Summa Th. III EN Qu.3 a.5
Objection: 1. It would seem that no other Divine Person could have assumed human nature except the Person of the Son. For by this assumption it has been brought about that God is the Son of Man. But it was not becoming that either the Father or the Holy Ghost should be said to be a Son; for this would tend to the confusion of the Divine Persons. Therefore the Father and Holy Ghost could not have assumed flesh.
2. Further, by the Divine Incarnation men have come into possession of the adoption of sons, according to Rm 8,15: "For you have not received the spirit of bondage again in fear, but the spirit of adoption of sons." But sonship by adoption is a participated likeness of natural sonship which does not belong to the Father nor the Holy Ghost; hence it is said (Rm 8,29): "For whom He foreknew He also predestinated to be made conformable to the image of His Son." Therefore it seems that no other Person except the Person of the Son could have become incarnate.
3. Further, the Son is said to be sent and to be begotten by the temporal nativity, inasmuch as He became incarnate. But it does not belong to the Father to be sent, for He is innascible, as was said above (I 32,3; I 43,4). Therefore at least the Person of the Father cannot become incarnate.
On the contrary Whatever the Son can do, so can the Father and the Holy Ghost, otherwise the power of the three Persons would not be one. But the Son was able to become incarnate. Therefore the Father and the Holy Ghost were able to become incarnate.
I answer that As was said above (Articles ,2,4), assumption implies two things, viz. the act of the one assuming and the term of the assumption. Now the principle of the act is the Divine power, and the term is a Person. But the Divine power is indifferently and commonly in all the Persons. Moreover, the nature of Personality is common to all the Persons, although the personal properties are different. Now whenever a power regards several things indifferently, it can terminate its action in any of them indifferently, as is plain in rational powers, which regard opposites, and can do either of them. Therefore the Divine power could have united human nature to the Person of the Father or of the Holy Ghost, as It united it to the Person of the Son. And hence we must say that the Father or the Holy Ghost could have assumed flesh even as the Son.
Reply to Objection: 1. The temporal sonship, whereby Christ is said to be the Son of Man, does not constitute His Person, as does the eternal Sonship; but is something following upon the temporal nativity. Hence, if the name of son were transferred to the Father or the Holy Ghost in this manner, there would be no confusion of the Divine Persons.
2. Adoptive sonship is a certain participation of natural sonship; but it takes place in us, by appropriation, by the Father, Who is the principle of natural sonship, and by the gift of the Holy Ghost, Who is the love of the Father and Son, according to Ga 4,6: "God hath sent the Spirit of His Son into your hearts crying, Abba, Father." And therefore, even as by the Incarnation of the Son we receive adoptive sonship in the likeness of His natural sonship, so likewise, had the Father become incarnate, we should have received adoptive sonship from Him, as from the principle of the natural sonship, and from the Holy Ghost as from the common bond of Father and Son.
3. It belongs to the Father to be innascible as to eternal birth, and the temporal birth would not destroy this. But the Son of God is said to be sent in regard to the Incarnation, inasmuch as He is from another, without which the Incarnation would not suffice for the nature of mission.
Objection: 1. It would seem that two Divine Persons cannot assume one and the same individual nature. For, this being granted, there would either be several men or one. But not several, for just as one Divine Nature in several Persons does not make several gods, so one human nature in several persons does not make several men. Nor would there be only one man, for one man is "this man," which signifies one person; and hence the distinction of three Divine Persons would be destroyed, which cannot be allowed. Therefore neither two nor three Persons can take one human nature.
2. Further, the assumption is terminated in the unity of Person, as has been said above (Article ). But the Father, Son, and Holy Ghost are not one Person. Therefore the three Persons cannot assume one human nature.
