ABSTRACT. It is my purpose here to show that, considered exclusively as a critique of Cartesian dualism, Wittgenstein&039;s later philosophy is quite conclusive without the private language argument. His critique of the Cartesian doctrine of the self as immaterial thinking substance remains decisive (albeit less multi-dimensional) when freed from its associations with the latter, and when the focus is narrowed to the account, in The Blue Book, of the two senses attaching to the first person pronoun, "I". I conclude that the exhibition of the non-demonstrative, non-referring nature of "I" in its psychological or subject use demonstrates a deep-seated fallacy at the root of the Cartesian Cogito principle.