Article 1 — Whether this union was brought about in the person or in the nature

First, it is asked (Parallel texts: Thomas Aquinas, Summa theologiae (ST) III, q. 2, aa. 1–2; Commentary on the Sentences, bk. 3 (In III Sent.), d. 5, q. 1, aa. 2–3; Summa contra Gentiles (SCG) IV, cc. 35, 41; Disputed Questions on Truth, q. 20, a. 1; Commentary on Romans, ch. 1, lect. 2; Commentary on Philippians, ch. 2, lect. 2.) whether this union was brought about in the person or in the nature. It seems that it was in the nature.

Obj. 1: For Athanasius says that just as the rational soul and the body are one man, so God and man are one Christ. (Athanasius, Athanasian Creed 10 (Patrologia Graeca [PG] 28:1583).) But the rational soul and the body are united into one human nature. Therefore, God and man are united into the one nature of Christ.

Obj. 2: Besides, Damascene says in the third book of On the Orthodox Faith, this produces the error of the heretics, because they say the nature and the hypostasis are the same. (John Damascene (d. 749 AD), On the Orthodox Faith, bk. 3, ch. 3 (PG 94:991–92).) But this does not seem to be false, because in anything simple, and especially in God, suppositum and nature are the same. Therefore, what the heretics say, that if the union of the Word was brought about in the person, it was brought about in the nature, is not false.

Obj. 3: Besides, Damascene says in the third book that the two natures were mutually united unchangeably and inalterably. (John Damascene, On the Orthodox Faith, bk. 3, ch. 3 (PG 94:987–88).) But the union of natures seems to imply a natural union. Therefore, the union was brought about in the nature.

Obj. 4: Besides, in all those things in which the suppositum possesses something beyond the nature of the species, either an accident or individual matter, it is necessary that the suppositum differ from the nature, as is clear from the Philosopher in book 7 of the Metaphysics. (Aristotle, Metaphysics 7.11, 1037b7; 7.6, 1031a19; Aquinas, Commentary on Aristotle’s Metaphysics, bk. 7, lect. 3, nn. 1320–24; bk. 7, lect. 5–6.) But if the union of human nature to the Word did not occur in the human nature, it will not belong to the nature of the species of the Word itself. Therefore, it would follow that the suppositum of the Word would be different from the divine nature of the Word, which is impossible. Therefore, it seems that the union was brought about in the nature.

Obj. 5: Besides, every union is terminated in something one, which is posterior to the union itself. But the unity of the person of the Word, since it is eternal, is not posterior to the union which was brought about in the fullness of time. Therefore, the union was not brought about in the person.

Obj. 6: Besides, a union entails a certain addition. Hence, a union cannot be brought about in something which is of highest simplicity. But the person of the Word, since he is true God, is of the highest simplicity. Therefore, a union cannot be brought about in the person of the Word.

Obj. 7: Besides, two things which are not of one genus cannot be united in something, for one thing does not arise from a line and whiteness. But human nature differs much more from the divine nature than those things which differ in a genus. Therefore, the union of human and divine natures cannot be brought about in one person at the same time.

Obj. 8: Besides, the person and the nature of the Word differ only according to the mode of understanding, insofar as a relation of origin is entailed in the person of the Word, but not in the nature. Yet the Word is not related to human nature through the relation of origin, but to the Father. Therefore, the Word and the Word’s nature are related to the assumed nature in the same way. If, therefore, the union was brought about in the person, it would have been brought about in the nature.

Obj. 9: Besides, the Incarnation stimulates us to love God incarnate. But we should not love one divine person more than another; for since their goodness is the same, the love ought to be the same. Therefore, the union of the Incarnation occurred in the nature common to the three persons.

Obj. 10: Besides, according to the Philosopher in book 2 of On the Soul, in living things living is being. (Aristotle, On the Soul 2.4, 415b12; 415a23–b28; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 7, n. 319.) But in Christ, life is two-fold, namely, human and divine. Therefore, being is two-fold for him and, consequently, there is a two-fold person, for being is of the suppositum or the person. Therefore, the union was not brought about in the person.

