The Dualism of Descartes

- René Descartes lived 1596-1650 and is often called the “Father of Modern Philosophy.”

- He was also a natural scientist and a mathematician and his work in those fields is still studied today.

- Beginning in 1643 he began a correspondence with princess Elizabeth of Bohemia, as both a friend and, ultimately, a fellow philosopher. Many think that Descartes never fully responded to some of Elizabeth’s critiques of his philosophy.

- He died of pneumonia in 1650, while serving at the court of the Queen of Sweden, in Stockholm.

- He invented a field of math called Analytic Geometry, which later lead to the invention of Calculus.

- He says his intention is to write about the soul, “as if no one had written on these matters before.

- By a “Physical thing” or “Physical object” we will mean anything that can be studied by the methods of the physical sciences (mainly physics, chemistry & biology). Examples of physical objects include tables, chairs, clouds, and human bodies.

Some definitions to begin with

- The view called “physicalism” is the view that only physical things exist. In this class we will focus on “physicalism about human beings”: the view that human beings are physical objects.

- “Dualism” is the view that the world contains both physical and non-physical objects (substances). But most of the time when philosophers use the word “dualism” they mean “dualism about human beings,” or “dualism about the mind.”

- There are lots of good common-sense reasons to be a physicalist. After all if I ask you to point to yourself, you will point at a physical object. If suzie isn’t a physical object then what would it mean to say, “Suzie got squashed by an anvil”?

Some definitions to begin with

- But there are also reasons to be a dualist. For instance, dualism is ONE way of explaining these two claims:

1) The physical sciences cannot fully explain human experience.2) There is life after death.

So if you believe one or both of these claims is true, dualism might be a more attractive view to you.

- Probably most believers in Christianity and Islam are dualists, even if they have never thought about it carefully or used the term. Most believe that they themselves will continue to exist as a “soul” after their body dies. Descartes was one of these believers, and his arguments for dualism are probably the most influential in history.

NOTE: Catholicism has had a love-hate relationship with dualism. Some great Catholic thinkers are sympathetic with Cartesian dualism, to some degree. Yet, one of the greatest Catholic thinkers, St. Thomas Aquinas, categorically rejects dualism.

“But I have just said that I have no senses and no body. This is the sticking point: What follows from this? Am I not so bound up with a

body and with senses that I cannot exist without them? But I have convinced myself that there is absolutely nothing in the world, no sky,

no earth, no minds, no bodies. Does it now follow that I too do not exist? No: if I convinced myself of something then I certainly existed.”

Descartes’ idea here seems to be that, although he can convince himself to doubt the existence of everything else

(including all physical things) he cannot convince himself to doubt his own existence. After all, if he could convince

himself that he didn’t exist, who would he have convinced?

Descartes writes:

“But there is a deceiver of supreme power and cunning who is deliberately and constantly deceiving me. In that case I too undoubtedly exist, if he is deceiving me; and let him deceive me as much as he can, he

will never bring it about that I am nothing, so long as I think that I am something. So after considering everything very thoroughly, I must finally conclude that this proposition, I am, I exist, is necessarily true

whenever it is put forward by me or conceived in my mind.”

So even if there is such a deceiver, he concludes that he can still be absolutely certain that he exists.

But now Descartes tries to imagine that there is an all-powerful evil “demon” or “deceiver” who is constantly

deceiving him about everything:

Is he right?

Here is what Descartes’ argument might look like:

1. If I am thinking (doubting, wondering, being convinced, being deceived etc.) then I exist.

2. I am thinking.

I exist

The argument is valid.

And most people find it difficult to deny either of its premises.

But even if the argument is sound, why should we care?

C.

I existI can at least imagine a

situation where no physical objects exist.

Yet, Descartes also said:

“But I have convinced myself that there is absolutely nothing

in the world, no sky, no earth, no minds, no bodies.”

I can imagine a situation where I exist, but no

physical objects exist.

I can imagine a situation where I exist, but no

physical objects exist.

But being able to imagine something doesn’t tell us anything about whether it is true!

Descartes needs a few more premises if he wants to prove something interesting.

“First, I know that everything which I clearly and distinctly understand is capable of being created by God so as to correspond exactly to 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.”

I can imagine a situation where I exist, but no

physical objects exist.

Here comes one premise…

“First, I know that everything which I clearly and distinctly understand is capable of being created by God so as to correspond exactly to 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.”

If I can imagine a situation then that

situation is possible

It is possible that I exist, but no physical objects

exist.

I can imagine a situation where I exist, but no

physical objects exist.

“First, I know that everything which I clearly and distinctly understand is capable of being created by God so as to correspond exactly to 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.”

If I can imagine a situation then that

situation is possible

It is possible that I exist, but no physical objects

exist.

If it is possible that x ≠ y then x ≠ y.

It is possible that I ≠ my body.

I ≠ my body.

I can imagine a situation where I exist, but no

physical objects exist.

If I can imagine a situation then that

situation is possible

It is possible that I exist, but no physical objects

exist.

