an also: the more so that the power of the Father is not diminished
after begetting the Son.

_On the contrary,_ In God "that which is possible," and "that which is"
do not differ. If, therefore, in God it were possible for there to be
several Sons, there would be several Sons. And thus there would be
more than three Persons in God; which is heretical.

_I answer that,_ As Athanasius says, in God there is only "one Father,
one Son, one Holy Ghost." For this four reasons may be given.

The first reason is in regard to the relations by which alone are
the Persons distinct. For since the divine Persons are the relations
themselves as subsistent, there would not be several Fathers, or
several Sons in God, unless there were more than one paternity, or
more than one filiation. And this, indeed, would not be possible
except owing to a material distinction: since forms of one species
are not multiplied except in respect of matter, which is not in God.
Wherefore there can be but one subsistent filiation in God: just as
there could be but one subsistent whiteness.

The second reason is taken from the manner of the processions. For God
understands and wills all things by one simple act. Wherefore there
can be but one person proceeding after the manner of word, which
person is the Son; and but one person proceeding after the manner of
love, which person is the Holy Ghost.

The third reason is taken from the manner in which the persons
proceed. For the persons proceed naturally, as we have said
(A. 2), and nature is determined to one.

The fourth reason is taken from the perfection of the divine persons.
For this reason is the Son perfect, that the entire divine filiation
is contained in Him, and that there is but one Son. The argument is
similar in regard to the other persons.

Reply Obj. 1: We can grant, without distinction, that the Son has the
same power as the Father; but we cannot grant that the Son has the
power "generandi" [of begetting] thus taking "generandi" as the
gerund of the active verb, so that the sense would be that the Son
has the "power to beget." Just as, although Father and Son have the
same being, it does not follow that the Son is the Father, by reason
of the notional term added. But if the word "generandi" [of being
begotten] is taken as the gerundive of the passive verb, the power
"generandi" is in the Son--that is, the power of being begotten. The
same is to be said if it be taken as the gerundive