Note 19 — Chapter III

Let me say, in passing, that this separation that Descartes thinks he can establish between perception and ideation, is only conceivable on condition that it be not too closely examined, and that no exact definition of ideation be given. If we remark, in fact, that all thought is a reproduction, in some degree, of a sensation, we arrive at this conclusion: that a thought operated by a soul distinct from the body would be a thought completely void and without object, it would be the thought of nothingness. It is not, therefore, conceivable. Consequently the criterion, already so dangerous, which Descartes constantly employs—to wit: that what we clearly conceive is true—cannot apply to thought, if we take the trouble to analyse it and to replace a purely verbal conception by intuition.