truth.

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