QuoteDescartes's statement became a fundamental element of Western philosophy, as it purported to provide a certain foundation for knowledge in the face of radical doubt. While other knowledge could be a figment of imagination, deception, or mistake, Descartes asserted that the very act of doubting one's own existence served—at minimum—as proof of the reality of one's own mind; there must be a thinking entity—in this case the self—for there to be a thought.
One critique of the dictum, first suggested by Pierre Gassendi, is that it presupposes that there is an "I" which must be doing the thinking. According to this line of criticism, the most that Descartes was entitled to say was that "thinking is occurring", not that "I am thinking".[5]
It's interesting that Gassendi, notable fan of Epicurus, is listed there as having an objection. Would be interesting to know what else Gassendi thought about Descartes