Chapter 39 — The teaching of the Catholic Church on the Incarnation of Christ

From the foregoing chapters it is plain that according to the tradition of Catholic faith we must confess that in Christ there is one perfect divine nature, and a perfect human nature composed of a rational soul and human flesh. Also, that these two natures are united in Christ not by mere indwelling, nor accidentally as a man to his clothes, nor by mere personal habitude and property, but in one hypostasis and one suppositum. In this way alone can we safeguard the teaching of the Scriptures about the Incarnation. We have already observed that sacred Scripture, without making any distinction, ascribes divine things to the man; and things pertaining to the man to God. Therefore, in both cases it is the same one to whom reference is made.

But, seeing that opposite statements cannot be true about the same subject in the same respect, and that the divine and human things that are said about Christ are opposed to one another—for instance, that he suffered and was impassible, that he died and was immortal, and so on—it follows that divine and human things must be said of Christ in different respects. Accordingly, as regards the subject of which these things are predicated, we must make no distinction, and hold to unity; but as regards the things in respect of which these predications are made, a distinction is to be observed. Natural properties are attributed to a thing in respect of its nature: thus a stone falls down in respect of its nature as a heavy body. Accordingly, since divine and human things are attributed to Christ in different respects, it follows that in Christ there are two distinct unmixed natures. Now natural properties are attributed to something that belongs by its own nature to the genus of substance, and this is a hypostasis or suppositum of that nature. And since human and divine things predicated of Christ are attributed to one undivided subject, it follows that Christ is one hypostasis and one suppositum subsisting in the human and divine natures. In this way, divine things are truly and properly attributed to that man inasmuch as that man indicates a suppositum of both natures, human and divine. Vice versa, human things are attributed to the Word inasmuch as he is a suppositum of human nature.

Hence also it is clear that although the Son took flesh, it does not follow that either Father or Holy Spirit became incarnate, since the Incarnation was effected by union not in the nature common to the three persons, but in the hypostasis or person, in which the three persons are distinct. And thus, even as in the Trinity there are several persons subsisting in one nature, so in the mystery of the Incarnation is there one person subsisting in two natures.