cate comes, however, Aristotle’s conception of Possible Being, a conception which plays a great part in the whole Aristotelian theory of Nature. The ens in potentia of the Aristotelian system occupies a place in a realistic doctrine. Aristotle insists that possibilities are in one sense real beings. Is not an architect a house-builder even when he is not building houses? Is not the sleeper potentially awake? Is not every natural process the realization of possibility?
But the doctrine of course has its obscurities. Where, in the independently real world, which Aristotle all the while assumes, are the mere possibilities when they are not yet realized? If one fairly faces this question, one finds that the possibilities appear to be in some sense ideal. They suggest even to Aristotle his theory of Nature as desiring or willing the yet unfulfilled possibilities, — a theory to which he nowhere gives a perfectly rounded expression. And it often seems as if the Possible Being of this Aristotelian doctrine would have to be expressed in terms of validity rather than in terms of the mere realistic entities themselves. It is true that the architect can build, the sleeper wake. These truths are valid. They are, for Aristotle, valid about independently real beings; and his doctrine is that there is also an independent or realistic type of Being corresponding to their validity; but this sort of Being, this ens in potentia, tends on the whole to assume the essentially ideal form of our present conception of what it is to be. Aristotle, in any case, never really solved the problem of the relation of these two types of being.
