According to Descartes, the Meditations and Objections and Replies contain a logically sound proof that he has a Cartesian mind, along with a comprehensive explanation of that proof. A close look at these texts, however, reveals that things are not quite as sound and comprehensive as Descartes says they are. For the proof -- which is formally presented in the Sixth Meditation -- contains a dubious premise. When some of his objectors point this out, Descartes replies that the truth of the premise was firmly established in the Second Meditation. But this comes as a rather startling reply, since in the Second Meditation itself, and numerous other ,places, Descartes (quite correctly) denies that such a premise is ever established there. So, in spite of Descartes's attempt to locate a justification for it, the said premise remains unjustified and dubious.
In the pages that follow I try to present this criticism in more detail. In doing so I examine several parts of the Meditations. Descartes makes it fairly clear that the Sixth Meditation proof is not isolated from the rest of the Meditations, but rather is to a great extent motivated and driven by the material that precedes it. So, as well as examining the Sixth Meditation proof, I also examine the 'method of doubt' in the First Meditation, the cogito ergo sum and sum res cogitans passages in the Second Meditation, and the passages concerned with clear and distinct ideas and God in the Third, Fourth and Fifth Meditations. Once the import of these passages becomes clear, it becomes relatively easy to see the weakness in Descartes's proof that he has a Cartesian mind.