FORE:Descartes�� theory of the universe included, however, something more than extension (or matter) and motion. This was Thought. If we ask whence came the notion of Thought, our philosopher will answer that it was obtained by looking into himself. It was, in reality, obtained by looking into Aristotle, or into some text-book reproducing his metaphysics. But the Platonic element in his system enabled Descartes to isolate Thought much more completely than it had been isolated by Aristotle. To understand this, we must turn once more to the Timaeus. Plato made up his universe from space and Ideas. But the Ideas were too vague or too unintelligible for scientific purposes. Even mediaeval Realists were content to replace them by Aristotle��s much clearer doctrine of Forms. On the other hand, Aristotle��s First Matter was anything but a satisfactory conception. It was a mere abstraction; the390 unknowable residuum left behind when bodies were stripped, in imagination, of all their sensible and cogitable qualities. In other words, there was no Matter actually existing without Form; whereas Form was never so truly itself, never so absolutely existent, as when completely separated from Matter: it then became simple self-consciousness, as in God, or in the reasonable part of the human soul. The revolution wrought by substituting space for Aristotle��s First Matter will now become apparent. Corporeal substance could at once be conceived as existing without the co-operation of Form; and at the same stroke, Form, liberated from its material bonds, sprang back into the subjective sphere, to live henceforward only as pure self-conscious thought.