Danny asked:

We are studying Descartes in my philosophy class, and we are constantly being troubled by the
infamous statement, 'I think, therefore I am.' We argue as to whether or not the argument is SOUND,
and have yet to truly decide what the answer is... What are your thoughts on this?

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There two questions to ask here, which often get confused. The first question is, 'Does Descartes'
appeal to the indubitable presence of mental acts prove anything at all?' The second question is,
'Does Descartes' appeal to the indubitable presence of mental acts prove what he thinks it proves?'

The second question is relatively easy to answer. Descartes thought that what he had proved was the
existence of his 'I' as an immaterial substance with a past, present and potentially a future, the
continuing subject of mental predicates, the non-physical agent responsible for the mental acts of
thinking, feeling, desiring, perceiving. Kant decisively refuted this claim with a thought experiment
about a line of colliding billiard balls. Imagine that there is not one 'I', but a series of 'I's each lasting
only a short period of time, each communicating its total state to the next. In other words, there is no
logical basis for countingmental substances, as defined by Descartes. 'I think' proves only that
somethingthinks now. Or perhaps, as some would claim, only that there is a thinkinghappening now.

Many more readers of Descartes would give a positive answer to the first question, whether his
appeal to the indubitable presence of mental acts and events proves anything at all.

The 'I know I'm different a zombie' argument which I mentioned above, is one such example. In my
response to Jason's question I claimed that this argument is not convincing, because a zombie who
was my exact double in every physical respect would 'say' exactly the same thing.

But here is an argument I find much harder to refute. It seems to me, reflecting on the sheer
contingency of my existence, that there might not have been me,but instead someone exactly like
me, writing these words, thinking these thoughts. Not a zombie, this time, but someone who
physically andmentally had all that I had. What every act of thinking, feeling, perceiving shows is that
there is 'I' where there might not have been 'I'. — Just what that meansis something I have puzzled
over for a long time.

Geoffrey Klempner