Can we know reality as it Can we know reality as it really is?really is?

Representative realism, Representative realism, idealism, phenomenalism, and idealism, phenomenalism, and

causal realismcausal realism

RationalismRationalism

The rationalists (such as Descartes) The rationalists (such as Descartes) argued that we could not get knowledge argued that we could not get knowledge from sense experience, for it is often from sense experience, for it is often wrong and does not provide the proof we wrong and does not provide the proof we need for knowledge.need for knowledge.

The rationalists thought the only way to The rationalists thought the only way to get such proof was by reason (as in get such proof was by reason (as in mathematics).mathematics).

EmpiricismEmpiricism

A contrasting tradition of early modern A contrasting tradition of early modern (1600-1800) philosophers claimed that (1600-1800) philosophers claimed that anything we can know comes from the anything we can know comes from the senses.senses.

The most famous empiricist philosophers The most famous empiricist philosophers of this age were three Britons: John Locke, of this age were three Britons: John Locke, George Berkeley, and David Hume.George Berkeley, and David Hume.

(They didn’t call themselves “empiricists.”)(They didn’t call themselves “empiricists.”)

John Locke (1632-1704)John Locke (1632-1704)

Locke thought no Locke thought no ideas were innately ideas were innately clear and distinct. clear and distinct. Instead the mind is a Instead the mind is a blank slate (“tabula blank slate (“tabula rasa”) at birth, rasa”) at birth, gradually filled by gradually filled by experience.experience.

1.1. There are many cases where we do not see There are many cases where we do not see real objects (hallucinations, dreams), or do not real objects (hallucinations, dreams), or do not see them as they really are (optical illusions, see them as they really are (optical illusions, myopia, vision vs. microscopes, perspectives).myopia, vision vs. microscopes, perspectives).

2.2. But we are seeing But we are seeing somethingsomething in those cases. in those cases.3.3. So in those cases we don’t see reality directly: So in those cases we don’t see reality directly:

we see we see representationsrepresentations (or “ideas”). (or “ideas”).4.4. These cases aren’t obviously different from the These cases aren’t obviously different from the

“real” cases (we believe them). “real” cases (we believe them). 5.5. So we So we alwaysalways see representations. see representations.

The Illusion Argument and how it leads The Illusion Argument and how it leads to representative realismto representative realism

Perception according to LockePerception according to Locke

Idea in the mindIdea in the mind(directly perceived)(directly perceived)

Material objectMaterial object(cause of the idea)(cause of the idea)

The representation problem: how can we know The representation problem: how can we know whether there whether there isis a real material object? a real material object?

Suppose a circular hotplate on an oven is glowing Suppose a circular hotplate on an oven is glowing red hot. I bring my hand close to it and feel red hot. I bring my hand close to it and feel warmth, then pain …warmth, then pain …

The warmth and pain, we tend to think, are The warmth and pain, we tend to think, are not in the hotplate, but “in the mind.”not in the hotplate, but “in the mind.”

The The shapeshape of the hotplate though, we tend of the hotplate though, we tend to think, is “in the object.”to think, is “in the object.”

So is the So is the colorcolor of the hotplate “in the mind” of the hotplate “in the mind” or “in the object”?or “in the object”?

What’s real and what’s in the mind?What’s real and what’s in the mind?

Color: in your mind or in the object?Color: in your mind or in the object?

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Locke, Locke, Essay,Essay, II viii 10: II viii 10:

““Such Such QualitiesQualities, which in truth are , which in truth are nothing in the Objects themselves, but nothing in the Objects themselves, but Powers to produce various Sensations Powers to produce various Sensations in us by their in us by their primary qualitiesprimary qualities, , i.e.i.e. by by the Bulk, Figure, Texture, and Motion of the Bulk, Figure, Texture, and Motion of their insensible parts, as Colours, their insensible parts, as Colours, Sounds, Tastes, Sounds, Tastes, etc.etc. These I call These I call secondary qualitiessecondary qualities.”.”

Locke’s textLocke’s text

Primary and secondary qualitiesPrimary and secondary qualities

Secondary qualities are subject to relativity Secondary qualities are subject to relativity and illusion: and illusion: What tastes sweet to one What tastes sweet to one person may not taste sweet to another. person may not taste sweet to another. What looks red to one person may not look What looks red to one person may not look red to another.red to another.

