e l a t i o n s h i p s i s

r e p r e s e n t e d i n t h e d o m i n a n c e h i e r a r c h y ( d e p i c t e d o n t h e

r i g h t i n t h e f i g ur e ) . T h e s p a c e s in F i g u r e 1 a r e s n a p s h o t s

i l lu s t r at i n g t h e r e s u l t s o f a s e q u e n c e o f o p e r a t i o n s , s u c h

a s p u s h e s o n t o a n d p o p s f r o m a s t a c k . A p u s h o c c u r s

w h e n t h e D S P f o r a n e w s e g m e n t c o n t r i b u t e s t o t h e D SP

f o r t h e im m e d i a t e l y p r e c e d i n g se g m e n t . W h e n t h e D S P

c o n t r i b u t e s t o s o m e i n t e n t i o n h i g h e r i n t h e d o m i n a n c e

h i e r a r c h y , s e v e r a l f o c u s s p a c e s a r e p o p p e d f r o m t h e s t a c k

b e f o r e t h e n e w o n e i s i n s e r te d .

T w o e s s e n t i a l p r o p e r t i e s o f t h e f o c u s i n g s t r u c t u r e a r e

n o w c l e a r . F i r s t, t h e f o c u s i n g s t r u c t u r e is p a r a s i t i c u p o n

t h e i n t e n t i o n a l s t r u c t u r e , i n t h e s e n s e t h a t t h e r e l a t i o n -

s h ip s a m o n g D S P s d e t e r m i n e p u s h e s a n d po p s . N o t e

h o w e v e r , t h a t t h e r e l e v a n t o p e r a t i o n m a y s o m e t i m e s b e

i n d i c a t e d i n t h e l a n g u a g e it s e lf . F o r e x a m p l e , t h e c u e

w o r d first o f t e n i n d i c a t e s t h e s t a r t o f a s e g m e n t w h o s e

D S P c o n t r i b u t e s t o t h e D S P o f t h e p r e c e d i n g s e g m e n t .

S e c o n d , t h e f o c u s i n g s t r u c t u r e , l i k e t h e i n t e n t i o n a l a n d

l i n g u is t i c s t r u c t u r e s , e v o l v e s a s t h e d i s c o u r s e p r o c e e d s

N o n e o f t h e m e x i s t s a pr i o ri . E v e n i n t h o s e r a r e c a s e s i n

w h i c h a n I C P h a s a c o m p l e t e p l a n f o r t h e d i s c o u r s e p r i o

t o u t t e r i n g a s i n g l e w o r d , t h e i n t e n t i o n a l s t r u c t u r e i

c o n s t r u c t e d b y th e C P s a s t h e d i s c o u r s e p r o g r e s s e s . T h i s

d i s c o u r s e - t i m e c o n s t r u c t i o n o f t h e i n t e n t i o n a l s t r u c t u r e

m a y b e m o r e o b v i o u s l y tr u e f o r s p e a k e r s a n d h e a r e r s o

s p o k e n d i s c o u r s e t h a n f o r r e a d e r s a n d w r i t e r s o f t e x ts

b u t , e v e n f o r t h e w r i t e r , t h e i n t e n t i o n a l s t r u c t u r e i s d e v e l

o p e d a s t h e t e x t i s b e i n g w r i t t e n .

F i g u r e 1 i l l us t r a te s s o m e f u n d a m e n t a l d i s t i nc t i o n s

b e t w e e n t h e i n t e n t i o n a l a n d a t t e n t i o n a l c o m p o n e n t s o

d i s c o u r s e s t r u c t u r e . F i r s t , t h e d o m i n a n c e h i e r a r c h y

p r o v i d e s , a m o n g o t h e r t h i n g s, a c o m p l e t e r e c o r d o f t h e

d i s c o u r s e - l e v e l i n t e n t i o n s a n d t h e i r d o m i n a n c e ( a s w e l

a s , w h e n r e l e v a n t , s a t i s f a c t i o n - p r e c e d e n c e ) r e l a t i o n s h i p s ,

w h e r e a s t h e f o c u s i n g s t r u c t u r e a t a n y o n e t i m e c a n e s s e n -

t i a l l y c o n t a i n o n l y i n f o r m a t i o n t h a t i s r e l e v a n t t o

p u r p o s e s i n a p o r t i o n o f t h e d o m i n a n c e h i e r a r c h y .

S e c o n d , a t t h e c o n c l u s i o n o f a d i s c o u r s e , i f i t c o m p l e t e s

n o r m a l l y , t h e f o c u s s t a c k w i l l b e e m p t y , w h i l e t h e i n t e n -

t i o n a l s t r u c t u r e w i l l h a v e b e e n f u l ly c o n s t r u c t e d . T h i r d

w h e n t h e d i s c o u r s e i s b e i n g p r o c e s s e d , o n l y t h e a t t e n -

t i o n a l s ta t e c a n c o n s t r a i n t h e i n t e r p r e t a t i o n o f r e f e r r i n g

e x p r e s s i o n s d i r e c t l y .

W e c a n n o w a l s o c l a r i f y s o m e m i s i n t e r p r e t a t i o n s o f

f o c u s - s p a c e d i a g r a m s a n d t a s k s t r u c t u r e i n o u r e a r l i e r

w o r k ( G r o s z 1 9 7 8 a , 1 9 8 1 , 1 9 7 4 ) . T h e f o c u s - s p a c e h i e r -

a r c h i e s in t h a t w o r k a r e b e s t s e e n a s r e p r e s e n t i n g a t t e n -

t i o n a l s t a t e . T h e t a s k s t r u c t u r e w a s u s e d i n t w o w a y s :

1. t o r e p r e s e n t c o m m o n k n o w l e d g e a b o u t t h e t a s k ;

2 . a s a s p e c i a l c a s e o f t h e i n t e n t io n a l s t r u c t u r e w e p o s i

i n t h i s p a p e r .

A l t h o u g h t h e s a m e r e p r e s e n t a t i o n a l s c h e m e w a s u s e d f o r

e n c o d i n g t h e f o c u s - s p a c e h i e r a r c h i e s a n d t h e t a s k s t r u c -

t u r e ( p a r t i t i o n e d n e t w o r k s : H e n d r i x 1 9 7 9 ) , t h e t w o

s t r u c t u r e s w e r e d i s ti n c t.

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( b )

F i g u re 1 . D i s c o u r s e S e g m e n t s , F o c u s S p a c e s a n d D o m i n a n c e H i e r a rc h y .

C o m p u t at io n a l L i n g u is t ic s , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r 1 9 8 6 1 8 1

7/17/2019 Grosz & Sidner (1986)


B a r b a r a J. Grosz a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e

S e v e r a l r e s e a r c h e r s ( e .g . , L i n d e a n d G o g u e n 1 9 7 8 ,

R e i c h m a n - A d a r 1 9 8 4 ) m i s i n t e r p r e t e d t h e o r i g i n a l

r e s e a r c h i n a n u n f o r t u n a t e a n d u n i n t e n d e d w a y : t h e y

t o o k t h e f o c u s - s p a c e h i e r a r c h y t o i n c l u d e ( o r b e i d e n t i c a l

t o ) t h e t a s k st r u c tu r e . T h e c o n f l a t i o n o f th e s e t w o s t r u c -

t u r e s f o r c e s a s in g le s t r u c t u r e t o c o n t a i n i n f o r m a t i o n

a b o u t a t t e n t i o n a l s t a t e , i n t e n t i o n a l r e l a t io n s h i p s , a n d

g e n e r a l t a sk , k n o w l e d g e . I t p r e v e n t s a t h e o r y f r o m

a c c o u n t i n g a d e q u a t e l y f o r c e r t a i n a s p e c t s o f d i s c o u r s e ,

i n c l u d i n g i n t e r r u p t i o n s ( s e e S e c t i o n 5 ) .

A s e c o n d i n s t a n c e o f c o n f u s i o n w a s t o i n f e r ( i n c o r -

r e c t l y ) t h a t t h e t a s k s t r u c t u r e w a s n e c e s s a r i l y a p r e b u i l t

t r e e . I f t h e t a s k s t r u c t u r e i s t a k e n t o b e a s p e c i a l c a s e o f

i n t e n t i o n a l s t r u c t u re , i t b e c o m e s c l e a r t h a t t h e t r e e s t r u c -

t u r e i s s i m p l y a m o r e c o n s t r a i n e d s t r u c t u r e t h a n o n e

m i g h t r e q u i re f o r o t h e r d i s c o u r se s ; t h e n a t u r e o f t h e t a s k

r e l a t e d t o t h e t a s k - o r i e n t e d d i s c o u r s e i s s u c h t h a t t h e

d o m i n a n c e h ie r ~ ir c hy o f t h e i n t e n t i o n a l s t r u c t u r e o f t h e

d i a lo g u e h a s b o t h d o m i n a n c e a n d s a t i s f a c t i o n - p re c e d e n c e

r e l a t io n s h i p s , 5 w h i l e o t h e r d i s c o u r s e s m a y n o t e x h i b i t

s i g n i f i c a n t p r e c e d e n c e c o n s t r a i n t s a m o n g t h e D S P s .

F u r t h e r m o r e , t h e r e h a s n e v e r b e e n a n y r e a s o n t o a s s u m e

t h a t t h e t a s k s t r u c t u r e s i n t a s k - o r i e n t e d d i a l o g u e s a r e

p r e b u i lt , a n y m o r e t h a n t h e i n t e n t i o n a l s t r u c t u r e o f a n y

o t h e r k i n d o f d i s c o u r s e s. I t i s r a t h e r t h a t o n e o b j e c t i v e o f

d i s c o u r s e t h e o r y ( n o t a t o p i c c o n s i d e r e d h e r e , h o w e v e r )

i s t o e x p l a i n h o w t h e O C P b u i l d s u p a m o d e l o f t h e t a s k

s t r u c t u r e b y u s i n g i n f o r m a t i o n s u p p l i e d i n t h e d i s c o u r s e .

H o w e v e r , i t i s i m p o r t a n t t o n o t e t h a t c o n f l a t i n g t h e

a f o r e m e n t i o n e d t w o r o l e s o f i n f o r m a t i o n a b o u t t h e t a s k

i t s e l f ( a s a p o r t i o n o f g e n e r a l c o m m o n s e n s e k n o w l e d g e

a n d a s a s p e c i a l c a s e o f i n t e n t i o n a l s t r u c t u r e ) w a s r e g r e t -

t a b l e , a s i t f a i l s t o m a k e a n i m p o r t a n t d i s t i n c t i o n .

F u r t h e r m o r e , a s i s c l e a r w h e n i n t e n t i o n a l s t r u c t u r e s a r e

c o n s i d e r e d m o r e g e n e r a ll y , s u c h a c o n f l a t i o n o f r o l e s

d o e s n o t a l lo w f o r d if f e r e n ce s b e t w e e n w h a t o n e k n o w s

a b o u t a t a s k a n d o n e ' s i n t e n t i o n s f o r ( o r w h a t o n e m a k e s

e x p l ic i t in d i s c o u r s e a b o u t ) p e r f o r m i n g a t a s k .

I n s u m m a r y , t h e f o c u s i n g s t r u c t u r e i s t h e c e n t r a l

r e p o s i t o r y f o r t h e c o n t e x t u a l i n f o r m a t i o n n e e d e d t o p r o c -

e s s u t t e r a n c e s a t e a c h p o i n t i n t h e d i s c o u r s e . I t d i s t i n -

g u i s h e s t h o s e o b j e c t s , p r o p e r t i e s , a n d r e l a t i o n s t h a t a r e

m o s t s a l i e n t a t t h a t p o i n t a n d , m o r e o v e r , h a s l i n k s t o

r e l e v a n t p a r t s o f b o t h t h e l in g u is t ic a n d i n t e n t i o n a l s t r u c -

t u r e s. D u r i n g a d i s c ou r s e , a n in c r e a s i n g a m o u n t o f i n f o r -

m a t i o n , o n l y s o m e o f w h i c h c o n t i n u e s t o b e n e e d e d f o r

t h e i n t e r p r e t a t i o n o f s u b s e q u e n t u t t e r a n c e s , i s d i s c u s se d .

H e n c e , i t b e c o m e s m o r e a n d m o r e n e c e s s a r y t o b e a b l e

t o i d e n t i f y r e l e v a n t d i s c o u r s e s e g m e n t s , t h e e n t i t i e s t h e y

m a k e s a l i e nt , a n d th e i r D S P s. T h e r o l e o f a t t e n t i o n a l

s t a t e i n d e l i n e a t i n g t h e i n f o r m a t i o n n e c e s s a r y f o r u n d e r -

s t a n d i n g i s t h u s c e n t r a l t o d i s c o u r s e p r o c e s s i n g .

3 T w o E X A M PL E S

T o i l l u s t r a t e t h e b a s i c t h e o r y w e h a v e j u s t s k e t c h e d , w e

w i l l g i v e a b r i e f a n a l y s i s o f t w o k i n d s o f d i s c o u r s e : a n

a r g u m e n t f r o m a r h e t o r i c t e x t a n d ~i t a s k - o r i e n t e d

d i a l o g u e . F o r e a c h e x a m p l e w e d i s c u s s t h e s e g m e n t a t i o n

o f t h e d i s c o u r s e , t h e i n t e n t i o n s t h a t u n d e r l i e t h i s s e g m e n -

t a t i o n , a n d t h e r e l a t i o n s h i p s a m o n g t h e v a r i o u s D S P s . I n

e a c h c a s e , w e p o i n t o u t s o m e o f t h e l i n g u i s t i c d e v i c e s

u s e d t o i n d i c a t e s e g m e n t b o u n d a r i e s a s w e l l a s s o m e o f

t h e e x p r e s s i o n s w h o s e i n t e r p r e t a t i o n s d e p e n d o n t h o s e

b o u n d a r i e s . T h e a n a l y s i s is c o n c e r n e d w i t h s p e c i f y i n g

c e r t a i n a s p e c t s o f t h e b e h a v i o r t o b e e x p l i c a t e d b y a

t h e o r y o f d i sc o u r s e ; t h e r e m a i n d e r o f t h e p a p e r p r o v i d e s

a p a r t i a l a c c o u n t o f t h is b e h a v i o r .

3.1 AN ARGUME NT

O u r f i r s t e x a m p l e i s a n a r g u m e n t t a k e n f r o m a r h e t o r i c

t d x t ( H o l m e s a n d G a l l a g h e r 1 9 1 76 ) . I t i s a n e x a m p l e u s e d

b y C o h e n ( 1 9 8 3 ) i n h e r w o r k o n t h e s t r u c t u r e o f a r g u -

m e n t s . F i g u r e 2 s h o w s t h e d i a l o g u e a n d t h e e i g h t

d i s c o u r s e s e g m e n t s o f w h i c h i t i s c o m p o s e d . T h e d i v i s i o n

o f t h e a r g u m e n t i n to s e p a r a t e ( n u m b e r e d ) c l a u s e s i s

C o h e n ' s , b u t o u r a n a l y s i s o f t h e d i s c o u r s e s t r u c t u r e i s

d i f f e r e n t , s in c e i n C o h e n ' s a n a l y s i s , e v e r y u t t e r a n c e i s

d i r e c t l y s u b o r d i n a t e d t o a n o t h e r u t t e r a n c e , a n d t h e r e i s

o n l y o n e s t r u c t u r e t o e n c o d e l i n g u i s t i c s e g m e n t a t i o n a n d

t h e p u r p o s e s o f u t t e r a n c e s . A l t h o u g h b o t h a n a l y s e s

s e g m e n t u t t e r a n c e ( 4 ) s e p a r a t e l y f r o m u t t e r a n c e s ( 1 - 3 ) ,

s o m e r e a d e r s p l a c e t h i s u t t e r a n c e i n D S1 w i t h u t t e r a n c e s

( 1 ) t h r o u g h ( 3 ) ; t h i s is a n e x a m p l e o f t h e k i n d o f d i s a -

g r e e m e n t a b o u t b o u n d a r y u t t e r a n c e s f o u n d i n M a n n ' s

d a t a ( a s d i s c u s s e d i n S e c t i o n 2 . 1 ). T h e t w o p l a c e m e n t s

l e a d t o s l i g h t l y d i f f e r e n t D S P s , b u t n o t t o r a d i c a l l y d i f f e r -

e n t i n t e n ti o n a l s t r uc t u r e s . B e c a u s e t h e d i ff e r e n c e s d o n o t

a f f e c t t h e m a j o r t h r u s t o f t h e a r g u m e n t , w e w i l l d i s c u s s

o n l y o n e s e g m e n t a t i o n .

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Barbara J. Grosz and Candace L. S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e

DS0

DS2

3

5

D S 6

I

I . _ _ .

DS7

1. The mov ie s a re so a t t ra c t i ve t o t he g rea t Amer i ca n pub l i c ,

2. e spec i a l l y t o young peop le ,

3. t ha t i t i s t ime to t ake ca re f u l t hough t abou t t he i r e f fec t on mind

and mora l s .

4 . Ough t any pa re n t t o pe rmi t h i s ch i l d ren t o a t t end a mov ing p i c tu re

show o f t en o r w i thou t be ing qu i t e ce r t a in o f t he show he pe rmi t s

them to see?

5. No one can deny , o f cou r se , t ha t g rea t educa t iona l and e th i ca l

ga in s may be made t h rough the mov ies

6. becau se o f t he i r a s ton i s h ing v iv idness .

7. Bu t t he impor t an t fac t t o be de t e r mined i s t he t o t a l r e su l t o f

con t in uous and i nd i s c r im ina t e a t t en dance on shows o f t h i s k ind.

8. Can i t be o the r t han ha rm fu l?

9. In t he f i r s t p l ace t h e cha r ac t e r o f t he p l ays is se ldom o f t he

best .

10. One has on ly t o read t he eve r -p r esen t mov ie b i l l b oa rd t o see how

c h e a p , m e l o d r a m a t i c a n d v u l g a r m os t of t h e p h o t o p l a y s a r e .

11 . Even the bes t p l ays , moreove r , a re bound to be exc i t i ng and

o v e r - e m o t i o n a l .

12 . Wi thout spoke n words , fac i a l exp r ess io n and ges tu re mus t ca r r y t he

mean ing :

13. bu t on ly s t ro ng emot ion , o r bu f fo one ry can be rep r esen t ed t h rou gh

f a c i al e x p r e s s i o n a n d g e s t u r e .

14. The more reas onab l e and qu i e t a sp ec t s o f l ife a re ne cessa r i l y

n e g l e c t e d .

15. How can ou r y oung peop le d r ink i n t h rou gh the i r eyes a con t inu ous

s p e c t a c l e o f i n t e n s e a n d s t r a i n e d a c t i v i t y a n d f e el i n g w i t h o u t

h a r m f u l e f f e c t s ?

16. P a ren t s and t each e rs w il l do wel l t o gua rd t he you ng aga ins t

o v e r i n d u l g e n c e i n t h e t a s t e f o r t h e m o v i e .

Figure 2. The Movies Essay.


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B a r b a r a J. Grosz a n d C a n d a c e L . S i d n e r A t t e n t i o n , I n t e n t io n s , a n d t h e S t r u c t u r e o f D i s c o u r s e

F i g u r e 3 l is t s t h e p r i m a r y c o m p o n e n t o f t h e D S P f o r

e a c h o f t h e s e s e g m e n t s a n d F i g u r e 4 s h o w s t h e d o m i -

n a n c e r e l a t i o n s h ip s t h a t h ol d a m o n g t h e s e i nt e n t i o n s. I n

S e c t i o n 7 w e d i s c u s s a d d i t i o n a l c o m p o n e n t s o f t h e

d i s c o u r s e s e g m e n t p u r p o s e ; b e c a u s e t h e s e a d d i t i o n a l

c o m p o n e n t s a r e m o r e i m p o r t a n t f o r c o m p l e t e n e s s o f t he

t h e o r y t h a n f o r d e t e r m i n i n g t h e e s se n t i a l d o m i n a n c e a n d

s a t i s f a c t i o n - p r e c e d e n c e r e l a t i o n s h i p s b e t w e e n D S P s , w e

o m i t su c h d e ta i l s h e r e . R a t h e r t h a n c o m m i t o u r s e l v e s t o

a f o r m a l l a n g u a g e i n w h i c h t o e x p r e s s t h e i n t e n t i o n s o f

t h e d i s c o u r s e , w e w il l u s e a s h o r t h a n d n o t a t i o n a n d

E n g l i s h s e n t e n c e s t h a t a r e i n t e n d e d t o b e a g l o s s f o r a

f o r m a l s t a t e m e n t o f t h e a c t u a l i n t e n ti o n s .