Obj. 11: Besides, just as the form of a part is compared to matter, so the form of a whole is compared to a suppositum. But the form of a part cannot exist except in its own matter. Therefore, the form of the whole, which is the nature, cannot exist except in its own suppositum, which is a human person. And by the same reason the divine nature exists in the divine person. Therefore, if there were two natures there, it would be necessary that there be two persons there.

Obj. 12: Besides, everything which is truly predicated of something, is able to stand in for it. But the divine nature is truly predicated of the person of the Word. Therefore, it is able to supposit for the person of the Word. If, therefore, the union was brought about in the person, it can be truly said that it was brought about in the nature.

Obj. 13: Besides, everything that is united to something is united either accidentally or essentially. But human nature is not united to the Word accidentally, because it would thus retain its own personality and there would be two persons. For every substance added to another retains its own singularity, as the garment which has been put on or the horse which is being ridden. Therefore, human nature comes to the Word essentially as though pertaining to the essence or nature of the Word. Therefore, the union occurred in the nature.

Obj. 14: Besides, nothing that is included in another stretches out to something outside, just as what is found in a place is not also outside the place. But the suppositum of any nature is found in that nature, hence it is called a thing of nature. In this way, the individual is included under a species, just as the species is included under a genus. So, since the Word is the suppositum of the divine nature, it is not able to stretch out to some other nature so as to be its suppositum, unless one nature is brought about.

Obj. 15: Besides, nature is related to suppositum through a more formal and more simple mode, and the nature constitutes it. Yet human nature cannot be related to the person of the Word in this way. Therefore, the person of the Word cannot be a person of human nature.

Obj. 16: Besides, action is attributed to the suppositum or person, since actions belong to particular things, according to the Philosopher. (Aristotle, Metaphysics 1.1, 981a12–24.) But there are two actions in Christ as Damascene proves in book 3. (John Damascene, On the Orthodox Faith, bk. 3, ch. 15 (PG 94:1059–60).) Therefore, there are two persons there. Therefore, the union is not brought about in the person.

Obj. 17: Besides, person is properly defined as a nature made distinct as a property. If, therefore, the union occurred in the person, it follows that it occurred in the nature.

On the contrary (1), there is what Augustine says in the book On the Faith, to Peter, (A spurious text, attributed to Augustine; it is actually: Fulgentius, On the Faith, to Peter the Deacon, ch. 17 (Patrologia Latina [PL] 40:772).) the truth of the two natures remain in Christ according to one person.

Furthermore (2), in To Orosius, (A spurious text, attributed to Augustine.) he also says, we know two natures in the one person of the Son.

I answer that, for a clear understanding of this question, first, it is necessary to consider what a nature is; second, what a person is; and third, how the union of the Word incarnate occurred in the person, not in the nature.

Therefore, it should be known that the name “nature” is taken from being born. Hence, nature, or “about to be born,” was first said of the actual birth of living things, namely, of plants and animals. Next, the name nature was transferred to the principle of the aforementioned nativity. And since the principle of this kind of nativity is interior, the name “nature” was further extended to signifying a more interior principle of motion, according to what is said in book 2 of the Physics, that nature is a principle of motion in which motion is essential, not accidental. (Aristotle, Physics 2.1, 192b20–23; Aquinas, Commentary on Aristotle’s Physics, bk. 2, lect. 1, n. 145.) Since natural motion especially in generation is terminated at the essence of a species, we may say further, the essence of a species, which a definition signifies, is called a nature. Hence, Boethius also says in On the Two Natures that nature is the specific difference informing each and every thing. (Boethius, On the Person and the Two Natures: A Treatise Against Eutyches and Nestorius, ch. 1 (PL 64:1342).) And it is in this way that nature is taken here.

However, in order to understand what a person is, it must be considered that if there is some thing in which there is nothing other than the essence of the species, the essence of the species itself will be subsisting individually through itself. Thus, in a thing of this kind, nature and suppositum would be really the same, differing only in account; that is, the thing is called a nature insofar as it is the essence of the species, but it is called a suppositum insofar as it subsists through itself.