3. Further, Damascene says (De Fide Orth. iii, 3,4), and Augustine (De Trin. i, 11,12,13), that from the Incarnation of God the Son it follows that whatever is said of the Son of God is said of the Son of Man, and conversely. Hence, if three Persons were to assume one human nature, it would follow that whatever is said of each of the three Persons would be said of the man; and conversely, what was said of the man could be said of each of the three Persons. Therefore what is proper to the Father, viz. to beget the Son, would be said of the man, and consequently would be said of the Son of God; and this could not be. Therefore it is impossible that the three Persons should assume one human nature.
On the contrary The Incarnate Person subsists in two natures. But the three Persons can subsist in one Divine Nature. Therefore they can also subsist in one human nature in such a way that the human nature be assumed by the three Persons.
I answer that As was said above (Question , Article , ad 1), by the union of the soul and body in Christ neither a new person is made nor a new hypostasis, but one human nature is assumed to the Divine Person or hypostasis, which, indeed, does not take place by the power of the human nature, but by the power of the Divine Person. Now such is the characteristic of the Divine Persons that one does not exclude another from communicating in the same nature, but only in the same Person. Hence, since in the mystery of the Incarnation "the whole reason of the deed is the power of the doer," as Augustine says (Ep ad Volusianum cxxxvii), we must judge of it in regard to the quality of the Divine Person assuming, and not according to the quality of the human nature assumed. Therefore it is not impossible that two or three Divine Persons should assume one human nature, but it would be impossible for them to assume one human hypostasis or person; thus Anselm says in the book De Concep. Virg. (Cur Deus Homo ii, 9), that "several Persons cannot assume one and the same man to unity of Person."
Reply to Objection: 1. In the hypothesis that three Persons assume one human nature, it would be true to say that the three Persons were one man, because of the one human nature. For just as it is now true to say the three Persons are one God on account of the one Divine Nature, so it would be true to say they are one man on account of the one human nature. Nor would "one" imply unity of person, but unity in human nature; for it could not be argued that because the three Persons were one man they were one simply. For nothing hinders our saying that men, who are many simply, are in some respect one, e.g. one people, and as Augustine says (De Trin. vi, 3): "The Spirit of God and the spirit of man are by nature different, but by inherence one spirit results," according to 1Co 6,17: "He who is joined to the Lord is one spirit."
2. In this supposition the human nature would be assumed to the unity, not indeed of one Person, but to the unity of each Person, so that even as the Divine Nature has a natural unity with each Person, so also the human nature would have a unity with each Person by assumption.
3. In the mystery of the Incarnation, there results a communication of the properties belonging to the nature, because whatever belongs to the nature can be predicated of the Person subsisting in that nature, no matter to which of the natures it may apply. Hence in this hypothesis, of the Person of the Father may be predicated what belongs to the human nature and what belongs to the Divine; and likewise of the Person of the Son and of the Holy Ghost. But what belongs to the Person of the Father by reason of His own Person could not be attributed to the Person of the Son or Holy Ghost on account of the distinction of Persons which would still remain. Therefore it might be said that as the Father was unbegotten, so the man was unbegotten, inasmuch as "man" stood for the Person of the Father. But if one were to go on to say, "The man is unbegotten; the Son is man; therefore the Son is unbegotten," it would be the fallacy of figure of speech or of accident; even as we now say God is unbegotten, because the Father is unbegotten, yet we cannot conclude that the Son is unbegotten, although He is God.
Objection: 1. It would seem that one Divine Person cannot assume two human natures. For the nature assumed in the mystery of the Incarnation has no other suppositum than the suppositum of the Divine Person, as is plain from what has been stated above (Question , Articles ,6). Therefore, if we suppose one Person to assume two human natures, there would be one suppositum of two natures of the same species; which would seem to imply a contradiction, for the nature of one species is only multiplied by distinct supposita.
2. Further, in this hypothesis it could not be said that the Divine Person incarnate was one man, seeing that He would not have one human nature; neither could it be said that there were several, for several men have distinct supposita, whereas in this case there would be only one suppositum. Therefore the aforesaid hypothesis is impossible.
