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 one's belief in their own existence would be secure, for there is no way one could be deceived unless one existed in order to be deceived. But I have convinced myself that there is absolutely nothing in the world, no sky, no earth, no minds, no bodies. Does it now follow that I, too, do not exist? No. If I convinced myself of something [or thought anything at all], then I certainly existed. But there is a deceiver of supreme power and cunning who deliberately and constantly deceives me. In that case, I, too, undoubtedly exist, if he deceives me;