If there were anything within a thing beyond the essence of the species, which the definition signifies, it would be something other, either an accident or the matter of an individual. The suppositum will then not be entirely the same as that nature, but it will be constituted by an addition to the nature, as is most evident in those things which are composed of matter and form. And what was said concerning the suppositum must be understood concerning the person in a rational nature, since a person is nothing other than a suppositum of a rational nature according to what Boethius says in the book On the Two Natures, that person is an individual substance of a rational nature. (Boethius, On the Person and the Two Natures: A Treatise Against Eutyches and Nestorius, ch. 3 (PL 64:1343).)

Hence, it is obvious that nothing prevents some things being united in a person which are not united in the nature. For an individual substance of a rational nature can have something which does not pertain to the nature of a species, and this is united to it personally, not naturally. Therefore, in this manner it must be understood that the human nature was united to the Word of God in the person, not in the nature. For if it does not pertain to the divine nature, nevertheless it pertains to his person, insofar as the person of the Word joined human nature to himself by assuming it. But concerning the manner of this kind of conjunction doubt and discord occurs. For we see in creatures that something comes to another in two ways, namely, accidentally and essentially.

Therefore, Nestorius, and Theodorus of Mopsuestia before him, posited that the human nature was conjoined to the Word accidentally, namely, according to the indwelling of grace, positing that the Word of God had been united to the man Christ as if by dwelling in him as in his temple. But we see that every substance accidentally conjoined to another retains its own proper singularity separately, as when clothes are put on by man or a house contains an inhabitant. Hence, it follows that man will have a proper singularity which is his personality. Therefore, according to Nestorius it followed that the person of man in Christ was a distinct person from the person of the Word, and that one was the son of man and the other the Son of God. Hence, the Blessed Virgin was not acknowledged as the mother of God, but the mother of a man. But this is entirely absurd.

First, indeed, this is because Sacred Scripture speaks in one way concerning men, in whom the Word of God dwelled through grace, and in another way concerning Christ. For concerning other men, it says that the Word of the Lord was brought to a given prophet, but concerning Christ it says, the Word was made flesh (John 1:14), that is, a man, as if the Word itself were personally a man.

Second, this is because the Apostle in the letter to the Philippians (Phil 2:7) calls this union an emptying of the Son of God. But it is clear that the indwelling of grace is not adequate to the account of emptying. Otherwise, emptying would belong not only to the Son, but also to the Father and to the Holy Spirit, concerning which the Lord says, he shall abide with you, and shall be in you (John 14:17); and concerning himself and the Father, we will come to him, and will make our abode with him (John 14:23). Therefore, on account of this and many other things, the aforesaid error was condemned in the Council of Ephesus. (The third ecumenical council, in 431 AD.)

Certain men, holding with Nestorius that human nature had come to the Word accidentally, wanted to avoid the duality of persons which Nestorius posited, positing that the Word assumed a soul and a body to itself not united to each other, so that a human person would not be produced from a soul and a body. But from this a greater absurdity follows, that is, that Christ was not truly a man, since the account of a man consists in the union of a soul and a body. And thus, this error was also condemned under Alexander III in the Council of Tours. (In the year 1163 AD.)

But others took the other side, positing that human nature was joined to the Word essentially; so that it is as if one nature or essence was produced out of the divine and human nature. And on this point indeed Apollinaris made three claims, as Pope Leo says in a certain letter to those living in Constantinople. (See Leo the Great, Letter 59 (PL 54:865–74); Letter 124 (PL 54:1062–68).) First, he posited that a soul was not united to Christ, but that the Word had come to the flesh in place of the soul. As a result, one nature was produced from the Word and the flesh, just as in us one nature is produced from the soul and the body. In this doctrine Apollinaris also followed Arius. But since the evangelical Scriptures explicitly speak about the soul of Christ, according to that passage of John 10:18, I have power to lay down my soul, he fell into the second opinion, so that he even posited that there was a sensitive soul in Christ, but not a rational soul; rather, he posited that the Word took the place of the intellect in the man Christ.

