Plotinus is driven by this perplexity to reconsider the whole theory of Matter.[477] He takes Aristotle’s doctrine as the groundwork of his investigation. According to this, all existence is divided into Matter and Form. What we know of things—in other words, the sum of their differential characteristics—is their Form. Take away this, and the unknowable residuum is their Matter. Again, Matter is the vague indeterminate something out of which particular Forms are developed. The two are related as Possibility to Actuality, as the more generic to the more specific substance through every grade of classification and composition. Thus there are two Matters, the one sensible and the other intelligible. The former constitutes the common substratum of bodies, the other the common element of ideas.[478] The general distinction between Matter and Form was originally suggested to Aristotle by Plato’s remarks on the same subject; but he differs from his master in two important particulars. Plato, in his _Timaeus_, seems to identify Matter with space.[479] So far, it is a much more positive conception than the ὕλη of the _Metaphysics_. On the other hand, he constantly opposes it to reality as something non-existent; and he at least implies that it is opposed to absolute good as a principle of absolute evil.[480] Thus while the Aristotelian world is formed by the development of Power into Actuality, the Platonic world is composed by the union of Being and not-Being, of the Same and the Different, of the One and the Many, of the Limit and the Unlimited, of Good and Evil, in varying proportions with each other.