Commentaria in Summam contra Gentiles, Liber I

After Saint Thomas has removed from God the imperfection of temporal being, he now removes from the passive power its imperfection ¹. Concerning this, however, he does two things: first, he removes the passive power; second, he draws out one corollary ².

I. As to the first, the following conclusion is laid down: God is not in passive potency.

For the understanding of which it must be known that, although God has no passive power and is receptive of nothing external to Himself, what is inquired into here concerns only the power toward substantial esse, which is separable from act in itself. For it is evident that Saint Thomas is here speaking of that passive power which is removed by eternity: since he derives its removal from God from His eternity. Now this is a power separable from act. For that power which is inseparable from act in itself, as one whose capacity is completed by a single act, does not conflict with eternity: as is evident in the heavenly bodies.

But if it were said that every passive power is repugnant to eternity, since what is eternal must properly be free from all mutation, both intrinsic and extrinsic, and wherever any passive power exists, that thing is mutable, at least from without—this cannot be the mind of St. Thomas: for it is established that in the preceding chapter he proved God to be eternal only in this sense, that He has no beginning or end of duration, in the same way that time and motion and the heavenly bodies were held by the philosophers to be eternal; not, however, so that all transmutation is absolutely excluded.

The sense of the conclusion, therefore, is that in God there is no potentiality with respect to substantial esse separable from the act which He has. And it is the same as if it were said that God is not composed of matter and form, in the way that corruptible things, which are not eternal, have composition ³. And this sense is now proved.

Nevertheless, although he principally intends this meaning, he also inserts certain arguments by which it is proved not only that it is not in potency, but also that in it there is nothing that has the character of potency: for, if that is (1), it is plainly evident that it cannot be in potency.

II. The first argument, therefore, is this. God, considered in himself, cannot not exist. Therefore in him there is no potency with respect to esse. — The antecedent is evident: because he is eternal. — The consequence is proved. Because in whatever substance potency is admixed, in respect of what it has of potency it can not exist: for what can exist can also not exist.

It must be noted, for the understanding of this argument, that the assumption taken for the proof of the consequence is not understood of the ability not to be through an extrinsic power (although in that sense it is true): for neither is esse received in potency according to an extrinsic power. Rather, the ability not to be is taken from within: namely, that it has in itself that whereby it may at some time fail, as happens in corruptible things.

This is clear from the proof of the preceding point. For it is proved that God cannot not be because He is eternal. Now the eternal, like the heavens, has from within itself the property of not being able not to be, although from without it could fail to be. Hence it was also said that God cannot not be in Himself, that is, by some intrinsic principle.

It is also evident from what was assumed for the proof of the consequence. And the proposition is true if it is taken according to the sense of the conclusion; in another sense, however, it would be false. For in a substance, the admixture of potency can be understood in two ways. In one way, because it has within itself several parts, one of which is related to another as potency to act and as the receptive to the form, although it cannot be separated from act of itself. In another way, because it has within itself a potential part separable from act in itself, insofar as it is receptive of another act. To that in which potency is admixed in the first way, it is not necessary that it be able not to exist from within itself, as in the celestial bodies, according to those who posit them as composed of matter and form, as is clearly evident: for potency is in them, and yet they are incorruptible. But that in which potency is admixed in the second way (in which sense the conclusion is understood) can sometimes not exist. For if that potency can be separated from act, that which has such a potency can not exist: just as, because the matter of Socrates can receive another form and thus lack the form it has, Socrates can not exist.

St. Thomas adds, moreover, that a thing, insofar as it is in potency, can be non-being. First, because if something consists of potency and act, the capacity for non-being does not belong to it by reason of the act it has, but by reason of its potency, which is receptive of another form. Second, because if it has a potency toward substantial esse, it can be non-being substantially; but if it has a potency toward some accidental esse, it can be non-being accidentally, as white or black and the like; and, speaking universally, it can be non-being with respect to that toward which it is in potency.

III. Second. God has nothing prior to himself; therefore he is not in potency. The antecedent is evident, because he is the first being and the first cause. The consequence is proved: because act is simply prior to potency, although within one and the same thing potency is prior to act in time; for what is in potency is not brought into act except by some being in act. Therefore, if God were in potency, there would be some being in act prior to him. Therefore, etc.

To make this argument evident, it must be noted that the act's being prior to potency simply can be understood in two ways: in one way, by priority of nature and causality; in another way, by priority of duration. And although it is true in both ways, as is clear from Aristotle, Metaphysics IX ⁴, and from the doctrine of St. Thomas there and in lectio 7, and in De Potentia, q. VII, a. 1, nevertheless it is true in one way and not in the other.

For if we speak of priority of nature and causality, this is true absolutely: and of that, I say, which is produced successively, and of that which is produced in an instant.