I O : ( I n t e n d

I 1 : ( I n t e n d

I 2 : ( I n t e n d

1 3 : ( I n t e n d

1 4 : ( I n t e n d

1 5 : ( I n t e n d

I 6 : ( I n t e n d

1 7 : ( I n t e n d

I C P ( B el ie v e O C P P O ) )

w h e r e P O = t h e p r o p o s i t i o n t h a t p a r e n t s a n d t e a c h e r s s h o u l d g u a r d t h e y o u n g

f r o m o v e r i n d u l g e n c e i n th e m o v i e s .

I C P ( B e l i e ve O C P P 1 ) )

w h e r e P 1 = t h e p r o p o s i t i o n t h a t i t i s t i m e t o c o n s i d e r t h e e f f e c t o f m o v i e s o n

m i n d a n d m o r a l s .

I C P ( B e li e ve O C P P 2 ) )

w h e r e P 2 = t h e p r o p o s i t i o n t h a t y o u n g p e o p l e c a n n o t d r i n k i n t h r o u g h t h e i r e y e s

a c o n t i n u o u s s p e c t a c l e o f i n te n s e a n d s t r a i n e d a c t i v i t y w i t h o u t h a r m f u l e f f e c t s .

I C P ( B e li e ve O C P P 3 ) )

w h e r e P 3 - - t h e p r o p o s i t i o n t h a t i t i s u n d e n i a b l e t h a t g r e a t e d u c a t i o n a l a n d

e t h i c a l g a i n s m a y b e m a d e t h r o u g h t h e m o v i e s .

I C P ( B e l ie v e O C P P 4 ) )

w h e r e P 4 = t h e p r o p o s i t i o n t h a t a l t h o u g h t h e r e a r e g a i n s , t h e t o t a l r e s u l t o f

c o n t i n u o u s a n d i n d i s c r i m i n a t e a t t e n d a n c e a t m o v i e s is h a r m f u l .


w h e r e P 5 = t h e p r o p o s i t i o n t h a t t h e c o n t e n t o f m o v i e s ( i. e ., t h e c h a r a c t e r o f t h e

p l a y s ) i s n o t t h e b e s t .


w h e r e P 6 = t h e p r o p o s i t i o n t h a t t h e s t o ri e s ( i. e ., th e p l a y s ) i n m o v i e s a r e e x c i t -

i n g a n d o v e r - e m o t i o n a l .


w h e r e P 7 = t h e p r o p o s it i o n th a t m o v i e s p o r t r a y s t r o n g e m o t i o n a n d b u f f o o n e r y

w h i l e n e g l e c t in g t h e q u i e t a n d r e a s o n a b l e a s p e c t s o f l i fe .

F i g u re 3. P r i m a r y i n te n t i o n s o f t h e D S P s f o r M o v i e s e s s a y .

I 0 D O M I 1

I 0 D O M 12

1 2 D O M 1 3

1 2 D O M 1 4

1 4 D O M 1 5

1 4 D O M 1 6

1 6 D O M 1 7

F i g u re 4 . D o m i n a n c e r e l a t i o n s h i p s f o r t h e D S P s o f t h e M o v i e s e s s a y .

184

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~ f

B a r b a r a

J. Grosz

a n d C a n d a e e L . S i d n e r A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e

All the primary intentions for this essay are intentions

that the reader (OCP) come to believe some proposition.

Some of these propositions, such as P5 and P6, can be

read off the surface utterances directly. Other prop-

ositions and the intemions of which they are part, such as

P2 and 12, are moCe indirect. Like the Gric ean utter -

ance'-level intentions (the analogy with these will be

explored in Section 7), DSPs may or may not be directly

expressed in the discourse. In particular, they may be

expressed in any of the following ways:

1 . e x p l i c i t l y

as in

I i n t e n d f o r y o u t o b e l ie v e t h a t i t 's t i m e

t o c o n s i d e r t h e e f f e c t s o f m o v i e s o n m i n d a n d m o r a l s .

[which would pr oduce I1 ]

2 . d i r e c t ly , i n o n e u t t e r a n c e ,

as in (3) [which does

prod uce I 1 ]

3 . d i r e c t l y , t h r o u g h m u l t i p l e u t t e r a n c e s ,

as in using (7)

and the utterance

I t c a n o n l y b e h a r m f u l

to produce

14,

4 . b y d e r i v a t i o n , i n o n e o r m o r e u t t e r a n c e s w i t h a n a s s o c i -

a t e d c o n t e x t ,

as in (15) to produce 12.

Not only may information about the DSP be conveyed

by a number of features of the utterances in a discourse,

but it also may come in any utterance in a segment. For

example, although I0 is the DP, it is stated directly only in

the last utterance of the essay. This leads to a number of

questions about the ways in which OCPs can recognize

discourse purposes, and about those junctures at which

they need to do so. We turn to these matters directly in

Subsection 4.1.

This discourse also provides several examples of the

different kinds of interactions that can hold between the

linguistic expressions in a discourse and the discourse

structure. It includes examples of the devices that may be

used to mark overtly the boundaries between discourse

segments - examples of the use of aspect, mood, and

particular cue phras es - as well as of the use of referrin g

expressions that are affected by discourse segment boun-

daries.

The use of cue phrases to indicate discourse bounda-

ries is illustrated in utterances (9) and (11); in (9) the

phrase

i n t h e f i r s t p l a c e

marks the beginning of DS5 while

in (11)

m o r e o v e r

ends DS5 and marks the start of DS6.

These phrases also carry information about the inten-

tional structure, namely, that DSP5 and DSP6 are domi-

nated b y DSP4. In some cases, cue phrases have multiple

functions; they convey propositional content as well as

marking discourse segment boundaries.. The

b u t

in utter-

ance (7) is an example of such a multiple function use.

The boundaries between DS1 and DS2, DS4 and DS5,

and DS4 and DS2 reflect changes of aspect and mood.

The switch from declarative, present tense to interroga-

tive modal aspect does not in itself seem to signal the

boundary (for recognition purposes) in this discourse

unambiguously, but it does indicate a possible line of

demarcation which, in fact, is valid.

The effect of segmentation on referring expressions is

shown by the use of the generic noun phrase

a m o v i n g

p i c t u r e s h o w

in (4). Althoug h a reference to the movies

was made with a pronoun

( t h e i r )

in (3), a full noun

phrase is used in (4). This use reflects, and perha ps in

part marks, the boundary between the segments DS1 and

DS2.

Finally, this discourse has an example of the trade-off

between explicitly marking a discourse boundary, as well

as the relationship between the associated DSPs, and

reasoning about the intentions themselves. There is no

overt linguistic marker of the beginning of DS7; its sepa-

ration must be inferred from DSP7 and its relationship to

DSP6.

3.2 A TASK-ORIENTED DIALOGUE

The second example is a fragment of a task-oriented

dialogue taken from Grosz (1981; it is from the same

corpus that was used by Grosz 1974). Figure 5 contains

the dialogue fragment and indicates the boundaries for its

main segments. 7 Figure 6 gives the prima ry co mpo nent of

the DSPs for this fragment and shows the dominance

relationships between them.

In contrast with the movies essay, the primary compo-

nents o f the DSPs in this dialogue are mo stly intentions of

the segment's ICP that the OCP intend to perform some

action. Also, unlike the essay, the dialogue has two

agents initiating the different discourse segments. In this

particular segment, the expert is the ICP of DS1 and DS5,

while the appren tice is the ICP of DS2-4. To furnish a

complete account of the intentional structure of this

discourse, one must be able to say how the satisfaction of

one agent's intentions can contribute to satisfying the

intentions of another agent. Such an account is beyo nd

the scope of this paper, but in Section 7 we discffss some

of the complexities involved in providing one (as well as

its role in discourse theory).

For the purposes of discussing this example, though,

we need to postulate two properties of the relationships

among the participants' intentions. These properties

seem to be rooted in features of cooperative behavior

and depend on the two participants' sharing some partic-

ular knowledge of the task. First, it is a share d belief

that, unless he states otherwise, the OCP will adopt the

intention to perform an action that the ICP intended him

to. Second, in adopting the intention to carry out that

action, the OCP also intends to perform whatever

subactions are necessary. Thus, once the apprentice,

intends to remove the flywheel, he also commits himself

to the collateral intentions of loosening the setscrews and

pulling the wheel off. Note, however, that not all the

subactions need to be introduced explicitly into the

discourse. The apprentice may do several actions that are

never mentioned, and the expert may assume that these

are being undertaken on the basis of other information

that the apprentice obtains. The partiality of the inten-

tional structure stems to some extent from these charac-

teristics of intentions and actions.

C o m p u t a t i o n a l L i n g u i s t i c s , V o l u m e

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Barbara J . Grosz and Candace L . S idner At tent ion , In tentions , and the S tructure

of Discourse

DS1 (1)

(2)

(3)

(4)

DS2 (5 )

( S )

(7)

( B )

( 9 )

1 0 )

(11)

DS3

(12)

( 1 3 )

( 1 4 )

15)

16)

(17)

DS4 (18)

(19)

(z0)

( z l )

(zz)

(z3)

(24)

(z5)

E: F i r s t you have t o remov e the f l ywhee l .

A: How do I rem ove the f lywhe el?

E: F i r s t , l oose n t he two a l l en head se t sc rews

hold ing i t to the shaft , then pul l i t o ff .

A: OK.

I can on ly f i nd one sc rew . Where ' s t he o the r one?

E: On the hub of the f lywheel .

A: Tha t ' s t he one I found . Where ' s t he o the r one?

E: Abou t n ine ty deg re es a roun d the hub f rom the f i r s t one .

A: I don ' t unde rs t and . I can only f ind one. Oh

wai t , yes I th i nk I was on the wron g wheel .

E: Show me what you are doing .

A: I was on th e wro ng wheel and l can f ind

them bo th now.

The t oo l I have i s awkward . I s t he re ano the r

too l t ha t I cou ld u se i n s t e ad?

E: Show me the tool you are using .

A: OK.

E: Are you su re you a re u s ing t he r i gh t s i ze

k e y ?

A: I ' l l t ry some oth ers .

I fou nd an angle I can get a t i t.

The two sc rews a re l oose , bu t I 'm hav ing t roub l e

ge t t i ng t he whee l o f f .

E: Use the whe elp ul l er Do you know how to use

i t?

A: No .

E: Do you know what i t looks l ike?

A: Yes.

E: Show it to me please.

A: OK.

E: Good , Loosen t he sc rew in t he cen t e r and

p lace t he j aws a round the hub o f t he

wheel , t hen t i gh t en t he sc rew on to t he

cen t e r o f t he sha f t . The whee l shou ld

slide off.

Figure 5. A segment of a task-oriented dialogue.

As in the movies essay, some of the DSPs for this

dialogue are expressed directly in utterances. Fo r

instance, utterances (1), (5), and (12) directly express

the primary components of DSP1, DSP2 and DSP3,

respectively. The primary compone nt of DSP4 is a

derived intention. The surface intention of

but I m

having trouble getting the wheel off

is tha t the apprentice

intends the expert to believe that the apprentice is having

trouble takin g off the flywheel. 14 is derived fr om the

utterance and its surface intention, as well as from

features of discourse, conventions about what intentions

are associated with the

1 am having trouble doing X

type

186

of utterance, and what the 1CP and OCP know about the

task they have undertaken.

The dominance relationship that holds between I1 and

12, as well as the one that holds between I1 and 13, may

seem problematic at first glance. It is not clear how

locating any single setscrew contributes to removing the

flywheel. It is even less clear how, in and of itself, identi-

fying ano the r tool does. Two facts provide the link: first,

that the apprentice (the OCP of DS1) has taken on the

task of removing the flywheel; second, that the appren-

tice and expert share certain knowledge about the task.

Some of this shared task knowledge comes from the

discourse per se [e.g., utterance (3)], but some of it

Computat ional

Linguistics, Volume

1 2 , N u m b e r 3 , J u l y - S e p te m b e r

1986

7/17/2019 Grosz & Sidner (1986)



c o m e s f r o m g e n e r a l k n o w l e d g e , p e r c e p t u a l i n f o r m a t i o n ,

a n d t h e li k e. T h u s , a c o m b i n a t i o n o f i n f o r m a t i o n i s r e l e -

v a n t t o d e t e r m i n i n g 1 2 a n d 1 3 a n d t h e i r r e l a t i o n s h i p s t o

I 1 , i n c l u d i n g a l l o f t h e f o l l o w i n g : t h e f a c t t h a t I 1 is p a r t

o f t h e i n t e n t i o n a l s t r u c t u r e , t h e f a c t t h a t t h e a p p r e n t i c e i s

c u r r e n t l y w o r k i n g o n s a t i s f y i n g I 1 , t h e u t t e r a n c e - l e v e l

i n t e n t io n s o f u t t e r a n c e s ( 5 ) a n d ( 1 2 ) , a n d g e n e r a l k n o w -

l e d g e a b o u t t h e t a s k .

T h e s a t i s f a c t i o n - p r e c e d e n c e r e l a t i o n s a m o n g 1 2 , 1 3 ,

a n d 1 4 a r e n o t c o m m u n i c a t e d d i r e c t l y i n t h e d i a l o g u e ,

b u t , l i k e d o m i n a n c e r e l a t i o n s , d e p e n d o n d o m a i n k n o w -

l e d ge . O n e p i e c e o f r e l e v a n t k n o w l e d g e i s t h a t a s a t is f a c -

t i o n p r e c e d e n c e r e l a t i o n e x i s t s b e t w e e n l o o s e n i n g t h e

s e t s c r e w s a n d pu l l i n g o f f t h e f l y w h e e l . T h a t r e l a t i o n is

s h a r e d k n o w l e d g e t h a t i s s t a t e d d i r e c t l y

(F ir s t loosen . . . .

t h n p u l l ) .

T h e r e l a t io n , a l o n g w i t h t h e f a c t t h a t b o t h 1 2

a n d 1 3 c o n t r i b u t e t o l o o s e n i n g t h e s e t s c r e w s , a n d t h a t 1 4

c o n t r i b u t e s t o p u l l i n g o f f t h e f l y w h e e l , m a k e s i t p o s s i b l e

t o c o n c l u d e 1 3 S P 1 4 a n d 1 2 S P 14 . T o c o n c l u d e t h a t 1 2

S P 13 , t h e a p p r e n t i c e m u s t e m p l o y k n o w l e d g e o f h o w t o

g o a b o u t l o o s e n i n g s c r e w - l i k e o b j e c t s .

T h e d o m i n a n c e a n d s a t i s f a c t i o n - p r e c e d e n c e r e l a t i o n s

f o r t h i s t a s k - o r i e n t e d f r a g m e n t f o r m a t r e e o f i n t e n t i o n s

r a t h e r t h a n j u s t a p a r t i a l o r d e r i n g . I n g e n e r a l , h o w e v e r ,

f o r a n y f r a g m e n t , t a s k - o r i e n t e d o r o t h e r w i s e , t h i s i s n o t

n e c e s s a r y .

I t i s e s s e n t i a l t o n o t i c e t h a t t h e i n t e n t i o n a l s t r u c t u r e i s

n e i t h e r i d e n t i c a l t o n o r i s o m o r p h i c t o a g e n e r a l p l a n f o r

r e m o v i n g th e f l y w h e e l . I t i s n o t i d e n t ic a l b e c a u s e a p l a n

e n c o m p a s s e s m o r e t h a n a c o l l e c t i o n o f i n t e n t i o n s a n d

r e l a t i o n s h i p s b e t w e e n t h e m ( c o m p a r e P o l l a c k ' s ( 1 9 8 6 )

c r i ti q u e o f A I p l a n n i n g f o r m a l i s m s a s t h e b a s i s f o r i n f e r -

r i n g i n t e n t io n s i n d i s c o u r se ) . I t is n o t i s o m o r p h i c b e c a u s e

t h e i n t e n t i o n a l s t r u c t u r e h a s a d i f f e r e n t s u b s t r u c t u r e f r o m

t h e g e n e r a l p l a n f o r r e m o v i n g t h e f l y w h e e l . I n a d d i t io n

t o t h e i n t e n t i o n s a r i s i n g f r o m s t e p s i n t h e p l a n , t h e i n t e n -

t i o n a l s t r u c t u r e t y p i c a l l y c o n t a i n s D S P s c o r r e s p o n d i n g t o

i n t e n t i o n s g e n e r a t e d b y t h e p a r t i c u l a r e x e c u t i o n o f t h e

t a s k a n d t h e d i a l o gu e . F o r e x a m p l e , th e g e n e r a l p l a n f o r

t h e d i s a s s e m b l y o f a f ly w h e e l i n c l u d e s s u b p l a n s f o r l o o s -

e n i n g t h e s e t s c r e w s a n d p u l l in g o f f t h e w h e e l ; i t m i g h t

a l s o in c l u d e s u b p l a n s ( o f t h e l o o s e n i n g s t e p ) f o r f i n di n g

t h e s e t s c r e w s , f i n d i n g a t o o l w i t h w h i c h t o l o o s e n t h e

s c r e w s , a n d l o o s e n i n g e a c h s c r e w i n d i v i d u a l l y . H o w e v e r ,

t h i s p l a n w o u l d n o t c o n t a i n c o n t i n g e n c y s u b p l a n s f o r

w h a t t o d o w h e n o n e c a n n o t f i n d t h e s c r e w s o r r e a l i z e s

t h a t t h e a v a i l a b l e t o o l i s u n s a t i s f a c t o r y . I n t e n t i o n s I 2 a n d

I 3 s t e m f r o m d i f f i c u l t i e s e n c o u n t e r e d i n l o c a t i n g a n d

l o o s e n i n g t h e s e t s c re w s . T h u s , t h e i n te n t i o n a l s t r u c t u r e

f o r t h is f r a g m e n t i s n o t i s o m o r p h i c t o t h e g e n e r a l p l a n f o r

r e m o v i n g t h e f l y w h e e l .

U t t e r a n c e ( 1 8 ) o f f e r s a n o t h e r e x a m p l e o f t h e d i ff e r -

e n c e b e t w e e n t h e i n t e n t i o n a l s t r u c t u r e a n d a g e n e r a l p l a n

f o r th e t a s k . T h i s u t t e r a n c e i s p a r t o f D S 4 - n o t j u s t p a r t

o f DS 1 - e v e n t h o u g h i t c o n t a i n s r e f e r e n c e s t o m o r e t h a n

o n e s i n g l e p a r t o f t h e o v e r a l l t a s k ( w h i c h i s w h a t I 1 i s

a b o u t ) . I t f u n c t i o n s t o e s t a b l i s h a n e w D S P , 1 4 , a s m o s t

s a l ie n t . R a t h e r t h a n b e i n g r e g a r d e d a s a r e p o r t o n t h e

o v e r a l l s t a t u s o f t h e t a s k , t h e f i r s t c l a u s e i s b e s t s e e n a s

m o d i f y i n g t h e D S P . 8 W i t h i t, t h e a p p r e n t i c e t e l ls t h e

e x p e r t t h a t t h e t r o u b l e i n r e m o v i n g t h e w h e e l i s n o t w i t h

t h e s c r e w s . T h u s , a l t h o u g h g e n e r a l t a s k k n o w l e d g e i s

u s e d i n d e t e r m i n i n g t h e i n t e n t i o n a l s t r u c t u r e , i t i s n o t

id en t i ca l t o i t .