What basis does Locke have for making this What basis does Locke have for making this distinction?distinction?

Primary and secondary qualities Primary and secondary qualities

• But primary qualities, such as whether or But primary qualities, such as whether or not an apple is not an apple is roundround or or in motionin motion, are , are not not subjective. subjective.

• The apple has whatever shape it has The apple has whatever shape it has objectively, and its motion likewise. (If we objectively, and its motion likewise. (If we disagree about the shape, or the motion of disagree about the shape, or the motion of the apple, we haven’t looked carefully the apple, we haven’t looked carefully enough.)enough.)

All our ideas come from experience.All our ideas come from experience.

We We assumeassume a “real essence”: an underlying a “real essence”: an underlying thing made of matter (molecules, atoms, thing made of matter (molecules, atoms, etc.) causing what we see.etc.) causing what we see.

What we see is the “nominal essence”: the What we see is the “nominal essence”: the observable properties (a mix of primary and observable properties (a mix of primary and secondary qualities) by which we identify secondary qualities) by which we identify things.things.

Locke’s scientific realismLocke’s scientific realism

George Berkeley (1685-1753)George Berkeley (1685-1753)argues that material thingsargues that material thingsindependent of mind areindependent of mind arelogically self-contradictory.logically self-contradictory.

He argues that the only way He argues that the only way we make sense of the world we make sense of the world is as a set of is as a set of mentalmental entities (minds and entities (minds and ideas experienced by those minds).ideas experienced by those minds).

Berkeley’s idealismBerkeley’s idealism

Berkeley rejects Locke’s scientific realism Berkeley rejects Locke’s scientific realism by noting that we can’t form any idea of by noting that we can’t form any idea of matter without using secondary qualities.matter without using secondary qualities.

He thinks Locke invents a primary quality He thinks Locke invents a primary quality idea of matter which is unreal; our ideas idea of matter which is unreal; our ideas are always experiences.are always experiences.

Berkeley attacks Locke for abstracting Berkeley attacks Locke for abstracting away from experience: he claims to be the away from experience: he claims to be the better empiricist!better empiricist!

Berkeley vs. LockeBerkeley vs. Locke

If we say we never see reality directly but If we say we never see reality directly but only through experience, then we cannot only through experience, then we cannot know that our experience resembles know that our experience resembles reality. reality. If all knowledge comes from experience, If all knowledge comes from experience, then we have no knowledge of “reality as it then we have no knowledge of “reality as it is independent of experience.”is independent of experience.”(Try it: describe reality without using (Try it: describe reality without using anyany ideas from experience.) ideas from experience.)

Berkeley vs. representative realismBerkeley vs. representative realism

1.1. Objects only appear in experience.Objects only appear in experience.

2.2. All experience is in someone’s mind.All experience is in someone’s mind.

3.3. So, objects only appear in So, objects only appear in someone’s mind.someone’s mind.

The notion of objects outside of any The notion of objects outside of any mind (“matter”) is self-contradictory.mind (“matter”) is self-contradictory.

Berkeley’s basic argumentBerkeley’s basic argument

Berkeley combines Locke’s principle Berkeley combines Locke’s principle that that we only directly see ideas we only directly see ideas with with the common sense view that the common sense view that we we directly see thingsdirectly see things. (Things = Ideas). (Things = Ideas)

Skepticism is avoided by identifying Skepticism is avoided by identifying objects with perceptions.objects with perceptions.

He dismantles the primary/secondary He dismantles the primary/secondary quality distinction.quality distinction.

Berkeley’s idealismBerkeley’s idealism

According to Berkeley, objects (trees, According to Berkeley, objects (trees, tables, etc.) are real, but they are not tables, etc.) are real, but they are not things made out of matter (molecules, things made out of matter (molecules, atoms, etc., existing outside minds). We atoms, etc., existing outside minds). We never see such non-mental matter; it is never see such non-mental matter; it is unreal and incoherent.unreal and incoherent.Objects are mentalObjects are mental: collections of sense : collections of sense experiences. The tree is the experience of experiences. The tree is the experience of rough bark, the experience of seeing rough bark, the experience of seeing green leaves, etc.green leaves, etc.

