Cartesian doubt him. While methodic doubt has a nature, one need not hold that knowledge is impossible in order to apply the method of doubt. Indeed, Descartes' attempt to apply the method of doubt to the existence of himself spawned the proof of his famous saying, ""Cogito, ergo sum"" (I think, therefore I am). That is, Descartes tried to doubt his own existence, but found that even his doubting showed that he existed, since he could not doubt if he did not exist. Cartesian doubt Cartesian doubt is a form of methodological skepticism associated with the writings and methodology of René Descartes
Cogito, ergo sum the "I" from the thinking thing. Here, the "cogito" has already assumed the "I"'s existence as that which thinks. For Kierkegaard, Descartes is merely "developing the content of a concept", namely that the "I", which already exists, thinks. As Kierkegaard argues, the proper logical flow of argument is that existence is already assumed or presupposed in order for thinking to occur, not that existence is concluded from that thinking. Bernard Williams claims that what we are dealing with when we talk of thought, or when we say "I am thinking," is something conceivable from a third-person perspective; namely objective "thought-events"