I n t h is d i a l o g u e , t h e r e a r e f e w e r i n s t a n c e s i n w h i c h c u e

p h r a s e s a r e e m p l o y e d t o i n d i c a t e s e g m e n t b o u n d a r i e s

t h a n o c c u r i n t h e m o v i e s e s sa y . T h e p r i m a r y e x a m p l e i s

t h e u s e o f

f i r s t

i n ( 1 ) t o m a r k t h e s t a r t o f th e s e g m e n t

a n d t o i n d i c a t e t h a t i t s D S P i s t h e f i r s t o f s e v e r a l

i n t e n t i o n s w h o s e s a t i s f a c t i o n w i ll c o n t r i b u t e t o s a t i s fy i n g

t h e l a r g e r d i s c o u r se o f w h i c h t h e y a r e a p a r t .

P r i m a r y I n t e n t i o n s :

I I ( I n t e n d

Exper t

( I n t e n d

Appren t ic e

( R e m o v e A f l y w h e e l ) ))

I 2 : ( I n t e n d A ( I n t e n d E (T e l l E A ( L o c a t i o n o t h e r s e t s c r e w ) ) ) )

I 3 : ( I n t e n d A ( I n t e n d E ( I d e n t if y E A a n o t h e r t o o l ) ) )

I 4 : ( I n t e n d A ( I n t e n d E ( T e l l E A ( H o w ( G e t o f f A w h e e l ) ) ) ) )

I 5 : ( I n t e n d E ( K n o w - H o w - t o A (U s e A w h e e l p u l l e r) ) )

D o m i n a n c e R e l a t i o n s h i p s :

I 1 D O M I 2

I 1 D O M I 3

I 1 D O M I 4

I 4 D O M I 5

S a t i s f a c t i o n - P r e c e d e n c e R e l a t i o n s h i p s :

I 2 S P I 3

I 2 S P I 4

I 3 S P I 4

Figure 6 . I n t e n t i o n a l s t r u c t u r e f o r th e t a s k - o r i e n t e d d i a l o g u e s e g m e n t .


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The dialogue includes a clear example of the influence

of discourse structure on referring expressions. The

phrase the screw in the center is used in (25) to refer to

the center screw of the wheelpuller, not one of the two

setscrews mentioned in (18). This use of the phrase is

possible because of the attentional state of the discourse

structure at the time the phrase is uttered.

4 PROCESSING ISSUES

In previous sections of the paper, we abstracted from the

cognitive states of the discourse participants. The various

components of discourse structure discussed so far are

properties of the discourse itself, not of the discourse

participants. To use the theory in constructing computa-

tional models requires determining how each of the indi-

vidual components projects onto the model of an

individual discourse participant. In this regard, the prin-

cipal issues include specifying

1. how the ICP indicates and the OCP recognizes the

beginning and end of a discourse segment,

2. how the OCP recognizes the discourse segment

purposes, and

3. how the focus space stack operates.

In essence, the OCP must judge for each utterance

whether it starts a new segment, ends the current one

(and possibly some of its embedding segments), or

contributes to the current one. The informatio n available

to the OCP for recognizing that an utterance starts a new

segment includes any explicit linguistic cues contained in

the utter ance (see Section 6 9 as well as the relatio nship

between its utterance-level intentions and the active DSPs

(i.e., those in some focus space that is still on the stack).

Likewise, the fact that an utterance ends a segment may

be indicated explicitly by linguistic cues or implicitly from

its utterance-level intentions and their relationship to

elements of the intentional structure. If neither of these is

the case, the utterance is part of the current segment.

Thus, intention recognition and focus space management

play key roles in processing. Moreover, they are also

related: the intentional structure is a primary factor in

determining focus space changes, and the focus space

structure helps constrain the intention recognition proc-

ess.

4.1 INTENTION RECOGNITIO N

The recognition of DP/DSPs is the central issue in the

computation al modeling of intentional structure. If, as

we have claimed, for the discourse to be coherent and

comprehensible, the OCP must be able to recognize both

the DP/DSPs 10 and relationships (dominanc e and satis-

faction-precedence) between them, then the question of

how the OCP does so is a crucial issue.

For the discourse as a whole, as well as for each of its

segments, the OCP must identify both the intention that

serves as the discourse segment purpose and its relation-

ship to other discourse-level intentions. In particular, the

OCP must be able to recognize which other DSPs that

specific intention dominates and is dominated by, and,

where relevant, with which other DSPs it has satisfac-

tion-pr ecedence relationships. Two issues that are

central to the recognition problem are what information

the OCP can utilize in effecting the recognition and at

what point in the discourse that information becomes

available.

An adequate computational model of the recognition

process depends critically on an adequate theory of

intention and action; this, of course, is a large research

problem in itself and one not restricted to matters of

discourse. The need to use such a model for discourse,

however, adds certain constraints on the adequacy of any

theory or model. Pollack (1986) describes several prop-

erties such theories and models must possess if they are

to be adequate for supporting recognition of intention in

single-utterance queries; she shows how current AI plan-

ning models are inadequate and proposes an alternative

planning formalism. The need to enable recognition of

discourse-level intentions leads to yet another set of

requirements.

As will become clear in what follows, the information

available to the OCP comes from a variety of sources.

Each of these can typically provide partial information

about the DSPs and their relationships. These s ources are

each partially constraining, but only in their ensemble do

they constrain in full. To the extent that more informa-

tion is furnished by any one source, commensurately less

is needed from the others. The overall processing model

must be one of constraint satisfaction that can operate on

partial information. It must allow for incrementally

constraining the range of possibilities on the basis of new

information that becomes available as the segment

progresses.

4.1.1 INFORMATION CONSTRAINING THE DSP

At least three different kinds of information play a role in

the determination of the DSP: specific linguistic markers,

utterance-level intentions, and general knowledge about

actions and objects in the domain of discourse. Eac h

plays a part in the OCP's recognition of the DSP and can

be utilized by the ICP to facilitate this recognition.

Cue phrases are the most distinguished linguistic

means that speakers have for indicating discourse

segment boundaries and conveying information about the

DSP. Recen t evidence by Hirschb erg and Pierre humber t

(i~986) suggests that certain intonational properties of

utterances also provide partial information about the DSP

relationships. Because some cue phrases may be used as

clausal connectors, there is a need to distinguish their

discourse use from their use in conveying propositional

conte nt at the utterance level. For example, the word bu

functions as a boundary marker in utterance (7) of the

discourse in Section 3.1, but it can also be used solely (as

in the current utterance) to convey propositional content

(e.g., the conjunction of two propositions) and serve to

connect two clauses within a segment.

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As discussed in Section 6, cue phrases can provide

information about dominance and satisfaction-prece-

dence relationships between segments' DSPs. However,

they may not completely specify which DSP dominates or

satisfaction-precedes the DSP of the segment they start.

Furthermore, cue phrases that explicitly convey informa-

tion only about the attentional structure (see Section 6)

may be ambiguous about the state to which attention is

to shift. For example, if there have been several inter-

ruptions (see Section 5), the phrase but anyway indicates

a return to some previously interrupted discourse, but

does not specify which one. Although cue phrases do not

completely specify a DSP, the information they provide is

useful in limiting the options to be considered.

The second kind of information the OCP has available

is the utterance-level intention of each utterance in the

discourse. As the discussion of the movies example

(Section 3.1) pointed out, the DSP may be identical to

the utterance-level intention of some utterance in the

segment. Alternatively, the DSP may combine the

intentions of several utterances, as is illustrated in the

following discourse segment:

I want you to ar range a trip for me to Palo Alto.

It will be for two weeks.

I only fly on TWA.

The DSP for this segment is, roughly, that the ICP

intends for the OCP to make (complete) trip arrange-

ments for the ICP to go to Palo Alto for two weeks,

under the constraint that any flights be on TWA. The

Gricean intentions for these three utterances are as

follows:

U t t e r a n c e I :

ICP intends that OCP believe that ICP

intends that OCP intend to make trip plans

for ICP to go to

Palo Alto

U t t e r a n c e 2 : ICP intends that OCP believe that ICP

intends OCP to believe that the trip will last

two weeks

U t t e r a n c e 3 :

ICP intends that OCP believe that ICP

intends OCP to believe that ICP flies only on

TWA

These intentions must be combined in some way to

produ ce the DSP. The proc ess is quite complex, since the

OCP must recognize that the reason for utterances 2 and

3 is not simply to have some new beliefs about the ICP,

but to use those beliefs in arranging the trip. While this

example fits the schema of a request followed by two

informings, schemata will not suffice to represent the

behavior as a general rule. A different sequence of utter-

ances with different utterance-level intentions can have

the same DSP; this is the case in the following segment:

S 1: Have I told you yet to arrange my trip to Palo Alto?

Remember that I will fly only on TWA. OK?

$2: OK.

$3: I'm planning on staying for two weeks.

It is possible for a sequence that consists of a request

followed by two informings not to result in a modifica-

tion of the trip plans. For example, in the following

sequence the third utterance results in changing the way

the arrangements are made, rather than constraining the

nature of the arrangements themselves.

I want you to arrange a two-week trip for me to Palo

Alto. I fly only on TWA. The rates go up tomorrow,

so you'll want to call today.

Not only is the contribution of utterance-level

intentions to DSPs complicated, but in some instances the

DSP for a segment may both constrain and be partially

determined by the Gricean intention for some utterance

in the segment. For example, the Gricean-intention for

utterance (15) in the movies example (Section 3.1) is

derived from a combination of facts about the utterance

itself, and from its place in the discourse. On the surfac e,

(15) appears to be a question addressed to the OCP; its

intention would be roughly that the ICP intends the OCP

to believe that the ICP wants to know how young people,

etc. But (15) is actually a rhetor ical questio n and has a

very different intention associated with it - namely, that

the ICP intends the OCP to believe proposition P2

(namely, that young people cannot drink in through their

eyes a continuous spectacle of intense and strained activ-

ity without harniful effects). In this example, this partic-

ular intention is also the primar y com pone nt of the DSP.

The third kind of information that plays a role in

determining the DP/DSPs is shared knowledge about

actions and objects in the domain of discourse. This

shared knowledge is especially important when the

linguistic markers and utterance-level intentions are

insufficient for determining the DSP precisely.

In Section 7 we introduce two relations, a s u p p o r t s

relation between propositions and a generates relation

between actions, and present two rules stating equiv-

alences; one links a dominance relation between two

DSPs with a supports relation between propositions and

the other links a dominance relation between DSPs to a

generates relation between actions. Use of these rules in

one direction allows for (partially) determining what

supports or generates relationship holds from the domi-

nance relationship. But the rules can be used in the oppo-

site direction also: if, from the content of utterances and

reasoning about the domain of discourse, a supports or

generates relationship can be determined, then the domi-

nates relationship between DSPs can be determined. In

such cases it is important to derive the dominance

relationship so that the appropriate intentional and atten-

tional structures are available for processing or determin-

ing the interpretation of the subsequent discourse.

From the perspective of recognition, a trade-off

implicit in the two equivalences is impor tant. If the ICP

makes the dominance relationship between two DSPs

explicit (e.g., with cue phrases), then the OCP can use

this information to help recognize the (ICP's beliefs

about the) supports relationship. Conversely, if the ICP's

utterances make clear the (ICP's beliefs about the)

supports or generates relationship, then the OCP can use

C o m p u t a t i o n a l L i n g u i s ti c s , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r

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B a r b a r a J . G r o s z a n d C a n d a e e L . S i t h a e r

A t t e n t i o n , I n t e n t i o n s , a n d t h e S t r u c t u r e o f D i s c o u r s e

t h i s i n f o r m a t i o n t o h e l p r e c o g n i z e t h e d o m i n a n c e

r e l a ti o n s h ip . A l t h o u g h i t i s m o s t h e l p fu l t o u s e th e d o m i -

n a n c e r e l a t i o n s h i p s t o c o n s t r a i n t h e s e a r c h f o r a p p r o p r i -

a t e s u p p o r t s a n d g e n e r a t e s r e l a t i o n s h i p s, s o m e t i m e s t h e s e

l a t t e r r e l a t i o n s h i p s c a n b e i n f e r r e d r e a s o n a b l y d i r e c t l y

f r o m t h e u t t e r a n c e s i n a. s e g m e n t u s i n g g e n e r a l k n o w -

l e d g e a b o u t t h e o b j e c t s a n d a c t i o n s i n t h e d o m a i n o f

d i s c o u r se . I t r e m a i n s a n o p e n q u e s t io n w h a t i n f e r e n c e s

a r e n e e d e d a n d h o w c o m p l e x i t w i l l b e t o c o m p u t e

s u p p o r t s a n d g e n e r a t e s r e l a t i o n s h i p s if t h e d o m i n a n c e

r e l a t i o n s h i p i s n o t d i r e c t l y i n d i c a t e d i n a d i s c o u r s e .

U t t e r a n c e s f r o m t h e m o v i e s e s s a y i l l u s t r a t e t h i s t r a d e -

o f f . I n u t t e r a n c e ( 9 ) , t h e p h r a s e in the f irs t p lace

e x p r e s s e s t h e d o m i n a n c e r e l a t i o n s h i p b e t w e e n D S P s o f

t h e n e w s e g m e n t D S 5 a n d t h e p a r e n t s e g m e n t D S 4 d i r e c t -

l y. B e c a u s e o f t he d o m i n a n c e r e l a t i o n s h ip ( a s w e l l as t h e

i n t e n t i o n s e x p r e s s e d i n t h e u t t e r a n c e s ) , t h e O C P c a n

d e t e r m i n e t h a t t h e I C P b e l i e v e s t h a t t h e p r o p o s i t i o n t h a t

t h e c o n t e n t o f t h e p l a y s i s n o t t h e b e s t p r o v i d e s s u p p o r t

f o r t h e p r o p o s i t i o n t h a t t h e r e s u l t o f i n d i s c r i m i n a t e m o v i e

g o i n g i s h a r m f u l . H e n c e d e t e r m i n i n g d o m i n a n c e y i e l ds

t h e s u p p o r t r e l a t io n . T h e s u p p o r t r e l a t i o n c a n a ls o y i e l d

d o m i n a n c e . U t t e r a n c e s ( 1 2 ) - ( 1 4 ) , w h i c h c o m p r i s e D S 7,

a r e n o t e x p li c i tl y m a r k e d f o r a d o m i n a n c e r e l a t i on . I t c a n

b e i n f e r r e d f r o m t h e f a c t t h a t t h e p r o p o s i t i o n s i n

( 1 2 ) - ( 1 4 ) p r o v i de s u p p o r t f o r th e p r o p o s i t io n e m b e d d e d

i n D S P 6 ( t h a t i s , t h a t t h e s t o r i e s i n m o v i e s a r e e x c i t i n g

a n d o v e r - e m o t i o n a l ) t h a t D S P 6 d o m i n a t e s D S P 7 .

F i n a ll y , t h e m o r e i n f o r m a t i o n a n I C P s u p p l i e s e x p l ic i t -

l y i n t h e a c t u a l u t t e r a n c e s o f a d i s c o u r s e , t h e l e s s r e a s o n -

i n g a b o u t d o m a i n i n f o r m a t i o n a n O C P h a s t o d o t o

a c h i e v e r e c o g n i ti o n . C o h e n ( 1 9 8 3 ) h a s m a d e a si m i l a r

c l a i m r e g a r d i n g t h e p r o b l e m o f r e c o g n i z i n g t h e r e l a t i o n -

s h i p b e t w e e n o n e p r o p o s i t i o n a n d a n o t h e r .

4 . 1 .2 W H E N I S T H E I N T E N T I O N R E C O G N I Z E D ?

A s d i s c u s s e d i n S e c t i o n 2 . 2 , t h e i n t e n t i o n a l s t r u c t u r e

e v o l v e s a s th e d i s c o u r s e d o e s . B y t h e s a m e t o k e n , t h e

d i s c o u r s e p a r t i c i p a n t s ' m e n t a l - s t a t e c o r r e l a t e s o f th e

i n t e n t i o n a l s t ru c t u r e a r e n o t p r e b u i l t; n e i t h e r p a r t i c i p a n t

m a y h a v e a c o m p l e t e m o d e l o f t h e i n t e n t i o n a l s t r u c t u re

i n m i n d u n t il t h e d i s c o u r s e i s c o m p l e t e d . T h e d o m i -

n a n c e r e l a t i o n s h i p s t h a t a c t u a l l y s h a p e t h e i n t e n t i o n a l

s t r u c t u r e c a n n o t b e k n o w n a p r i o r i , b e c a u s e t h e s p e c i f i c

i n t e n t i o n s t h a t w i ll c o m e i n t o p l a y a r e n o t k n o w n ( n e v e r

b y t h e O C P , h a r d l y e v e r b y t h e I C P ) u n t i l t h e u t t e r a n c e s

i n t h e d i s c o u rs e h a v e b e e n m a d e . A l t h o u g h i t i s a s s u m e d

t h a t t h e p a r t i c i p a n t s ' c o m m o n k n o w l e d g e i n c l ud e s 11

e n o u g h i n f o r m a t i o n a b o u t t h e d o m a i n t o d e t e r m i n e v a r i -

o u s r e l a t i o n s h ip s s u c h a s s u p p o r t s a n d g e n e r a t e s , i t is n o t

a s s u m e d t h a t , p r i o r t o a d i s c o u r s e , t h e y a c t u a l l y h a d

i n f e r r e d a n d a r e a w a r e o f a l l t h e r e l a t i o n s h i p s t h e y w i l l

n e e d f o r t h a t d i s c o u r s e .

B e c a u s e a n y o f t h e u t t e r a n c e s i n a s e g m e n t m a y

c o n t r i b u t e i n f o r m a t i o n r e l e v a n t t o a c o m p l e t e d e t e r m i -

n a t i o n o f t h e D S P , t h e r e c o g n i t i o n p r o c e s s i s n o t

c o m p l e t e u n ti l t h e e n d o f t h e s e g m e n t . H o w e v e r , t h e O C P

m u s t b e a b l e t o r e c o g n i z e a t l e a s t a g e n e r a l i z a t i o n o f t h e

D S P so t h a t h e c a n m a k e t h e p r o p e r m o v e s w i t h r e s p e c t

t o t h e a t t e n t i o n a l s t r u c t u r e . T h a t i s , s o m e c o m b i n a t i o n o f

e x p l ic i t i n d i c a t o r s a n d i n t e n t i o n a l a n d p r o p o s i t i o n a l

c o n t e n t m u s t a l l o w t h e O C P t o a s c e r t a i n w h e r e t h e D S P

w i l l f i t i n t h e i n t e n t i o n a l s t r u c t u r e a t t h e b e g i n n i n g o f a

s e g m e n t , e v e n i f t h e s p e c i f i c i n t e n t i o n t h a t i s t h e D S P

c a n n o t b e d e t e r m i n e d u n t i l t h e e n d o f t h e s e g m e n t .

U t t e r a n c e ( 1 5 ) i n t h e m o v i e s e x a m p l e i l l u s t ra t e s t h is

p o in t . T h e a u t h o r w r i te s , H o w c a n o u r y o u n g p e o p l e

d r i n k i n t h r o u g h t h e i r e y e s a c o n t i n u o u s s p e c t a c l e o f

i n t e n s e a n d s t r a i n e d a c t i v i t y a n d f e e l i n g w i t h o u t h a r m f u l

e f f e c t s ? T h e p r i m a r y i n t e n t i o n 1 2 i s d e r i v e d f r o m t h i s

u t t e r a n c e , b u t t h i s c a n n o t b e d o n e u n t i l v e r y l a t e in t h e

d i s c o u r s e s e g m e n t [ s i n c e ( 1 5 ) o c c u r s a t t h e e n d o f D S 2] .

F u r t h e r m o r e , t h e s e g m e n t f o r w h i c h 1 2 i s p r i m a r y h a s

c o m p l e x e m b e d d i n g o f o t h e r s eg m e n t s . U t t e r a n c e ( 1 6 ) ,

i n t e n t i o n I 0 , a n d D S 0 c o n s t i t u t e a n o t h e r e x a m p l e o f t h e

e x p r e s s i o n o f a p r i m a r y i n t e n t i o n l a t e i n a d i s c o u r s e

s e g m e n t . I n t h a t c a se , I 0 c a n n o t b e c o m p u t e d u n t i l ( 1 6 )

h a s b e e n r e a d , a n d ( 1 6 ) i s n o t o n l y t h e l a s t u t t e r a n c e i n

D S 0, b u t is o n e t h a t c o v e r s t h e e n t i r e e s s a y . I f a n O C P

m u s t r e c o g n i z e a D S P t o u n d e r s t a n d a s e g m e n t , t h e n w e

a s k : h o w d o e s t h e O C P r e c o g n i z e a D SP w h e n t h e u t t e r -

a n c e f r o m w h i c h i t s p r i m a r y i n t e n t i o n i s d e r i v e d c o m e s s o

l a t e in t h e s e g m e n t ?

