absolute sense, is wont to be designated
as belonging to that of which it is the form, as we say "the virtue
of Peter." On the other hand, the thing having form is not wont to be
designated as belonging to the form except when we wish to qualify or
designate the form. In which case two genitives are required, one
signifying the form, and the other signifying the determination of
the form, as, for instance, when we say, "Peter is of great virtue
[magnae virtutis]," or else one genitive must have the force of two,
as, for instance, "he is a man of blood"--that is, he is a man who
sheds much blood [multi sanguinis]. So, because the divine essence
signifies a form as regards the person, it may properly be said that
the essence is of the person; but we cannot say the converse, unless
we add some term to designate the essence; as, for instance, the
Father is a person of the "divine essence"; or, the three persons are
"of one essence."

Reply Obj. 5: The preposition "from" or "out of" does not designate
the habitude of a formal cause, but rather the habitude of an
efficient or material cause; which causes are in all cases
distinguished from those things of which they are the causes. For
nothing can be its own matter, nor its own active principle. Yet a
thing may be its own form, as appears in all immaterial things. So,
when we say, "three persons of one essence," taking essence as having
the habitude of form, we do not mean that essence is different from
person, which we should mean if we said, "three persons from the same
essence."

Reply Obj. 6: As Hilary says (De Synod.): "It would be prejudicial to
holy things, if we had to do away with them, just because some do not
think them holy. So if some misunderstand _homoousion,_ what is that
to me, if I understand it rightly? . . . The oneness of nature does
not result from division, or from union or from community of
possession, but from one nature being proper to both Father and Son."
_______________________

THIRD ARTICLE [I, Q. 39, Art. 3]

Whether Essential Names Should Be Predicated in the Singular of the
Three Persons?

Objection 1: It would seem that essential names, as the name "God,"
should not be predicated in the singular of the three persons, but in
the plural. For as "man" signifies "one that has humanity," so God
signifies "one that has Godhead." But the three persons are three who
have Godhead. Therefore the three persons are "three Gods."

Obj. 2: Furth