Reading : Western Philosophy III.4 "The Incorporeal Mind"

This passage includes portions of the 2nd and 6th meditations. In the first meditation, Descartes concluded "cogito ergo sum" - I am thinking, therefore I exist: the only thing of which he can be certain, and the foundation for all subsequent proofs.

The second meditation asks the question "what am I?" and concludes "a thinking thing"; in the third, he proves God's existence (using the "trademark argument"). The fourth and fifth meditations deal with corporeal substance, and in the sixth meditation he addresses the distinctions between corporeal and thinking substance.

Descartes proof that the two are distinct can be broken down:

• P1: "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" (p149). Sometimes referred to as the argument from clear and distinct perception
• P2: "I have a clear and distinct idea of myself as ... a thinking, non-extended thing" (p150).
• P3: "I have a distinct idea of body [as an] extended, non=thinking thing" (p15).
• C : "it is certain that I am really distinct from my body"

This argument might be challenged, either on the basis of validity (the conclusion does not follow from the premises) or soundness - that is, if the premises are not valid.

The argument does seem to be valid. If P1, P2 and P3 are true, then C must follow. However, some might argue that P1 is not valid. For example, there is a difference between the "a right angled triangle" and "the property of obeying pythagorus' theorem", but while these two are different, you could not separate them - you could not have a right angled triangle without that property, and vice-versa.

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