W e c o n j e c t u r e w i t h r e g a r d t o s u c h s e g m e n t s a s D 2 o f

t h e m o v i e s e s s a y t h a t t h e p r i m a r y i n t e n t i o n ( e .g . , 1 2) m a y

b e d e t e r m i n e d p a r t i a l ly ( a n d h e n c e a g e n e r a l i z e d v e r s i o n

b e c o m e r e c o g n i z a b l e ) b e f o r e t h e p o i n t a t w h i c h i t i s

a c t u a l l y e x p r e s s e d i n t h e d i s c o u r s e . W h i l e t h e D P / D S P

m a y n o t b e e x p r e s s e d e a r l y , t h e r e i s s t i l l part ia l in forma-

tion a b o u t it . T h i s p a r t i a l i n f o r m a t i o n o f t e n s u f f i c e s t o

e s t a bl i sh d o m i n a n c e ( o r s a t i s f a c t io n - p r e c e d e n c e )

r e l a t i o ns h i p s f o r a d d i t i o n a l s e g m e n t s . A s t h e s e l a t t e r a r e

p l a c e d i n t h e h i e r a r c h y , t h e i r D S P s c a n p r o v i d e f u r t h e r

p a r t i a l i n f o r m a t i o n f o r t h e u n d e r s p e c i f i e d D S P . F o r

e x a m p l e , e v e n t h o u g h t h e i n t e n t i o n I 0 i s e x p r e s s e d

d i r e c t l y o n l y in t h e l a s t u t t e r a n c e o f t h e m o v i e s e s s a y ,

u t t e r a n c e ( 4 ) e x p r e s s e s a n i n t e n t i o n t o k n o w w h e t h e r p

o r ~ p i s t r u e ( i . e . , w h e t h e r o r n o t p a r e n t s s h o u l d l e t c h i l -

d r e n s e e m o v i e s o f t e n a n d w i t h o u t c lo s e m o n i t o r i n g ) . I 0

i s a n i n t e n t i o n t o b e l i e v e , w h o s e p r o p o s i t i o n i s a g e n e r -

a l i z a t i o n o f t h e ~ p e x p r e s s e d i n (4 ) . C o n s i d e r a l s o t h e

p r i m a r y i n t e n t i o n 14 . I t o c c u r s in a s e g m e n t e m b e d d e d

w i t h i n D S 2 , i s m o r e g e n e r a l t h a n 1 2, b u t i s a n a p p r o x i -

m a t i o n t o it . I t w o u l d n o t b e s u r p r i s i n g t o d i s c o v e r t h a t

O C P s c a n i n f a c t p r e d i c t s o m e t h i n g c l o s e t o 1 2 o n t h e

b a s i s o f 14 , u t t e r a n c e s ( 9 ) - ( 1 4 ) , a n d t h e p a r t i a l d o m i -

n a n c e h i e r a r c h y a v a i l a b l e a t e a c h p o i n t i n t h e d i s c o u r s e .

4 . 2 U S E O F T H E A T Y E N T IO N A L S T A T E M O D E L

T h e f o c u s s p a c e s t r u c t u r e e n a b l e s c e r t a i n p r o c e s s i n g

d e c i s i o n s t o b e m a d e l o c a l l y . I n p a r t i c u l a r , i t l i m i t s t h e

i n f o r m a t i o n t h a t m u s t b e c o n s i d e r e d i n r e c o g n i z i n g t h e

D S P a s w e ll a s t h a t c o n s i d e r e d i n id e n t i f y i n g t h e r e f e r e n t s

o f c e r t a i n c l a s s e s o f d e f i n i te n o u n p h r a s e s .

1 9 0

C o m p u t a t i o n a l L i n g u i s ti c s , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r

1 9 8 6

7/17/2019 Grosz & Sidner (1986)



A primary role of the focus space stack is to constrain

the range of DSPs considered as candidates for domi-

nation or satisfaction-precedence of the DSP of the

curre nt segment. Only those DSPs in some space on the

focusi ng stack are viable prospects. As a result of this

use of the focusing structure, the theory predicts that this

decision will be a local one with respect to attentional

state. Because two focus spaces may be close to each

other in the attentional structure without the discourse

segments they arise from necessarily being close to one

another and vice versa, this prediction corresponds to a

claim that locality in the focusing structure is what

matters to determination of the intentional structure.

A second role of the focusing structure is to constrain

the OCP's search for possible referents of definite noun

phrases and pronouns . To illustrate this role, we will

consider the phrase

the screw in the center

in utterance

(25) of the task-oriented dialogue of Section 3. The

focus stack configuration when utterance (25) is spoken

is shown in Figure 7. The stack contains (in bott om- to-

top order) focus spaces FSI, FS4, and FS5 for segments

DS1, DS4, and DS5, respective ly. Fo r DS5 the wheel pul-

ler is a focused entity, while for DS4 the two setscrews

are (because they are explicitly mentioned). The entities

in FS5 are considered before those in FS4 as potential

referents. The wheelpuller has three screws: two small

screws fasten the side arms, and a large screw in the

center is the main functioning part. As a result, this large

screw is implicitly in focus in FS5 (Grosz 1977) and thus

identified as the referent without the two setscrews ever

being considered.

Attentional state also constrains the search for refer-

ents of pronouns. Because pronouns contain less explicit

information about their referents than definite

descriptions, additional mechanisms are needed to

account for what may a nd may not be pronominalized in

the discourse. One such mechanis m is centering (which

we previously called immediate focusing; Grosz, Joshi,

and Weinstein 1983; Sidner 1979).

Centering, like focusing, is a dynamic behavior, but is

a more local phenom enon. In brief, a backwar d-looki ng

center is associated with each utterance in a discourse

segment; of all the focused elements the backward-look-

ing center is the one that is central in that utterance (i.e.,

the uttering of the particular sequence of words at that

point in the discourse). A combination of syntactic,

semantic, and discourse information is used to identify

the backward-looking center. The fact that some entity is

the backward-looking center is used to constrain the

search for the referent of a pronoun in a subsequent

uttera nce. Note that unlike the DSP, which is con sta nt

for a segment, the backward-looking center may shift:

different entities may become more salient at different

points in the segment.

The presence of both centers and DSPs in this theory

leads us to an intriguing conjecture: that topi c is a

concept that is used ambiguously for both the DSP of a

segment and the center. In the literature the concept of

topi c has appeare d in many guises. In syntactic form it

is used to describe the preposing of syntactic constituents

in English and the wa marking in Japanese. Resear ch-

ers have used it to describe the sentence topic (i.e., what

the sentence is about; Firbas 1971, Sgall, Haji~ov~, and

SETSCREWS 3

FLYWHEELIo

DSP 1

FS1

SCREW 1

SCREW 2

DSP 2

FS2

SETSCREWS 3

FLYWHEELIo

DSP 1

FS1

ALLEN WRENCH 9

KEYS14

DSP 3

FS3

SETSCREWS 3

FLYWHEELlo

DSP 1

FS1

WHEEL PULLER 8

DSP 5

FS5

SETSCREWS 3

FLYWHEELIo

DSP 4

FS4

SETSCREWS 3

FLYWHEELlo

DSP 1

FS1

t i m e

Figure 7. Focus Stack Transitions Leading up to Utteranc e (25).

C o m p u t a t i o n a l L i n g u i st i cs , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r 1 9 8 6 1 9 1

7/17/2019 Grosz & Sidner (1986)


Barbara J . Grosz and Candace L . S idner At tent ion , In tent ions , and the S tructure of Discourse

B e n e s o v a 1 9 7 3 ) , a n d a s a p r a g m a t i c n o t i o n ( R e i n h a r t

1 9 8 1 ) ; o t h e r s w a n t t o u s e t h e t e r m f o r d i s c o u r s e t o p i c ,

e i t h e r t o m e a n w h a t t h e d i s c o u r s e i s a b o u t , o r t o b e

d e f i n e d a s t h o s e p r o p o s i t i o n ( s ) t h e I C P p r o v i d e s o r

r e q u e s t s n e w i n f o r m a t i o n a b o u t ( s e e R e i n h a r t ( 1 9 8 1 ) f o r

a r e v i e w o f m a n y o f t h e n o t i o n s o f a b o u t n e s s a n d t o p i c ) .

I t a p p e a r s t h a t m a n y o f t h e d e s c r i p t i o n s o f s e n t e n c e t o p i c

c o r r e s p o n d ( t h o u g h n o t a l w a y s ) t o c e n t e r s , w h i l e

d i s c o u r s e t o p i c c o r r e s p o n d s t o t h e D S P o f a s e g m e n t o r o f

t h e d i s c o u r s e .

5 APPLICATI ON OF THE THEORY: INTERRUPTIONS

I n t e r r u p t i o n s i n d i s c o u r s e s p o s e a n i m p o r t a n t t e s t o f a n y

t h e o r y o f d i s c o u r s e s t r u c tu r e . B e c a u s e p r o c e s s i n g a n

u t t e r a n c e r e q u i r e s a s c e r t a i n i n g h o w i t f i ts w i t h p r e v i o u s

d i s c o u r s e , i t i s c r u c i a l t o d e c i d e w h i c h p a r t s o f t h e p r e v i -

o u s d i s c o u r s e a r e r e l e v a n t t o i t , a n d w h i c h c a n n o t b e .

I n t e r r u p t i o n s , b y d e f i n it i o n , d o n o t f i t; c o n s e q u e n t l y t h e i r

t r e a t m e n t h a s i m p l i c a t i o n s f o r t h e t r e a t m e n t o f t h e

n o r m a l f l o w o f d i s c o u r se . I n t e r r u p t i o n s m a y t a k e m a n y

f o r m s - s o m e a r e n o t a t a ll r e l e v a n t t o t h e c o n t e n t a n d

f l o w o f t h e i n t e r r u p t e d d i s c o u r s e , o t h e r s a r e q u i t e r e l e -

v a n t , a n d m a n y f a l l s o m e w h e r e i n b e t w e e n t h e s e

e x t r e m e s . A t h e o r y m u s t d i f f e r e n ti a t e t h e se c a s e s a n d

e x p l a i n ( a m o n g o t h e r t hi n g s ) w h a t c o n n e c t i o n s e x i s t

b e t w e e n t h e m a i n d is c o u r s e a n d t h e in t e r r u p t i o n , a n d

h o w t h e r e l a t i o n s h i p b e t w e e n t h e m a f f e c t s t h e p r o c e s s i n g

o f t h e u t t e r a n c e s i n b o t h .

T h e i m p o r t a n c e o f d i s t i n g u i s h i n g b e t w e e n i n t e n t i o n a l

s t r u c t u r e a n d a t t e n t i o n a l s t a t e i s e v i d e n t in t h e t h r e e

e x a m p l e s c o n s i d e r e d i n S u b s e c t i o n s 5 . 2 , 5 .3 , a n d 5 . 4.

T h e d i s t i n c t i o n a l s o p e r m i t s u s t o e x p l a i n a t y p e o f

b e h a v i o r d e e m e d b y o t h e r s t o b e s i m i la r - s o - c a l l e d

s e m a n t i c r e t u r n s - a n i s s u e w e e x a m i n e i n S u b s e c t i o n

5 .5 .

T h e s e e x a m p l e s d o n o t e x h a u s t t h e t y p e s o f i n t e r -

r u p t i o n s t h a t c a n o c c u r i n d i s c o u r s e . T h e r e a r e o t h e r

w a y s t o v a r y t h e e x p l i c i t l i n g u i s t i c ( a n d n o n l i n g u i s t i c )

i n d i c a t o r s u s e d t o i n d i c a t e b o u n d a r i e s , t h e r e l a t i o n s h i p s

b e t w e e n D S P s , a n d t h e c o m b i n a t i o n s o f f o c u s s p a c e

r e l a t i o n s h i p s p r e s e n t . H o w e v e r , t h e e x a m p l e s p r o v i d e

i l l u s t r a t i o n s o f i n t e r r u p t i o n s a t d i f f e r e n t p o i n t s a l o n g t h e

s p e c t r u m o f r e l e v a n c y t o t h e m a i n d i s c o ur s e . B e c a u s e

t h e y c a n b e e x p l a i n e d m o r e a d e q u a t e l y b y t h e t h e o r y o f

d i s c o u r s e s t r u c t u re p r e s e n t e d h e r e t h a n b y p r e v i o u s t h e o -

r i es , t h e y s u p p o r t t h e i m p o r t a n c e o f t h e d i s t i n c ti o n s w e

h a v e d r a w n .

5.1 PRELIMINARY DEFINI TIONS

F r o m a n i n t u i t i v e v i e w , w e o b s e r v e t h a t i n t e r r u p t i o n s a r e

p i e c e s o f d i s c o u r s e t h a t b r e a k t h e f l o w o f th e p r e c e d i n g

d i s c o u r se . A n i n t e r r u p t i o n i s i n s o m e w a y d is t i n ct f r o m

t h e r e s t o f t h e p r e c e d i n g d i s c o u r s e ; a f t e r t h e b r e a k f o r

t h e i n t e r r u p t i o n , t h e d i s c o u r s e r e t u r n s t o t h e i n t e r r u p t e d

p i e c e o f d i s c o u r se . I n th e e x a m p l e b e l o w , f r o m P o l a n y i

a n d S c h a ( f o r t h c o m i n g ) , t h e r e a r e t w o ( s e p a r a t e )

d i s c o u r s e s , D 1 i n d i c a t e d i n n o r m a l t y p e , a n d D 2 i n i t a l i c s .

D 2 i s a n i n t e r r u p t i o n t h a t b r e a k s t h e f l o w o f D 1 a n d i s

d i s t i n c t f r o m D 1.

D I : J o h n c a m e b y

a n d l e f t t h e g r o c e r i e s

D 2 : Stop that

you kids

D I : a n d I p u t t h e m a w a y

a f t e r h e l e f t

U s i n g t h e t h e o r y d e s c r i b e d i n p r e v i o u s s e c t i o n s , w e

c a n c a p t u r e t h e a b o v e i n tu i t i on s a b o u t t h e n a t u r e o f

i n t e r r u p t i o n s w i t h t w o s l ig h t l y d i f f e r e n t d e f i n i t i o n s . T h e

s t r o n g d e f i n i t io n h o l d s f o r t h o s e i n t e r r u p t i o n s w e c l a s s i f y

a s t r u e in t e r r u p t i o n s a n d d i g r e s s io n s , w h i l e t h e w e a k e r

f o r m h o l d s f o r t h o s e t h a t a r e f l a s h b a c k s . T h e t w o d e f i -

n i t i o n s a r e a s f o l l o w s :

Strong def ini t ion: A n i n t e r r u p t i o n i s a d i s c o u r s e

s e g m e n t w h o s e D S P is n o t d o m i n a t e d n o r s a t i s f a c -

t i o n - p r e c e d e d b y t h e D S P o f a n y p r e c e d i n g s e g m e n t .

W e a k d e f i n i t i o n : A n i n t e r r u p t i o n i s a d i s c o u r s e

s e g m e n t w h o s e D S P is n o t d o m i n a t e d n o r s a t i s f a c -

t i o n - p r e c e d e d b y t h e D S P o f th e i m m e d i a t e l y p r e c e d -

i n g s e g m e n t .

N e i t h e r o f t h e a b o v e d e f i n i t i o n s i n c l u d e s a n e x p l i c i t

m e n t i o n o f o u r in t u i ti o n th a t t h e r e i s a r e t u r n t o t h e

i n t e r r u p t e d d i s c o u r s e a f t e r a n in t e r r u p t i o n . T h e r e t u r n i s

a n e f f e c t o f t h e n o r m a l p r o g r e s s o f a c o n v e r s a t i o n . I f w e

a s s u m e a f o c u s s p a c e i s n o r m a l l y p o p p e d f r o m t h e f o c u s

s t a c k i f a n d o n l y i f a s p e a k e r h a s s a t i s f i e d t h e D S P o f i t s

c o r r e s p o n d i n g s e g m e n t , t h e n i t n a t u r a l l y f o l l o w s b o t h

t h a t t h e f o c u s s p a c e f o r t h e i n t e r r u p t i o n w i l l b e p o p p e d

a f t e r t h e i n t e r ru p t i o n , a n d t h a t t h e f o c u s s p a c e f o r t h e

i n t e r r u p t e d s e g m e n t w i l l b e a t t h e t o p o f t h e s t a c k

b e c a u s e i t s D S P i s y e t t o b e s a t i s f i e d .

T h e r e a r e o t h e r k i n d s o f d i s c o u r s e s e g m e n t s t h a t o n e

m a y w a n t t o c o n s i d e r i n li g h t o f t h e i n t e r r u p t i o n c o n t i n -

u u m a n d t h e s e d e f in i t io n s . C l a r i f i c a t i o n d i a l o g u e s ( A l l e n

1 9 7 9 ) a n d d e b u g g i n g e x p l a n a t i o n s ( S i d n e r 1 9 8 3 ) a r e t w o

s u c h p o s si b i l it i e s . B o t h o f t h e m , u n l i k e th e i n t e r r u p t i o n s

d i s c u s s e d h e r e , s h a r e a D S P w i t h t h e i r p r e c e d i n g s e g m e n t

a n d t h u s d o n o t c o n f o r m t o o u r d e f i n i t i o n o f i n t e r r u p t i o n .

T h e s e k i n d s o f d is c o u r s e s m a y c o n s t i t u t e a n o t h e r g e n e r a l

c l a s s o f d i s c o u r s e s e g m e n t s t h a t , l i k e i n t e r ru p t i o n s , c a n

b e a b s t r a c t l y d e f i n e d .

5.2 TYPE 1: TRUE INTERRUPTIONS

T h e f i rs t k i n d o f i n t e r r u p t i o n i s t h e t r u e i n t e r r u p t i o n ,

w h i c h f o l l o w s t h e s t r o n g d e f i n i t i o n o f i n t e r r u p t i o n s . I t i s

e x e m p l i f i e d b y t h e i n t e r r u p t i o n g i v e n in t h e p r e v i o u s

s u b s e c t i o n . D i s c o u r s e s D 1 a n d D 2 h a v e d is t i nc t , u n r e -

l a te d p u r p o s e s a n d c o n v e y d i f f e r e n t i n f o r m a t i o n a b o u t

p r o p e r t i e s , o b j e c t s , a n d r e l a t io n s . S i n c e D 2 o c c u r s w i t h i n

D 1 , o n e e x p e c t s t h e d i s c o u rs e s t r u c t u r e s f o r t h e t w o

s e g m e n t s to b e s o m e h o w e m b e d d e d a s we ll . T h e t h e o r y

d e s c r i b e d i n t h i s p a p e r d i f f e r s f r o m P o l a n y i a n d S c h a ' s

( 1 9 8 4 ; a n d o t h e r m o r e r a d i c a l l y d i f f e r e n t p r o p o s a l s a s

w e l l; e. g ., L i n d e a n d G o g u e n 1 9 7 8 , C o h e n 1 9 8 3 , R e i c h -

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man-Adar 1984) because the embedding occurs only in

the attentional structure. As shown in Figure 8, the

focus space for D2 is pushed onto the stack above the

focus space for D1, so that the focus space for D2 is

more salient than the one for D 1, until D2 is comple ted.

The intentional structures for the two segments are

distinct. There are two DP/DSP structures for the utter-

ances in this sequence - one for those in D1 an d the

other for those in D2. It is not necessary to relate these

two; indeed, from an intuitive point of view, they are not

related.

