Summa Th. III EN Qu.2 a.7
Objection: 1. It would seem that the union of the Divine and human natures is not anything created. For there can be nothing created in God, because whatever is in God is God. But the union is in God, for God Himself is united to human nature. Therefore it seems that the union is not anything created.
2. Further, the end holds first place in everything. But the end of the union is the Divine hypostasis or Person in which the union is terminated. Therefore it seems that this union ought chiefly to be judged with reference to the dignity of the Divine hypostasis, which is not anything created. Therefore the union is nothing created.
3. Further, "That which is the cause of a thing being such is still more so" (Poster. i). But man is said to be the Creator on account of the union. Therefore much more is the union itself nothing created, but the Creator.
On the contrary Whatever has a beginning in time is created. Now this union was not from eternity, but began in time. Therefore the union is something created.
I answer that The union of which we are speaking is a relation which we consider between the Divine and the human nature, inasmuch as they come together in one Person of the Son of God. Now, as was said above (I 13,7), every relation which we consider between God and the creature is really in the creature, by whose change the relation is brought into being; whereas it is not really in God, but only in our way of thinking, since it does not arise from any change in God. And hence we must say that the union of which we are speaking is not really in God, except only in our way of thinking; but in the human nature, which is a creature, it is really. Therefore we must say it is something created.
Reply to Objection: 1. This union is not really in God, but only in our way of thinking, for God is said to be united to a creature inasmuch as the creature is really united to God without any change in Him.
2. The specific nature of a relation, as of motion, depends on the subject. And since this union has its being nowhere save in a created nature, as was said above, it follows that it has a created being.
3. A man is called Creator and is God because of the union, inasmuch as it is terminated in the Divine hypostasis; yet it does not follow that the union itself is the Creator or God, because that a thing is said to be created regards its being rather than its relation.
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.
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.
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 (Article ), 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.
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.
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.
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.
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.
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.
2. This reason regards the things united, and not the Person in Whom the union takes place.
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.
4. 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.
Objection: 1. It would seem that the union of the Incarnation did not take place by grace. For grace is an accident, as was shown above (I-II 110,2). But the union of the human nature to the Divine did not take place accidentally, as was shown above (Article ). Therefore it seems that the union of the Incarnation did not take place by grace.
2. Further, the subject of grace is the soul. But it is written (Col 2,9): "In Christ [Vulg.: 'Him'] dwelleth all the fulness of the Godhead corporeally." Therefore it seems that this union did not take place by grace.
3. Further, every saint is united to God by grace. If, therefore, the union of the Incarnation was by grace, it would seem that Christ is said to be God no more than other holy men.
On the contrary Augustine says (De Praed. Sanct. xv): "By the same grace every man is made a Christian, from the beginning of his faith, as this man from His beginning was made Christ." But this man became Christ by union with the Divine Nature. Therefore this union was by grace.
I answer that As was said above (I-II 110,1), grace is taken in two ways:--first, as the will of God gratuitously bestowing something; secondly, as the free gift of God. Now human nature stands in need of the gratuitous will of God in order to be lifted up to God, since this is above its natural capability. Moreover, human nature is lifted up to God in two ways: first, by operation, as the saints know and love God; secondly, by personal being, and this mode belongs exclusively to Christ, in Whom human nature is assumed so as to be in the Person of the Son of God. But it is plain that for the perfection of operation the power needs to be perfected by a habit, whereas that a nature has being in its own suppositum does not take place by means of a habit.And hence we must say that if grace be understood as the will of God gratuitously doing something or reputing anything as well-pleasing or acceptable to Him, the union of the Incarnation took place by grace, even as the union of the saints with God by knowledge and love. But if grace be taken as the free gift of God, then the fact that the human nature is united to the Divine Person may be called a grace, inasmuch as it took place without being preceded by any merits---but not as though there were an habitual grace, by means of which the union took place.
Reply to Objection: 1. The grace which is an accident is a certain likeness of the Divinity participated by man. But by the Incarnation human nature is not said to have participated a likeness of the Divine nature, but is said to be united to the Divine Nature itself in the Person of the Son. Now the thing itself is greater than a participated likeness of it.
