known by intuition. The limits of our knowledge, therefore, are determined by the simple truths we possess, their possible fruitfulness, and their adequacy to the explanation of the real. In the Regulæ and the Principles, Descartes gives the same enumeration of these simple truths, namely, figure, extension, motion, etc.; knowledge, doubt, ignorance, volition, and the like; existence, duration, unity. Since these conceptions are 'simple natures,' we cannot know them at all without knowing them completely. They are of course not derived from sense perception, and are wholly distinct from them in nature. They are innate ideas directly implanted in the mind by God.
If we examine these innate ideas, however, we find that they are all abstract conceptions, and simple only so long as they remain abstract. Hence, when Descartes maintains that all knowledge is derived from these abstract conceptions taken by themselves, "he falls back into that rationalistic view of knowledge which he criticises so excellently in his attack on the syllogism" (p. 39). This rationalistic theory which Descartes eventually adopts can be understood only in the light of the scholastic doctrine of essence. According to that doctrine each substance has an essence peculiar to itself which determines all its properties. If we know the essence at all we know it completely, and can deduce all the properties which flow from it. This implies, of course, that the connection of ideas is the same as that of things. Descartes accepts this view with all its implications. His criterion of truth means that what is inseparable in thought is inseparable in the real, and, further, that when the mind can perceive no connection between ideas, there is no connection between the existences corresponding to the ideas.
This theory of knowledge accounts for the Occasionalism implicit in Descartes' s metaphysics. Since, as a matter of fact, the particularity and variety of the real cannot be deduced from isolated abstract conceptions, Descartes is forced at every turn to explain the concrete content of the world by reference to the will of God. "The continued reference to God for explanation of finite phenomena is no admission of ignorance of the true explanation, but is always based on the certain and absolute knowledge that they are due neither to mind nor to matter, and that, therefore, so far as they have any reality they must be wholly dependent on what is outside both. Since mind and body are in thought completely transparent to us, each being exhaustively known in conception, where no necessary connection is visible between them, or between either of them and what is conjoined with it in experience, there can be none, and such conjunction as is vouched