The focusing structure for true interruptions is differ-

ent from that for the normal embedding of segments,

because the focusing boundary between the interrupted

discourse and the in terru ption is impene trable . 12 (This is

depicted in the figure by a line with intersecting hash

marks betwee n focus spaces). The impenetrable bound a-

ry between the focus spaces prevents entities in the spac-

es below the boundary from being available to the spaces

above it. Because the second discourse shifts attention

totally to a new purpose (and may also shift the identity

of the intended hearers), the speaker cannot use any

DISCOURCESEGMENTS

FOCUSSPACESTACK

DOMINANCE HIERARCHY

DI : JOHNCAME BYAND

LEFT THE GROCERIES \

D2: STOP THA T YOU KIDS

D1 cont: AND I PUT THEM

AWAY AFTER HE LEFT

\

A

/

\

\

KIDS 1

KIDS 1 STOP ...

DSP 2

FS5

; - , - , ; - , - , , - . - - . ; - r. t

JOHN 10

GROCERIES14

JOHN'S COMING 15

DSP 1

FS4

(EMPTY)

a )

DISCOURSE SEGMENTS

FOCUS SPACE STACK

DOMINANCE HIERARCHY

f~

DI : JOHN CAME BY AND

LEFT THE GROCERIES

D2: STOP THA T YOU KIDS

D1 cont: AND I PUT THEM

AWAY AFTER HE LEFT

/

/

JOHNlo

GROCERIES14

JOHN'SCOMING15

DSP 1

FS4

(EMPTY)

b )

F i g u r e

8. The structures of a true interruption.

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referential expressions during it that depend on the

accessibility of entities fro m the first discourse. Since the

boundary between the focus space for D1 and the one

for D2 is impenetrable, if D2 were to include an utter-

ance such as

p u t t h e m a w a y ,

the pronoun would have to

refer deictically, and not anaphorically, to the groceries.

In this sample discourse, however, D1 is resumed

almost immediately. The pronoun

t h e m

in

a n d I p u t t h e m

a w a y

cannot refer to the children (the focus space for D2

has been popped from the stack), but only to the

groceries. For this to be clear to the OCP, the ICP must

indicate a retur n to D 1 explicitly. One linguistic indicator

in this example is the change of mood from imperative.

Indicators that the

s to p t h a t

utterance is an interruption

include the change to imperative mood and the use of the

vocative (Polanyi and Scha 1983). Two other indicators

may be assumed to have been present at the time of the

discourse - a chang e of into natio n (imagine a slightly

shrill tone of command with an undercurrent of annoy-

ance) and a shift of gaze (toward and then away from

the kids). It is also possible that the type of pause pres-

ent in such cases is evidence of the interruption, but

further research is needed to establish whether this is

indeed the case.

In contrast to previous accounts, we are not forced to

integrate these two discourses into a single grammatical

structure, or to answer questions about the specific

relationship between segments D2 and D1, as in

Reichman's model (Reichman-Adar 1984). Instead, the

intuition that readers have of an embedding in the

discourse structure is captured in the attentional state by

the stacking of focus spaces. In addition, a read er's intui-

tive impression of the distinctness of the two segments is

captured in their different intentional (DP/DSP) struc-

tures.

5 .3 T Y P E 2 : F L A S H B A C K S A N D F I L L IN G IN M I S S I N G P L A C E S

Sometimes an ICP interrupts the flow of discussion

because some purposes, propositions, or objects need to

be brought into the discourse but have not been: the ICP

forgot to include those entities first, and so must now go

back and fill in the missing inform ation. A flashback

segment occurs at that point in the discourse. The flash-

back is defined as a segment whose DSP satisfaction-pre-

cedes the interrupted segment and is dominated by some

othe r segme nt's DSP. Henc e, it is a specialization of the

weak definition of interruptions. This type of inter-

ruptio n differs fro m true interruptions both intentionally

and linguistically: the DSP for the flashback bears some

relationship to the DP for the whole discourse. The

linguistic indicator of the flashback typically includes a

comm ent about something going wrong. In addition the

audience always remains the same, whereas it may

change for a true interruption (as in the example of the'

previous section).

In the example below, taken from Sidner (1982), the

ICP is instructing a mock-up system (mimicked by a

person) about how to define and display certain informa-

tion in a particular knowledge-representation language.

Again the interruption is indicated by italics.

OK. Now how do I say that Bill is

W h o o p s I f o r g o t a b o u t A B C .

I n e e d a n i n d i v id u a l c o n c e p t f o r t h e c o m p a n y A B C

. . .[ r e m a i n d e r o f d i s c o u r se s e g m e n t o n A B C ] . . .

Now back to Bill. How do I say that Bill is an employee

of ABC?

The DP for the larger discourse from which this

sequence was taken is to provide information about vari-

ous companies (including ABC) and their employees.

The oute r segm ent in this example - DBill - has a DSP -

D S P B i l l - to tell about Bill, while the inner segment -

D A B C - - has a D S P - D S P A B C -- t o convey certain infor-

mation about ABC. Because of the nature of the infor-

mation being told, there is order in the final structure of

the DP/DSPs: information about ABC must be conveyed

before all of the information abou t Bill can be. The ICP

in this instance does not realize this constraint until after

he begins. The flas hbac k interruption allows him to

s a t i s f y D S P A B C while suspending satisfaction of D S P B i l l

(which he then resumes). Hence, there is an intentional

structure rooted at DP and with

D S P A B C

and

D S P B i u a s

o rd ered

sister nodes. The following three relationships

hold betwee n the differ ent DSPs:14

DP DOM DSPABC

DP DOM DSPBill

DSPABC SP DSPBill

This kind of interruption is distinct from a true inter-

ruption because there is a connection, although indirect,

between the DSPs for the two segments. Furthermore,

the linguistic features of the start of the interruption

signify that there is a precedence relation between these

DSPs (and hence that the correc tion is necessary). Flash-

backs are also distinct from normally embedded

discourses because of the precedence relationship

between the DSPs for the two segments and the order in

which the segments occur.

The available linguistic data permit three possible

attentional states as appropriate models for flashback-

type interruptions: one is identical to the state that would

ensue if the flashback segment were a normally embed-

ded segment, the second resembles the model of a true

interruption, and the third differs from the others by

requiring an auxiliary stack. An example of the stack for

a normally embedded sequence is given in Section 4.2

Figure 9 illustrates the last possibility. The focus space

for the flashbac k - FSABC -- is pushed onto the stack

after an appropriate number of spaces, including the

focus space for the outer segment - F S B i l l , have been

popped from the main stack and pushed onto an auxiliary

stack. All of the entities in the focus spaces remaining on

the main stack are normally accessible for reference, but

none of those on the auxiliary stack are. In the example

in the figure, entities in the spaces fro m FS A to FS B are

accessible as well (though less salient than) those ir/

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s p a c e F S A B C . E v i d e n c e f o r t h is k i n d o f s t a c k b e h a v i o r

c o u l d c o m e f r o m d i s c o u r s e s i n w h i c h p h r a s e s i n t h e

s e g m e n t a b o u t A B C c o u l d r e f e r t o e n t i t i e s r e p r e s e n t e d i n

F S B , b u t n o t t o t h o s e i n F S B i u o r F S C . A f t e r a n e x p l i c i t

i n d i ca t i o n t h a t t h e re i s a r e tu rn t o D S P B i l l ( e . g . , t h e Now

back to Bill u s e d i n t h i s e x a m p l e ) , a n y f o c u s s p a c e s l e f t

o n t h e s t a c k f r o m t h e f l a s h b a c k a r e p o p p e d o f f , a n d a l l

s p a c e s o n t h e a u x i l i a r y s t a c k ( i n c l u d i n g F SB il l ) a r e

r e t u r n e d t o t h e m a i n s t a c k . N o t e , h o w e v e r , t h a t t h i s

m o d e l d o e s n o t p r e c l u d e t h e p o s s i b i l i t y o f a r e t u r n t o

s o m e s p a c e b e t w e e n F S A a n d F S B b e f o r e p o p p i n g t h e

a u x i li a r y s t a c k . W h e t h e r t h e r e a r e d i s c o u r s e s t h a t i nc l u d e

s u c h a r e t u r n a n d a r e d e e m e d c o h e r e n t i s a n o p e n q u e s -

t i o n .

T h e a u x i l i a r y s t a c k m o d e l d i f f e r s f r o m t h e o t h e r t w o

m o d e l s b y t h e r e f e r e n c e s p e r m i t t e d a n d b y t h e s p a c e s

t h a t c a n b e p o p p e d t o . G i v e n t h e i n i t i a l c o n f i g u r a t i o n i n

F i g u r e 9 , i f t h e s e g m e n t w i t h D SP A B C w e r e n o r m a l l y

e m b e d d e d , F S AB C w o u l d j u s t b e a d d e d t o t h e t o p o f t h e

s t a c k . I f i t w e r e a t r u e i n t e r r u p t i o n , t h e s p a c e w o u l d a l s o

' b e a d d e d t o t h e s t a c k , b u t w i t h a n i m p e n e t r a b l e b o u n d a -

r y b e t w e e n i t a n d F S B il l. I n t h e n o r m a l s t a c k m o d e l , e n t i -

t i e s i n t h e s p a c e s l o w e r i n t h e s t a c k w o u l d b e a c c e s s i b l e ;

i n t h e t r u e i n t e r r u p t i o n t h e y w o u l d n o t . I n e i t h e r o f t h e s e

t w o m o d e l s , h o w e v e r , F SB ill w o u ld b e t h e s p a c e r e t u r n e d

t o f i r s t . T h e a u x i l i a r y s t a c k m o d e l i s o b v i o u s l y m o r e

c o m p l i c a t e d t h a n t h e o t h e r t w o a l te r n a t i v e s . W h e t h e r it

( o r s o m e e q u i v a l e n t a l t e r n a t i v e ) i s n e c e s s a r y d e p e n d s o n

f a c t s o f d i s c o u r s e b e h a v i o r t h a t h a v e n o t y e t b e e n d e t e r -

m i n e d .

5 .4 TYPE3: DIGRESSIONS

T h e t h i r d t y p e o f i n t e r r u p t i o n , w h i c h w e c a l l a d i g r e s s i o n ,

i s d e f i n e d a s a s t r o n g i n t e r r u p t i o n t h a t c o n t a i n s a r e f e r -

e n c e t o s o m e e n t i t y t h a t i s s a l i e n t i n b o t h t h e i n t e r r u p t i o n

a n d th e in t e r r u p t e d s e g m e n t . F o r e x a m p l e , i f w h i l e

d i s c u ss i n g B i ll 's r o le i n c o m p a n y A B C , o n e c o n v e r s a t i o n a l

p a r t i c i p a n t i n t e r r u p t s w i t h , Speaking of Bill, that reminds

me, he came to dinner last week, B i l l r e m a i n s s a l i e n t , b u t

t h e D P c h a n g e s . D i g r e s s i o n s c o m m o n l y b e g i n w i t h

p h r a s e s s u c h a s speaking of John o r that reminds me,

a l t h o u g h n o c u e p h r a s e n e e d b e p r e s e n t , a n d that reminds

me m a y a l s o s ig n a l o t h e r s t a c k a n d i n t e n t i o n s h i ft s .

I n t h e p r o c e s s i n g o f d i g r e s s i o n s , t h e d i s c o u r s e - l e v e l

i n t e n t i o n o f t h e d i g r e s s io n f o r m s t h e b a s e o f a s e p a r a t e

i n t e n t i o n a l s t r u c t u r e , j u s t a s i n t h e c a s e o f t r u e i n t e r -

r u p t i o n s . A n e w f o c u s s p a c e i s f o r m e d a n d p u s h e d o n t o

t h e s t a c k , b u t i t c o n t a i n s a t l e a s t o n e - a n d p o s s i b l y o t h e r

- e n t i ti e s f r o m t h e i n t e r r u p t e d s e g m e n t ' s f o c u s s p a ce .

L i k e t h e f l a s h b a c k - t y p e i n t e r r u p t i o n , t h e d i g r e s s i o n m u s t

u s u a l l y b e c l o s e d w i t h a n e x p l i c i t u t t e r a n c e s u c h a s

getting back to ABC... o r anyway.

M A I N

S T A C K

F S B I L L

FS C

F S B

FS A

M A I N A U X I L I A R Y

S T A C K S T A C K

F SAB c

FS B

FS A

F SBI LL

FS c

t i m e

S T A C K A T t I S T A C K S A T t 2

F i g u r e

9 . T h e a u x i l ia r y s t a c k m o d e l f o r f l a s h b a c k s .


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5.5 NONINTERRUPTIONS - SEMANTIC RETURNS

One case of discourse behavior that we must distinguish

comprises the so-called semantic returns observed by

Reichman (1981) and discussed by Polanyi and Scha

(1983). In all the interruptions we have considered so

far, the stack must be popped when the interruption is

over and the interrupted discourse is resumed. The focus

space for the interrupted segment is return ed to. In the

case of semantic returns, entities and DSPs that were sali-

ent during a discourse in the past are taken up once

again, but are explicitly reintroduced. For example,

suppose that yesterday two people discussed how badly

Jack was behaving at the party; then today one of them

says

R e m e m b e r o u r d i sc u s s io n a b o u t J a c k a t t h e p a r t y ?

W e l l , a l o t o f o t h e r p e o p l e t h o u g h t h e a c t e d j u s t a s b a d l y a s

w e th o u g h t h e d id . The utterances today recall, or return

to, yesterday's conversation to help satisfy the intention

that more be said about Jack's poor behavior.

Anything that can be talked about once can be talked

about again. However, if there is no focus space on the

stack corresponding to the segment and DSP being

discussed further, then, as Polanyi and Scha (1983) point

out, there is no popping of the stack. There need not be

any discourse underway when a semantic return occurs;

in such cases, the focus stack will be empty. Thus, unlike

the returns that follow normal

returns involve a push onto the

containing, among other things,

reintroduced entities.

interruptions, semantic

stack of a new space

representations of the

The separation of attentional state from intentional

structure makes clear not only what is occurring in such

cases, but also the intuitions underlying the term seman-

tic return. In reintroducing some entities fr om a previous

discourse, conversational participants are establishing

some connection between the DSP of the new segment

and the intentional structure of the original discourse. It

is not a return to a previous focus space because the

focus space for the original discourse is gone from the

stack, and the items to be referred to must be re-establ-

ished explicitly. For example, the initial refe rence to

Jack in the preceding example cannot be accomplished

with a pronoun; with no prior mention of Jack in the

current discussion, one cannot say,

R e m e m b e r o u r

d i sc u ss io n a b o u t h im a t t h e p a r t y .

The intuitive

impression of a return in the strict sense is only a return

to a previous intentional structure.

6 APPLICATION OF THE THEORY: CUE WORD S

Both attentional state and intentional structure change

during a discourse. ICPs rarely change attention by

directly and explicitly referring to attentional state (e.g.,

using the phrase

N o w l e t ' s t u r n o u r a t t e n t i o n t o . . . ) .

Like-

wise, discourses only occasionally include an explicit

reference to a change in purpose (e.g., with an utterance

such as

N o w I w a n t to e x p la i n t h e t h e o r y o f d y n a m i c

p r o g r a m m i n g ) .

More typically, ICPs employ indirect

means of indicating that a change is coming and what

kind of change it is. Cue phrases provide abbreviated,

indirect means of indicating these changes.

In all discourse changes, the ICP must provide infor-

mation that allows the OCP to determine all of the

following:

1. that a change of attention is imminent;

2. whether the change returns to a previous focus space

or creates a new one;

3. how the intention is related to other intentions;

4. what preceden ce relationships, if any, are relevant;

5. what intention is entering into focus.

Cue phrases can pack in all of this information, except

for (5). In this section, we explore the predictions of our

discourse structure theory about different uses of these

phrases and the explanations the theory offers for their

various roles.

We use the configuration of attentional state and

intentional structure illustrated in Figure 10 as the start-

ing point of our analysis. In the initial configuration, the

focus space stack has a space with DSP X at the bottom

and another space with DSP A at the top. The intentional

structure includes the information that X dominates A.

From this initial configuration, a wide variety of moves

may be made. We examine several changes and the cue

phrases that can indicate each of them. Because these

phrases and words in isolation may ambiguously play

either discourse or other functional roles, we also discuss

the other uses whenever appropriate. Furthe rmor e, cue

phrases do not function unambiguously with respect to a

particular discourse role. Thus for example,

f i r s t

can be

used for two different moves that we discuss below.

First, consider what happens when the ICP shifts to a

new DSP, B, that is dominated by A (and corresponding-

ly by X). The dominanc e relationship between A and B

becom es part of the intentional structure. In addition,

the change in DSP results in a change in the focus stack.

The focus stack models this change, which we call n e w

d o m i n a n c e , by a having new space pushed onto the stack

with B as the DSP of that space (as illustrated in Figure

11). The space cont ainin g A is salient, but less so than

the space with B. Cue phrase(s) to signal this case, and

only this one, must communicate two pieces of informa-

tion: that there is a change to som e new purpo se (result-

ing in a new focus space being created in the attentional

state model rather than a return to one on the stack) and

that the new purpose (DSP B) is dominated by DSP A.

Typical cue phrases for this kind of change are

f o r e x a m -

p l e

and

to wi t ,

and sometimes

f i r s t

and

sec o n d .

Cue phrases can also exhibit the existence of a satis-

faction- precede nce relationship. If B is to be the first in

a list of DSPs dominated by A, then words such as

f i r s t

and

i n t h e f i r s t p l a c e

can be used to communicate this

fact. Later in the discourse, cue phrases such as

sec o n d ,

th ird ,

and

f i n a l l y

can be used to indicate DSPs that are

dominat ed by A and satisfaction-prece ded by B. In these

cases, the focus space containing B would be popped

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B a r b a r a J. Grosz a n d C a n d a c e L. Sidner Attention, Intentions, and the Struct ure of Discourse

f r o m t h e s t a c k a n d t h e n e w f o c u s s p a c e i n s e r t e d a b o v e

t h e o n e c o n t a i n i n g A .

T h e r e a r e t h r e e o t h e r k i n d s o f d i s c o u r s e s e g m e n t s t h a t

c h a n g e t h e i n t e n t i o n a l s t r u c t u r e w i t h a r e s u l t i n g p u s h o f

n e w f o c u s s p a c e s o n t o t h e s t a c k : t h e t r u e - i n t e r r u p t i o n ,

w h e r e B i s n o t d o m i n a t e d b y A ; t h e f l a s h b a c k , w h e r e B

s a t i s f a c t i o n - p r e c e d e s A ; a n d t h e d i g r e s s i o n , w h e r e B i s

n o t d o m i n a t e d b y A , b u t s o m e e n t i t y f r o m t h e f o c u s

s p a c e c o n t a i n i n g A i s c a r r ie d o v e r t o t h e n e w f o c u s

s p a c e .

O n e w o u l d e x p e c t t h a t t h e r e m i g h t b e c u e p h r a s e s t h a t

w o u l d d i s t in g u i sh a m o n g a l l f o u r o f t h e s e k i n d s o f c h a n g -

e s . J u s t t h a t i s s o . T h e r e a r e c u e p h r a s e s t h a t a n n o u n c e

o n e a n d o n l y o n e k i n d o f c h a n g e . T h e c u e p h r a s e s

m e n t i o n e d a b o v e f o r ne w d o m i n a n c e a r e n e v e r u s e d fo r

t h e t h r e e ki n d s o f d is c o u r s e i n t e r r u p t i o n p u s h e s . T h e c u e

p h r a s e s f o r t r u e - i n t e r r u p t i o n s e x p r e s s t h e i n t e n t i o n t o

i n t e r r u p t ( e . g . E x c u s e m e a m i n u t e , o r m u s t i n t e r r u p t )

w h i l e t h e d i s t i n c t c u e p h r a s e f o r f l a s h b a c k s ( e . g . Oops,

f o r g o t a b o u t . . . ) i n d i c a t e s t h a t s o m e t h i n g i s o u t o f o r d e r .

T h e t y p i c a l o p e n i n g c u e p h r a s e s o f t h e d i g r e s s i o n

m e n t i o n t h e e n t i t y t h a t is b e i n g c a r d e d f o r w a r d ( e .g .

S p e a k i n g o f J o h n . .. o r D i d y o u h e a r a b o u t J o h n ? ).