But this is unfitting, because according to this the Word did not assume a human, but a bestial nature, as Augustine argued against him in the Book of Eighty-Three Different Questions. (Augustine, Book of Eighty-Three Different Questions, q. 80, para. 1 (PL 40:93).) His third teaching was that the flesh of Christ was not taken from a woman but made from the Word changed into flesh and even conversely. But this is most impossible, because the Word of God, since he is truly God, is completely immutable. For these doctrines of Apollinaris were condemned in the Council of Constantinople, (That is, the second ecumenical council and the First Council of Constantinople, in 381 AD.) as was that of Eutyches, who followed his third teaching, in the Council of Chalcedon. (The fourth ecumenical council, in 451 AD.)

So, therefore, if the union was not made in the person, but only according to inhabiting, as Nestorius claimed, nothing new happened in the Incarnation of Christ. But that the union occurred in the nature, as Apollinaris and Eutyches claimed, is completely impossible. For since the species of things are like numbers in which added and subtracted units vary the species, as is said in book 8 of the Metaphysics, (Aristotle, Metaphysics 8.3, 1043b36–1044a2.) it is impossible that whatever nature is complete in itself should receive the addition of another nature. (Cf. William of Auxerre, Summa aurea.) Or if it did receive, it would not be the same nature, but another one. But the divine nature is most complete. Similarly, even the human nature has the completion of its own species. Hence, it is impossible that one nature should be joined to another in a natural union. Even if it were possible, then surely that which was produced from both would be neither a human nature nor a divine nature; and thus, Christ would be neither man nor God, which is unfitting. Therefore, it remains that the human nature was united to the Word neither accidentally, nor essentially, but substantially, insofar as substance signifies a hypostasis, and hypostatically or even personally.

But there is no example of this union in created things nearer than the example Athanasius posits, of the union of the rational soul to the body. (Athanasius, Athanasian Creed 10 (PG 28:1583).) This is not, indeed, in the way that the soul is the form of the body, because the Word cannot be a form in matter, but in the way that the body is the instrument of the soul—not, indeed, an extrinsic and foreign instrument, but an instrument that is its own and conjoined. Hence, Damascene said that the human nature is the implement of the Word. (John Damascene, On the Orthodox Faith 3.15 (PG 94:1059–60).) However, we would find a closer example, as Augustine says in Contra Felicianus, (Rather: Vigilius of Thapsus (5th cent. AD), Contra Felicianus, ch. 12 (PL 42:1166).) if we suppose, as many want to, that there is a generic soul in the world, which, forming matter to its uses, makes one person of itself.

Nevertheless, all examples of this kind are deficient. For the union of an instrument is accidental, but this is a certain singular union above every mode of union known to us. For just as God is goodness itself and his own being, so also he is unity itself through his essence. Thus, as his power is not limited to these modes of goodness and being which are in creatures, but is able to make new kinds of goodness and being unknown to us, so also he was able to make a new kind of union through the infinity of his own power, in order for human nature to be united to the Word personally, but not accidentally, although no adequate example for this can be found in creatures. Hence, Augustine, speaking of this mystery in the epistle To Volusianus, said, if a reason is sought, it is not wonderful; if an example is demanded, it is not unique. We must grant that something is possible for God, which we confess that we cannot investigate; for in such things the entire reason for the thing made is the power of the maker. (Augustine, Epistulae, letter 137, “To Volusianus,” ch. 2, para. 8 (Corpus Scriptorum Ecclesiasticorum Latinorum [CSEL] 44; PL 33:519).) Dionysius says in the second chapter of On the Divine Names, according to us Jesus is a divine composition, that is a union, and he is ineffable by any word and unknown to the mind, and also to the first of the most worthy angels himself. (Pseudo-Dionysius, On the Divine Names, ch. 2, para. 9 (PG 3:647).)

Reply Obj. 1: A similarity is not observed according to this, that from a soul and a body there is one nature of man, but according to this, that one person is constituted from both.

Reply Obj. 2: Although nature and suppositum, or person, do not differ really in divine things, nevertheless they differ in account, as was said. (Above: resp.) Because the same thing is subsisting in human nature and in the divine, but the essence composed from both is not the same, hence it is that the union was made in the person, to whose account it pertains to subsist. Yet subsisting does not pertain to the nature which implies the essence of the thing.

Reply Obj. 3: The natures were indeed united in Christ, yet not in the nature, but in the person. This is evidence for the fact that the natures are said to be unchangeably and unalterably united.

