Des Cartes has given us, among others, the axiom "That two substances are really distinct when their ideas are complete, and no way imply each other. The idea of extension is complete and distinct from the idea of thought, which latter is also clear and distinct by itself. It follows, therefore, that substance and mind are distinct in essence." Des Cartes has, from the vagueness of some of his statements, subjected himself to the charge of asserting the existence of innate ideas, and the following quotations will speak for themselves on the subject:--"When I said that the idea of God is innate in us, I never meant more than this, that Nature has endowed us with a faculty by which we may know God; but I have never either said or thought that such ideas had an actual existence, or even that they were a species distinct from the faculty of thinking.... Although the idea of God is so imprinted on our minds, that every person has within him the faculty of knowing him, it does not follow that there may not have been various individuals who have passed through life without ever making this idea a distinct object of apprehension; and, in truth, they who think they have an idea of a plurality of Gods, have no idea of God whatever." This seems explicit as negativing the charge of holding the doctrine of innate ideas; but in the _Edinburgh Review_ several passages are given, amongst which is the following:--"By the word idea I understand all that can be in our thoughts; and I distinguish three sorts of ideas--adventitious, like the common idea of the sun, framed by the mind, such as that which astronomical reasoning gives of the sun; and innate, as the idea of God, mind, body, a triangle, and generally all those which represent true, immutable, and eternal essences." With regard to these rather opposite statements, Lewes says, "If Des Cartes, when pressed by objections, gave different explanations, we must only set it down to a want of a steady conception of the vital importance of innate ideas to his system. The fact remains that innate ideas form the necessary groundwork of the Cartesian doctrine.... The radical error of all ontological speculation lies in the assumption that we have ideas independent of experience; because experience can only tell us of ourselves or of phenomena; of noumena it can tell us nothing.... The fundamental question, then, of modern philosophy is this--Have we any ideas independent of experience?"