DISCOURSE SE GMENTS

FOCUS SPACE STACK DOMINANC E HIER ARCH Y

teN,..~ 4,Uhu

dU,QI,p~iL~.

; t

/

/

\

x l

DSP = A

DSP = X

X DOMINATES A

F i g u r e 1 0. A n i n i t ia l d i s c o u r s e s t r u c t u r e c o n f i g u r a t i o n .

ATTENTIONAL~TATE CHANGE

DOMINANCE HIERARCHY

DSP = A

DSP = X

DSP = B

DSP = A

DSP = X

X DOMINATES A

A DOMINATES B

t I

t 2

F i g u re 1 1 . A t t e n t i o n a l a n d i n t e n t i o n a l s t r u c t u r e s f o r a n e w s u b s e g m e n t .

C o m p u t a t i o n a l L i n g u i st i c s , V o l u m e

12, Number 3, July-September 1986 197

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Cue phrases can also exhibit the satisfaction of a DSP,

and hence the completion of a discourse segment. The

completion of a segment causes the current space to be

popped from the stack. There are many means of

linguistically marking completions. In texts, paragraph

and chapter boundaries and explicit comments (e.g.

T h e

E n d ) are common. In conversations, completion can be

indicated either with cue phrases such as

f i n e

or

O K 1 5

or

with more explicit references to the satisfaction of the

intention (e.g.,

T h a t ' s a l l f o r p o i n t 2 ,

or

T h e a y e s h a v e i t . ) .

Most cue phrases that communicate changes to atten-

tional state announce pops of the focus stack. However ,

at least one cue phrase can be construed to indicate a

push, namely, T h a t r e m i n d s m e . By itself, this phrase does

not specify any particular change in intentional structure,

but merel y shows that ther e will be a new DSP. Since

this is equivalent to indicating that a new focus space is

to be pushed onto the stack, this cue phrase is best seen

as conveying attentional information.

Cue phrases that indicate pops to some other space

back in the stack include

b u t a n y w a y , a n y w a y , i n a n y c a s e ,

and

n o w b a c k t o . . .

When the current focus space is

popped from the stack, a space already on the stack

becomes most salient. Fro m the configuration in Figure

10, the space with A is popped from the stack, perhaps

with others, and another space on the stack becomes the

top of the stack. Popping back changes the stack without

creating a new DSP, or a dominance or satisfaction-

precedence relationship. The pop entails a return to an

old DSP; no change is effected in the intentional struc-

ture.

There are cue phrases, such as

n o w

and

n e x t ,

that

signal a change of attentional state, but do not distinguish

between the creation of a new focus space and the return

to an old one. These words can be used for either move.

For example, in a task-oriented discourse during which

some task has been mentioned but put aside to ask a

question, the use of

n o w

indicates a change of focus. The

utterance following n o w , however, will either return the

discussion to the deferred task or will introduce some

new task for consideration.

Note, finally, that a pop of the focus stack may be

achieved without the use of cue phrases as in the follow-

ing fragment of a task-oriented dialogue (Grosz 1974):

A: One bolt is stuck, i'm trying to use both the pliers and

the wrench to get it unstuck, but I haven't had much

luck.

E: Don 't use pliers. Show me what you are doing.

A: I'm pointing at the bolts.

E: Show me the 1/2 combina tion wrench, please.

A: OK.

E: Good, now show me the 1/2 box wrench.

A: I already got it loosened.

The last utterance in this fragment returns the

discourse to the discussion of the unstuck bolt. The pop

can be inferred only from the content of the main portion

of the utterance. The pronou n (or, more accurately, the

fact that it cannot be referring to the wrench) is a cue

that a pop is needed, but only the reference to the loos-

ening action allows the OCP to recognize to which

discourse segment this utterance belongs, as discussed by

Sidner (1979) and Robinson (1981). A summary of the

uses of cue phrases is given in Figure 12.

Attentional Change

(push) now, next, that reminds me, and, but

(pop to) anyway, but anyway, in any case, now back to

(complete) the end, ok, fine, (paragrap h break)

True interruption

I must interrupt, excuse me

Flashbacks

Oops, I forgot.

Digressions

By the way, incidentally, speaking of,

Did you hear about .... That r eminds me

Satisfaction-precedes

in the first place, first, second, finally, moreover,

furthermore

New dominance

for example, to wit, first, second, and, moreover,

furthermore, therefore, finally

Figure 12. The uses of cue phrases.

1 9 8 C o mp u ta t io n a l L ing u is ti c s, V o lu me 1 2 , N u m b er 3 , J u ly - S ep temb er 1 98 6

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Barbara J . Grosz and Candace L . S idner At tent ion , In tentions , and the S tructure of Discourse

T h e c a s e s l i s t e d h e r e d o n o t e x h a u s t t h e c h a n g e s i n

f o c u s s p a c e s a n d i n t h e d o m i n a n c e h i e r a r c h y t h a t c a n b e

r e p r e s e n t e d - n o r h a v e w e f u r n i s h e d a s e t o f r u l e s t h a t

s p e c i f y w h e n c u e p h r a s e s a r e n e c e s s a r y . A d d i t i o n a l

c a s e s , e s p e c i a l l y s p e c i a l s u b c a s e s o f t h e s e , m a y b e p o s s i -

b l e . W h e n d i s c o u r s e i s v i e w e d i n t e r m s o f i n t e n ti o n a l

s t r u c t u r e a n d a t t e n t i o n a l s t a t e , i t i s c l e a r e r j u s t w h a t

k i n d s o f i n f o r m a t i o n l i n g ui s ti c e x p r e s s i o n s a n d i n t o n a t i o n

c o n v e y t o th e h e a r e r a b o u t t h e d i s c o u r s e s t r uc t u r e .

F u r t h e r m o r e , i t i s c l e a r t h a t l i n g u i s t i c e x p r e s s i o n s c a n

f u n c t i o n a s c u e p h r a s e s , a s w e l l a s s e n t e n t ia l c o n n e c t i o n s ;

t h e y c a n t e l l t h e h e a r e r a b o u t c h a n g e s i n t h e d i s c o u r s e

s t r u c t u r e a n d b e c a r r i e r s o f d i s c o u r s e , r a t h e r t h a n

s e n t e n c e - l e v e l s e m a n t i c , m e a n i n g .

7 SOME PROPERTIES A N D P R O B L E M S O F

DISCOURSE-LEVEL INTENTIONS

T h e i n t e n t i o n s t h a t s e r v e a s D P / D S P s a r e n a t u r a l e x t e n -

s i o ns o f th e i n t e n t i o n s G r i c e ( 1 9 6 9 ) c o n s i d e r s e s s e n t i a l

t o d e v e l o p i n g a t h e o r y o f u t t e r e r ' s m e a n i n g . T h e r e i s a

c r u c i a l d i f f e r e n c e , h o w e v e r , b e t w e e n o u r u s e o f d i s c -

o u r s e - l e v e l i n t e n t i o n s i n th i s p a p e r ( a n d t h e t h e o r y , a s

d e v e l o p e d s o f a r ) a n d G r i c e ' s u s e o f u t t e r a n c e - l e v e l

i n t e n t i o n s . W e a r e n o t y e t a d d r e s s i n g t h e i s s u e o f

d i s c o u r s e

m e a n i n g ,

b u t a r e c o n c e r n e d w i t h t h e r o l e o f

D p / D S P s i n d e t e r m i n i n g d i s c o u r s e s t ruc ture a n d i n s p e c i -

f y i n g h o w t h e s e i n t e n t i o n s c a n b e r e c o g n i z e d b y a n O C P .

A l t h o u g h t h e i n t e n t i o n a l s t r u c t u r e o f a d i s c o u r s e p l a y s a

r o l e i n d e t e r m i n i n g d i s c o u r s e m e a n i n g , t h e D P / D S P s d o

n o t i n a n d o f t h e m s e l v e s c o n s t i t u t e d i s c o u rs e s e g m e n t

m e a n i n g . T h e c o n n e c t i o n b e t w e e n i n t e n t i o n a l s t r u c t u r e

a n d d i s c o u r s e m e a n i n g i s s i m i la r t o t h a t b e t w e e n a t t e n -

t i o n a l a n d c o g n i t i v e s t a t e s ; t h e a t t e n t i o n a l s t a t e p l a y s a

r o l e i n a h e a r e r ' s u n d e r s t a n d i n g o f w h a t t h e s p e a k e r

m e a n s b y a g i v e n s e q u e n c e o f u t t e r a n c e s i n a d i s c o u r s e

s e g m e n t , b u t i t i s n o t t h e o n l y a s p e c t o f c o g n i t i v e s t a t e

t h a t c o n t r i b u t e s t o t h i s u n d e r s t a n d i n g .

W e w i l l d r a w u p o n s o m e p a r t i c u l a r s o f G r i c e ' s d e f i -

n i t i o n o f u t t e r e r ' s m e a n i n g t o e x p l a i n D S P s m o r e f u l l y .

H i s i n i ti a l d e f i n i t i o n i s a s f o l l o w s :

U m e a n t s o m e t h i n g b y u t t e r i n g x i s t r u e i f f [ fo r

s o m e a u d i e n c e A ] :

1 . U i n t e n d e d , b y u t t e r i n g x , t o i n d u c e a c e r t a i n

r e s p o n s e i n A

2 . U i n t e n d e d A to r e c o g n i z e ,

a t l e as t i n p a r t f r o m

t he u t t e ranc e o f x , t h a t U in t e n d e d t o p r o d u c e

t h a t r e s p o n s e

3 . U i n t e n d e d t h e f u l f i l l m e n t o f t h e i n t e n t i o n

m e n t i o n e d i n ( 2 ) t o b e a t l e a s t in p a r t A ' s

r e a s o n f o r f u l f i l l i n g t h e i n t e n t i o n m e n t i o n e d i n

( 1 ) .

G r i c e r e f i n e s t h i s d e f i n i t i o n t o a d d r e s s a n u m b e r o f

c o u n t e r e x a m p l e s . T h e f o l lo w i n g p o r t i o n o f h i s f i n a l

d e f i n i t i o n 16 i s r e l e v a n t t o t h i s p a p e r :

B y u t t e r i n g x U m e a n t t h a t * 6 p is tr u e i f f

( ~ tA ) (3 f [ f e a t u r e s o f t h e u t t e r a n c e ] ) ( 3c [ w a y s o f

c o r r e l a t i n g f w i t h u t t e r a n c e s 1 7 ] ) :

( a ) U u t t e r e d x i n t e n d i n g

1 . A t o t h i n k x p o s s e s s e s f

2 . A t o t h i n k f c o r r e l a t e d i n w a y c w i t h ~ - i n g t h a t p

3 . A t o t h i n k , o n t h e b a s i s o f f u l f i ll m e n t o f ( 1 ) a n d

( 2 ) t h a t U i n t e n d s A t o t h i n k t h a t U ff s t h a t p

4 . A o n t h e b a s i s o f f u l f i l l m e n t o f ( 3 ) t o t h i n k t h a t

U ~ks th at p

5 . a n d ( i n s o m e c a s e s ) , A o n t h e b a s i s o f f u l fi l l-

m e n t o f ( 4 ) h i m s e l f t o ~ k t h a t p

G r i c e t a k e s * ~ p to b e t h e m e a n i n g o f t h e u t t e r a n c e ,

w h e r e * ff i s a m o o d i n d i c a t o r a s s o c i a t e d w i t h t h e p r o p o s i -

t i o n a l a t t i t u d e q~ ( e . g ., * q ~ = a s s e r t a n d ~ k = b e l i e v e ) . H e

c o n s i d e r s a t t i t u d e s l i k e b e l ie v i n g t h a t I C P i s a G e r m a n

s o l d ie r a n d i n t e n d i n g t o g i v e t h e I C P a b e e r a s e x a m p l e s

o f t h e k i n d s o f ~b-ing t h a t p t h a t u t t e r a n c e i n t e n t i o n s c a n

e m b e d . F o r e x p o s i t o r y p u r p o s e s , w e u s e t h e fo l l o w i n g

n o t a t i o n t o r e p r e s e n t t h e s e u t t e r a n c e - l e v e l i n t e n t i o n s :

I n t e n d ( I C P , B e l i e v e ( O C P , I C P is a G e r m a n s o l d i e r ) )

I n t e n d ( I C P , I n t e n d ( O C P , O C P g i v e I C P a b e e r ) )

T o e x t e n d G r i c e ' s d e f i n i t io n t o d i s c o u r s e s , w e r e p l a c e

t h e u t t e r a n c e x w i t h a d i s c o u r s e s e g m e n t D S , t h e u t t e r e r

U w i t h t h e i n i t i a t o r o f a d i s c o u r s e s e g m e n t I C P , a n d t h e

a u d i e n c e A w i t h t h e O C P . T o c o m p l e t e t hi s e x t e n s i o n ,

t h e f o l l o w i n g p r o b l e m s m u s t b e r e s o l v e d :

1 . s p e c i f y i n g t h e d i s c o u r s e - l e v e l in t e n t i o n s a n d a t t i t u d e s

t h a t c o r r e s p o n d t o t h e u t t e r a n c e - l e v e l i n t e n t i o n s a n d

~ ' s t ha t p ;

2 . i d e n t i f y in g t h e k i n d s o f f s t h a t c o n t r i b u t e t o d e t e r -

m i n i n g d i s c o u r s e - l e v e l i n t e n t io n s ;

3 . i d e n t i fy i n g t h e m o d e s o f c o r r e l a t i o n ( t h e c ' s ) b e t w e e n

f e a t u r e s o f t h e d i s c o u r s e s e g m e n t s a n d t y p e s o f d i s c -

o u r s e - l e v e l i n t e n t io n s ;

4 . s p e c i f y i n g h o w t h e d i s c o u r s e - l e v e l i n t e n t io n s c a n b e

r e c o g n i z e d b y a n O C P .

A l t h o u g h e a c h o f t h e s e i s s u e s i s a n u n r e s o l v e d p r o b -

l e m i n d i s c o u r s e t h e o r y , t h i s p a p e r h a s p r o v i d e d p a r t i a l

a n s w e r s . T h e e x a m p l e s p r e s e n t e d i ll u s tr a t e t h e r a n g e o f

d i s c o u r s e - l e v e l i n t e n t io n s ; t h e s e i n t e n t i o n s a p p e a r t o b e

s i m i l a r t o u t t e r a n c e - l e v e l i n t e n t i o n s i n k i n d , b u t d i f f e r i n

t h a t t h e y o c c u r i n a c o n t e x t i n w h i c h s e v e r a l u t t e r a n c e s

m a y b e re q u i r e d t o e n s u r e t h e i r c o m p r e h e n s i o n a n d s a t i s -

f a c t i o n . T h e f e a t u r e s s o f a r i d e n t i fi e d as c o n v e y i n g

i n f o r m a t i o n a b o u t D S P s a r e : s p e c i f i c li n g ui s ti c m a r k e r s

( e .g . , c u e p h r a s e s , i n t o n a t i o n ) , u t t e r a n c e - l e v e l i n t e n t i o n s ,

a n d p r o p o s i t i o n a l c o n t e n t o f t h e u t t e r a n c e s . W e h a v e n o t

e x p l o r e d t h e p r o b l e m o f i d e n t i f y i n g m o d e s o f c o r r e l a t i o n

i n a n y d e t ai l , b u t i t i s c l e a r t h a t t h o s e m o d e s t h a t o p e r a t e

a t t h e u t t e r a n c e l e v e l a l s o f u n c t i o n a t t h e d i s c o u r s e l e v e l.

A s d i s c u s s e d p r e v i o u s l y , t h e p r o p e r t r e a t m e n t o f t h e

r e c o g n i t i o n o f d i s c o u r s e - l e v e l i n t e n t i o n s i s e s p e c i a l l y

n e c e s s a r y f o r a c o m p u t a t i o n a l l y u s e f u l a c c o u n t o f

d i s c o u r se . A t t h e d i s c o u r s e l e v e l , j u s t a s a t t h e u t t e r a n c e

l e v e l , t h e i n t e n d e d r e c o g n i t i o n o f i n t e n t i o n s p l a y s a

C o m p u t a ti o n a l L i n g u is t ic s , V o l u m e 12 , N u m b e r 3 , J u l y - S e p t e m b e r 19 8 6 19 9

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c e n t r a l ro l e . T h e D S P s a r e i n t e n d e d t o b e r e c o g n i z e d :

t h e y a c h i e v e t h e i r e f f e c t s , i n p a r t , b e c a u s e t h e O C P

r e c o g n i z e s t h e I C P ' s i n t e n t i o n f o r t h e O C P t o ~ t h a t p .

T h e O C P ' s r e c o g n i t i o n o f t h i s i n t e n t i o n i s c r u c i a l t o i t s

a c h i e v i n g t h e d e s i r e d e f f e c t . I n S e c t i o n 4 w e d e s c r i b e d

c e r t a i n c o n s t r a i n t s o n t h e r e c o g n i t i o n p r o c e s s .

7.1 THE BASIC GENERALIZATION

I n e x t e n d i n g G r i c e ' s a n a l y s is t o t h e d i s c o u r s e l e v e l , w e

h a v e t o c o n s i d e r n o t o n l y i n d i v i d u a l b e l i e f s a n d

i n t e n t io n s , b u t a l s o t he r e l a t i o n s h ip s a m o n g t h e m t h a t

a r i se b e c a u s e o f th e r e l a t i o n s h i p s a m o n g v a r i o u s

d i s c o u r s e s e g m e n t s ( a n d u t t e r a n c e s w i t h i n a s e g m e n t )

a n d t h e p u r p o s e s t h e s e g m e n t s s e r v e w i t h r e s p e c t t o t h e

e n t i r e d i s c o u r s e . T o c l a r i f y t h e s e r e l a t i o n s h i p s , c o n s i d e r

a n a n a l o g o u s s i t u a t i o n w i t h n o n l i n g u i s t i c a c t i o n s . 18 A n

a c t i o n m a y d i v id e i n t o s e v e r a l s u b a c t io n s ; f o r e x a m p l e ,

t h e p l a n t i n g o f a r o s e b u s h d i v i d e s i n t o p r e p a r i n g t h e s o i l ,

d i g g i n g a h o l e , p l a c i n g t h e r o s e b u s h i n t h e h o l e , f i l l i n g

t h e r e s t o f t h e h o l e w i t h s o i l , a n d w a t e r i n g t h e g r o u n d

a r o u n d t h e b u s h . T h e i n t e n t i o n t o p e r f o r m t h e p l a n t i n g

a c t i o n i n c l ud e s s e v e r a l s u b s i d i a r y in t e n t i o n s ( o n e f o r

e a c h o f t h e s u b a c t i o n s - n a m e l y , t o d o i t) .

I n d i s c o u r s e , i n a m a n n e r t h a t i s a n a l o g o u s t o n o n l i n -

g u i s t i c a c t i o n s , t h e D P ( a n d s o m e D S P s ) i n c l u d e s s e v e r a l

s u b s i d i a r y i n t e n t i o n s r e l a t e d t o t h e D S P s i t d o m i n a t e s .

F o r p u r p o s e s o f e x p o s i t i o n , w e w i l l u s e t h e t e r m p r i m a r y

i n t en t i on

t o d i s t in g u i s h t h e o v e r a l l i n t e n t i o n o f t h e D P

f r o m t h e s u b s i d i a r y i n t e n t i o n s o f t h e D P . F o r e x a m p l e i n

t h e m o v i e s a r g u m e n t o f S e c t i o n 3 .1 , t h e p r i m a r y i n t e n -

t i o n i s f o r t h e r e a d e r t o c o m e t o b e l i e v e th a t p a r e n t s a n d

t e a c h e r s s h o u l d k e e p c h i l d r e n f r o m s e e i n g t o o m a n y

m o v i e s ; i n t h e t a s k d i a l o g u e o f S e c t i o n 3 . 2 , t h e i n t e n t i o n

i s t h a t th e a p p r e n t i c e r e m o v e t h e f l y w h e e l . S u b s i d i a r y

i n t e n t i o n s i n c l u d e , r e s p e c t i v e l y , t h e i n t e n t i o n t h a t t h e

r e a d e r b e l i e v e t h a t i t i s i m p o r t a n t t o e v a l u a t e m o v i e s a n d

t h e i n t e n t i o n t h a t t h e e x p e r t h e l p t h e a p p r e n t i c e l o c a t e

t h e s e c o n d s e t s c r e w .

