Commentaria in Summam contra Gentiles, Liber IV

The fourth error¹ was that of certain people who, seeing that to posit only one person in Christ and two natures, as the faith asserts against Nestorius and Eutyches, seems foreign to those things which natural reason experiences, asserted such a position concerning the union. For lest they be forced to posit some hypostasis in Christ besides the person of the Word, as did Nestorius, they said that the soul and body were not united in Christ, nor was any substance made from them. Furthermore, lest they be forced to posit that the assumed soul and body belong to the eternal nature of the Word, they posited that the Word assumed them in an accidental manner, as a man assumes a garment, wishing by this to exclude the error of Eutyches.

I. Concerning this error, St. Thomas proceeds as follows. First, indeed, he refutes it; second, he removes its foundation².

As to the first, he argues first thus. From this position it follows that Christ was not a man: against what is found in 1 Tim. 2, Mediator of God etc. Therefore etc. — The consequence is clear. Because the soul and body by their union constitute a man: for a form coming to matter constitutes a species.

Second. Christ will be called a man equivocally, and will not be of the same species with us. Because each of us is called a man for this reason, that he is constituted of a rational soul and a body. But this is against the Apostle, Heb. 2. Therefore etc.

Third. It follows that Christ did not assume human nature. Because not every body belongs to human nature, but only a human body. But it is not a human body unless it is vivified through the union of a rational soul.

It should be noted that this position said that Christ assumed human nature because he assumed its essential parts, namely the soul and the body, although separated. And therefore, St. Thomas, showing that he did not assume a human body, which is a part of human nature, if he assumed a separated soul and body, excellently concludes against them that he did not assume human nature, even according to their own position.

II. Fourth. It follows that the soul of Christ is not a human soul: and consequently human nature was not in Christ. — The consequence is proved. A human soul is naturally unible to a body. Therefore a soul which is never united to a body to constitute something is not a human soul: because what is contrary to nature cannot be always. But the soul of Christ, according to this position, is never united to a body. Therefore it is not a human soul.

Concerning that proposition, What is contrary to nature cannot be always, it should be noted, according to the doctrine of St. Thomas in De Veritate, q. 24, a. 10, ad 1, that something happens to be against nature in two ways. In one way, because it is against the inclination of that which has a sufficient natural principle toward the opposite, from which that follows of necessity, unless it is impeded: just as to be moved upward is against the nature of a heavy thing. In another way, because it is against the natural inclination of something which does not have in itself a sufficient natural principle toward the opposite, as for a woman to be without offspring: for although it is natural for a woman to conceive a child, she cannot do this, however, except by receiving the seed of a man. That which is against nature in the first way cannot be always, as is the thought of Aristotle in I De Caelo³: but that which is against nature in the second way certainly can. Therefore the proposition of St. Thomas has truth concerning that which is contrary to nature in the first way. Moreover, this sense fits the proposal. Because a form which is naturally unible to a body has in itself a sufficient formal principle toward union with the body, while it is produced in esse by the agent, and does not require anything else for its union, through which it would be perfected so that it could be united.

III. Fifth, it is argued against their second statement. The Word is united to the soul and body accidentally, as to a garment. Therefore human nature was not the nature of the Word. Therefore after the union the Word was not subsisting in two natures.

Sixth. God cannot be said to have been born or to have suffered on account of the assumed body. For a man is not said to be born when he is clothed; nor to be wounded if his clothing is torn.

Seventh. If the Word assumed human nature as a garment by which he could appear to the eyes of men, he would have assumed a soul in vain, which according to its nature is invisible.

Eighth. The Son would not have assumed human flesh otherwise than the Holy Spirit assumed the appearance of a dove, in which he appeared. Which is false: because the Holy Spirit is not said to have become a dove, nor to be less than the Father according to the assumed nature.

Lastly. The absurdities of various heresies follow upon this position. Therefore etc. — The assumption is proved. Because from the fact that it says that the Son of God was united to a soul and flesh accidentally, it agrees with the opinion of Nestorius positing that this union was made according to the indwelling of the Word of God. — It also follows that the Word of God was not subsisting in two natures: which Eutyches posited. — But from the fact that it says that the soul and flesh are not united to constitute something, it agrees partly indeed with Arius and Apollinaris positing that the body of Christ was not animated by a rational soul; and partly with the Manichaean positing that Christ was not a true man, but a phantasmal one.

IV. As to the second⁴, St. Thomas says that this position took occasion from the words of the Apostle saying, Phil. 2, In habit found as a man. But he answers that this was said metaphorically, in some respect. For the assumed human nature has a certain likeness to a garment, inasmuch as through visible flesh the Word was seen, as a man is seen through a garment: but not because its union was in an accidental manner.

It should be noted, from the doctrine of St. Thomas in the Tertia Pars, q. 2, a. 6, and III Sent., d. 6, q. 3, a. 2⁵, that according to Damascene, in Book III⁶, and as is also said here, those things which are said metaphorically need not be similar in all respects. Therefore, since Christ is metaphorically said to be in habit found as a man, it is not necessary that his humanity be likened to a habit in all respects, but in some. For it is likened in three respects. First, indeed, because it comes to the divine person after his complete esse: just as a garment comes to a man. Second, because it is in itself a substance and comes to another, just as clothing is also a substance in itself and comes to a man. Third, because it is bettered from the union with the Word, and does not change the Word: just as clothing is formed according to the form of the one clothed, and does not change him. — But it differs, because a garment is not assumed for the esse of the one clothed: but humanity is indeed assumed for the esse of the divine supposit. On account of which, it is not said to be united to it accidentally, but essentially: although a garment comes to the one clothed accidentally.