Whether union is the same as assumption?
Objection 1: It would seem that union is the same as assumption. For relations, as motions, are specified by their termini. Now the term of assumption and union is one and the same, viz. the Divine hypostasis. Therefore it seems that union and assumption are not different.
Objection 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.
Objection 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 be said indifferently that the human nature is united with the Divine, or conversely. But the Divine Nature is not said to be assumed by the human, but conversely, because the human nature is joined to the Divine personality, so that the Divine Person subsists in human nature.
Reply to Objection 1: Union and assumption have not the same relation to the term, but a different relation, as was said above.
Reply to Objection 2: What unites and what assumes are not the same. For whatsoever Person assumes unites, and not conversely. For the Person of the Father united the human nature to the Son, but not to Himself; and hence He is said to unite and not to assume. So likewise the united and the assumed are not identical, for the Divine Nature is said to be united, but not assumed.
Reply to Objection 3: Assumption determines with whom the union is made on the part of the one assuming, inasmuch as assumption means taking unto oneself [ad se sumere], whereas incarnation and humanation (determine with whom the union is made) on the part of the thing assumed, which is flesh or human nature. And thus assumption differs logically both from union and from incarnation or humanation.
III · Q. 2, Art. 9: Whether the union of the two natures in Christ is the greatest of all unions?
Whether the union of the two natures in Christ is the greatest of all unions?
Objection 1: It would seem that the union of the two natures in Christ is not the greatest of all unions. For what is united falls short of the unity of what is one, since what is united is by participation, but one is by essence. Now in created things there are some that are simply one, as is shown especially in unity itself, which is the principle of number. Therefore the union of which we are speaking does not imply the greatest of all unions.
Objection 2: Further, the greater the distance between things united, the less the union. Now, the things united by this union are most distant---namely, the Divine and human natures; for they are infinitely apart. Therefore their union is the least of all.
Objection 3: Further, from union there results one. But from the union of soul and body in us there arises what is one in person and nature; whereas from the union of the Divine and human nature there results what is one in person only. Therefore the union of soul and body is greater than that of the Divine and human natures; and hence the union of which we speak does not imply the greatest unity.
On the contrary, Augustine says (De Trin. i, 10) that "man is in the Son of God, more than the Son in the Father." But the Son is in the Father by unity of essence, and man is in the Son by the union of the Incarnation. Therefore the union of the Incarnation is greater than the unity of the Divine Essence, which nevertheless is the greatest union; and thus the union of the Incarnation implies the greatest unity.
I answer that, Union implies the joining of several in some one thing. Therefore the union of the Incarnation may be taken in two ways: first, in regard to the things united; secondly, in regard to that in which they are united. And in this regard this union has a pre-eminence over other unions; for the unity of the Divine Person, in which the two natures are united, is the greatest. But it has no pre-eminence in regard to the things united.
Reply to Objection 1: The unity of the Divine Person is greater than numerical unity, which is the principle of number. For the unity of a Divine Person is an uncreated and self-subsisting unity, not received into another by participation. Also, it is complete in itself, having in itself whatever pertains to the nature of unity; and therefore it is not compatible with the nature of a part, as in numerical unity, which is a part of number, and which is shared in by the things numbered. And hence in this respect the union of the Incarnation is higher than numerical unity by reason of the unity of the Divine Person, and not by reason of the human nature, which is not the unity of the Divine Person, but is united to it.
Reply to Objection 2: This reason regards the things united, and not the Person in Whom the union takes place.
Reply to Objection 3: The unity of the Divine Person is greater than the unity of person and nature in us; and hence the union of the Incarnation is greater than the union of soul and body in us.
And because what is urged in the argument "on the contrary" rests upon what is untrue---namely, that the union of the Incarnation is greater than the unity of the Divine Persons in Essence---we must say to the authority of Augustine that the human nature is not more in the Son of God than the Son of God in the Father, but much less. But the man in some respects is more in the Son than the Son in the Father---namely, inasmuch as the same suppositum is signified when I say "man," meaning Christ, and when I say "Son of God"; whereas it is not the same suppositum of Father and Son.