B e c a u s e t h e b e l i e f s a n d i n t e n t i o n s o f a t l e a s t t w o

d i f f e r e n t p a r t i c i p a n t s a r e i n v o l v e d i n d i s c ou r s e , t w o p r o p -

e r t i e s o f t h e g e n e r a l - a c t i o n s i t u a t i o n ( a s s u m i n g a s i n g l e

a g e n t p e r f o r m s a ll a c t i o n s ) d o n o t c a r r y o v e r . F i r s t, i n a

d i s c o u r se , t h e I C P i n t e n d s t h e O C P t o r e c o g n i z e t h e I C P ' s

b e l i e f s a b o u t t h e c o n n e c t i o n s a m o n g v a r i o u s p r o p o s i t i o n s

a n d a c t i o n s . F o r e x a m p l e , i n t h e m o v i e s a r g u m e n t , t h e

r e a d e r ( O C P ) i s i n t e n d e d t o r e c o g n i z e t h a t t h e a u t h o r

( I C P ) b e l i e v e s s o m e p r o p o s i t i o n s p r o v i d e s u p p o r t f o r

o t h e r s ; i n t h e t a s k d i a l o g u e t h e e x p e r t ( I C P ) i n t e n d s t h e

a p p r e n t i c e ( O C P ) t o r e c o g n i z e t h a t t h e e x p e r t b e l i e v e s

t h e p e r f o r m a n c e o f c e r t a i n a c t i o n s c o n t r i b u t e s t o t h e

p e r f o r m a n c e o f o t h e r a c t i o n s . I n c o n t r a s t , i n t h e g e n e r -

a l - a c t i o n s i t u a t i o n i n w h i c h t h e r e i s n o c o m m u n i c a t i o n ,

t h e r e i s n o n e e d f o r r e c o g n i t i o n o f a n o t h e r a g e n t ' s b e l i e f s

a b o u t t h e i n t e r r e l a t i o n s h ip o f v a r i o u s a c t i o n s a n d

i n t e n t i o n s .

T h e s e c o n d d i f f e r e n c e c o n c e r n s t h e e x t e n t t o w h i c h

t h e s u b s i d i a r y a c t i o n s o r i n t e n t i o n s s p e c i f y th e o v e r a l l

a c t i o n o r i n t e n t io n . T o p e r f o r m s o m e a c t i o n , t h e a g e n t

m u s t p e r f o r m e a c h o f t h e s u b a c t i o n s i n v o lv e d ; b y

p e r f o r m i n g a ll o f t h e s e s u b a c t i o n s t h e a g e n t p e r f o r m s t h e

a c t i o n . I n c o n t r a s t i n a d i s c o u r s e , t h e p a r t i c i p a n t s s h a r e

t h e a s s u m p t i o n o f d i s c o u r s e s u f f i c i e n c y : i t i s a c o n v e n t i o n

o f t h e c o m m u n i c a t i v e s i t u a t i o n t h a t t h e I C P b e l i e v e s t h e

d i s c o u r s e i s s u f f i c ie n t t o a c h i e v e t h e p r i m a r y i n t e n t i o n o f

t h e D P . D i s c o u r s e s u f f i c i e n c y d o e s n o t e n t a i l l o g ic a l

s u f f i c i e n c y o r a c t i o n c o m p l e t e n e s s . I t i s n o t n e c e s s a r i l y

t h e c a s e t h a t s a t i s f a c t i o n o f a l l o f t h e D S P s i s s u f f i c i e n t i n

a n d o f i ts e l f f o r s a t i s f a c t i o n o f t h e D P . R a t h e r , t h e r e i s a n

a s s u m p t i o n t h a t t h e i n f o r m a t i o n c o n v e y e d i n t h e

d i s c o u r s e w i l l s u f f i c e i n c o n ju n c t i o n w i t h o t h e r i n f o r m a t i o n

t h e I C P b e l i e v es t h e O C P h a s ( o r c a n o b t a i n ) t o a l l o w f o r

s a t i s f a c t i o n o f t h e p r i m a r y i n t e n t i o n o f t h e D P . S a t i s f a c -

t i o n o f a l l o f t h e D S P s , i n c o n j u n c t i o n w i t h t h i s a d d i t i o n a l

i n f o r m a t i o n , is e n o u g h f o r s a t i s fa c t i o n o f t h e D P . H e n c e ,

i n d is c o u r s e t h e i n t e n t i o n a l s t r u c t u r e ( t h e a n a l o g u e o f t h e

a c t i o n h i e r a r c h y ) n e e d n o t b e c o m p l e t e .

F o r e x a m p l e , t h e p r o p o s i t i o n s e x p r e s s e d i n t h e m o v i e s

e s s a y d o n o t p r o v i d e a l o g i c a ll y s u f f i c i e n t p r o o f o f t h e

c l a i m . T h e a u t h o r f u r n i s h e s i n f o r m a t i o n h e b e l i e v e s t o b e

a d e q u a t e f o r t h e r e a d e r t o r e a c h t h e d e s i r e d c o n c l u s i o n

a n d a s s u m e s t h e r e a d e r w i l l s u p p l e m e n t w h a t i s a c t u a l l y

s a i d w i t h a p p r o p r i a t e a d d i t i o n a l i n f o r m a t i o n a n d r e a s o n -

i n g. L i k e w i s e , t h e t a s k d i a lo g u e d o e s n o t m e n t i o n a l l t h e

s u b t a s k s e x pl i ci t ly . I n s t e a d , t h e e x p e r t a n d a p p r e n t i c e

d i s c us s e x p l i c it l y o n l y t h o s e s u b t a s k s f o r w h i c h s o m e

i n s t r u c t i o n i s n e e d e d o r i n c o n n e c t i o n w i t h w h i c h s o m e

p r o b l e m a r i se s .

T o b e m o r e c o n c r e t e , w e s h a l l l o o k a t t h e e x t e n s i o n o f

t h e G r i c e a n a n a l y s i s f o r t w o p a r t i c u l a r c a s e s , o n e i n v o l v -

i n g a b e l i e f , t h e o t h e r a n i n t e n t i o n t o p e r f o r m s o m e

a c t i o n . W e s h a ll c o n s i d e r o n l y t h e s i m p l e s t s i t u a t io n s , i n

w h i c h t h e p r i m a r y in t e n ti o n s o f t h e D P / D S P s a r e a b o u t

e i t h e r b e l ie f s o r a c t i o n s , b u t n o t a m i x t u r e . A l t h o u g h t h e

t a s k d i a l o g u e o b v i o u s l y i n v o l v e s a m i x t u r e , t h i s i s a n

e x t r e m e l y c o m p l i c a t e d i s s ue t h a t d e m a n d s a d d i ti o n a l

r e s e a r c h .

7.2 THE BELIEF CASE

I n t h e b e l i e f c a s e , th e p r i m a r y i n t e n t i o n o f t h e D P i s t o

g e t t h e O C P t o b e l i e v e s o m e p r o p o s i t i o n , s a y p . E a c h o f

t h e d i s c o u r s e s e g m e n t s i s a l s o i n t e n d e d t o g e t t h e O C P t o

b e l i e v e a p r o p o s i t i o n , s a y q i f o r s o m e i = 1 . . . . n ( w h e r e

t h e r e a r e n d i sc o u r s e s e g m e n t s ) . I n a d d i t io n t o t h e p r i m a -

r y i n t e n t i o n - i . e ., t h a t t he O C P s h o u l d c o m e t o b e l i e v e p

t h e D P in c l u d e s a n i n t e n t i o n t h a t t h e O C P c o m e t o

b e l i e v e e a c h o f t h e q i a n d , i n a d d i t i o n , a n i n t e n t i o n t h a t

t h e O C P c o m e t o b e l i e v e t h e q i p r o v i d e s u p p o r t f o r p . W e

c a n r e p r e s e n t t h i s s c h e m a t i c a l l y a s : 19

Y i = 1 . . .. n I n t e n d ( I C P , B e l i e v e ( O C P , p ) A

B e l i e v e ( O C P , q i ) A

B e l i e ve ( O C P , S u p p o r t s ( p , q l A . . . A q n ) ) )

T h e r e a r e s e v e r a l t hi n g s to n o t e h e r e . T o b e g i n w i t h,

t h e f i r s t i n t e n t io n , ( I n t e n d I C P ( B e l i e v e ( O C P p ) ) , i s th e

p r i m a r y c o m p o n e n t o f t h e DS P . S e c o n d , e a c h o f t h e

20 0 Computational Linguistics, Volume 12, Number 3, July-Sept ember 1986

7/17/2019 Grosz & Sidner (1986)



i n t e n d e d b e l i e fs in th e s e c o n d c o n j u n c t c o r r e s p o n d s t o

t h e p r i m a r y c o m p o n e n t o f t h e D S P o f s o m e e m b e d d e d

d i s c o u r se s e g m e n t . T h i r d , t h e

supports

r e l a t i o n i s n o t

i m p l i ca t i o n. T h e O C P i s n o t i n t e n d e d t o b e l i e v e t h a t t h e

q i i m p l y p , b u t r a t h e r t o b e l i e v e t h a t t h e q i i n c o n j u n c t i o n

w i t h o t h e r f a c t s a n d r u l e s t h a t t h e I C P a s s u m e s t h e O C P

h a s a v a i l a b l e o r c a n o b t a i n a n d t h u s c o m e t o b e l i e v e a r e

s u f f i c i e n t f o r t h e O C P t o c o n c l u d e p . F o u r t h , t h e

D P / D S P m a y o n l y b e c o m p l e t e l y d e t e r m i n e d a t t h e e n d

o f t h e d i s c o u r s e ( s e g m e n t ) , a s w e d i s c u s s e d i n S e c t i o n 4 .

F i n a l l y , t o d e t e r m i n e h o w t h e d i s c o u r s e s e g m e n t s

c o r r e s p o n d i n g t o t h e q i a r e r e l a t e d t o t h e o n e c o r r e -

s p o n d i n g t o p , t h e O C P o n l y h a s t o b e l i e v e t h a t t h e I C P

b e l i e v e s a s u p p o r t s r e l a t i o n s h ip h o ld s . H e n c e , f o r t h e

p u r p o s e o f r e c o g n i z i n g t h e d i s c o u r s e s t r u c t u r e , i t w o u l d

b e s u f f i c i e n t f o r t h e t h i r d c l a u s e t o b e

. . . B e l i e v e ( O C P , B e l i e v e ( I C P ,

S u p p o r ts ( p , q l A . . .A q n ) ) )

H o w e v e r , t h e D P o f a b e l i e f - c a s e d i s c o u r s e i s n o t m e r e l y

t o g e t t h e O C P t o b e l i e v e p , b u t t o g e t t h e O C P t o b e l i e v e

p b y v i r t u e o f b e l i e v i n g t h e q i . T h a t t h i s i s s o c a n b e s e e n

c l e a r l y b y c o n s i d e r i n g s i t u a t i o n s i n w h i c h t h e O C P

a l r e a d y b e l i e v e s p a n d i s k n o w n b y t h e I C P t o d o s o , b u t

d o e s n o t h a v e a g o o d r e a s o n f o r b e l i e v i n g p . T h i s l a s t

p r o p e r t y o f t h e b e l i e f c a s e i s n o t s h a r e d b y t h e a c t i o n

c a s e .

T h e r e i s a n i m p o r t a n t r e l a t i o n s h i p b e t w e e n t h e

s u p p o r t s r e l a t i o n a n d t h e d o m i n a n c e r e l a t i o n t h a t c a n

h o l d b e t w e e n D P / D S P s ; i t i s c a p t u r e d i n t h e f o l lo w i n g

r u le ( u s i n g th e s a m e n o t a t i o n a s a b o v e ) :

¥ i = 1 . . .. n I n t e n d ( C P 1, B e l i e v e ( C P 2 , p ) ) A

I n t e n d ( C P p B e l i e v e ( C P 2 , q i ) ) A

B e l i e v e ( C P p S up p o r t s( p , q l A . . . A q n ) ) ~

D O M ( I n t e n d ( C P p B e l ie v e (C P 2 ,p ) )

I n t e n d ( C P 1 , B e l i e v e ( C P 2 , q i ) ) )

T h e i m p l i c a t io n i n t he f o r w a r d d i r e c t i o n s t a t e s t h a t i f a

c o n v e r s a t i o n a l p a r t i c i p a n t ( C P I ) b e l i e v e s t h a t t h e p r o p o -

s i t i o n p i s s u p p o r t e d b y t h e p r o p o s i t i o n q i , a n d h e i n t e n d s

a n o t h e r p a r t i c i p a n t ( C P 2 ) t o a d o p t t h e s e b e l i e f s , t h e n h i s

i n t e n t i o n t h a t CP 2 b e l i e v e p d o m i n a t e s h i s i n t e n t io n t h a t

C P 2 b e l i e v e q i- V i e w e d i n t u i t iv e l y , C P l ' s b e l i e f t h a t q i

p r o v i d e s s u p p o r t f o r p , u n d e r l i e s h i s i n t e n t i o n t o g e t CP 2

t o b e l i e v e p b y g e t t i n g h i m t o b e l i e v e q i . T h e s a t i s f a c t i o n

o f C P ~ ' s i n t e n t i o n t h a t C P 2 s h o u l d b e l i e v e q i w il l h e l p

s a t i s f y C P ~ ' s i n t e n t i o n t h a t

CP 2

b e l i e v e p . T h i s r e l a t i o n -

s h i p p l a y s a r o l e i n t h e r e c o g n i t i o n o f D S P s.

7.3 THE ACTION CASE

A n a n a l o g o u s s i t u a t i o n h o l d s f o r a d i s c o u r s e s e g m e n t

c o m p r i s i n g u t t e r a n c e s i n t e n d e d t o g e t t h e O C P t o

p e r f o r m s o m e s e t o f a c t i o n s d i r e c t e d a t a c h i e v i n g s o m e

o v e r a l l t a s k ( e . g ., s o m e s e g m e n t s i n th e t a s k - o r i e n t e d

d i a l o g u e o f S e c t i o n 3 . 2 ) . T h e f u l l s p e c i f i c a t i o n o f t h e

D P / D S P c o n t a i n s a

generates

r e l a t i o n t h a t i s d e r i v e d f r o m

a r e l a t i o n d e f i n e d b y G o l d m a n ( 1 9 7 0 ) . F o r t h i s c a s e , t h e

D P / D S P s a r e o f t h e f o l l o w i n g f o r m :

¥ i = 1 . . .. n I n t e n d ( IC P , I n t e n d ( O C P , D o ( A ) ) A

I n t e n d ( O C P , D o ( a i ) ) A

B e l i e v e ( O C P , B e l i e v e ( I C P ,

G e n e r a t e s ( A , a l A . . . A a n ) ) ) )

E a c h i n t e n t i o n t o a c t r e p r e s e n t e d i n t h e s e c o n d c o n j u n c t

c o r r e s p o n d s t o t h e p r i m a r y i n t e n t i o n o f s o m e d i s c o u r s e

s e g m e n t .

L i k e s u p p o r t s , t h e g e n e r a t e s r e l a t i o n i s p a r t i a l ( i t s

p a r t i a l i t y d i s t i n g u i s h e s i t i n p a r t f r o m G o l d m a n ' s

r e l a t i o n ) . T h u s , t h e O C P i s n o t i n t e n d e d t o b e l i e v e t h a t

t h e I C P b e l i e v e s t h a t p e r f o r m a n c e o f a i a l o n e i s s u ff i c i e n t

f o r p e r f o r m a n c e o f A , b u t r a t h e r t h a t d o i n g a ll o f t h e a i

a n d o t h e r a c t i o n s t h a t t h e O C P c a n b e e x p e c t e d t o k n o w

o r fi g u r e o u t c o n s t i t u t e s a p e r f o r m a n c e o f A . I n th e t a s k

d i a l o g u e o f S e c t i o n 3 .2 , m a n y a c t i o n s t h a t a r e e s s e n t i a l t o

t h e t a s k ( e . g . , t h e a p p r e n t i c e p i c k i n g u p t h e A l l e n w r e n c h

a n d a p p l y i n g i t c o r r e c t l y t o t h e s e t s c r e w s ) a r e n e v e r e v e n

m e n t i o n e d i n t he d i a l o g u e .

N o t e t h a t i t i s u n n e c e s s a r y f o r t h e I C P o r O C P t o h a v e

a c o m p l e t e p l a n r ~ l a t i n g a l l o f t h e a i t o A a t t h e s t a r t o f

t h e d i s c o u r s e ( o r d i s c o u r s e s e g m e n t ) . A l l th a t i s r e q u i r e d

i s t h a t , f o r a n y g i v e n s e g m e n t , t h e O C P b e a b l e t o d e t e r -

m i n e w h a t i n t e n t io n t o a c t t h e s e g m e n t c o r r e s p o n d s t o

a n d w h i c h o t h e r i n t e n t i o n s d o m i n a t e t h a t i n t e n t i o n .

F i n a l ly , u n l ik e t h e b e l i e f c a s e , th e t h i r d c o n j u n c t h e r e

r e q u i r e s o n l y t h a t t h e O C P r e c o g n i z e t h a t t h e I C P

b e l i e v e s a g e n e r a t e s r e l a t i o n s h i p h o l d s . T h e O C P c a n d o

A b y v i r t u e o f d o i n g t h e a i w i t h o u t c o m i n g h i m s e l f t o

b e l i e v e a n y t h i n g a b o u t t h e r e l a ti o n s h i p s b e t w e e n A a n d

the a i .

A s i n t h e b e l i e f c a s e , t h e r e i s a n e q u i v a l e n c e t h a t l i n k s

t h e g e n e r a t e s r e l a t i o n a m o n g a c t i o n s t o t h e d o m i n a n c e

r e l a t i o n b e t w e e n i n t e n t i o n s . S c h e m a t i c a l l y , i t i s a s

f o l l o w s :

¥ i = 1 . . . . n I n t e n d ( C P 1, I n t e n d ( C P 2, D o ( A ) ) ) A

I n t e n d ( C P 1 , I n t e n d ( C P 2 , D o ( a i ) ) ) A

B e l i e v e ( C P t , G e n e r a t e s ( A , a l A . . . A a n ) ) < >

D O M ( I n t e n d (C P 1 , I n te n d (C P 2 , D o ( A ) ) )

I n t e n d ( C P t, I n t e n d ( C P 2, D o ( a i ) ) ) )

T h i s e q u i v a l e n c e s t a t e s t h a t , i f a n a g e n t ( C P 1) b e l i e v e s

t h a t t h e p e r f o r m a n c e o f s o m e a c t i o n ( a i ) c o n t r i b u t e s i n

p a r t t o t h e p e r f o r m a n c e o f a n o t h e r a c t i o n ( A ) , a n d i f C P 1

i n t e n d s f o r

CP 2 to

( i n t e n d t o ) d o b o t h o f t h e s e a c t i o n s ,

t h e n h i s i n t e n t i o n t h a t C P 2 ( i n t e n d t o ) p e r f o r m a i is

d o m i n a t e d b y h is i n te n t i o n t h a t CP 2 ( i n t e n d t o ) p e r f o r m

A . V i e w e d i n t u i t i v e l y , C P 1 ' s b e l i e f t h a t d o i n g a i w i l l

c o n t r i b u t e t o d o i n g A u n d e r l i e s h i s i n t e n t i o n t o g e t

CP 2

t o d o A b y g e t t i n g CP 2 to d o a i. T h e s a t i s f a c t i o n o f C P t ' s

i n t e n t i o n f o r C P 2 t o d o a i w i l l h e l p s a t i s f y C P ~ ' s i n t e n t i o n

f o r

CP 2 to

d o A .