If it is possible that x ≠ y then x ≠ y.

It is possible that I ≠ my body.

I ≠ my body.

1.

2.

3.

4.

5.

C.

(Can you imagine this?I think I can.)

(Seems like God at least could make it happen if I can imagine

it. So it must be possible.)

(Follows from 1. and 2.)

(Follows from 3. plus the assumption that my body

is a physical object.)

?????

(Follows from 4. and 5.)

If it is possible that x ≠ y then x ≠ y.

“The principle of the necessity of identity”

(Or PNI, for short)

Is this true? To answer that question, let’s look at

another claim called…

If x = y then necessarily x = y.

We will see in a moment that Descartes’ premise above can be logically derived from the principle of the

necessity of identity (PNI).

But first, let’s take a closer look at the PNI itself.

Descartes’ premise

y = “The current president of the United States”

The first thing to note is that the PNI is not true if either ‘x’ or ‘y’

are descriptions that can pick out different particular objects.

If x = y then necessarily x = y.

In this case it is clear that “x = y” is TRUE, but CONTINGENT (that is, not necessary), since someone other than Donald Trump could be president).

Now consider the case where:

For example, suppose that:

x = Donald Trump (a particular person)

x = Clark Kent (a particular person)y = Superman (a particular person)

This is a case where the identity IS necessary. Can you see why?

“The principle of the necessity of identity”

If x = y then necessarily x = y.

What is the PNI saying then? Well, in ordinary English we might express it as:

Is this principle true? Here are a few questions to consider:

It seems like every individual thing has to be identical to itself: y = y is necessarily true!

But since “y = y” is necessary, if we suppose that “x = y” is true, then it too is necessary. In that case, “x = y” is just another way of writing “y = y”!

• Could you have existed but been someone other than you?

• If you existed without being yourself, wouldn’t that just be a state of affairs where you don’t exist at all?

• Could you have existed without being yourself?

“Nothing can be distinct from itself.”

If x = y then necessarily x = y.

Now with a little “logical surgery” we can derive the premise that Descartes needs from

the principle of the necessity of identity.

If it is possible that x ≠ y then x ≠ y.

If x = y then it is impossible that x ≠ y.

(Because: if necessarily A then it is impossible that not A.)

If it is possible that x ≠ y then not(x = y).So…

(Using the following principle:“If it is not impossible that A then

It is possible that not A.”)

Now we use the following logical rule:From (If A then B) we can infer:

(If not B then not A)(This is called the rule of “contraposition.”It is a simple consequence of modus tollens.)

Descartes’ premise

If it is possible that x ≠ y then x ≠ y.

I can imagine a situation where I exist, but no

physical objects exist.

If I can imagine a situation then that

situation is possible

It is possible that I exist, but no physical objects

exist.

It is possible that I ≠ my body.

I ≠ my body.

1.

2.

3.

4.

5.

C.

(Can you imagine this?I think I can.)

(Seems like God at least could make it happen if I can imagine

it. So it must be possible.)

(Follows from 1. and 2.)

(Follows from 3. plus the assumption that my body

is a physical object.)

(From the Principle of the Necessity of Identity)

(Follows from 4. and 5.)

I can imagine a situation where I exist, but no

physical objects exist.

Imagine a small town in the desert in West Texas where there is a barber named Ted. At Ted’s barber shop he offers two services,

shaves and haircuts. And, since he is the only barber in town, it turns out that Ted shaves every man in town who does not shave himself.

Can you imagine this situation?

If you can, and if anything you can imagine is possible, then this situation must be possible.

Who shaves Ted?But here is a question:

A possible problem for one of Descartes’ premises:

I can imagine a situation where I exist, but no

physical objects exist.

As it turns out, this is an entirely impossible situation!

We THINK we can imagine it, but we are wrong. There is a hidden contradiction in the situation being described.

What does that say about Descartes’ imagined situation where he exists, but no physical objects exist?

Imagine a small town in the desert in West Texas where there is a barber named Ted. At Ted’s barber shop he offers two services,

shaves and haircuts. And, since he is the only barber in town, it turns out that Ted shaves every man in town who does not shave himself.

Who shaves Ted?

I can imagine a situation where I exist, but no

physical objects exist.

If it is possible that x ≠ y then x ≠ y.

If I can imagine a situation then that

situation is possible

It is possible that I exist, but no physical objects

exist.

It is possible that I ≠ my body.

I ≠ my body.

1.

2.

3.

4.

5.

C.

So then, this premise might be false. Maybe Descartes only thinks he can imagine a situation where he exists, but no physical objects exist.

But then, if 1 turns out to be false, 3 will not follow (since it follows

only from 1 and 2 together).

And without 3, we don’t get 4 either.

And since the conclusion is supposed to follow from 4 & 5, it doesn’t

follow either!

I can imagine a situation where I exist, but no

physical objects exist.

So then, the real question is, is this premise true?

Or does the situation where a human being exists but no physical objects exist contain a hidden

contradiction, like the Ted-the-Barber situation did?