Chapter 49 — That the intellectual substance is not a body

From the foregoing it is shown that no intellectual substance is a body.

For no body is found to contain anything except by quantitative commensuration: therefore, if a thing contain a whole thing in the whole of itself, each part will contain a part, the greater part a greater part, and the lesser part a lesser part. But an intellect does not contain a thing understood by quantitative commensuration, because by its whole self it understands and comprehends both whole and part, things both great and small in quantity. Therefore, no intelligent substance is a body.

Moreover. No body can receive the substantial form of another body unless it lose its own form by corruption. But an intellect is not corrupted by receiving the forms of all bodies, but rather is perfected, since it is perfected by understanding, and understands by having in itself the forms of things understood. Therefore, no intellectual substance is a body.

Further. The principle of distinction between individuals of the same species is the division of matter in respect of quantity, for the form of this fire differs not from the form of that fire, except by the fact of its being in different parts into which matter is divided; nor is this otherwise than by division of quantity, without which substance is indivisible. Now that which is received into a body is received into it according to quantitative division. Therefore, a form is not received into a body, except as individualized. If, therefore, an intellect were a body, the intelligible forms of things would not be received into it except as individualized. But the intellect understands things by their forms which it has at its disposal. Consequently, the intellect would not understand universals, but only particulars. Now this is clearly false. Therefore, no intellect is a body.

Again. Nothing acts except in accordance with its species, because the form is the principle of action in everything. If, therefore, an intellect be a body, its action will not transcend the order of bodies. Therefore, it would understand nothing but bodies. Now this is clearly false, since we understand many things that are not bodies. Therefore, the intellect is not a body.

Again. If an intelligent substance is a body, it is either finite or infinite. Now, it is impossible for a body to be infinite actually, as is proved in the Physics. (Aristotle, Physics 3.5.) Therefore, it is a finite body, if we suppose it to be a body at all. But this is impossible, since in no body can there be infinite power, as we have proved above. (Bk. 1, ch. 20.) Now the power of the intellect in understanding is in a manner infinite, for by adding, it understands species of numbers to infinitude, and likewise species of figures and proportions. Moreover, it knows the universal, which is virtually infinite in its compass, since it contains individuals which are potentially infinite. Therefore, the intellect is not a body.

Moreover. It is impossible for two bodies to contain one another, since the container exceeds the contained. Yet two intellects contain and comprehend one another, when one understands the other. Therefore, the intellect is not a body.

Again. No body’s action reflects on the agent: for it is proved in the Physics (Aristotle, Physics 8.5.) that no body is moved by itself except in respect of a part (namely, so that one of its parts be mover and the other moved). Now the intellect by its action reflects on itself, for it understands itself not only as to a part, but as to the whole. Therefore, it is not a body.

Again. A body’s action is not the object of that body’s action, nor is its movement the object of its movement, as proved in the Physics. (Aristotle, Physics 5.2, 225b13–226a22.) But the action of the intellect is the object of its action: for just as the intellect understands a thing, so does it understand that it understands, and so on indefinitely. Therefore, an intellectual substance is not a body.

Hence it is that Sacred Scripture calls intellectual substances “spirits,” in which way it is accustomed to name God, who is incorporeal: God is a spirit (John 4:24). And it is said: for in her, namely divine wisdom, is the spirit of understanding, containing all intelligible spirits (Vulg., all spirits, intelligible, etc.) (Wis 7:23).

By this is excluded the error of the early natural philosophers, who held that there was none but corporeal substance: therefore, they said that even the soul is a body, either fire, air, or water, or something of the kind. (Aristotle, On the Soul 1.2.)

Which opinion some have endeavored to introduce into the Christian faith, by saying that the soul is the effigy of a body, like a body outwardly imitated.