Deductive argument

DEDUCTIVE ARGUMENT

LET’S REVIEW.

Induction: inference of a generalized conclusion from particular instances 

Deduction: inference in which the conclusion about particulars follows necessarily from general or universal premises

INDUCTION VS. DEDUCTION

NOTE #1:YOU ARE GOING TO

HATE TODAY’S LESSON.

NOTE #2:DON’T WORRY

ABOUT NAMES. JUST TRY TO THINK WITH

VENN DIAGRAMS.

PART I:VENN DIAGRAMS

WITH OVERLAP

FIRST WE DRAW THE VENN DIAGRAM.

All p are q.All q are r.Therefore all p are r.

All Boston folk are from Massachusetts.All Massachusetts folk are from America.All Boston folk are from America.

CATEGORICAL SYLLOGISM

If p, then q.If q, then r.Therefore, if p, then r.

If Sam is from Boston, then he is from Massachusetts.

If he is from Massachusetts, then he is from America.

Therefore, if Sam is from Boston, then he is from America.

HYPOTHETICAL SYLLOGISM

They’re basically the same.

WHAT’S THE RELATIONSHIP?

NEXT WE FIND OUT WHERE WE ARE IN

THE VENN DIAGRAM.

If p, then q.P.Therefore q.

If it is a dog, then it is a mammal.It is a dog.Therefore it is a mammal.

MODUS PONENDO PONENS

If p, then q.Not q.Therefore p.

If it is a dog, then it is a mammal.It is not a mammal.Therefore it is not a dog.

MODUS TOLLENDO TOLLENS (CONTRAPOSITIVE)

FALLACY TEST!!!

If p, then q.Q.Therefore p.

If it is a dog, then it is a mammal.It is a mammal.Therefore it is a dog.

What if it’s a bear? Bears are mammals.

CONVERSE FALLACY(AFFIRMING THE CONSEQUENT)

If p, then q.Not p.Therefore not q.

If it is a dog, then it is a mammal.It is not a dog.Therefore it is not a mammal.

What if it’s a bear? Bears are mammals.

INVERSE FALLACY(DENYING THE ANTECEDENT)

FINALLY WE PUT IT ALL TOGETHER.

If p, then q.If q, then r.Therefore, if p, then r.P.Therefore r.

If it is a dog, then it is a mammal.If it is a mammal, then it is an animal.Therefore, if it is a dog, then it is an animal.It is a dog.Therefore it is an animal.

PUT IT ALL TOGETHER!

PART II:VENN DIAGRAMS

WITHOUT OVERLAP

NOTE #3:EACH OF THESE

ARGUMENTS HAS A CONTRAPOSITIVE

VERSION. BUT WE’RE GOING TO FOCUS ON

THE POSITIVE.

FIRST WE DRAW THE VENN DIAGRAM.

Either p or q. If p, then r. If q, then s.Therefore either r or s.

Abdulhaye’s first language is either Darija or Tashlhit. If Abdulhaye’s first language is Darija, then he is

Arab. If Abdulhaye’s first language is Tashlhit, then he is

Tamazight.Therefore Abdulhaye is either Arab or Tamazight.

[CONSTRUCTIVE] DILEMMA

LET’S CREATE SOME DILEMMAS!

NEXT WE FIND OUT WHERE WE ARE IN

THE VENN DIAGRAM.

Either p or q.Not p.Therefore q.

Abdulhaye’s first language is either Darija or Tashlhit. It is not Darija.Therefore it is Tashlhit.

MODUS TOLLENDO PONENS(DISJUNCTIVE SYLLOGISM)

FINALLY WE PUT IT ALL TOGETHER.

Either p or q. If p, then r. If q, then s.Therefore either r or s.Not p.Therefore q.

Either we legalize prostitution or we keep it i llegal. If we legalize prostitution, we would be breaking Islamic

law! If we keep prostitution illegal, we maintain our Islamic

values.Therefore either we break Islamic law or we remain Islamic.Let’s not break Islamic law by legalizing prostitution.Therefore let’s remain Islamic by keeping it illegal.

PUT IT ALL TOGETHER!

NOTE #4:BE WARY OF FALSE

DILEMMAS AND “REDUCTIONS TO

THE ABSURD.”

REWORK YOUR DILEMMAS

USING BOTH TYPES OF ARGUMENT AT

THE SAME TIME

Homework.

READ CHAPTER 5 IN THE DEBATER’S

GUIDE.

FOR TOMORROW, PROVE USING DEDUCTION...

1. Prove by creating your own hypothetical syllogism and modus ponendo ponens: It is wrong for a man to have more than one wife.

2. Prove by creating your own dilemma and modus tollendo ponens: Morocco should be friends with North Korea.

3. Draw Venn diagrams for your arguments in (1) and (2).4. What is wrong with this argument?... If the government

cuts taxes, then the economy will improve. The economy improved. Therefore the government cut taxes

5. If the government invests in education, then more Moroccans have access to education. Does this mean that government investment causes the increase in access?

6. Make an analogy between the human body and human society.

HOMEWORK