ion is one and the same, viz. the Divine
hypostasis. Therefore it seems that union and assumption are not
different.

Obj. 2: Further, in the mystery of the Incarnation the same thing
seems to be what unites and what assumes, and what is united and what
is assumed. But union and assumption seem to follow the action and
passion of the thing uniting and the united, of the thing assuming
and the assumed. Therefore union seems to be the same as assumption.

Obj. 3: Further, Damascene says (De Fide Orth. iii, 11): "Union is
one thing, incarnation is another; for union demands mere copulation,
and leaves unsaid the end of the copulation; but incarnation and
humanation determine the end of copulation." But likewise assumption
does not determine the end of copulation. Therefore it seems that
union is the same as assumption.

_On the contrary,_ The Divine Nature is said to be united, not
assumed.

_I answer that,_ As was stated above (A. 7), union implies a certain
relation of the Divine Nature and the human, according as they come
together in one Person. Now all relations which begin in time are
brought about by some change; and change consists in action and
passion. Hence the _first_ and principal difference between
assumption and union must be said to be that union implies the
relation: whereas assumption implies the action, whereby someone is
said to assume, or the passion, whereby something is said to be
assumed. Now from this difference another _second_ difference arises,
for assumption implies _becoming,_ whereas union implies _having
become,_ and therefore the thing uniting is said to be united, but
the thing assuming is not said to be assumed. For the human nature is
taken to be in the terminus of assumption unto the Divine hypostasis
when man is spoken of; and hence we can truly say that the Son of
God, Who assumes human nature unto Himself, is man. But human nature,
considered in itself, i.e. in the abstract, is viewed as assumed; and
we do not say the Son of God is human nature. From this same follows
a _third_ difference, which is that a relation, especially one of
equiparance, is no more to one extreme than to the other, whereas
action and passion bear themselves differently to the agent and the
patient, and to different termini. And hence assumption determines
the term whence and the term whither; for assumption means a taking
to oneself from another. But union determines none of these things.
Hence it may b