If, however, we speak of priority of duration, it is not universally true in this way, but two limitations are required. The first is that what is in potency be reduced to act through successive transmutation. The second is that this potency be proximate potency, which can be reduced to act through a single transmutation, and not remote potency. This is clear from Aristotle, Metaphysics IX, text 12, and from St. Thomas, lect. 6 ⁵, where he explains how something is said to be in potency with respect to act. On account of the failure of the first condition, it is not necessary that what illuminates precede in time what is illuminated, because illumination is not a successive change but an instantaneous one. On account of the failure of the second condition, it is not necessary that being in act precede in duration prime matter, because, although it is in potency, it is not proximate potency but remote.

(1) if that is. — Has a homoteleuton dropped out, so that one ought to read: if that is which is necessary of itself, or something similar? Cf. the third argument in the text.

2. Thus, with the proposition understood, its truth clearly appears. For since matter is brought successively and in time, through the action of a being in act, to such a disposition that it becomes proximate matter, which can be reduced to act by a single action, it is evident that being in act precedes not only the thing produced in duration, but also its proximate potency: since between it and such a potency there intervenes the time during which it was led by the action of the agent to that disposition according to which it is proximate matter.

The truth of this exposition is also evident from the argument by which the said proposition is proved, namely that what is in potency is not reduced to act except by a being in act. For if it were understood of remote potency, or of bare matter, then this inference would be invalid: What is in potency is not brought into act except by some being in act; therefore act is prior in time to potency. But it would indeed follow that therefore act precedes the act successively produced by it. But if it is understood in the manner explained, the inference is sound. For if what is in potency before every action of the agent is reduced to act successively by that which exists in act, it follows that act precedes the proximate potency of that which is brought into act: since in time and successively matter is disposed by the agent with such a disposition as is the proximate and immediate disposition to the form.

Although the proposition is true both of priority of duration and of priority of nature, Saint Thomas nevertheless takes it here as true of priority of nature and causality. For the act is prior to that which is at one time in potency and at another in act; since nothing is prior to God in causality, because he is the first cause, it follows that he is not at one time in potency and at another in act.

IV. Third. God is of himself necessary esse. Therefore he is not possible esse. Therefore nothing of potency is found in his substance. — The first consequence is proved. Every possible esse has a cause, as was shown in the present chapter ⁶. But esse necessary of itself has no cause: otherwise it would not be esse necessary of itself. Therefore etc.

Note that although, if possible is taken as opposed to impossible, being necessary per se is also possible; nevertheless, if possible is taken as the same as contingent, namely what can be and not be, in which way it is opposed to necessary, no being necessary per se is possible; just as one of two opposites is not the other.

V. Fourth. The first agent is pure act. But God is the first agent. Therefore he is pure act. — The major is proved, because the opposite of the predicate entails the opposite of the subject. For it follows: it is not pure act; therefore it does not act by its whole self, but by some part of itself: because each thing acts insofar as it is in act. Therefore it acts by participation in something, not through essence. Therefore it is not the first agent.

To make this argument evident, it must be considered that whatever is received into some potency receives from that reception a certain limitation, just as whiteness received in a subject is limited to some degree of whiteness; and if it were abstracted from the subject, it would possess every perfection possible to it. For an act is made imperfect by the fact that it has esse received. From this it follows that act received in potency is participated: namely, because it does not have every perfection that could belong to it according to the account of its species. It follows rightly, therefore, that if something does not act with its whole self, it does not act through its essence—namely, such that its essence, which names the whole, would be the first agent—but rather by participation in something else, that is, through its actual part, which participates because it is received in another part that is potential. This plainly conflicts with the notion of a first agent: for what is first simply must also act first, and consequently not through anything else in any way; just as what is moved first must not be moved through a part, as is said in Book VII of the Physics ⁷.

VI. Fifth. God is entirely impassible and immutable. Therefore he has no passive potency. — The consequence is proved. Because each thing is naturally capable of being acted upon insofar as it is in potency, since motion is the act of a being in potency.

Sixth. There is something in the world that passes from potency into act. And it is not brought from potency into act by itself: for what is in potency does not yet exist, and consequently cannot act. Therefore we must arrive at something that is purely in act and in no way in potency. And this we call God. — The inference is proved. Because there is no proceeding to infinity among such things.

Against this argument an objection could be raised, because from the fact that one does not proceed to infinity among things brought from potency into act, it does not seem to follow that one must arrive at pure act, which is God, but rather at something that is not brought from potency into act. For if we suppose the heavens to have been produced from eternity, they will not have been reduced from passive potency into act, and yet they possess potency.

But this objection is removed if the aim of the conclusion is considered. For Saint Thomas does not intend in this chapter to prove that God is pure act, having nothing in himself that bears the character of potency; but rather that in God there is no potency separable from act, by which he would be said to be in passive potency to something else, just as air is in potency to fire being made from it, and universally all corruptible things are in potency to something else being generated from them.