Reply Obj. 4: Heretics, saying that the union did not occur in the person, but in the nature, did not think that the person and the nature differ—neither in reality nor in account—and thus they were deceived.

Reply Obj. 5: Something is properly called “united” according to a union, just as something is called “one” according to a unity. Thus, a union is not understood to be terminated in the divine person insofar as it is one in itself from eternity, but insofar as it is united to the human nature in time. Thus, according to the mode of understanding the union precedes the person, not as it is one, but as it is united.

Reply Obj. 6: A union is not said to have occurred in the divine person, as if the divine person itself were constituted out of two things united to each other. For this would be contrary to its highest simplicity. But a union is said to have occurred in the person, insofar as the simple divine person subsists in two natures, namely, the human and the divine.

Reply Obj. 7: Two things which are diverse according to genus may not be united in one essence or nature, yet nothing prevents that they should be united in one suppositum. In the same way, some essence does not come out of whiteness and line, yet they are found in one suppositum.

Reply Obj. 8: The person of the Son of God can be considered in two ways. One way is according to the common account of a person, as it signifies something subsisting; and according to this, the union occurred in the person according to the account of a person, as was said above. (Above: ad 2, resp.) In another way, that which is proper to the person of the Son can be considered in the person of the Son, namely, the relation by which he is referred to the Father. And the union of the two natures is not considered according to the account of this relation.

Reply Obj. 9: As the Incarnation adds nothing of goodness to the divine person, so also it adds nothing of lovability to him. Hence, the person of the Word incarnate should not be more loved than the person of the Word simply, although it must be loved according to another account, which account, nevertheless, is understood as falling under the universal goodness of the Word. On account of this also it does not follow that, if the union of the Incarnation occurred in one person and not in another, that on account of this, one person must be loved more than another.

Reply Obj. 10: Being belongs both to the subsisting person and to the nature in which the person subsists, in the sense that the person has being according to that nature. Therefore, the being of the person of the incarnate Word is one on the part of the subsisting person, but not on the part of the nature.

Reply Obj. 11: Nature is not related to suppositum in the same way as form is related to matter. For matter is not constituted in being except through a form; thus, form requires determinate matter which the form may make to exist actually. But a suppositum is constituted not only through the nature of a species, but it can also have certain other things. Thus, nothing prevents some nature being attributed to a suppositum of another nature.

Reply Obj. 12: The divine nature is predicated of the divine person according to the identity of the thing, but not according to the suitability of the mode of signifying. Thus, it is not necessary for one suppositum to take the place of the other. For this is also true in divine things: “the person begets”; while this is not true: “the essence begets.”

Reply Obj. 13: Human nature was united to the Word not, indeed, accidentally, nor also essentially, as if pertaining to the divine nature of the Word, but substantially, that is, hypostatically, as if pertaining to the hypostasis or person of the Word.

Reply Obj. 14: The person of the Word is included under the nature of the Word, nor can it extend itself to something beyond. But the nature of the Word, by reason of its own infinity, includes every finite nature. Thus, when the person of the Word assumes human nature, it does not extend itself beyond the divine nature, but the greater receives what is beneath it. Hence, it is said in Philippians 2:6–7 that the Son of God, being in the form of God, emptied himself—not only laying aside the greatness of the form of God, but also assuming the smallness of human nature.

Reply Obj. 15: Just as the nature of the Word is infinite, so too the person of the Word is infinite. Thus, the divine nature of the Word corresponds equally to the person of the Word in itself from an equality. But human nature corresponds to the Word inasmuch as it was made man. Hence, it is not necessary that the nature is simpler and more formal than the Word in itself, but rather, simpler and more formal than that man who is the Word made flesh and constituting himself inasmuch as he is a man.

Reply Obj. 16: Action is of a suppositum according to some nature or form, and thus actions are not only diversified according to the diversity of supposits, but also according the diversity of nature or form—just as also one action is seeing and another is hearing in one and the same man on account of diverse powers. Hence, there are two actions in Christ on account of the two natures, although there is one person or hypostasis.

Reply Obj. 17: A person is indeed a substance distinguished by a property pertaining to dignity, but not insofar as substance signifies an essence or nature, but inasmuch as it signifies a hypostasis.