What You See Is What You GetWhat You See Is What You Get

How can an idealist distinguish illusion How can an idealist distinguish illusion from reality if everything is mental?from reality if everything is mental?

How can different minds see the same How can different minds see the same objects, if they are all in our (separate) objects, if they are all in our (separate) minds?minds?

If objects are only ideas, how can objects If objects are only ideas, how can objects exist when no one is experiencing them?exist when no one is experiencing them?

Three problems for Berkeley’s idealismThree problems for Berkeley’s idealism

Berkeley answers all three questions with Berkeley answers all three questions with the same answer:the same answer:

God causes most of our sense data; God causes most of our sense data; sense data not from God is illusory.sense data not from God is illusory.

God sends the same ideas into different God sends the same ideas into different minds (so objects are the same).minds (so objects are the same).

God sees everything all the time, so God sees everything all the time, so objects are there even when people aren’t.objects are there even when people aren’t.

Berkeley: Berkeley: Reality Is God’s MindReality Is God’s Mind

Perception according to LockePerception according to Locke

Idea in the mindIdea in the mind(directly perceived)(directly perceived)

Material objectMaterial object(cause of the idea)(cause of the idea)

The representation problem: how can we know The representation problem: how can we know whether there whether there isis a real material object? a real material object?

Perception according to BerkeleyPerception according to Berkeley

Idea in the mind = the treeIdea in the mind = the tree(directly perceived; caused by God)(directly perceived; caused by God)

No representation problem, because what we No representation problem, because what we directly perceive (i.e. the idea) directly perceive (i.e. the idea) isis the tree. the tree.

Why believe it’s God rather than Why believe it’s God rather than a material world?a material world?

We have no knowledge of matter.We have no knowledge of matter.

We know our minds exist. We know ideas We know our minds exist. We know ideas and experience exist. We know our minds and experience exist. We know our minds can imagine experiences into existence.can imagine experiences into existence.

Some experiences aren’t caused by my Some experiences aren’t caused by my mind. By what then? mind. By what then?

But it must be a mind that can share the But it must be a mind that can share the same ideas with other minds, and perceive same ideas with other minds, and perceive ideas everywhere in the universe at once.ideas everywhere in the universe at once.

Idealism might seem to undermine physical Idealism might seem to undermine physical science, but Berkeley (following Newton) science, but Berkeley (following Newton) advocated instrumentalism:advocated instrumentalism:

The aim of science is to discover laws that The aim of science is to discover laws that give true predictions about what we see.give true predictions about what we see.

It is irrelevant whether the theoretical entities It is irrelevant whether the theoretical entities (e.g., atoms) have any real existence.(e.g., atoms) have any real existence.

God benevolently arranges experience to God benevolently arranges experience to follow these patterns, as “signs” enabling us to follow these patterns, as “signs” enabling us to direct our lives.direct our lives.

Berkeley’s instrumentalismBerkeley’s instrumentalism

Newton’s instrumentalismNewton’s instrumentalism

Newton’s public response to the objection Newton’s public response to the objection that he didn’t explain gravity:that he didn’t explain gravity:

““Hypotheses non fingo”Hypotheses non fingo”

– ““I make no hypotheses”: we don’t need to I make no hypotheses”: we don’t need to speculate about how gravity works (until we speculate about how gravity works (until we get more evidence).get more evidence).

– If the equations correctly describe what we If the equations correctly describe what we see, then that theory should be accepted, see, then that theory should be accepted, whatever the underlying reality might be.whatever the underlying reality might be.

InstrumentalismInstrumentalism

Instrumentalism is an application of Instrumentalism is an application of Berkeley-like ideas to science.Berkeley-like ideas to science.

It says scientific theories are models to It says scientific theories are models to explain and predict what we see, and that explain and predict what we see, and that we should judge them only on how well we should judge them only on how well they do that. they do that.

Whether theories describe “reality” adds Whether theories describe “reality” adds nothing beyond that, and so is nothing beyond that, and so is unimportant.unimportant.

PhenomenalismPhenomenalism

A secular version of Berkeley’s idealism is A secular version of Berkeley’s idealism is phenomenalismphenomenalism..