3. Further, in the mystery of the Incarnation the whole Divine Nature is united to the whole nature assumed, i.e. to every part of it, for Christ is "perfect God and perfect man, complete God and complete man," as Damascene says (De Fide Orth. iii, 7). But two human natures cannot be wholly united together, inasmuch as the soul of one would be united to the body of the other; and, again, two bodies would be together, which would give rise to confusion of natures. Therefore it is not possibly for one Divine Person to assume two human natures.
On the contrary Whatever the Father can do, that also can the Son do. But after the Incarnation the Father can still assume a human nature distinct from that which the Son has assumed; for in nothing is the power of the Father or the Son lessened by the Incarnation of the Son. Therefore it seems that after the Incarnation the Son can assume another human nature distinct from the one He has assumed.
I answer that What has power for one thing, and no more, has a power limited to one. Now the power of a Divine Person is infinite, nor can it be limited by any created thing. Hence it may not be said that a Divine Person so assumed one human nature as to be unable to assume another. For it would seem to follow from this that the Personality of the Divine Nature was so comprehended by one human nature as to be unable to assume another to its Personality; and this is impossible, for the Uncreated cannot be comprehended by any creature. Hence it is plain that, whether we consider the Divine Person in regard to His power, which is the principle of the union, or in regard to His Personality, which is the term of the union, it has to be said that the Divine Person, over and beyond the human nature which He has assumed, can assume another distinct human nature.
Reply to Objection: 1. A created nature is completed in its essentials by its form, which is multiplied according to the division of matter. And hence, if the composition of matter and form constitutes a new suppositum, the consequence is that the nature is multiplied by the multiplication of supposita. But in the mystery of the Incarnation the union of form and matter, i.e. of soul and body, does not constitute a new suppositum, as was said above (Article ). Hence there can be a numerical multitude on the part of the nature, on account of the division of matter, without distinction of supposita.
2. It might seem possible to reply that in such a hypothesis it would follow that there were two men by reason of the two natures, just as, on the contrary, the three Persons would be called one man, on account of the one nature assumed, as was said above (Article , ad 1). But this does not seem to be true; because we must use words according to the purpose of their signification, which is in relation to our surroundings. Consequently, in order to judge of a word's signification or co-signification, we must consider the things which are around us, in which a word derived from some form is never used in the plural unless there are several supposita. For a man who has on two garments is not said to be "two persons clothed," but "one clothed with two garments"; and whoever has two qualities is designated in the singular as "such by reason of the two qualities." Now the assumed nature is, as it were, a garment, although this similitude does not fit at all points, as has been said above (Question , Article , ad 1). And hence, if the Divine Person were to assume two human natures, He would be called, on account of the unity of suppositum, one man having two human natures. Now many men are said to be one people, inasmuch as they have some one thing in common, and not on account of the unity of suppositum. So likewise, if two Divine Persons were to assume one singular human nature, they would be said to be one man, as stated (Article , ad 1), not from the unity of suppositum, but because they have some one thing in common.
3. The Divine and human natures do not bear the same relation to the one Divine Person, but the Divine Nature is related first of all thereto, inasmuch as It is one with It from eternity; and afterwards the human nature is related to the Divine Person, inasmuch as it is assumed by the Divine Person in time, not indeed that the nature is the Person, but that the Person of God subsists in human nature. For the Son of God is His Godhead, but is not His manhood. And hence, in order that the human nature may be assumed by the Divine Person, the Divine Nature must be united by a personal union with the whole nature assumed, i.e. in all its parts. Now in the two natures assumed there would be a uniform relation to the Divine Person, nor would one assume the other. Hence it would not be necessary for one of them to be altogether united to the other, i.e. all the parts of one with all the parts of the other.
