Last week:

• The Mind-Body Problem(s) Introduced
• Descartes's Argument from Doubt

This week:

• Descartes's Epistemological Argument
• Frank Jackson's Knowledge Argument
• The Causal Argument against Dualism

Descartes's most influential argument for Substance Dualism occurs in a single paragraph in the 6th Meditation.

The first half of the key paragraph runs:

"First, I know that everything which I clearly and distinctly understand is capable of being created by God so as to correspond exactly with my understanding of it. Hence the fact that I can clearly and distinctly understand one thing apart from another is enough to make me certain that the two things are distinct, since they are capable of being separated, at least by God. The question of what kind of power is required to bring about such a separation does not affect the judgment that they are distinct."

Descartes Meditation V, CSM II:54, AT 7:78.

To a first approximation:

1. If I can clearly and distinctly understand X apart from Y, X can be separated from Y
2. If X can be separated from Y, X is distinct from Y
3. So X is distinct from Y if I can clearly and distinctly understand X apart from Y.

We'll see in a moment why we're supposed to think I can clearly and distinctly understand myself apart from my body, and so conclude that I am distinct from my body.

First, let's consider an objection, pressed by Caterus in the First Set of Objections:

Caterus offers another PARODY, aimed at undermining Descartes' claim that X is distinct from Y if I can clearly and distinctly understand X apart from Y:

1. X is distinct from Y if I can clearly and distinctly understand X apart from Y
2. I can clearly and distinctly understand God's mercy apart from God's justice
3. So, God's mercy is distinct from God's justice.

Descartes will accept 2, but want to resist 3. So he needs to deny 1!

In his Replies to Caterus, Descartes clarifies his position. In order to infer that X is distinct from Y, what we needed is a clear and distinct understanding of X as COMPLETE apart from Y.

And while,

• I can clearly and distinctly understand myself as complete apart from my body,
• I cannot clearly and distinctly understand God's mercy as complete apart from his justice

But what exactly does Descartes mean by a clear and distinct understanding of myself as complete apart from my body? And why does he think I can have one?

The second half of the key paragraph runs:

"Thus, simply by knowing that I exist and seeing at the same time that absolutely nothing belongs to my nature or essence except that I am a thinking thing, I can infer correctly that my essence consists solely in the fact that I am a thinking thing. It is true that I may have (or, to anticipate, that I certainly have) a body that is very closely joined to me. But, nevertheless, on the one hand I have a clear and distinct idea of myself, in so far as I am simply a thinking, non-extended thing; and on the other hand I have a distinct idea of body, in so far as this is simply an extended, non-thinking thing. And accordingly, it is certain that I am really distinct from my body, and can exist without it."

Descartes Meditation V, CSM II:54, AT 7:78.

In the Fourth Replies, Arnauld takes the argument to be:

1. I have a clear and distinct understanding of myself as complete apart from my body if I can clearly and distinctly perceive that thought but not extension belongs to my essence
2. I can clearly and distinctly perceive that thought but not extension belongs to my essence if I can be certain that I exist as a thinking thing even when doubting that I am an extended thing
3. I can be certain that I exist as a thinking thing even when doubting that I am an extended thing

Arnauld points out that this argument is no good. I can be certain that a triangle is right-angled while doubting (owing to ignorance) that it is Pythagorean.

It does not follow that I can clearly and distinctly perceive that being right-angled but not Pythagorean belongs to the triangle's essence!

In his Replies to Arnauld, Descartes clarifies that the argument is rather:

1. I have a clear and distinct understanding of myself as complete apart from my body if I can clearly and distinctly perceive that thought but not extension belongs to my essence
2. I can clearly and distinctly perceive that thought but not extension belongs to my essence if I can clearly and distinctly perceive that it is possible for me to exist without a body.
3. I can clearly and distinctly perceive that it is possible for me to exist without a body.

Why does Descartes think I can clearly and distinctly perceive that it is possible for me to exist without my body?

Because I can IMAGINE myself existing as a thinking thing without a body.

The argument in brief:

1. I can imagine myself existing without a body
2. If I can imagine myself existing without a body then I can exist without my body
3. If I can exist without my body, I am distinct from my body
4. So I am distinct from my body.

KRIPKE'S ARGUMENT

“Descartes, and others following him, argued that a person or mind is distinct from his body, since the mind could exist without the body. He might equally well have argued the same conclusion from the premise the body could have existed without the mind.”

Kripke Naming and Necessity, p. 144-5.

Kripke's version:

1. I can imagine my body existing without my mind
2. If I can imagine my body existing without my mind then my body can exist without my mind
3. If my body can exist without my mind, my body is distinct from my mind
4. So my body is distinct from my mind.

COMPARISON

These are both MODAL arguments for dualism.

They move from a claim about what is POSSIBLE (I can exist without my body, or my body can exist without my mind) to the claim that mind and body are somehow distinct.

However, the forms of dualism that they seek to establish are different.

Descartes is arguing for substances just like us except that they lack physical properties, GHOSTS or SPIRITS.

Kripke, by contrast, is arguing for substances just like us except lacking mental properties, ZOMBIES.

A BIG ISSUE

Each argument relies on a claim to the effect that what is (alleged to be) conceivable is in fact possible.

