I, Q. 2, Art. 3]

Whether the Union of the Word Incarnate Took Place in the Suppositum
or Hypostasis?

Objection 1: It would seem that the union of the Word Incarnate did
not take place in the suppositum or hypostasis. For Augustine says
(Enchiridion xxxv, xxxviii): "Both the Divine and human substance are
one Son of God, but they are one thing (_aliud_) by reason of the
Word and another thing (_aliud_) by reason of the man." And Pope Leo
says in his letter to Flavian (Ep. xxviii): "One of these is glorious
with miracles, the other succumbs under injuries." But "one"
(_aliud_) and "the other" (_aliud_) differ in suppositum. Therefore
the union of the Word Incarnate did not take place in the suppositum.

Obj. 2: Further, hypostasis is nothing more than a "particular
substance," as Boethius says (De Duab. Nat.). But it is plain that in
Christ there is another particular substance beyond the hypostasis of
the Word, viz. the body and the soul and the resultant of these.
Therefore there is another hypostasis in Him besides the hypostasis
of the Word.

Obj. 3: Further, the hypostasis of the Word is not included in any
genus or species, as is plain from the First Part (Q. 3, A. 5). But
Christ, inasmuch as He is made man, is contained under the species of
man; for Dionysius says (Div. Nom. 1): "Within the limits of our
nature He came, Who far surpasses the whole order of nature
supersubstantially." Now nothing is contained under the human species
unless it be a hypostasis of the human species. Therefore in Christ
there is another hypostasis besides the hypostasis of the Word of
God; and hence the same conclusion follows as above.

_On the contrary,_ Damascene says (De Fide Orth. iii, 3, 4, 5): "In
our Lord Jesus Christ we acknowledge two natures and one hypostasis."

_I answer that,_ Some who did not know the relation of hypostasis to
person, although granting that there is but one person in Christ,
held, nevertheless, that there is one hypostasis of God and another
of man, and hence that the union took place in the person and not in
the hypostasis. Now this, for three reasons, is clearly erroneous.
First, because person only adds to hypostasis a determinate nature,
viz. rational, according to what Boethius says (De Duab. Nat.), "a
person is an individual substance of rational nature"; and hence it
is the same to attribute to the human nature in Christ a proper
hypostasis and a proper person. And the holy Fathers, seeing