One cannot discuss contemporary philosophy of mind without the ghost of Descartes skulking around in the shadows. And one cannot understand Descartes without understanding his famous cogito insight, put forward for the first time publicly 350 years ago.¹ Twenty-five years ago I showed what the nerve of the Cartesian insight is². Descartes is not inferring sum from cogito, but demonstrating to himself his own existence by performing an act of thinking. The expression cogito does not mark a premise from which sum is inferred, but a thought-art which reveals (as long as it goes on) to Descartes the entity that he is. Descartes's little skit is analogous to someone's, say Mark Twain's, proving his existence to a skeptic by confronting the doubter and confirming his existence to him by saying: "I exist." Of course any other thought-act (in Descartes's case) or language act (in Mark Twain's case) would have done the trick equally well. This opens the door to Descartes's dramatic gambit of attempting to doubt, nay, to deny, everything. When he then tries to deny to himself his own existence, by so doing he on the contrary proves that he exists. In Mark Twain's case an analogous purpose is served by the language act of declaring the rumors of his demise to be exaggerated.