2. Habitual grace is only in the soul; but the grace, i.e. the free gift of God, of being united to the Divine Person belongs to the whole human nature, which is composed of soul and body. And hence it is said that the fulness of the Godhead dwelt corporeally in Christ because the Divine Nature is united not merely to the soul, but to the body also. Although it may also be said that it dwelt in Christ corporeally, i.e. not as in a shadow, as it dwelt in the sacraments of the old law, of which it is said in the same place (Col 2,17) that they are the "shadow of things to come but the body is Christ" [Vulg.: 'Christ's'], inasmuch as the body is opposed to the shadow. And some say that the Godhead is said to have dwelt in Christ corporeally, i.e. in three ways, just as a body has three dimensions: first, by essence, presence, and power, as in other creatures; secondly, by sanctifying grace, as in the saints; thirdly, by personal union, which is proper to Christ.
3. Hence the reply to the third is manifest, viz. because the union of the Incarnation did not take place by habitual grace alone, but in subsistence or person.
Objection: 1. It would seem that the union of the Incarnation followed upon certain merits, because upon Ps 32,22, "Let Thy mercy, o Lord, be upon us, as," etc. a gloss says: "Here the prophet's desire for the Incarnation and its merited fulfilment are hinted at." Therefore the Incarnation falls under merit.
2. Further, whoever merits anything merits that without which it cannot be. But the ancient Fathers merited eternal life, to which they were able to attain only by the Incarnation; for Gregory says (Moral. xiii): "Those who came into this world before Christ's coming, whatsoever eminency of righteousness they may have had, could not, on being divested of the body, at once be admitted into the bosom of the heavenly country, seeing that He had not as yet come Who, by His own descending, should place the souls of the righteous in their everlasting seat." Therefore it would seem that they merited the Incarnation.
3. Further, of the Blessed Virgin it is sung that "she merited to bear the Lord of all" [*Little Office of B. V. M., Dominican Rite, Ant. at Benedictus], and this took place through the Incarnation. Therefore the Incarnation falls under merit.
On the contrary Augustine says (De Praed. Sanct. xv): "Whoever can find merits preceding the singular generation of our Head, may also find merits preceding the repeated regeneration of us His members." But no merits preceded our regeneration, according to Titus 3:5: "Not by the works of justice which we have done, but according to His mercy He saved us, by the laver of regeneration." Therefore no merits preceded the generation of Christ.
I answer that With regard to Christ Himself, it is clear from the above (Article ) that no merits of His could have preceded the union. For we do not hold that He was first of all a mere man, and that afterwards by the merits of a good life it was granted Him to become the Son of God, as Photinus held; but we hold that from the beginning of His conception this man was truly the Son of God, seeing that He had no other hypostasis but that of the Son of God, according to Luke 1:35: "The Holy which shall be born of thee shall be called the Son of God." And hence every operation of this man followed the union. Therefore no operation of His could have been meritorious of the union.Neither could the needs of any other man whatsoever have merited this union condignly: first, because the meritorious works of man are properly ordained to beatitude, which is the reward of virtue, and consists in the full enjoyment of God. Whereas the union of the Incarnation, inasmuch as it is in the personal being, transcends the union of the beatified mind with God, which is by the act of the soul in fruition; and therefore it cannot fall under merit. Secondly, because grace cannot fall under merit, for the principle of merit does not fall under merit; and therefore neither does grace, for it is the principle of merit. Hence, still less does the Incarnation fall under merit, since it is the principle of grace, according to Jn 1,17: "Grace and truth came by Jesus Christ." Thirdly, because the Incarnation is for the reformation of the entire human nature, and therefore it does not fall under the merit of any individual man, since the goodness of a mere man cannot be the cause of the good of the entire nature. Yet the holy Fathers merited the Incarnation congruously by desiring and beseeching; for it was becoming that God should harken to those who obeyed Him.
Reply to Objection: 1. And thereby the reply to the First Objection is manifest.
2. It is false that under merit falls everything without which there can be no reward. For there is something pre-required not merely for reward, but also for merit, as the Divine goodness and grace and the very nature of man. And again, the mystery of the Incarnation is the principle of merit, because "of His fulness we all have received" (Jn 1,16).
3. The Blessed Virgin is said to have merited to bear the Lord of all; not that she merited His Incarnation, but because by the grace bestowed upon her she merited that grade of purity and holiness, which fitted her to be the Mother of God.
: Whether the grace of union was natural to the man Christ?
Objection: 1. It would seem that the grace of union was not natural to the man Christ. For the union of the Incarnation did not take place in the nature, but in the Person, as was said above (Article ). Now a thing is denominated from its terminus. Therefore this grace ought rather to be called personal than natural.
