Chapter 43 — That the human nature assumed by the Word did not exist before it was assumed, but was assumed by the Word at the moment of its conception

Since the Word assumed human nature into unity of person, as we have proved, (Ch. 41.) it follows that human nature did not exist before it was united to the Word.

For, if it was already in existence, there must have existed an individual with that human nature before the union, because a nature cannot exist except in an individual. Now an individual of human nature is a hypostasis and a person. Consequently, we shall have to say that the human nature to be assumed by the Word preexisted in some hypostasis or person. Therefore, if this already existing hypostasis or person remained after the nature was assumed, there would have been two hypostases or persons, one of the Word, the other, of a man, so that the union would not have taken place in the hypostasis or person. This is against faith. On the other hand, if that hypostasis or person did not remain in the nature in which it existed before being assumed by the Word, it must have been destroyed, for no individual can cease to be what it is without being corrupted. Hence this man who was in existence before the union must have been destroyed: consequently, the human nature in him must have been destroyed also. Therefore, it was impossible for the Word to assume an already existing man in unity of person.

Moreover. It would derogate from the perfection of the Incarnation of the Word of God, if he lacked any of those things that are natural to man. Now it is natural to man to be born in human fashion, and the Word of God would not have been born in human fashion if he had assumed an already existing man. For this man would have been a perfect man from his birth: consequently, his birth could not be ascribed to the Word of God, nor would the Blessed Virgin be called the mother of the Word. Now our faith holds that he was like us in all natural things save sin; and that the Son of God, as the Apostle declares, was made and born of a woman, and that the Virgin is the Mother of God. Therefore, it was not fitting that he should assume an already existing man.

Hence it follows that he united human nature to himself from the first moment of his conception. Just as the Word of God had to have a human birth in order to be a real natural man, like us in all natural things, so was it fitting that he should have a human conception, since in the order of nature a man is conceived before he is born. Now, if the human nature about to be assumed had existed in any state whatever before being united to the Word, that conception could not be ascribed to the Word of God, so that he might be said to have a human conception. Therefore, the Word of God had to be united to human nature from the very beginning of its conception.

Again. In the generation of a human being, the active form aims at completing human nature in a definite individual. But if the Word of God did not assume human nature at the very beginning of its conception, the active force, before the union, would have been directed to the formation of another human individual (that is, a human hypostasis or person); and, after the union, it would have directed the whole process of generation to another hypostasis or person, namely the Word of God, who was being born in human nature. Accordingly, there would not have been one generation, since it would have been directed to two persons; nor would the whole process have been uniform, and this would seem foreign to the order of nature. Therefore, it was fitting that the Word of God should assume human nature not after conception, but at the moment of conception.

Further. The order of human generation would seem to demand that the same one should be born as was conceived, and not another, since that conception is directed to birth. Consequently, if the Son of God had a human birth, it was fitting that he should have a human conception, and not assume an already existing man.