But once upon a time, it would have seemed possible to imagine water existing without oxygen. But even if it was ever conceivable, it wasn't possible - water is H₂O, so a world without oxygen is a world without water.

How, if at all, does the apparent conceivability of ghosts and zombies differ from this?

Frank Jackson famously offered what is called THE KNOWLEDGE ARGUMENT for property dualism.

"Mary is a brilliant scientist who is, for whatever reason, forced to investigate the world from a black and white room via a black and white television monitor. She specializes in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like ‘red’, ‘blue’, and so on."

Frank Jackson 'Epiphenomenal Qualia', p. 130.

"What will happen when Mary is released from her black and white room or is given a colour television monitor? Will she learn anything or not? It seems just obvious that she will learn something about the world and our visual experience of it. But then it is inescapable that her previous knowledge was incomplete. But she had all the physical information. Ergo there is more to have than that, and Physicalism is false."

Frank Jackson 'Epiphenomenal Qualia', p. 130.

The argument:

1. Mary knows all the physical facts about colour and colour vision
2. Mary does not know what it is like to see red
3. If Mary does not know what it is like to see red, she does not know all the facts about colour and colour vision
4. So some facts about colour or colour vision are not physical facts

(How are we supposed to get from this conclusion to PROPERTY dualism?

The assumption is that the non-physical fact that Mary doesn't know is a fact about the introspectively accessible properties - the QUALIA - of experiences of seeing red.)

What sort of knowledge does Mary gain when she leaves the room?

• PROPOSITIONAL KNOWLEDGE - S knows that P
• KNOWLEDGE BY ACQUAINTANCE - S knows O
• KNOW HOW - S knows how to X

THE ABILITY HYPOTHESIS

“If you have a new experience, you gain abilities to remember and to imagine. ... Further, you gain an ability to recognize the same experience if it comes again.”

David Lewis 'What Experience Teaches' p. 286.

THE ABILITY HYPOTHESIS:

S knows what it is like to see red IFF S can remember, imagine, and recognize the experience of seeing red

Plausibly, to know a fact is to have a piece of propositional knowledge.

So if knowing what it is like to see red is NOT propositional knowledge, we can deny 3.

(Notice that it is not enough to say that knowing what it is like to see red is a kind of know how. Lewis needs to insist that know how is NOT itself a kind of propositional knowledge.

Jason Stanley and Tim Williamson have argued that know how is a kind of propositional knowledge. If so, the Ability Hypothesis is not going to help the physicalist.)

TYE'S OBJECTIONS

THE ABILITY HYPOTHESIS:

S knows what it is like to see red IFF S is able to remember, imagine, and recognize the experience of seeing red

Is this ability NECESSARY for knowing what it is like?

Is this ability SUFFICIENT for knowing what it is like?

"I beseech you tell me how the soul of man (since it is but a thinking substance) can determine the spirits of the body to produce voluntary actions."

Princess Elisabeth of Bohemia, Letter to Descartes, May 1643.

Dualists of either variety have to explain how, if at all, the mental can causally interact with the physical.

• Descartes: how mental substances can exert causal influence over the body
• Property dualists: how mental properties can be causally efficacious

INTERACTION: Some physical effects have mental causes.

CAUSAL CLOSURE: Every physical effect has a complete physical cause.

An effect is OVERDETERMINED if it has more than one complete cause.

E.g.: X is simultaneously shot in the heart by Y and in the brain by Z.

Overdetermination is possible, but rare. We assume that the physical effects of mental causes are not generally overdetermined.

An argument against dualism:

1. Some physical effects have mental causes
2. Every physical effect has a complete physical cause
3. Physical effects of mental causes are not overdetermined
4. So mental causes are physical!

It seems we cannot endorse all four of:

• INTERACTION
• CAUSAL CLOSURE
• NO OVERDETERMINATION
• DUALISM

We've looked at Descartes's Epistemological Argument:

1. I can imagine myself existing without a body
2. If I can imagine myself existing without a body then I can exist without my body
3. If I can exist without my body, I am distinct from my body
4. So I am distinct from my body.

And Kripke's variant:

1. I can imagine my body existing without my mind
2. If I can imagine my body existing without my mind then my body can exist without my mind
3. If my body can exist without my mind, my body is distinct from my mind
4. So my body is distinct from my mind.

• Descartes's argument is an argument for ghosts or spirits, and so Substance Dualism.

• Kripke's is an argument for zombies, physical duplicates of us, and so Property Dualism.

• Both arguments rest on problematic assumptions about conceivability and possibility.

We also looked at Jackson's Knowledge Argument:

1. Mary knows all the physical facts about colour and colour vision
2. Mary does not know what it is like to see red
3. If Mary does not know what it is like to see red, she does not know all the facts about colour and colour vision
4. So some facts about colour or colour vision are not physical facts

• This is an argument for non-physical facts, and ultimately Property Dualism.

• Lewis's Ability Hypothesis makes trouble for the argument.

• But in light of Tye's criticisms, the status of the Ability Hypothesis is unclear.

Lastly, we looked at the Causal Argument against Dualism.

1. Some physical effects have mental causes
2. Every physical effect has a complete physical cause
3. Physical effects of mental causes are not overdetermined
4. So mental causes are physical

• Dualists have to give up INTERACTION, CAUSAL CLOSURE, or NO DETERMINATION.

Next week: Personal Identity.