Prima Pars, Question 119 — Summa Theologiae
Article 1. Whether some part of the food is changed into true human nature?
Objection 1. It would seem that none of the food is changed into true human nature. For it is written (Matthew 15:17): “Whatsoever entereth into the mouth, goeth into the belly, and is cast out into the privy.” But what is cast out is not changed into the reality of human nature. Therefore none of the food is changed into true human nature.
Objection 2. Further, the Philosopher (De Gener. i, 5) distinguishes flesh belonging to the “species” from flesh belonging to “matter”; and says that the latter “comes and goes.” Now what is formed from food comes and goes. Therefore what is produced from food is flesh belonging to matter, not to the species. But what belongs to true human nature belongs to the species. Therefore the food is not changed into true human nature.
Objection 3. Further, the “radical humor” seems to belong to the reality of human nature; and if it be lost, it cannot be recovered, according to physicians. But it could be recovered if the food were changed into the humor. Therefore food is not changed into true human nature.
Objection 4. Further, if the food were changed into true human nature, whatever is lost in man could be restored. But man’s death is due only to the loss of something. Therefore man would be able by taking food to insure himself against death in perpetuity.
Objection 5. Further, if the food is changed into true human nature, there is nothing in man which may not recede or be repaired: for what is generated in a man from his food can both recede and be repaired. If therefore a man lived long enough, it would follow that in the end nothing would be left in him of what belonged to him at the beginning. Consequently he would not be numerically the same man throughout his life; since for the thing to be numerically the same, identity of matter is necessary. But this is incongruous. Therefore the food is not changed into true human nature.
On the contrary, Augustine says (De Vera Relig. xi): “The bodily food when corrupted, that is, having lost its form, is changed into the texture of the members.” But the texture of the members belongs to true human nature. Therefore the food is changed into the reality of human nature.
I answer that, According to the Philosopher (Metaph. ii), “The relation of a thing to truth is the same as its relation to being.” Therefore that belongs to the true nature of any thing which enters into the constitution of that nature. But nature can be considered in two ways: firstly, in general according to the species; secondly, as in the individual. And whereas the form and the common matter belong to a thing’s true nature considered in general; individual signate matter, and the form individualized by that matter belong to the true nature considered in this particular individual. Thus a soul and body belong to the true human nature in general, but to the true human nature of Peter and Martin belong this soul and this body.
Now there are certain things whose form cannot exist but in one individual matter: thus the form of the sun cannot exist save in the matter in which it actually is. And in this sense some have said that the human form cannot exist but in a certain individual matter, which, they said, was given that form at the very beginning in the first man. So that whatever may have been added to that which was derived by posterity from the first parent, does not belong to the truth of human nature, as not receiving in truth the form of human nature.
But, said they, that matter which, in the first man, was the subject of the human form, was multiplied in itself: and in this way the multitude of human bodies is derived from the body of the first man. According to these, the food is not changed into true human nature; we take food, they stated, in order to help nature to resist the action of natural heat, and prevent the consumption of the “radical humor”; just as lead or tin is mixed with silver to prevent its being consumed by fire.
But this is unreasonable in many ways.
Firstly, because it comes to the same that a form can be produced in another matter, or that it can cease to be in its proper matter; wherefore all things that can be generated are corruptible, and conversely. Now it is manifest that the human form can cease to exist in this (particular) matter which is its subject: else the human body would not be corruptible. Consequently it can begin to exist in another matter, so that something else be changed into true human nature.