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 and that "I" know what "thinking" is. He suggested a more appropriate phrase would be "it thinks" wherein the "it" could be an impersonal subject as in the sentence "It is raining." The Danish philosopher Søren Kierkegaard calls the phrase a tautology in his "Concluding Unscientific Postscript". He argues that the "cogito" already presupposes the existence of "I", and therefore concluding with existence is logically trivial. Kierkegaard's argument can be made clearer if one extracts the premise "I think" into the premises "'x' thinks" and "I am that 'x'", where "x" is used as a placeholder in order to disambiguate