Phenomenalism is the view that all talk Phenomenalism is the view that all talk about physical objects can be translated about physical objects can be translated into talk about possible or actual sense into talk about possible or actual sense experience.experience.

Famous phenomenalists: Hume (?), Mill, Famous phenomenalists: Hume (?), Mill, Bertrand Russell (in his early period)Bertrand Russell (in his early period)

Phenomenalism Phenomenalism

So when I say “there is a desk in here”, I am So when I say “there is a desk in here”, I am more accurately saying “I am now having a more accurately saying “I am now having a visual experience of a tan, semi-rectangular visual experience of a tan, semi-rectangular object, which, if I touched it, would give me a object, which, if I touched it, would give me a tactile experience of cool, smooth resistance,” tactile experience of cool, smooth resistance,” etc.etc.

The The desk when no one is heredesk when no one is here is “ is “ifif someone someone with normal vision were here and the room was with normal vision were here and the room was brightly lit, he would have a visual experience of brightly lit, he would have a visual experience of a tan, semi-rectangular object…”a tan, semi-rectangular object…”

PhenomenalismPhenomenalism

The phenomenalist makes no claims The phenomenalist makes no claims about the causes of experience. Doesn’t about the causes of experience. Doesn’t claim there are material objects, doesn’t claim there are material objects, doesn’t say they are ideas in God’s mind, etc.say they are ideas in God’s mind, etc.The phenomenalist says such questions The phenomenalist says such questions are unanswerable, since all verifiable are unanswerable, since all verifiable claims must be based in experience. So claims must be based in experience. So there’s no point in asking.there’s no point in asking.Reality = actual & possible experiencesReality = actual & possible experiences

Phenomenalist perceptionPhenomenalist perception

Idea in the mind = the treeIdea in the mind = the tree(directly perceived, cannot ask about (directly perceived, cannot ask about

“causes”)“causes”)

No representation problem, because what we No representation problem, because what we directly perceive (i.e., the idea) directly perceive (i.e., the idea) isis the tree. the tree.

PhenomenalismPhenomenalism

The phenomenalist solves the Illusion The phenomenalist solves the Illusion Argument by the relation of an experience Argument by the relation of an experience to other experiences.to other experiences.If my experience of a bent straw in water is If my experience of a bent straw in water is followed by an experience of a straw that followed by an experience of a straw that isn’t bent when I pull it out, then the bent isn’t bent when I pull it out, then the bent experience was an illusion.experience was an illusion.That is, phenomenalists say truth is That is, phenomenalists say truth is coherent experiencecoherent experience. .

Criticisms of PhenomenalismCriticisms of Phenomenalism

Phenomenalism gives no explanation for Phenomenalism gives no explanation for the coherence of our experiences. the coherence of our experiences.

Translating all talk about objects into Translating all talk about objects into experience-talk seems incoherent: saying experience-talk seems incoherent: saying “the desk” is “the visual experience of a “the desk” is “the visual experience of a tan…” etc. depends on factors such as tan…” etc. depends on factors such as lighting, my eyes working properly, etc. lighting, my eyes working properly, etc. But those aren’t sense-experience claimsBut those aren’t sense-experience claims!!

Causal RealismCausal Realism

Causal realism is the view that physical Causal realism is the view that physical objects cause our perception, but that objects cause our perception, but that there are there are nono representations involved. representations involved.

We have beliefs We have beliefs causedcaused by objects but by objects but this interaction is not me having ideas of this interaction is not me having ideas of objects – it is a physical thing (e.g., a tree) objects – it is a physical thing (e.g., a tree) doing things to another physical thing (me, doing things to another physical thing (me, or more precisely, my brain). or more precisely, my brain).

Causal realist perceptionCausal realist perception

A TREEA TREE(physical object, NOT an “idea”, not a (physical object, NOT an “idea”, not a

perception, causing physical changes in perception, causing physical changes in another physical object [me])another physical object [me])

Causal Realism vs. Causal Realism vs. the Illusion Argumentthe Illusion Argument

The causal realist denies that we see any The causal realist denies that we see any representations. No ideas. Just things.representations. No ideas. Just things.– ““Did you see the way she looked?”Did you see the way she looked?”– ““Well, I saw Well, I saw the way she lookedthe way she looked, yes, but I , yes, but I

didn’t see didn’t see herher.”.”