2. Further, grace is divided against nature, even as gratuitous things, which are from God, are distinguished from natural things, which are from an intrinsic principle. But if things are divided in opposition to one another, one is not denominated by the other. Therefore the grace of Christ was not natural to Him.
3. Further, natural is that which is according to nature. But the grace of union is not natural to Christ in regard to the Divine Nature, otherwise it would belong to the other Persons; nor is it natural to Him according to the human nature, otherwise it would belong to all men, since they are of the same nature as He. Therefore it would seem that the grace of union is nowise natural to Christ.
On the contrary Augustine says (Enchiridion xl): "In the assumption of human nature, grace itself became somewhat natural to that man, so as to leave no room for sin in Him."
I answer that According to the Philosopher (Metaph. v, 5), nature designates, in one way, nativity; in another, the essence of a thing. Hence natural may be taken in two ways: first, for what is only from the essential principles of a thing, as it is natural to fire to mount; secondly, we call natural to man what he has had from his birth, according to Ep 2,3: "We were by nature children of wrath"; and Sg 12,10: "They were a wicked generation, and their malice natural." Therefore the grace of Christ, whether of union or habitual, cannot be called natural as if caused by the principles of the human nature of Christ, although it may be called natural, as if coming to the human nature of Christ by the causality of His Divine Nature. But these two kinds of grace are said to be natural to Christ, inasmuch as He had them from His nativity, since from the beginning of His conception the human nature was united to the Divine Person, and His soul was filled with the gift of grace.
Reply to Objection: 1. Although the union did not take place in the nature, yet it was caused by the power of the Divine Nature, which is truly the nature of Christ, and it, moreover, belonged to Christ from the beginning of His nativity.
2. The union is not said to be grace and natural in the same respect; for it is called grace inasmuch as it is not from merit; and it is said to be natural inasmuch as by the power of the Divine Nature it was in the humanity of Christ from His nativity.
3. The grace of union is not natural to Christ according to His human nature, as if it were caused by the principles of the human nature, and hence it need not belong to all men. Nevertheless, it is natural to Him in regard to the human nature on account of the "property" of His birth, seeing that He was conceived by the Holy Ghost, so that He might be the natural Son of God and of man. But it is natural to Him in regard to the Divine Nature, inasmuch as the Divine Nature is the active principle of this grace; and this belongs to the whole Trinity---to wit, to be the active principle of this grace.
We must now consider the union on the part of the Person assuming, and under this head there are eight points of inquiry:
(1) Whether to assume is befitting to a Divine Person?
(2) Whether it is befitting to the Divine Nature?
(3) Whether the Nature abstracted from the Personality can assume?
(4) Whether one Person can assume without another?
(5) Whether each Person can assume?
(6) Whether several Persons can assume one individual nature?
(7) Whether one Person can assume two individual natures?
(8) Whether it was more fitting for the Person of the Son of God to assume human nature than for another Divine Person?
Objection: 1. It would seem that it is not befitting to a Divine Person to assume a created nature. For a Divine Person signifies something most perfect. Now no addition can be made to what is perfect. Therefore, since to assume is to take to oneself, and consequently what is assumed is added to the one who assumes, it does not seem to be befitting to a Divine Person to assume a created nature.
2. Further, that to which anything is assumed is communicated in some degree to what is assumed to it, just as dignity is communicated to whosoever is assumed to a dignity. But it is of the nature of a person to be incommunicable, as was said above (I 29,1). Therefore it is not befitting to a Divine Person to assume, i.e. to take to Himself.
3. Further, person is constituted by nature. But it is repugnant that the thing constituted should assume the constituent, since the effect does not act on its cause. Hence it is not befitting to a Person to assume a nature.
On the contrary Augustine [*Fulgentius] says (De Fide ad Petrum ii): "This God, i.e. the only-Begotten one, took the form," i.e. the nature, "of a servant to His own Person." But the only-Begotten God is a Person. Therefore it is befitting to a Person to take, i.e. to assume a nature.
I answer that In the word "assumption" are implied two things, viz. the principle and the term of the act, for to assume is to take something to oneself. Now of this assumption a Person is both the principle and the term. The principle---because it properly belongs to a person to act, and this assuming of flesh took place by the Divine action. Likewise a Person is the term of this assumption, because, as was said above (Question , Articles ,2), the union took place in the Person, and not in the nature. Hence it is plain that to assume a nature is most properly befitting to a Person.
