Commentaria in Summam contra Gentiles, Liber IV

The seventh thing that St. Thomas¹ sets forth is that, although Christ is said to have been conceived of the Holy Spirit and the Virgin, the Holy Spirit nevertheless cannot be called the father of Christ according to human generation, just as the Virgin is called his mother.

I. It is proved first. Because the Holy Spirit did not produce the human nature in Christ from his own substance, but worked by his power alone toward its production.

Note that this argument proceeds from this supposition, that a son is generated from the substance of the begetter, that is, from the seed, which has its power from the form of the begetter, and is in potency to his substance or nature, as St. Thomas explains in Prima, q. cxix, a. ult., ad 1. — Although this can also be understood because the father's seed, which is his substance, not indeed as an actual part, but as in the proximate disposition to be a part of him, passes into the substance of the son, according to the opinion of some.

Secondly. Because this would be an inducement to this error, that Christ would be two sons, and consequently that in Christ there would be two persons: since the name of filiation pertains to the person, not to the nature. — The first consequence is proved. Because the Word of God has a distinct person in this respect, that he is the Son of God the Father, and he himself cannot be the son of the Holy Spirit.

Thirdly. Because the authority of the Father in divine matters and the name would be transferred to another person, namely to the Holy Spirit. Which is unfitting.

II. Note that it is not only not absolutely true that the Holy Spirit is the father of Christ, for the reasons stated above: but not even with this addition, inasmuch as he is man. Which St. Thomas signified when he said that he is not the father of Christ according to human generation.

But then a doubt arises, especially against the second argument. For if, because the Word of God cannot be the son of the Holy Spirit, it follows that Christ is two sons, granted that he is called the son of the Holy Spirit according to human nature, by the same reason it can be concluded that he is not the son of the Blessed Virgin. Because, since the Word of God cannot be the son of the Blessed Virgin, it follows that, if Christ is her son according to human nature, Christ is two sons.

2. It is answered, and it is said first, that the case is not the same regarding the Holy Spirit and the Blessed Virgin. For one son to be from two fathers is impossible: and therefore, where Christ is held to have for father the person of the Father in divine matters, and the person of the Holy Spirit according to human nature, it immediately follows that he is two sons. But it is not unfitting that one son be of two persons of whom one is the father and the other is the mother. Therefore, if Christ is held to be the Son of God the Father and of the Blessed Virgin, it does not follow that he is two sons.

But when it is said that the Word of God cannot even be the son of the Blessed Virgin: it is said that this is not true. For in order that someone be the son of someone as of a mother, it suffices that she supply the matter in the conception and be of the same species with him. This, however, the Blessed Virgin did in the human conception of the Word of God, and she is of the same species with him inasmuch as he is man. Therefore the Word of God can be called her son according to human conception. But in order that someone be called the son of someone as of a father, it is required that he receive being from him: as is said in Tertio, d. iv, q. 1, a. 2². But the Word of God, even according to human generation, does not have being from another divine person than the Father: because he does not have another being than the divine being. Therefore in no way can he be called the son of the Holy Spirit.

3. It can be said secondly that St. Thomas does not bring forward that argument to show that it is simply false that the Holy Spirit is the father of Christ: but, since this has been proved by the first argument, he shows that this, even if it were true, is not to be said, because of the danger and occasion of error. For although someone could say that it is not unfitting that Christ, being one in supposit, be the son of God the Father according to the divinity, and of the Holy Spirit according to the humanity; nevertheless many, considering that the name of son pertains to the person, and that the Word of God is not the son of the Holy Spirit according to the divinity, if Christ is held to be the son of the Holy Spirit, could easily slip into this error, that in Christ, besides the person of the Word, there would be another human person, according to which he would be called the son of the Holy Spirit. But this cannot be thought so easily if Christ is held to be the son of the Blessed Virgin: because, as has been said, it does not appear unfitting that he who is the Son of the eternal Father be also the son of the Blessed Virgin through the assumption of the humanity from her.

4. But note that Christ cannot only not be called the natural son of the Holy Spirit: but neither can he be called his son by grace or by creation. The reason for this is, according to St. Thomas, Tertia, q. xxxii, a. 3; and Tertio, the aforesaid distinction³, because when something is said of another according to the perfect meaning, in no way is it said of him according to an imperfect meaning, or with a diminishing determination: just as Socrates, who naturally and perfectly is called a man, according to the proper meaning of man, is never called a painted man. Whence, since Christ is called the natural Son of God and according to the perfect meaning of filiation, he cannot be called the son of God by grace or by creation.