The above sort of thinking is the mistake.The above sort of thinking is the mistake.

I don’t see a bent straw, I see a straight I don’t see a bent straw, I see a straight straw through water. I may be straw through water. I may be causedcaused to to hold a false belief as a result.hold a false belief as a result.

1.1. There are many cases where we do not see There are many cases where we do not see real objects (hallucinations, dreams), or do not real objects (hallucinations, dreams), or do not see them as they really are (optical illusions, see them as they really are (optical illusions, myopia, vision vs. microscopes, perspectives).myopia, vision vs. microscopes, perspectives).

2.2. But we are seeing But we are seeing somethingsomething in those cases. in those cases.3.3. So in those cases we don’t see reality directly: So in those cases we don’t see reality directly:

we see we see representationsrepresentations (or “ideas”). (or “ideas”).4.4. These cases aren’t obviously different from the These cases aren’t obviously different from the

“real” cases (we believe them). “real” cases (we believe them). 5.5. So we So we alwaysalways see representations. see representations.

The Illusion Argument and how it leads The Illusion Argument and how it leads to representative realismto representative realism

Causal realismCausal realism

The light reflected by the straw is refracted The light reflected by the straw is refracted as it goes from water to air. The resulting as it goes from water to air. The resulting light patterns are very similar to those of a light patterns are very similar to those of a flattened straw would make.flattened straw would make.

I may believe–if I am naïve–that the straw I may believe–if I am naïve–that the straw is bent. But such a false belief is not me is bent. But such a false belief is not me seeing an illusory experience. It is a real seeing an illusory experience. It is a real experience (light from a straw interacting experience (light from a straw interacting with my brain) I am wrong about.with my brain) I am wrong about.

Different causal inputsDifferent causal inputs

The world affects us and the brain interprets:The world affects us and the brain interprets:

The star-nosed mole has a ‘nose’ with 22 The star-nosed mole has a ‘nose’ with 22 fingers that builds a 3D world-model.fingers that builds a 3D world-model.

Lots of birds use magnetite to orient along the Lots of birds use magnetite to orient along the Earth’s magnetic field.Earth’s magnetic field.

Snakes have heat pits to detect infrared.Snakes have heat pits to detect infrared.

The ghost knifefish has electroreceptors.The ghost knifefish has electroreceptors.

Our eyes interpret color depending on the Our eyes interpret color depending on the background.background.

Your brain on data: Your brain on data: NeuroplasticityNeuroplasticity

In 1969, neurologist In 1969, neurologist Paul Bach-y-Rita Paul Bach-y-Rita enabled blind people to enabled blind people to correctly identify shapes correctly identify shapes by having machinery by having machinery translate light imagery translate light imagery into pads of bristles into pads of bristles giving patterned pokes giving patterned pokes to their back.to their back.

An argument for causal realism An argument for causal realism (John Searle’s)(John Searle’s)

1.1. Assume: we sometimes Assume: we sometimes succeed at succeed at communication.communication.

2.2. We do that with public We do that with public meanings in a public meanings in a public language. E.g., when language. E.g., when saying “this desk” we saying “this desk” we refer to the same thing.refer to the same thing.

3.3. So: language implies shared So: language implies shared thingsthings, which implies , which implies the reality of an objective external world.the reality of an objective external world.

4.4. So: if idealism or phenomenalism were right, there So: if idealism or phenomenalism were right, there wouldn’t be any successful communication.wouldn’t be any successful communication.

Can we justify realism?Can we justify realism?

However, an argument like Searle’s starts by However, an argument like Searle’s starts by assuming that assuming that there is real communicationthere is real communication. .

A skeptic would say that premise begs the A skeptic would say that premise begs the question: we need good reason to believe there question: we need good reason to believe there is an external world (including communication) in is an external world (including communication) in the first place. That’s the issue.the first place. That’s the issue.

Causal realism is hospitable to brains in vats!Causal realism is hospitable to brains in vats!

How can we justify external realism? We’ll try a How can we justify external realism? We’ll try a different answer to the skeptic after looking at different answer to the skeptic after looking at how skepticism attacks science. how skepticism attacks science.