Reply to Objection: 1. Since the Divine Person is infinite, no addition can be made to it: Hence Cyril says [*Council of Ephesus, Part I, ch. 26]: "We do not conceive the mode of conjunction to be according to addition"; just as in the union of man with God, nothing is added to God by the grace of adoption, but what is Divine is united to man; hence, not God but man is perfected.
2. A Divine Person is said to be incommunicable inasmuch as It cannot be predicated of several supposita, but nothing prevents several things being predicated of the Person. Hence it is not contrary to the nature of person to be communicated so as to subsist in several natures, for even in a created person several natures may concur accidentally, as in the person of one man we find quantity and quality. But this is proper to a Divine Person, on account of its infinity, that there should be a concourse of natures in it, not accidentally, but in subsistence.
3. As was said above (Question , Article ), the human nature constitutes a Divine Person, not simply, but forasmuch as the Person is denominated from such a nature. For human nature does not make the Son of Man to be simply, since He was from eternity, but only to be man. It is by the Divine Nature that a Divine Person is constituted simply. Hence the Divine Person is not said to assume the Divine Nature, but to assume the human nature.
Objection: 1. It would seem that it is not befitting to the Divine Nature to assume. Because, as was said above (Article ), to assume is to take to oneself. But the Divine Nature did not take to Itself human nature, for the union did not take place in the nature, as was said above (Question , Articles ,3). Hence it is not befitting to the Divine Nature to assume human nature.
2. Further, the Divine Nature is common to the three Persons. If, therefore, it is befitting to the Divine Nature to assume, it consequently is befitting to the three Persons; and thus the Father assumed human nature even as the Son, which is erroneous.
3. Further, to assume is to act. But to act befits a person, not a nature, which is rather taken to be the principle by which the agent acts. Therefore to assume is not befitting to the nature.
On the contrary Augustine (Fulgentius) says (De Fide ad Petrum ii): "That nature which remains eternally begotten of the Father" (i.e. which is received from the Father by eternal generation) "took our nature free of sin from His Mother."
I answer that As was said above (Article ), in the word assumption two things are signified---to wit, the principle and the term of the action. Now to be the principle of the assumption belongs to the Divine Nature in itself, because the assumption took place by Its power; but to be the term of the assumption does not belong to the Divine Nature in itself, but by reason of the Person in Whom It is considered to be. Hence a Person is primarily and more properly said to assume, but it may be said secondarily that the Nature assumed a nature to Its Person. And after the same manner the Nature is also said to be incarnate, not that it is changed to flesh, but that it assumed the nature of flesh. Hence Damascene says (De Fide Orth. iii, 6): "Following the blessed Athanasius and Cyril we say that the Nature of God is incarnate."
Reply to Objection: 1. "Oneself" is reciprocal, and points to the same suppositum. But the Divine Nature is not a distinct suppositum from the Person of the Word. Hence, inasmuch as the Divine Nature took human nature to the Person of the Word, It is said to take it to Itself. But although the Father takes human nature to the Person of the Word, He did not thereby take it to Himself, for the suppositum of the Father and the Son is not one. and hence it cannot properly be said that the Father assumes human nature.
2. What is befitting to the Divine Nature in Itself is befitting to the three Persons, as goodness, wisdom, and the like. But to assume belongs to It by reason of the Person of the Word, as was said above, and hence it is befitting to that Person alone.
3. As in God "what is" and "whereby it is" are the same, so likewise in Him "what acts" and "whereby it acts" are the same, since everything acts, inasmuch as it is a being. Hence the Divine Nature is both that whereby God acts, and the very God Who acts.
Objection: 1. It would seem that if we abstract the Personality by our mind, the Nature cannot assume. For it was said above (Article ) that it belongs to the Nature to assume by reason of the Person. But what belongs to one by reason of another cannot belong to it if the other is removed; as a body, which is visible by reason of color, without color cannot be seen. Hence if the Personality be mentally abstracted, the Nature cannot assume.
2. Further, assumption implies the term of union, as was said above (Article ). But the union cannot take place in the nature, but only in the Person. Therefore, if the Personality be abstracted, the Divine Nature cannot assume.
3. Further, it has been said above (I 40,3) that in the Godhead if the Personality is abstracted, nothing remains. But the one who assumes is something. Therefore, if the Personality is abstracted, the Divine Nature cannot assume.