S o , f o r e x a m p l e , i n t h e t a s k - o r i e n t e d d i a l o g u e o f

S e c t i o n 3 . 2 , t h e e x p e r t k n o w s t h a t u s i n g t h e w h e e l p u l l e r

i s a n e c e s s a r y p a r t o f r e m o v i n g t h e f l y w h e e l . H i s i n t e n -

t i o n t h a t t h e a p p r e n t i c e i n t e n d t o u s e t h e w h e e l p u U e r i s

t h u s d o m i n a t e d b y h i s i n t e n t i o n t h a t t h e a p p r e n t i c e

i n t e n d t o t a k e o f f t h e f l y w h e e l . S a t i s f a c t i o n o f t h e i n t e n -

t i o n t o u s e t h e w h e e l p u l l e r w i l l c o n t r i b u t e t o s a t i s f y i n g

C o m p u t a t i o n a l L i n g u i s t i c s , V o l u m e 1 2 , N u m b e r 3 , J u l y - S e p t e m b e r 1986 201

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Barbara J . Grusz and Candace L . S idner At tent ion , In tent ions , and the S tructure of Discourse

t h e i n t e n t i o n t o r e m o v e t h e f l y w h e e l . I n g e n e r a l , t h e

a c t i o n a i d o e s n o t h a v e t o b e a n e c e s s a r y a c t i o n t h o u g h i t

i s i n th i s e x a m p l e ( a t l e a s t i f t h e t a s k i s d o n e c o r r e c t l y ) .

A d e f i n i t i v e s t a t e m e n t c h a r a c t e r i z i n g p r i m a r y a n d

s u b s i d ia r y i n t e n t i o n s f o r t a s k - o r i e n t e d d i a l o gu e s a w a i t s

f u r t h e r r e s e a r c h n o t o n l y i n d i s c o u r s e t h e o r y , b u t a l s o i n

t h e t h e o r y o f i n t e n t i o n s a n d a c t i o n s . I n p a r t i c u l a r , a

c l e a r e r s t a t e m e n t o f th e i n t e r a c t i o n s a m o n g t h e

i n t e n t i o n s o f t h e v a r i o u s d i s c o u r s e p a r t i c i p a n t s ( w i t h

r e s p e c t t o b o t h l i n g u i s t i c a n d n o n l i n g u i s t i c a c t i o n s )

a w a i t s t h e f o r m u l a t i o n o f a b e t t e r t h e o r y o f c o o p e r a t i o n

a n d m u l t i a g e n t a c t i v i t y .

7.4 RHETORICALRELATIONS

W e a r e n o w i n a p o s i t i o n t o c o n t r a s t t h e r o l e o f

D P / D S P s , s u p p o r t s , g e n e r a t e s , D O M , a n d S P in o u r t h e o -

r y w i t h t h e r h e t o r i c a l r e l a t i o n s t h a t , a c c o r d i n g t o a

n u m b e r o f a l te r n a t i v e t h e o r ie s ( e . g. , G r i m e s 1 9 7 5 , H o b b s

1 9 79 , M a n n a n d T h o m p s o n 1 9 8 3 , R e i c h m a n - A d a r 1 9 8 4 ,

M c K e o w n 1 9 8 5 ) , a r e c la i m e d t o u n d e r l ie d i s c o u r s e s t r u c -

t u r e. A m o n g t h e v a r i ou s rh e t o r i c a l r e l a t i o n s t h a t h a v e

b e e n i n v e s t i g a t e d a r e e l a b o r a t i o n , s u m m a r i z a t i o n ,

e n a b l e m e n t , ju s t if i c a t io n , a n d c ha l l e n ge . A l t h o u g h t h e

t h e o r i e s e a c h i d e n t i f y d i f f e r e n t s p e c i f i c r e l a t i o n s , t h e y a l l

u s e s u c h r e l a t i o n s a s t h e b a s i s f o r d e t e r m i n i n g d i s c o u r s e

s t r u c t u r e .

T h e s e r h e t o r i c a l r e l a t i o n s a p p l y s p e c i f i c a l l y t o l i n g u i s -

t i c b e h a v i o r a n d m o s t o f t h e m i m p l i c i t l y i n c o r p o r a t e

i n t e n t i o ns ( e .g . , th e i n t e n t i o n t o s u m m a r i z e , t h e i n t e n t i o n

t o j u s ti f y ) . T h e i n t e n t i o n s t h a t t y p i c a ll y s e r v e a s D P / D S P s

i n o u r t h e o r y a r e m o r e b a s i c t h a n t h o s e t h a t u n d e r l i e

s u c h r h e t o r i c a l r e l a t i o n s i n t h a t t h e y a r e n o t s p e c i a l i z e d

f o r l i n g u i s t i c b e h a v i o r ; i n m a n y c a s e s , t h e i r s a t i s f a c t i o n

c a n b e r e a l i z e d b y n o n l i n g u i s t i c a c t i o n s a s w e l l a s l i n g u i s -

t i c o n es .

T h e s u p p o r t s a n d g e n e r a t e s r e l a t i o n s t h a t m u s t s o m e -

t i m e s b e i n f e r r e d t o d e t e r m i n e d o m i n a t i o n a r e a l s o m o r e

b a s i c t h a n r h e t o r i c a l r e l a t i o n s ; t h e y a r e g e n e r a l r e l a t i o n s

t h a t ho l d b e t w e e n p r o p o s i t i o n s a n d a c t io n s . H e n c e , t h e

i n f e r r i n g o f r e l a t i o n s h i p s s u c h a s s u p p o r t s a n d g e n e r a t e s

i s s i m p l e r t h a n t h a t o f r h e t o r i c a l r e l a t i o n s h i p s . T h e

d e t e r m i n a t i o n o f w h e t h e r a s u p p o r t s o r g e n e r a t e s

r e l a t i o n s h i p e x i s t s d e p e n d s o n l y o n f a c t s o f h o w t h e

w o r l d i s , n o t o n f a c t s o f t h e d i s c o u r s e . I n c o n t r a s t , t h e

r e c o g n i t i o n o f r h e t o r i c a l r e l a t i o n s r e q u i r e s t h e c o m b i n e d

u s e o f di s c o u r s e a n d d o m a i n i n f o r m a t i o n .

F o r s e v e r a l r e a s o n s , r h e t o r i c a l r e la t i o n s h i p s d o n o t

h a v e a p r i v i l e g e d s t a t u s i n t h e a c c o u n t g i v e n h e r e .

A l t h o u g h t h e y a p p e a r t o p r o v i d e a m e t a l e v e l d e s c r i p t i o n

o f t h e d i s c o u r s e , t h e i r r o l e i n d i s c o u r s e i n t e r p r e t a t i o n

r e m a i n s u n c l ea r . A s r e g a r d s d i s c o u r s e p r o c e s s i n g , i t

s e e m s o b v i o u s t h a t t h e I C P a n d O C P h a v e e s s e n t i a l l y

d i f f e r e n t a c c e s s to t h e m . I n p a r ti c u l a r , th e I C P m a y w e l l

h a v e s u c h r h e t o r ic a l r e l a t i o ns h i p s i n m i n d a s h e

p r o d u c e s u tt e r a n c e s ( a s i n M c K e o w n ' s ( 1 9 8 5 ) s y s t e m ) ,

w h e r e a s i t i s m u c h l e ss c l e a r w h e n ( i f a t a l l) t h e O C P

i n f e r s th e m . A c l a i m o f t h e t h e o r y b e i n g d e v e l o p e d i n th i s

p a p e r is t h a t a d i s c o u r s e c a n b e u n d e r s t o o d a t a b a s i c

l e v e l e v e n i f t h e O C P n e v e r d o e s o r c a n c o n s t r u c t , l e t

a l o n e n a m e , s u c h r h e t o r i c a l r e l a t io n s h i p s . F u r t h e r m o r e ,

i t a p p e a r s t h a t t h e s e r e l a t i o n s h i p s c o u l d b e r e c a s t a s a

c o m b i n a t i o n o f d o m a i n - s p e c i f i c i n f o r m a t i o n , g e n e r a l

r e l a t i o n s b e t w e e n p r o p o s i t i o n s a n d a c t i o n s ( e . g . , s u p p o r t s

a n d g e n e r a t e s ) , a n d g e n e r a l r e l a t i o n s b e t w e e n i n t e n t i o n s

( e .g . , d o m i n a t i o n a n d s a t i s f a c t i o n - p r e c e d e n c e ) . 2 0 E v e n

s o , r h e t o r i c a l r e l a t i o n s h i p s a r e , i n a ll l i k e l i h o o d , u s e f u l t o

t h e t h e o r e t i c i a n a s a n a n a l y t i c a l t o o l f o r c e r t a i n a s p e c t s

o f d i s c o u r s e a n a l y s i s .

8 CONCLUSIONS AND FUTU RE RESEARCH

T h e t h e o r y o f d i s c o u r s e s t r u c t u r e p r e s e n t e d i n t h i s p a p e r

i s a g e n e r a l i z a t i o n o f t h e o r i e s o f t a s k - o r i e n t e d d i a l o g u e s .

I t d i ff e r s f r o m p r e v i o u s g e n e r a l i z a t i o n s i n t h a t i t c a r e f u l ly

d i s t in g u i s h e s t h r e e c o m p o n e n t s o f d i s c o u r s e s t r u c t u re :

o n e l i n g u i s t i c , o n e i n t e n t i o n a l , a n d o n e a t t e n t i o n a l . T h i s

d i s t i n c t i o n p r o v i d e s a n e s s e n t i a l b a s i s f o r e x p l a i n i n g

i n t e r r u p t io n s , c u e p h r a s e s , a n d r e f e r r i n g e x p r e s s i o n s .

T h e p a r t i c u l a r i n t e n t i o n a l s t r u c t u r e u s e d a l s o d i f f e r s

f r o m t h e a n a l o g o u s a s p e c t o f p r e v i o u s g e n e r a l i z a t io n s .

A l t h o u g h , l i k e t h o s e g e n e r a l i z a t i o n s , i t s u p p l i e s t h e p r i n -

c i pa l f r a m e w o r k f o r d is c o u rs e s e g m e n t a t i o n a n d d e t e r -

m i n e s s t r u c t u r a l r e l a t i o n s h i p s f o r t h e f o c u s i n g s t r u c t u r e

( p a r t o f t h e a t t e n t i o n a l s t a t e ) , u n l i ke i t s p r e d e c e s s o r s i t

d o e s n o t d e p e n d o n t h e s p e c i a l d e t a i l s o f a n y s i n g l e

d o m a i n o r t y p e o f d i s c o u rs e .

A l t h o u g h a d m i t t e d l y s t il l i n c o m p l e t e , t h e t h e o r y d o e s

p r o v i d e a s o l i d b a s i s f o r i n v e s t i g a t i n g b o t h t h e s t r u c t u r e

a n d m e a n i n g o f d i s c o u r s e , a s w e l l a s f o r c o n s t r u c t i n g

d i s c o u r s e - p r o c e s s i n g s y s t e m s . S e v e r a l d i f f ic u l t r e s e a r c h

p r o b l e m s r e m a i n t o b e e x p l o r e d . O f t h e s e , w e t a k e t h e

f o l l o w i n g t o b e o f p r i m a r y i m p o r t a n c e :

1 . S p e c i f i c a t i o n o f t h e r e l a t i o n s h i p b e t w e e n d i s c o u r s e -

l e v e l ( D P / D S P ) a n d u t t e r a n c e - l e v e l i n t e n t i o n s ;

2 . I d e n t i f i c a t i o n o f th e i n f o r m a t i o n t h a t d i s c o u r s e p a r t i c -

i p a n t s u s e t o r e c o g n i z e t h e s e i n t e n t i o n s , a n d t h e w a y s

i n w h i c h t h e y u t i l iz e i t ;

3 D e v e l o p m e n t o f a n a d e q u a t e t r e a t m e n t o f t h e i n te r -

a c t i o n a m o n g i n t e n t i o n s o f m u l t i p l e p a r t i c ip a n t s ;

4 . I n v e s t i g a t i o n o f t h e e f f e c t o f m u l t i p le D S P s o n t h e

t h e o r y ;

5 . I n v e s t i g a t i o n o f a l t e r n a t i v e m o d e l s o f a t t e n t i o n a l

s t a t e .

F i n a l l y , t h e t h e o r y s u g g e s t s s e v e r a l i m p o r t a n t c o n j e c -

t u r e s . F i r st , t h a t a d i s c o u r s e i s c o h e r e n t o n l y w h e n i t s

d i s c o u r s e p u r p o s e i s s h a r e d b y a l l t h e p a r t i c i p a n t s a n d

w h e n e a c h u t t e r a n c e o f th e d i s c o u r se c o n t r i b u t e s t o

a c h i e v i n g t h i s p u r p o s e , e i t h e r d i r e c t l y o r i n d i r e c t l y , b y

c o n t r i b u t i n g t o t h e s a t i s f a c t i o n o f a d i s c o u r s e s e g m e n t

p u r p o s e . S e c o n d , g e n e r a l i n t u it i o n s a b o u t t o p i c c o r r e -

s p o n d m o s t c l o s e ly t o D P / D S P s , r a t h e r t h a n t o s y n t a c t i c

o r a t te n t i o n a l c o n c e p t s . F i n a l ly , t h e t h e o r y s u g g e s t s th a t

t h e s a m e i n t e n t i o n a l s t r u c t u r e c a n g i v e r i s e t o d i f f e r e n t

a t t e n t i o n a l s t ru c t u r e s t h r o u g h d i f f e r e n t d i s c o u r s e s . T h e

d i f f e r e n t a t t e n t i o n a l s t r u c t u r e s w i l l b e m a n i f e s t i n p a r t

2 0 2 C o m p u t a ti o n a l L i n g u is t ic s , V o l u m e 12 , N u m b e r 3 , J u l y - S e p t e m b e r 19 8 6

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Barbara J . Grosz and Candace L . S idner At tent ion , In tentions , and the S tructure of Discourse

b e c a u s e d i f f e r e n t r e f e r r i n g e x p r e s s i o n s w i l l b e v a l i d , a n d

i n p a r t b e c a u s e d i f f e r e n t c u e p h r a s e s a n d o t h e r i n d i c a t o r s

w i l l b e n e c e s s a r y , o p t i o n a l , o r r e d u n d a n t .

AKNOWLEDGMENTS

W e h a v e b e n e f i t e d g r e a t l y f r o m d i s c u s s i o n s w i t h M a r t h a

P o l l a c k , R a y P e r r a u l t , a n d S c o t t W e i n s t e i n . T h e p a p e r

h a s b e n e f i t e d f r o m t h e c o m m e n t s o f J o n B a r w i s e , M a r c i a

D e r r , B r a d G o o d m a n , D a v i d I s r a e l , A m i c h a i K r o n f e l d ,

M i t c h M a r c u s , M a r t h a P o l l a c k , R a y P e r r a u lt , J o h n P e r r y ,

J a n e R o b i n s o n , S t u a r t S h i e b e r , R a l p h W e i s c h e d e l , S c o t t

W e i n s t e i n , a n d t h e a n o n y m o u s r e v i e w e r s f o r

Computational L inguistics.

W h a t e v e r e r r o r s r e m a i n a r e ,

o f c o u r s e , a l l o u r s .

T h i s p a p e r w a s m a d e p o s s i b l e b y a g i f t f r o m t h e

S y s t e m D e v e l o p m e n t F o u n d a t i o n . S u p p o rt w a s a l s o

p r o v id e d f o r t h e s e c o n d a u t h o r b y t h e A d v a n c e d

R e s e a rc h P r o j e ct s A g e n c y o f t h e D e p a r tm e n t o f D e f e n s e

a n d w a s m o n i t o r e d b y O N R u n d e r C o n t r a c t N o .

N 0 0 0 1 4 - 8 5 - C - 0 0 7 9 . T h e v i e w s a n d c o n c l u s i o n s c o n t a i n e d

i n t h i s d o c u m e n t a r e t h o s e o f t h e a u t h o r s a n d s h o u l d n o t

b e i n t e r p r e t e d a s n e c e s s a r i l y r e p r e s e n t i n g t h e o f f i c i a l

p o l i c i e s , e i t h e r e x p r e s s e d o r im p l i e d , o f t h e D e f e n s e

A d v a n c e d R e s e a r c h P r o j e c t s A g e n c y o r th e U . S . G o v e r n -

m e n t .

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NOT E S

1. The use of the phrase linguistic structure to refer to the struc-

ture of sequences of utterances is a natural extension of its use in

traditional linguistic theories to refer to the syntactic structure of

individual sentences. To avoid confusi on the phrase linguistic

structure will be used in this paper only to refer to the structure

of a sequence of utterances composing a discourse or discourse

segment.

2. Mann has also reported that the subjects did not label segments

nearly so consistently. We believe this fact is related to the kinds

of relations the labels were depen dent upon. As discussed in

Section 7.4, there is a difference between the intentional structure

we describe and the relations that others use.

3. Referring expression s can also be used to mark a discourse bound-

ary. For example, novelists sometimes use pronouns to indicate a

new scene in a story.

4. These two relations are similar to ones that play a role in parsing

at the sentence level: immedia te dominan ce and linear precedence.

However, the dominance relation, like the one in Marcus and

Hindle 's D-theor y (Marcus et al. 1983), is partial (i.e., nonimm e-

diate).

5. Even in the task case the orderings may be partial. In fact, the

systems built for task-oriented dialogues (Robinson 1981, Walker

1978) did not use a prebuilt tree, but constructe d the tree - based

on a partially-ord ered model - only as a given discourse evolved.

6. The observant reader will note that this was written in the early

days of the cinema, before the advent of sound; hence the quota-

tion marks around movies. Note also that utterance (7) contains

a somewhat odd preposition, and utterance (16) somewhat odd

definite noun phrases. We have quoted the text exactly as it was

printed.

7. The segmentation omits some levels of detail. For example, utter-

ances 19-24 are a segment within DSS. Rather than present this

detail, we concentrate on the larger segments here so as to focus

on the major issues with which this paper is concerned.

8. This modification folds in an informing action with the request.

Such combining of two t ypes of speech acts is similar to the action

subsumption that Appelt (1985) discusses in regard to referring

expressions.

9. Hirschberg and Pierrehumbert (1986) have shown recently that

intonational features, most notably pitch range, can also be used

to indicate discourse segment boundaries.

10. We assume here that the OCP must recognize intentions rather

than actions. The argument that such is the case is beyond the

scope of this paper. At a very general level, it centers on the

possibility that the very same sequence of utterance actions will

correspond to two different discourse structures with the differ-

ence statable only in terms of the ICP's intentions. The possibility

of such sequences was suggested to us by Michael Bratman

[personal communication]. The irony contained in such a clause as

you ' re a re a l swee thear t illustrates the need t o consider intentions.

11. This knowledge may be available prior to the discourse or from

information supplied by previous utterances in the discourse.

12. This bounda ry is clearly atypical of stacks. It suggests that ulti-

mately the stack model is not quite what is needed. What struc-

ture should replace the stack remains unclear to us.

13. Because this is so clearly the case on other grounds, the segment

boundary is obvious even to a reader aft er the fact.

14. From just the fragment presented, all that can be determined is

that the two dominates relationships are domination but not direct

domination.

15. O K is many ways ambiguous. It may also mean (at least) I heard

w h a t y o u s a i d , h e a r d a n d i n t e n d t o d o w h a t y o u i n t e n d m e t o in t e n d,

1 a m d o n e w h a t I u n d e r t o o k t o d o , or I a p p r o v e w h a t y o u a r e a b o u t t o

do.

16. This portion is taken from Redefinition IVB: a further redefinition

deals with abstracting about audience and would unnecessarily

complicate ou r initial view of inten tion s and discourse.

17. Grice (1969) mentions iconic, conventional, and associative

modes, giving examples of each.

18. This analogy is meant to help clarify and motivat e the discussion.

Although it also suggests some important problems in common

between research on discourse and research on theories of action

and intention, those issues are the subject of an other paper.

19. Here again we use a notational shorthand rather than a formal

language to make some of the relationships clearer.

20. This claim reflects a move analogous to the one made by Cohen

and Levesque (1985) in showing that the definitions of various

speech acts can be derived as lemmas within a general theory of

rational behavior.

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Grosz & Sidner (1986)