CHAPTER XVI—That in God there is no Passive Potentiality³⁷³⁷Potentia passiva, the Aristotelian ‘potentiality’ in its opposition to ‘act.’ Taken actively, the word potentia is to be rendered ‘Power,’ not ‘potentiality.’ As God possesses the power to create whatever can be made at all, there is in Him the promise and potency of all possible being. In Him all things that are or ever can be exist ‘eminently and virtually.’ He is all that they are, but in a better and more excellent way, — in some such way as a seal is in regard of all the impressions that ever can be taken of it, or as a king in regard of a viceroy or lord-lieutenant: so much so that actual creation makes no addition to God or to the sum total of Being absolutely speaking. — Cf. Isa. xl.

EVERYTHING that has in its substance an admixture of potentiality, to the extent that it has potentiality is liable not to be: because what can be, can also not be. But God in Himself cannot not be, seeing that He is everlasting; therefore there is in God no potentiality.

2. Although in order of time that which is sometimes in potentiality, sometimes in actuality, is in potentiality before it is in actuality, yet, absolutely speaking, actuality is prior to potentiality,³⁸³⁸‘Actuality is prior to potentiality.’ The whole metaphysical proof of the existence of God may be said to be summed up in these words. because potentiality does not bring itself into actuality, but is brought into actuality by something which is already in actuality.³⁹³⁹A metaphysical and therefore more general statement of the physical law of inertia. Everything therefore that is any way in potentiality has something else prior to it. But God is the First Being and the First Cause, and therefore has not in Himself any admixture of potentiality.

4. Everything acts inasmuch as it is in actuality.⁴⁰⁴⁰‘Every agent acts inasmuch as it is in actuality,’ is a favourite axiom of the schoolmen, to which there is a reciprocal: ‘Everything that is acted upon is acted upon inasmuch as it is in potentiality’: which is also put thus, ‘Everything received is received according to the mode of the recipient.’ ‘To be in actuality,’ is something akin to the modern conception of ‘energy.’ Every agent then acts according to its proximately available energy. A man does only what he is ‘up to doing.’ Whatever then is not all actuality, does not act by its whole self, but by something of itself. But what does not act by its whole self, is not a prime agent; for it acts by participation in something else, not by its own essence. The prime agent then, which is God, has no admixture of potentiality, but is pure actuality.

6. We see that there is that in the world which passes from potentiality to actuality. But it does not educe itself from potentiality to actuality, because what is in potentiality is not as yet, and therefore cannot act. Therefore there must be some other prior thing, whereby this thing may be brought out from potentiality to actuality. And again, if this further thing is going out from potentiality to actuality, there must be posited before it yet some other thing, whereby it may be reduced to actuality. But this process cannot go on for ever: therefore we must come to something that is only in actuality, and nowise in potentiality; and that we call God.⁴¹⁴¹This last is in substance the whole argument of Chap. XIII. St Thomas is thinking of such an instance in the first place as the birth of a child, or the growth of a crop of wheat. Intellectual agents have some limited power of educing themselves from potentiality to actuality, e.g., from armed peace to war: but their case is not under consideration here.