[potatoyogurt]

I think the problem goes even further. The cogito assumes an "I" that it never really establishes. "I think, therefore some thoughts exist" seems to hard to challenge, but who is to say that these thoughts are continuous or coherent, that they really define a single entity "I?"

[dantheman]

I believe the argument is that he is a thinking thing. And the "I" is merely for convenience he assumes no body, etc. I think, I can't remember, he even considers if the grand deceiver could change his thoughts and memories. I haven't discussed this in a decade :/

[diggum]

ding! For a statement that is supposed to be free of assumptions, assuming there's a thinker instead of just thoughts, is a pretty big leap.

[sl8r]

"When I analyze the process that is expressed in the sentence, 'I think', I find a whole series of daring assertions that would be difficult, perhaps impossible, to prove; for example that it is _I_ who thinks, that there must necessarily be something that thinks, that thinking is an activity or operation on the part of a being who is thought of as a cause, that there is an 'ego', and finally, that it is already determined what is to be designated by thinking - that I _know_ what thinking is. For if I had not already decided within myself what it is, by what standard could I determine whether that which is just happening is perhaps not 'willing' or 'feeling'? ... Whoever ventures to answer these metaphysical questions at once by an appeal to a sort of _intuitive_ perception, like the person who says, 'I think, and know that this, at least, is true, actual and certain' - will encounter nowadays a smile and two question marks from a philosopher nowadays. 'Sir', the philosopher will perhaps give him to understand, 'it is improbable that you are not mistaken, but why insist on the truth?'"