Objection: 1. It would seem that it was not more fitting that the Son of God should become incarnate than the Father or the Holy Ghost. For by the mystery of the Incarnation men are led to the true knowledge of God, according to Jn 18,37: "For this was I born, and for this came I into the world, to give testimony to the truth." But by the Person of the Son of God becoming incarnate many have been kept back from the true knowledge of God, since they referred to the very Person of the Son what was said of the Son in His human nature, as Arius, who held an inequality of Persons, according to what is said (Jn 14,28): "The Father is greater than I." Now this error would not have arisen if the Person of the Father had become incarnate, for no one would have taken the Father to be less than the Son. Hence it seems fitting that the Person of the Father, rather than the Person of the Son, should have become incarnate.
2. Further, the effect of the Incarnation would seem to be, as it were, a second creation of human nature, according to Ga 6,15: "For in Christ Jesus neither circumcision availeth anything, nor uncircumcision, but a new creature." But the power of creation is appropriated to the Father. Therefore it would have been more becoming to the Father than to the Son to become incarnate.
3. Further, the Incarnation is ordained to the remission of sins, according to Mt 1,21: "Thou shalt call His name Jesus. For He shall save His people from their sins." Now the remission of sins is attributed to the Holy Ghost according to Jn 20,22-23: "Receive ye the Holy Ghost. Whose sins you shall forgive, they are forgiven them." Therefore it became the Person of the Holy Ghost rather than the Person of the Son to become incarnate.
On the contrary Damascene says (De Fide Orth. iii, 1): "In the mystery of the Incarnation the wisdom and power of God are made known: the wisdom, for He found a most suitable discharge for a most heavy debt; the power, for He made the conquered conquer." But power and wisdom are appropriated to the Son, according to 1Co 1,24: "Christ, the power of God and the wisdom of God." Therefore it was fitting that the Person of the Son should become incarnate.
I answer that It was most fitting that the Person of the Son should become incarnate. First, on the part of the union; for such as are similar are fittingly united. Now the Person of the Son, Who is the Word of God, has a certain common agreement with all creatures, because the word of the craftsman, i.e. his concept, is an exemplar likeness of whatever is made by him. Hence the Word of God, Who is His eternal concept, is the exemplar likeness of all creatures. And therefore as creatures are established in their proper species, though movably, by the participation of this likeness, so by the non-participated and personal union of the Word with a creature, it was fitting that the creature should be restored in order to its eternal and unchangeable perfection; for the craftsman by the intelligible form of his art, whereby he fashioned his handiwork, restores it when it has fallen into ruin. Moreover, He has a particular agreement with human nature, since the Word is a concept of the eternal Wisdom, from Whom all man's wisdom is derived. And hence man is perfected in wisdom (which is his proper perfection, as he is rational) by participating the Word of God, as the disciple is instructed by receiving the word of his master. Hence it is said (Si 1,5): "The Word of God on high is the fountain of wisdom." And hence for the consummate perfection of man it was fitting that the very Word of God should be personally united to human nature.Secondly, the reason of this fitness may be taken from the end of the union, which is the fulfilling of predestination, i.e. of such as are preordained to the heavenly inheritance, which is bestowed only on sons, according to Rm 8,17: "If sons, heirs also." Hence it was fitting that by Him Who is the natural Son, men should share this likeness of sonship by adoption, as the Apostle says in the same chapter (Rm 8,29): "For whom He foreknew, He also predestinated to be made conformable to the image of His Son."Thirdly, the reason for this fitness may be taken from the sin of our first parent, for which the Incarnation supplied the remedy. For the first man sinned by seeking knowledge, as is plain from the words of the serpent, promising to man the knowledge of good and evil. Hence it was fitting that by the Word of true knowledge man might be led back to God, having wandered from God through an inordinate thirst for knowledge.
Reply to Objection: 1. There is nothing which human malice cannot abuse, since it even abuses God's goodness, according to Rm 2,4: "Or despisest thou the riches of His goodness?" Hence, even if the Person of the Father had become incarnate, men would have been capable of finding an occasion of error, as though the Son were not able to restore human nature.
