Commentaria in Summam contra Gentiles, Liber IV

The second error concerning the soul of Christ¹ is that of Apollinaris: who, although he had earlier followed Arius, yet having been convicted by the aforesaid testimonies, afterwards confessed that in Christ there was a sensitive soul, without intellect and mind; and he said that the Word of God was in place of intellect and mind to that soul.

I. But that this does not suffice to avoid the aforesaid absurdities is argued as follows. First. If in Christ there was a sensitive soul without reason, it was not of the same species as our soul, which possesses reason: since, according to the Philosopher, Metaphys. VIII, in definitions and species any essential difference added or subtracted changes the species. Therefore neither was Christ himself of the same species with us. — The consequence is proved. Because man obtains the human species from the fact that he has a mind and reason.

Second. It follows that the soul of Christ is contained under one of the species of sensitive soul lacking reason, namely under the species of the soul of a lion or of a horse² or of some other beast. Because a sensitive soul lacking reason is like a genus containing several species under itself: now, nothing is in a genus that is not in some species of it. But this is completely absurd. Therefore etc.

Third. It would follow that Christ would not have had members such as human members are. — The consequence is proved. Because, since the body is compared to the soul as matter to form, and as an instrument to the principal agent; and matter must be proportioned to form, and the instrument to the principal agent: there must also be a diversity of bodies according to the diversity of souls.

It should be noted that the soul both gives being to the body and uses it for extrinsic operations. Insofar as it gives being to it, it is compared to it as form to matter: for it belongs to form to give being to matter. Insofar, however, as it moves it, not indeed as merely moved, but as moved moving something else extrinsic, it is compared to it as the principal mover to an instrument: for it belongs to the notion of an instrument to be a moved mover. In both ways, however, the body must be proportioned to the soul: for a determinate form is not received in just any matter, but in determinate matter proportioned to itself; nor does every principal agent use just any instrument indifferently, but a determinate agent uses certain and determinate instruments. Therefore St. Thomas very well proves that there is a diversity of bodies according to the diversity of souls, from the fact that the body is compared to the soul both as matter to form and as an instrument to the principal agent.

Fourth. In Christ there was wonder, as is clear from Matt. VIII. Therefore there was also something besides the divinity and the sensitive soul: namely, a human mind. — The consequence is proved. Because wonder, which arises from ignorance of the cause, can belong neither to the Word of God, since he is God; nor to the sensitive soul, since it does not belong to it to be concerned about the knowledge of causes.

II. From the aforesaid St. Thomas infers two corollaries. The first is that, when it is said, The Word was made flesh, it is not understood as if the Word was changed into flesh, or assumed flesh alone, or a sensitive soul alone without a mind; but flesh is taken for the whole man, to express the weakness of the human nature which the Word assumed. For soul is also sometimes used in the Scriptures for the whole man: as when it is said, Exod. I, All the souls were etc. Flesh also is sometimes used for the whole man: as when it is said in Isaiah XL, All flesh shall see etc.

The second corollary is that the dogma of Origen is false, who says that the soul of Christ was created from the beginning, before bodily creatures, and was assumed by the Word, and was at last clothed with flesh. For it is clear from what has been said that Christ had human flesh and a human soul. Now, it was shown above that human souls do not pre-exist their own bodies.