To determine the question, we must consider that something may be included in the meaning of a less common term, which is not included in the more common term; as "rational" is included in the meaning of "man," and not in the meaning of "animal." So that it is one thing to ask the meaning of the word animal, and another to ask its meaning when the animal in question is man. Also, it is one thing to ask the meaning of this word "person" in general; and another to ask the meaning of "person" as applied to God. For "person" in general signifies the individual substance of a rational figure. The individual in itself is undivided, but is distinct from others. Therefore "person" in any nature signifies what is distinct in that nature: thus in human nature it signifies this flesh, these bones, and this soul, which are the individuating principles of a man, and which, though not belonging to "person" in general, nevertheless do belong to the meaning of a particular human person.
Now distinction in God is only by relation of origin, as stated above (Q. 28, AA. 2, 3), while relation in God is not as an accident in a subject, but is the divine essence itself; and so it is subsistent, for the divine essence subsists. Therefore, as the Godhead is God so the divine paternity is God the Father, Who is a divine person. Therefore a divine person signifies a relation as subsisting. And this is to signify relation by way of substance, and such a relation is a hypostasis subsisting in the divine nature, although in truth that which subsists in the divine nature is the divine nature itself. Thus it is true to say that the name "person" signifies relation directly, and the essence indirectly; not, however, the relation as such, but as expressed by way of a hypostasis. So likewise it signifies directly the essence, and indirectly the relation, inasmuch as the essence is the same as the hypostasis: while in God the hypostasis is expressed as distinct by the relation: and thus relation, as such, enters into the notion of the person indirectly. Thus we can say that this signification of the word "person" was not clearly perceived before it was attacked by heretics. Hence, this word "person" was used just as any other absolute term. But afterwards it was applied to express relation, as it lent itself to that signification, so that this word "person" means relation not only by use and custom, according to the first opinion, but also by force of its own proper signification.
Reply Obj. 1: This word "person" is said in respect to itself, not to another; forasmuch as it signifies relation not as such, but by way of a substance—which is a hypostasis. In that sense Augustine says that it signifies the essence, inasmuch as in God essence is the same as the hypostasis, because in God what He is, and whereby He is are the same.
Reply Obj. 2: The term "what" refers sometimes to the nature expressed by the definition, as when we ask; What is man? and we answer: A mortal rational animal. Sometimes it refers to the suppositum, as when we ask, What swims in the sea? and answer, A fish. So to those who ask, Three what? we answer, Three persons.
Reply Obj. 3: In God the individual—i.e. distinct and incommunicable substance—includes the idea of relation, as above explained.
Reply Obj. 4: The different sense of the less common term does not produce equivocation in the more common. Although a horse and an ass have their own proper definitions, nevertheless they agree univocally in animal, because the common definition of animal applies to both. So it does not follow that, although relation is contained in the signification of divine person, but not in that of an angelic or of a human person, the word "person" is used in an equivocal sense. Though neither is it applied univocally, since nothing can be said univocally of God and creatures (Q. 13, A. 5). _______________________
QUESTION 30
THE PLURALITY OF PERSONS IN GOD
(In Four Articles)
We are now led to consider the plurality of the persons: about which there are four points of inquiry:
(1) Whether there are several persons in God?