2. The first creation of things was made by the power of God the Father through the Word; hence the second creation ought to have been brought about through the Word, by the power of God the Father, in order that restoration should correspond to creation according to 2Co 5,19: "For God indeed was in Christ reconciling the world to Himself."
3. To be the gift of the Father and the Son is proper to the Holy Ghost. But the remission of sins is caused by the Holy Ghost, as by the gift of God. And hence it was more fitting to man's justification that the Son should become incarnate, Whose gift the Holy Ghost is.
We must now consider the union on the part of what was assumed. About which we must consider first what things were assumed by the Word of God; secondly, what were co-assumed, whether perfections or defects.
Now the Son of God assumed human nature and its parts. Hence a threefold consideration arises. First, with regard to the nature; secondly, with regard to its parts; thirdly, with regard to the order of the assumption.
Under the first head there are six points of inquiry:
(1) Whether human nature was more capable of being assumed than any other nature?
(2) Whether He assumed a person?
(3) Whether He assumed a man?
(4) Whether it was becoming that He should assume human nature abstracted from all individuals?
(5) Whether it was becoming that He should assume human nature in all its individuals?
(6) Whether it was becoming that He should assume human nature in any man begotten of the stock of Adam?
Objection: 1. It would seem that human nature is not more capable of being assumed by the Son of God than any other nature. For Augustine says (Ep ad Volusianum cxxxvii): "In deeds wrought miraculously the whole reason of the deed is the power of the doer." Now the power of God Who wrought the Incarnation, which is a most miraculous work, is not limited to one nature, since the power of God is infinite. Therefore human nature is not more capable of being assumed than any other creature.
2. Further, likeness is the foundation of the fittingness of the Incarnation of the Divine Person, as above stated (Question , Article ). But as in rational creatures we find the likeness of image, so in irrational creatures we find the image of trace. Therefore the irrational creature was as capable of assumption as human nature.
3. Further, in the angelic nature we find a more perfect likeness than in human nature, as Gregory says: (Hom. de Cent. Ovib.; xxxiv in ), where he introduces Ez 28,12: "Thou wast the seal of resemblance." And sin is found in angels, even as in man, according to Jb 4,18: "And in His angels He found wickedness." Therefore the angelic nature was as capable of assumption as the nature of man.
4. Further, since the highest perfection belongs to God, the more like to God a thing is, the more perfect it is. But the whole universe is more perfect than its parts, amongst which is human nature. Therefore the whole universe is more capable of being assumed than human nature.
On the contrary It is said (Pr 8,31) by the mouth of Begotten Wisdom: "My delights were to be with the children of men"; and hence there would seem some fitness in the union of the Son of God with human nature.
I answer that A thing is said to be assumable as being capable of being assumed by a Divine Person, and this capability cannot be taken with reference to the natural passive power, which does not extend to what transcends the natural order, as the personal union of a creature with God transcends it. Hence it follows that a thing is said to be assumable according to some fitness for such a union. Now this fitness in human nature may be taken from two things, viz. according to its dignity, and according to its need. According to its dignity, because human nature, as being rational and intellectual, was made for attaining to the Word to some extent by its operation, viz. by knowing and loving Him. According to its need---because it stood in need of restoration, having fallen under original sin. Now these two things belong to human nature alone. For in the irrational creature the fitness of dignity is wanting, and in the angelic nature the aforesaid fitness of need is wanting. Hence it follows that only human nature was assumable.
Reply to Objection: 1. Creatures are said to be "such" with reference to their proper causes, not with reference to what belongs to them from their first and universal causes; thus we call a disease incurable, not that it cannot be cured by God, but that it cannot be cured by the proper principles of the subject. Therefore a creature is said to be not assumable, not as if we withdrew anything from the power of God, but in order to show the condition of the creature, which has no capability for this.
