Commentaria in Summam contra Gentiles, Liber II

I. From the foregoing conclusion another conclusion is inferred as a corollary ¹, namely: In intellectual substances there is a composition of act and potency.

It is proved first. In a created intellectual substance there are found essence and esse, which is the complement of the existing essence. Therefore in it there is composition of potency and act. — The consequence is proved: because in whatever two things are found such that one is the complement of the other, the relation of one to the other is as the relation of potency to act.

Second. Esse is present in created substances as an act. Therefore the substance itself is potency with respect to esse. Therefore etc. — The antecedent is proved: because all created substances have esse from the first agent; but whatever is present in something by an agent must be its act, since it belongs to an agent to make something actual. — The first inference is also proved: because that in which act is present is potency.

Concerning the assumption made in the proof of the antecedent, a doubt arises. For in a composite of matter and form, prime matter is present from God. And yet matter is not the act of the composite. Therefore it is false that what is present in something by an agent must be its act.

It is answered that Saint Thomas does not say that everything which is in a thing from an agent must be its act, but everything which inheres in it. Now to inhere belongs to what arrives afterward, whether in duration or in the order of generation, but not to what precedes and is presupposed. Therefore the sense of the proposition is: everything which belongs to a thing from an agent by way of arriving to it must be its act. But matter does not arrive at the composite; rather it is presupposed to it. Hence there is no objection against the meaning of the text.

Third. All created things participate in esse, since God alone is being essentially. Therefore, etc. — The consequence is proved. For the participated is related to the participant as act to potency, since it is by the participated that the participant is actually such.

It must be noted that when it is said that God alone is being essentially, being is taken participially, as signifying esse: but not nominally, as signifying essence ².

Fourth. Every created substance is assimilated to God according to esse, as was shown above. Therefore etc. — The consequence is proved. Because the assimilation of anything to its efficient cause comes about through act: since it acts upon what is like itself insofar as it is in act.