Now a person in human nature is not presupposed to assumption;
rather, it is the term of the assumption, as was said (Q. 3, AA. 1,
2). For if it were presupposed, it must either have been
corrupted--in which case it was useless; or it remains after the
union--and thus there would be two persons, one assuming and the
other assumed, which is false, as was shown above (Q. 2, A. 6). Hence
it follows that the Son of God nowise assumed a human person.

Reply Obj. 1: The Son of God assumed human nature _in atomo,_ i.e. in
an individual, which is no other than the uncreated suppositum, the
Person of the Son of God. Hence it does not follow that a person was
assumed.

Reply Obj. 2: Its proper personality is not wanting to the nature
assumed through the loss of anything pertaining to the perfection of
the human nature but through the addition of something which is above
human nature, viz. the union with a Divine Person.

Reply Obj. 3: Absorption does not here imply the destruction of
anything pre-existing, but the hindering what might otherwise have
been. For if the human nature had not been assumed by a Divine
Person, the human nature would have had its own personality; and in
this way is it said, although improperly, that the Person "absorbed
the person," inasmuch as the Divine Person by His union hindered the
human nature from having its personality.
_______________________

THIRD ARTICLE [III, Q. 4, Art. 3]

Whether the Divine Person Assumed a Man?

Objection 1: It would seem that the Divine Person assumed a man. For
it is written (Ps. 64:5): "Blessed is he whom Thou hast chosen and
taken to Thee," which a gloss expounds of Christ; and Augustine says
(De Agone Christ. xi): "The Son of God assumed a man, and in him bore
things human."

Obj. 2: Further, the word "man" signifies a human nature. But the Son
of God assumed a human nature. Therefore He assumed a man.

Obj. 3: Further, the Son of God is a man. But He is not one of the
men He did not assume, for with equal reason He would be Peter or any
other man. Therefore He is the man whom He assumed.

_On the contrary,_ Is the authority of Felix, Pope and Martyr, which
is quoted by the Council of Ephesus: "We believe in our Lord Jesus
Christ, born of the Virgin Mary, because He is the Eternal Son and
Word of God, and not a man assumed by God, in such sort that there is
another besides Him. For the Son of God did not assume a man, so that
there be another besides Him.