2. The likeness of image is found in human nature, forasmuch as it is capable of God, viz. by attaining to Him through its own operation of knowledge and love. But the likeness of trace regards only a representation by Divine impression, existing in the creature, and does not imply that the irrational creature, in which such a likeness is, can attain to God by its own operation alone. For what does not come up to the less, has no fitness for the greater; as a body which is not fitted to be perfected by a sensitive soul is much less fitted for an intellectual soul. Now much greater and more perfect is the union with God in personal being than the union by operation. And hence the irrational creature which falls short of the union with God by operation has no fitness to be united with Him in personal being.
3. Some say that angels are not assumable, since they are perfect in their personality from the beginning of their creation, inasmuch as they are not subject to generation and corruption; hence they cannot be assumed to the unity of a Divine Person, unless their personality be destroyed, and this does not befit the incorruptibility of their nature nor the goodness of the one assuming, to Whom it does not belong to corrupt any perfection in the creature assumed. But this would not seem totally to disprove the fitness of the angelic nature for being assumed. For God by producing a new angelic nature could join it to Himself in unity of Person, and in this way nothing pre-existing would be corrupted in it. But as was said above, there is wanting the fitness of need, because, although the angelic nature in some is the subject of sin, their sin is irremediable, as stated above (I 64,2).
4. The perfection of the universe is not the perfection of one person or suppositum, but of something which is one by position or order, whereof very many parts are not capable of assumption, as was said above. Hence it follows that only human nature is capable of being assumed.
Objection: 1. It would seem that the Son of God assumed a person. For Damascene says (De Fide Orth. iii, 11) that the Son of God "assumed human nature 'in atomo,'" i.e. in an individual. But an individual in rational nature is a person, as is plain from Boethius (De Duab. Nat.). Therefore the Son of God assumed a person.
2. Further, Damascene says (De Fide Orth. iii, 6) that the Son of God "assumed what He had sown in our nature." But He sowed our personality there. Therefore the Son of God assumed a person.
3. Further, nothing is absorbed unless it exist. But Innocent III [*Paschas. Diac., De Spiritu Sanct. ii] says in a Decretal that "the Person of God absorbed the person of man." Therefore it would seem that the person of man existed previous to its being assumed.
On the contrary Augustine [*Fulgentius] says (De Fide ad Petrum ii) that "God assumed the nature, not the person, of man."
I answer that A thing is said to be assumed inasmuch as it is taken into another. Hence, what is assumed must be presupposed to the assumption, as what is moved locally is presupposed to the motion. Now a person in human nature is not presupposed to assumption; rather, it is the term of the assumption, as was said (Question , Articles ,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 (Question , Article ). Hence it follows that the Son of God nowise assumed a human person.
Reply to Objection: 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.
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.
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.
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."
2. Further, the word "man" signifies a human nature. But the Son of God assumed a human nature. Therefore He assumed a man.
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."
I answer that As has been said above (Article ), what is assumed is not the term of the assumption, but is presupposed to the assumption. Now it was said (Question , Articles ,2) that the individual to Whom the human nature is assumed is none other than the Divine Person, Who is the term of the assumption. Now this word "man" signifies human nature, as it is in a suppositum, because, as Damascene says (De Fide Orth. iii, 4,11), this word God signifies Him Who has human nature. And hence it cannot properly be said that the Son assumed a man, granted (as it must be, in fact) that in Christ there is but one suppositum and one hypostasis. But according to such as hold that there are two hypostases or two supposita in Christ, it may fittingly and properly be said that the Son of God assumed a man. Hence the first opinion quoted in Sent. iii, D. 6, grants that a man was assumed. But this opinion is erroneous, as was said above (Question , Article ).
Reply to Objection: 1. These phrases are not to be taken too literally, but are to be loyally explained, wherever they are used by holy doctors; so as to say that a man was assumed, inasmuch as his nature was assumed; and because the assumption terminated in this---that the Son of God is man.
