Duane asked:

I think this is from Descartes:

a) For any two things, if they are identical, then all statements describing one of those things must
describe the other. b) I can picture existing without my body. c) I can not picture existing without my
soul. Ergo, d) My soul and my body are not identical (i.e. Cartesian dualism obtains)

Hmm...I always like these simple arguments, please comment. Thanks. (I wonder if I could put that
argument into some sort of symbolic logic. . .)

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Yes it is from Descartes and I like these simple arguments also. The trouble with this one is first trying
to decide how Descartes is arguing — there are many different interpretations.

The first and most common interpretation is that Descartes is appealing to what is now called
Leibniz's Law. "If we can say something true about A, which is not true about B, then A and B are not
the same thing." If this is how Descartes is arguing then it is clearly invalid since there are many
situations where Leibniz's law breaks down. For example, I may believe that Elvis is a bar tender, but
believe that the man I am now looking at is not a bar tender and therefore that this man is not Elvis.
Nevertheless, it may be that the man is Elvis. This objection applies to the argument you presented in
your question so that simple argument is simple to invalidate.

A second interpretation is by a fellow called Hooker (Hooker, M. 'Descartes denial of mind-body
identity' reprinted in Descartes: Critical and Interpretative EssaysJohn Hopkins UP 1978). This is
definitely not simple, but I think it is valid:

1. I can conceive of myself existing and no bodies existing.

2. For all propositions P, if P is conceivable then P is possible.

3. Therefore, it is possible that I exist and no bodies exist.

4. For all x, if x is a body, then x is essentially a body.

5. Therefore, if I am a body, then I am essentially a body.

6. If I am essentially a body, it is not possible that I exist and that no bodies exist.

— Contradiction!

7. Therefore, I am not essentially a body.

8. Therefore (from 5) I am not a body.

If this argument is valid we must question the premises, if we want to argue against it. I think premise
1. is the most questionable. What would it be like to exist without a body? Even if we could imagine
what it would be like, is disembodiment a real possibility?

Brian Tee
Dept of Philosophy
University of Sheffield.