Commentaria in Summam contra Gentiles, Liber IV

The third point that St. Thomas premises ¹ is that it was necessary for the human nature not to pre-exist before it was united to the Word.

I. This is proved, first ². That nature to be assumed would have pre-existed in some hypostasis or person. Therefore it would be necessary to say either that both hypostases, namely of the Word and of the man, remained; or that that hypostasis or person would not remain in that nature in which, to be assumed by the Word, it had pre-existed. If the first, then two hypostases or persons would have remained after the union, and thus the union would not have been made in a person, which is against the judgment of faith. If the second, this could not have happened without corruption, since no singular ceases to be what it is except through corruption. And thus it would have been necessary for that man to be corrupted, and consequently the human nature existing in him. And thus the pre-existing man would not have been assumed. — The assumed premise is proved. Because there would have had to be some individual of that human nature pre-existing before the union, since nature cannot pre-exist except in individuals. But the individual of human nature is a hypostasis and person.

2. Concerning this proposition, The individual of human nature is a hypostasis and person, a doubt arises. For human nature in Christ is individual; for it is not universal humanity, but singular and this humanity. If, therefore, the individual of human nature is a hypostasis and person, it follows that there are two persons in Christ. The opposite of this is stated here, and the Catholic faith holds it.

It is answered, from the doctrine of St. Thomas, Tertia, q. 16, a. 12 ³, that an individual of substance can be taken in two ways. In one way, for any singular substance whatever; in which way a man's hand can be called an individual substance. In another way, for a complete substance subsisting per se separately from others; in which way Boethius takes it when he defines a person, that it is an individual substance of a rational nature ⁴.

It is said, therefore, that St. Thomas takes individual in the second way, but not in the first way. Hence it does not follow that there are two persons in Christ on the grounds that the humanity in Christ is singular and individual in the first way. For although it is not universal humanity, but this humanity, it is nevertheless not individual in the second way, since it exists in another, namely in the divine supposit, and does not have ultimate completion.

3. Where it must be noted, setting aside the opinions of many ⁵ and the position of Capreolus ⁶, that person adds over and above this singular humanity something positive of the genus of substance, which is the ultimate term and ultimate completion of nature; which is signified by this name personality, and is formally and intrinsically constitutive of a person in personal esse, just as a point is the ultimate term and ultimate completion of a finite line. Therefore, although it is granted that the humanity in Christ is singular, it is not granted that it is a person, because it does not have that ultimate term, since it was prevented from having it by the divine Word assuming it. For to one who considers the statements of St. Thomas diligently, it must be said that hypostasis and person add something positive over and above the singular nature, as Cardinal Cajetan remarkably shows, Tertia, q. 4, a. 2 ⁷, citing also what is said here: namely, that if that pre-existing person did not remain, this could not have happened without the corruption of that man, and consequently of the nature existing in him; for it is clear that a substance is not said to be corrupted except through the loss of something substantial and positive. — The same is also had from Tertia, q. 4, a. 2, in the body and to the 3rd; likewise III Sent., d. 5, q. 3, a. 3.

II. Secondly ⁸. It would detract from the perfection of the Incarnation of the Word of God. Therefore etc. — The assumed premise is proved. Because it is natural to man to be born by a human birth. But the Word of God would not have this, because that man in his birth would have existed as a mere man. And thus his birth could not be attributed to the Word; nor could the Blessed Virgin be called the Mother of God; even though faith confesses him to be like us in all things, without sin, in natural matters, namely made of a woman and born, and the Blessed Virgin to be the Mother of God.

Note that the foundation of this reason consists in this: that the Word of God could not be said to have been born by a human birth. Because by a human birth that is born which is man. But when the man pre-existing the assumption was born, the Word would not have been that man, but the man being born would have been a mere man. And thus it could not have been said that, when that man who was to be assumed was born, the Word of God was born. — Moreover, from this it further follows that the Virgin could not be called the Mother of God, since motherhood follows upon human birth.

III. From this he further deduces that the Word united human nature to himself from the very beginning of conception.

It is proved, first ⁹, because if the human nature to be assumed had been in any state whatever prior to being united to the Word, the Word could not be said to have been conceived by a human conception. But this detracts from the humanation of the Word. Because just as the Word of God is required to have been born by a human birth in order to be a true and natural man, so he is required to have been conceived by a human conception, since, according to the order of nature, a man is not born unless he is first conceived.

For the evidence of this reason, it must be considered, first ¹⁰, that for something to be said to be conceived by a human conception, it is required that the whole conception, from the beginning of conception up to the end, be attributed to it. But in whatever state the human nature would have been before it was assumed, whether, I say, in a complete state or in an incomplete state, the whole human conception could not have been attributed to the Word of God, because conception is not attributed to him except by reason of the assumption; but from the very beginning of conception the human nature would not have been assumed by the Word. Therefore it could not be said of the Word of God that he was conceived by a human conception. And this is the intent of this reason.

It must be considered, secondly ¹¹, that a man can be called natural in many ways: namely, either with respect to the active principle, the intrinsic natural principles, and the order of proceeding; or with respect to the intrinsic principles and the order of proceeding; or with respect to the intrinsic natural principles. In this last way Adam, produced immediately by God, could be called a natural man, because he consisted of the principles from which the nature of man is constituted; but not in the other ways, because he was neither produced according to the order of nature, nor by a natural agent. — In the second way, Christ was a natural man, because he both had a true human nature and, according to the order of nature on the part of the one begotten, was generated. But not in the first way, because he was not produced by a natural agent. — But other men are called natural in the first way.

When, therefore, it is said here to be required, in order for the Word of God to be a true and natural man, that he be born by a human birth and conceived by a human conception, the expression "true and natural man" is taken in the second way, and not in the first and third.

2. Secondly ¹², because the human generation of Christ would not have been one in number, nor would it have been uniform throughout the whole. Because, since in human generation the active power acts toward the completion of the nature in some determinate individual, if the Word of God had not assumed human nature from the beginning of conception, the active power in his generation before conception would have ordered its action to some hypostasis of human nature; but after conception, it would have ordered the whole generation to another hypostasis, namely to the Word of God; and thus the generation would have been ordered to two persons.

3. It must be noted, when it is said that the generation would not be uniform throughout the whole, that the generation of a mere man is called uniform throughout the whole because from the beginning up to the end it is the generation of a man. But the generation of Christ, positing that the human nature had been conceived prior to being assumed, would not have been from the beginning up to the end the generation of a man; but at first it would indeed have been the generation of a man according as a mere man would have been generated through it, for that prior instant in which the man would have been conceived and not assumed; but afterwards it would have been the generation of the Word of God, for that duration in which the human nature had been assumed by the Word of God. And therefore it would not be uniform throughout the whole.

If it should be said that, by the same reasoning, not even the generation of a mere man can be called uniform throughout the whole, because a living thing is generated prior to an animal, and an animal prior to a man: — it is answered that the reasoning is not the same. Because a living thing and an animal in the generation of a man are not something complete in species, but are ordered to man as to that which is complete in species, and from this the generation has it that it is called uniform. Hence, when both a living thing and an animal are generated, by that generation a man is said to be generated. But in that generation of Christ there would be two things complete in nature: namely, the mere man conceived prior to being assumed, and the Word of God assuming the man himself. Therefore it would not be uniform throughout the whole.

IV. Thirdly ¹³. Because the order of human generation seems to require that he who is conceived, the very same one be born, and not another, since conception is ordered to birth.