Why are so many people quoting augustine/descartes with the "I think therefore I am" argument. It is full of daring premises, such that it would be, for all practical purposes, impossible to prove these said premises and thus negating the arguments soundness and ultimately its validity.
The main problem with assuming that one thinks is that they assume they are the ones that are actually thinking. It is obvious that something we call thinking is going on, but we cannot say that we are the ones doing it. The "I think" statement implies what Nietzsche called an 'ego', meaning that something is doing the thinking rather than thinking simply happening on its own.
A further problem is we assume what thinking is, how can we discern it from a 'feeling'. To 'know' what things are we must compare prior learning to contemporary events, to know what thinking is one must do such a comparison to assign the current sensation a category. Meaning, that to know what thinking is we have to think about it. Logical fallacy anyone? Specifically a circular argument or begging the question. We can never know what thinking is, becasue we have to thinking about it to begin, which obviously isn't a valid method of deduction.
Finally the statement assumes that thought originates when we choose it. Using "I" in the sentence implies that you are the prerequisite to the action, and you originate it, when it seems just as logical that thought occurs for no reason, specifically not becasue anyone wishes it to be so. "Thinking" appears to force itself upon the "thinker" rather than the opposite.
Being an existentialist I see no need to build truths, furthermore I see all 'truth' as flawed as our senses are imperfect. However it appears to me that a certain 'feeling' or 'sensation' that we call thinking occurs, we cannot understand it or know anything about it other than it happens. A simple and pithily way to tie this rather axiomatic level of deduction up is "The only contingent certainty, is thinking occurs."
BTW The majority of the arguments I've put forward tie in with "Beyond Good and Evil" - Nietzsche. I'm open to a critique of my counter-argument to the descartes school of skepticism, if anyone would like to that is.