2. The word "man" signifies human nature in the concrete, inasmuch as it is in a suppositum; and hence, since we cannot say a suppositum was assumed, so we cannot say a man was assumed.
3. The Son of God is not the man whom He assumed, but the man whose nature He assumed.
Objection: 1. It would seem that the Son of God ought to have assumed human nature abstracted from all individuals. For the assumption of human nature took place for the common salvation of all men; hence it is said of Christ (1Tm 4,10) that He is "the Saviour of all men, especially of the faithful." But nature as it is in individuals withdraws from its universality. Therefore the Son of God ought to have assumed human nature as it is abstracted from all individuals.
2. Further, what is noblest in all things ought to be attributed to God. But in every genus what is of itself is best. Therefore the Son of God ought to have assumed self-existing [per se] man, which, according to Platonists, is human nature abstracted from its individuals. Therefore the Son of God ought to have assumed this.
3. Further, human nature was not assumed by the Son of God in the concrete as is signified by the word "man," as was said above (Article ). Now in this way it signifies human nature as it is in individuals, as is plain from what has been said (Article ). Therefore the Son of God assumed human nature as it is separated from individuals.
On the contrary Damascene says (De Fide Orth. iii, 11): "God the Word Incarnate did not assume a nature which exists in pure thought; for this would have been no Incarnation, but a false and fictitious Incarnation." But human nature as it is separated or abstracted from individuals is "taken to be a pure conception, since it does not exist in itself," as Damascene says (De Fide Orth. iii, 11). Therefore the Son of God did not assume human nature, as it is separated from individuals.
I answer that The nature of man or of any other sensible thing, beyond the being which it has in individuals, may be taken in two ways: first, as if it had being of itself, away from matter, as the Platonists held; secondly, as existing in an intellect either human or Divine. Now it cannot subsist of itself, as the Philosopher proves (Metaph. vii, 26,27,29,51), because sensible matter belongs to the specific nature of sensible things, and is placed in its definition, as flesh and bones in the definition of man. Hence human nature cannot be without sensible matter. Nevertheless, if human nature were subsistent in this way, it would not be fitting that it should be assumed by the Word of God. First, because this assumption is terminated in a Person, and it is contrary to the nature of a common form to be thus individualized in a person. Secondly, because to a common nature can only be attributed common and universal operations, according to which man neither merits nor demerits, whereas, on the contrary, the assumption took place in order that the Son of God, having assumed our nature, might merit for us. Thirdly, because a nature so existing would not be sensible, but intelligible. But the Son of God assumed human nature in order to show Himself in men's sight, according to Baruch 3:38: "Afterwards He was seen upon earth, and conversed with men."Likewise, neither could human nature have been assumed by the Son of God, as it is in the Divine intellect, since it would be none other than the Divine Nature; and, according to this, human nature would be in the Son of God from eternity. Neither can we say that the Son of God assumed human nature as it is in a human intellect, for this would mean nothing else but that He is understood to assume a human nature; and thus if He did not assume it in reality, this would be a false understanding; nor would this assumption of the human nature be anything but a fictitious Incarnation, as Damascene says (De Fide Orth. iii, 11).
Reply to Objection: 1. The incarnate Son of God is the common Saviour of all, not by a generic or specific community, such as is attributed to the nature separated from the individuals, but by a community of cause, whereby the incarnate Son of God is the universal cause of human salvation.
2. Self-existing [per se] man is not to be found in nature in such a way as to be outside the singular, as the Platonists held, although some say Plato believed that the separate man was only in the Divine intellect. And hence it was not necessary for it to be assumed by the Word, since it had been with Him from eternity.
3. Although human nature was not assumed in the concrete, as if the suppositum were presupposed to the assumption, nevertheless it is assumed in an individual, since it is assumed so as to be in an individual.
Summa Th. III EN Qu.3 a.5