Aristotle further says on this subject (Metaph. XII. 6): “It may be that what has potentiality is not real; it is of no avail therefore to make substances eternal, as the idealists do, if they do not contain a principle which can effect change. And even this is insufficient, if it is not active, because in that case there is no change. Yea, even if it were active, but its substance only a potentiality, there would be in it no eternal movement, for it is possible that what is according to potentiality may not exist. We must therefore have a principle whose substance must be apprehended as activity.” Thus in mind energy is substance itself. “But here a doubt seems to spring up. For all that is active seems to be possible, but all that is possible does not seem to energize, so that potentiality seems to be antecedent,” for it is the universal. “But if this were the case, no one of the entities would be in existence, for it is possible that a thing may possess a capacity of existence, though it has never yet existed. But energy is higher than potentiality. We must thus not assert, as theologians would have us do, that in the eternal ages there was first chaos or night” (matter), “nor must we say with natural philosophers that everything existed simultaneously. For how could the First be changed, if nothing in reality were cause? For matter does not move itself, it is the Master who moves it. Leucippus and Plato accordingly say that motion has always existed, but they give no reason for the assertion.” Pure activity is, according to Aristotle (Metaph. IX. 8), before potentiality, not in relation to time, but to essence. That is to say, time is a subordinate moment, far removed from the universal; for the absolute first Being is, as Aristotle says at the end of the sixth chapter of the twelfth book, “that which in like activity remains always identical with itself.” In the former assumption of a chaos and so on, an activity is posited which has to do with something else, not with itself, and has therefore a pre-supposition; but chaos is only bare possibility.