Reply Obj. 3: The word "God" stands for the person in a different way from that in which this word "man" does; for since the form signified by this word "man"—that is, humanity—is really divided among its different subjects, it stands of itself for the person, even if there is no adjunct determining it to the person—that is, to a distinct subject. The unity or community of the human nature, however, is not a reality, but is only in the consideration of the mind. Hence this term "man" does not stand for the common nature, unless this is required by some adjunct, as when we say, "man is a species"; whereas the form signified by the name "God"—that is, the divine essence—is really one and common. So of itself it stands for the common nature, but by some adjunct it may be restricted so as to stand for the person. So, when we say, "God generates," by reason of the notional act this name "God" stands for the person of the Father. But when we say, "God does not generate," there is no adjunct to determine this name to the person of the Son, and hence the phrase means that generation is repugnant to the divine nature. If, however, something be added belonging to the person of the Son, this proposition, for instance, "God begotten does not beget," is true. Consequently, it does not follow that there exists a "God generator," and a "God not generator"; unless there be an adjunct pertaining to the persons; as, for instance, if we were to say, "the Father is God the generator" and the "Son is God the non-generator" and so it does not follow that there are many Gods; for the Father and the Son are one God, as was said above (A. 3).
Reply Obj. 4: This is false, "the Father begot God, that is Himself," because the word "Himself," as a reciprocal term, refers to the same suppositum. Nor is this contrary to what Augustine says (Ep. lxvi ad Maxim.) that "God the Father begot another self [alterum se]," forasmuch as the word "se" is either in the ablative case, and then it means "He begot another from Himself," or it indicates a single relation, and thus points to identity of nature. This is, however, either a figurative or an emphatic way of speaking, so that it would really mean, "He begot another most like to Himself." Likewise also it is false to say, "He begot another God," because although the Son is another than the Father, as above explained (Q. 31, A. 2), nevertheless it cannot be said that He is "another God"; forasmuch as this adjective "another" would be understood to apply to the substantive God; and thus the meaning would be that there is a distinction of Godhead. Yet this proposition "He begot another God" is tolerated by some, provided that "another" be taken as a substantive, and the word "God" be construed in apposition with it. This, however, is an inexact way of speaking, and to be avoided, for fear of giving occasion to error.
Reply Obj. 5: To say, "God begot God Who is God the Father," is wrong, because since the word "Father" is construed in apposition to "God," the word "God" is restricted to the person of the Father; so that it would mean, "He begot God, Who is Himself the Father"; and then the Father would be spoken of as begotten, which is false. Wherefore the negative of the proposition is true, "He begot God Who is not God the Father." If however, we understand these words not to be in apposition, and require something to be added, then, on the contrary, the affirmative proposition is true, and the negative is false; so that the meaning would be, "He begot God Who is God Who is the Father." Such a rendering however appears to be forced, so that it is better to say simply that the affirmative proposition is false, and the negative is true. Yet Prepositivus said that both the negative and affirmative are false, because this relative "Who" in the affirmative proposition can be referred to the suppositum; whereas in the negative it denotes both the thing signified and the suppositum. Whence, in the affirmative the sense is that "to be God the Father" is befitting to the person of the Son; and in the negative sense is that "to be God the Father," is to be removed from the Son's divinity as well as from His personality. This, however, appears to be irrational; since, according to the Philosopher (Peri Herm. ii), what is open to affirmation, is open also to negation. _______________________
FIFTH ARTICLE [I, Q. 39, Art. 5]
Whether Abstract Essential Names Can Stand for the Person?
Objection 1: It would seem that abstract essential names can stand for the person, so that this proposition is true, "Essence begets essence." For Augustine says (De Trin. vii, i, 2): "The Father and the Son are one Wisdom, because they are one essence; and taken singly Wisdom is from Wisdom, as essence from essence."
Obj. 2: Further, generation or corruption in ourselves implies generation or corruption of what is within us. But the Son is generated. Therefore since the divine essence is in the Son, it seems that the divine essence is generated.
Obj. 3: Further, God and the divine essence are the same, as is clear from what is above explained (Q. 3, A. 3). But, as was shown, it is true to say that "God begets God." Therefore this is also true: "Essence begets essence."
Obj. 4: Further, a predicate can stand for that of which it is predicated. But the Father is the divine essence; therefore essence can stand for the person of the Father. Thus the essence begets.
Obj. 5: Further, the essence is "a thing begetting," because the essence is the Father who is begetting. Therefore if the essence is not begetting, the essence will be "a thing begetting," and "not begetting": which cannot be.