On the contrary In the Godhead Personality signifies a personal property; and this is threefold, viz. Paternity, Filiation and Procession, as was said above (I 30,2). Now if we mentally abstract these, there still remains the omnipotence of God, by which the Incarnation was wrought, as the angel says (Lc 1,37): "No word shall be impossible with God." Therefore it seems that if the Personality be removed, the Divine Nature can still assume.
I answer that The intellect stands in two ways towards God. First, to know God as He is, and in this manner it is impossible for the intellect to circumscribe something in God and leave the rest, for all that is in God is one, except the distinction of Persons; and as regards these, if one is removed the other is taken away, since they are distinguished by relations only which must be together at the same time. Secondly, the intellect stands towards God, not indeed as knowing God as He is, but in its own way, i.e. understanding manifoldly and separately what in God is one: and in this way our intellect can understand the Divine goodness and wisdom, and the like, which are called essential attributes, without understanding Paternity or Filiation, which are called Personalities. And hence if we abstract Personality by our intellect, we may still understand the Nature assuming.
Reply to Objection: 1. Because in God "what is," and "whereby it is," are one, if any one of the things which are attributed to God in the abstract is considered in itself, abstracted from all else, it will still be something subsisting, and consequently a Person, since it is an intellectual nature. Hence just as we now say three Persons, on account of holding three personal properties, so likewise if we mentally exclude the personal properties there will still remain in our thought the Divine Nature as subsisting and as a Person. And in this way It may be understood to assume human nature by reason of Its subsistence or Personality.
2. Even if the personal properties of the three Persons are abstracted by our mind, nevertheless there will remain in our thoughts the one Personality of God, as the Jews consider. And the assumption can be terminated in It, as we now say it is terminated in the Person of the Word.
3. If we mentally abstract the Personality, it is said that nothing remains by way of resolution, i.e. as if the subject of the relation and the relation itself were distinct because all we can think of in God is considered as a subsisting suppositum. However, some of the things predicated of God can be understood without others, not by way of resolution, but by the way mentioned above.
Objection: 1. It would seem that one Person cannot assume a created nature without another assuming it. For "the works of the Trinity are inseparable," as Augustine says (Enchiridion xxxviii). But as the three Persons have one essence, so likewise They have one operation. Now to assume is an operation. Therefore it cannot belong to one without belonging to another.
2. Further, as we say the Person of the Son became incarnate, so also did the Nature; for "the whole Divine Nature became incarnate in one of Its hypostases," as Damascene says (De Fide Orth. iii, 6). But the Nature is common to the three Persons. Therefore the assumption is.
3. Further, as the human nature in Christ is assumed by God, so likewise are men assumed by Him through grace, according to Rm 14,3: "God hath taken him to Him." But this assumption pertains to all the Persons; therefore the first also.
On the contrary Dionysius says (Div. Nom. ii) that the mystery of the Incarnation pertains to "discrete theology," i.e. according to which something "distinct" is said of the Divine Persons.
I answer that As was said above (Article ), assumption implies two things, viz. the act of assuming and the term of assumption. Now the act of assumption proceeds from the Divine power, which is common to the three Persons, but the term of the assumption is a Person, as stated above (Article ). Hence what has to do with action in the assumption is common to the three Persons; but what pertains to the nature of term belongs to one Person in such a manner as not to belong to another; for the three Persons caused the human nature to be united to the one Person of the Son.
Reply to Objection: 1. This reason regards the operation, and the conclusion would follow if it implied this operation only, without the term, which is a Person.
2. The Nature is said to be incarnate, and to assume by reason of the Person in Whom the union is terminated, as stated above (Articles ,2), and not as it is common to the three Persons. Now "the whole Divine Nature is" said to be "incarnate"; not that It is incarnate in all the Persons, but inasmuch as nothing is wanting to the perfection of the Divine Nature of the Person incarnate, as Damascene explains there.
3. The assumption which takes place by the grace of adoption is terminated in a certain participation of the Divine Nature, by an assimilation to Its goodness, according to 2P 1,4: "That you may be made partakers of the Divine Nature"; and hence this assumption is common to the three Persons, in regard to the principle and the term. But the assumption which is by the grace of union is common on the part of the principle, but not on the part of the term, as was said above.
Summa Th. III EN Qu.2 a.7