Commentaria in Summam contra Gentiles, Liber IV

The fourth point that St. Thomas premised¹ is that in the very beginning of conception the rational soul was united to the body.

I. It is proved first. The Word of God assumed a body from the very beginning of conception. Therefore the rational soul was then united to the body. — The consequence is proved. Because the Word of God assumed a body by the mediation of the soul: since it is not more assumable than other bodies except through the rational soul.

It must be observed, from the teaching of St. Thomas in the Tertia, q. vi, a. 1; and in III Sent., d. ii, q. ii², that the Word of God is not said to have assumed a body by the mediation of the rational soul as if He assumed the soul prior in duration to the body; but because He assumed it prior by the order of nature, and according to the grade of dignity, inasmuch as the soul is more worthy than the body. From this, it can also be called a medium between the body and the Word according to the order of causality: inasmuch as the human body would not be more assumable, as is also said here, than other bodies, except through an order to the rational soul, according to which it has the character of being a human body.

Secondly. Given the personality of the begotten man, it is necessary to posit a body and a rational soul. But in the conception itself there was the personality of Christ the man. Therefore it was necessary that the body and soul be present there. — The major premise is proved. Because in human generation the hypostasis or person, for whose constitution the body and soul are ordered, is posterior, as being that which is most perfect in it. But when that which is posterior is posited, that which is prior according to generation must also be posited. — But the minor is proved: because the personality of the man Christ is none other than the personality of the Word of God. But the personality of the Word of God was present in the conception, namely in human nature: since the Word united a human body to Himself in the very conception.

Note that in this reasoning some propositions have been posited explicitly which St. Thomas does not posit formally, but only implicitly. This was done in order to make the reasoning clearer.

Thirdly. It was not fitting for the Word of God to be united to a body not yet ensouled, namely by a rational soul. Therefore etc. — The assumption is proved. Because whatever is corporeal is unformed prior to animation, and not yet having the perfection of nature. But it was unfitting for the Word of God, who is the source and origin of all perfections and forms, to be united to some unformed thing that did not yet have the perfection of nature.

It must be observed, when it is said that every corporeal thing before animation is unformed, that the term unformed is not taken for that which lacks every form, but for that which lacks the complement of species and nature. For anything corporeal in human generation preceding the introduction of the intellective soul is incomplete and imperfect; and it is placed per se in no species, but is reduced to the species of man as the imperfect to the genus of its perfect state.

II. From the premises St. Thomas infers that that body assumed from the beginning of conception was formed. Understand this of accidental formation, which is the due disposition of the members, or organization.

It is proved. First, because the Word of God ought to assume nothing unformed. — Next, because from the beginning of conception the soul was united to the body. But similarly the soul, like any other natural form, requires its proper matter, which is an organized body: since it is the entelechy of an organic body, etc. — Next, because the organization of the body, in the order of generation, precedes the introduction of the rational soul. But once the posterior is posited, it was necessary for the prior to be posited as well.

If someone should say that, by the same reasoning, that body ought to have had the complement of due quantity: — St. Thomas answers, saying that this does not have to be: because nothing prevents the increase of quantity up to the due measure from following the animation of the body.

It is concluded therefore that in the very beginning of conception the body was organized and formed, but not yet having the due quantity.

III. For the evident understanding of the things that are said here, it must be considered first, from the teaching of St. Thomas in the Tertia, q. xxxiii, a. 1, and III Sent., d. iii, q. ii, a. 1 at the end, that concerning the conception of the body we can consider three things: namely, that which precedes the conception; that in which the nature of conception consists; and that which follows upon the conception. The first is the local motion of the blood to the place of generation; the second is the formation of the body; the third is the growth by which the body is brought to its due quantity. For the first and the last, it is repugnant to be in an instant: since motion cannot be in an instant. But for the second, it is not repugnant to be in an instant, by an infinite power, which can in an instant dispose matter to its due form.

In the conception of other men, therefore, from the beginning at which the thing begins to be conceived, the body is not organized and formed, nor is it in the ultimate complement for the reception of the rational soul; but it is disposed successively and by degrees, and tends toward the complement and animation; when this has taken place, the thing is said to be conceived. And therefore conception itself also has succession. Whence a mere man is not said to be simultaneously conceived and to have been conceived: but first he is conceived, and afterward he is conceived. — But in the conception of Christ, from the very beginning at which Christ was said to be conceived, the body was organized, and formed, and ensouled with a rational soul; nor was there any succession in the formation of the body and its disposition for the rational soul; but all the aforesaid were simultaneous; because, as was said above³, the divine Word assumed nothing unformed, but conception is not attributed to Him except by reason of the assumption. And therefore the conception of Christ was itself in an instant, and Christ was simultaneously being conceived and conceived: although the growth of His body to the due quantity was not in an instant. Rightly, therefore, is it said here that from the beginning of conception the body of Christ was both formed and ensouled.