as explained when we treated of the divine unity (Q.
11, A. 2).

It must be observed, nevertheless, that the opposite arguments do not
sufficiently prove the point advanced. Although the idea of solitude
is excluded by plurality, and the plurality of gods by unity, it does
not follow that these terms express this signification alone. For
blackness is excluded by whiteness; nevertheless, the term whiteness
does not signify the mere exclusion of blackness.
_______________________

FOURTH ARTICLE [I, Q. 30, Art. 4]

Whether This Term "Person" Can Be Common to the Three Persons?

Objection 1: It would seem that this term "person" cannot be common to
the three persons. For nothing is common to the three persons but the
essence. But this term "person" does not signify the essence directly.
Therefore it is not common to all three.

Obj. 2: Further, the common is the opposite to the incommunicable.
But the very meaning of person is that it is incommunicable; as
appears from the definition given by Richard of St. Victor (Q. 29, A.
3, ad 4). Therefore this term "person" is not common to all the three
persons.

Obj. 3: Further, if the name "person" is common to the three, it is
common either really, or logically. But it is not so really;
otherwise the three persons would be one person; nor again is it so
logically; otherwise person would be a universal. But in God there is
neither universal nor particular; neither genus nor species, as we
proved above (Q. 3, A. 5). Therefore this term 'person' is not common
to the three.

_On the contrary,_ Augustine says (De Trin. vii, 4) that when we ask,
"Three what?" we say, "Three persons," because what a person is, is
common to them.

_I answer that,_ The very mode of expression itself shows that this
term "person" is common to the three when we say "three persons"; for
when we say "three men" we show that "man" is common to the three.
Now it is clear that this is not community of a real thing, as if one
essence were common to the three; otherwise there would be only one
person of the three, as also one essence.

What is meant by such a community has been variously determined by
those who have examined the subject. Some have called it a community
of exclusion, forasmuch as the definition of "person" contains the
word "incommunicable." Others thought it to be a community of
intention, as the definition of person contains the word "individual";
as we say that to be a species is co