Chapter 57 — The opinion of Plato concerning the union of the intellectual soul with the body

Moved by these and like reasons, some have asserted that no intellectual substance can be the form of a body. But since man’s very nature seemed to controvert this opinion, in that he appears to be composed of intellectual soul and body, they devised certain solutions so as to save the nature of man.

Accordingly, Plato and his school held that the intellectual soul is not united to the body as form to matter, but only as mover to movable, for he said that the soul is in the body as a sailor in a boat. (Aristotle, On the Soul 2.1, 413a6–8.) In this way, the union of soul and body would only be by virtual contact, of which we have spoken above. (Ch. 56.)

But this would seem inadmissible. For according to the contact in question, there does not result one thing simply, as we have proved. (Ch. 56.) However, there results a man from the union of soul and body. It follows, then, that a man is not one simply, and neither consequently a being simply, but accidentally.

In order to avoid this, Plato said that a man is not a thing composed of soul and body, but that the soul itself using a body (Plato, Alcibiades, bk. 1, 129e–130e.) is a man: thus Peter is not a thing composed of man and clothes, but a man using clothes.

But this is shown to be impossible. For animal and man are sensible and natural things. But this would not be the case if the body and its parts were not of the essence of man and animal, and the soul were the whole essence of both, as the aforesaid opinion holds: for the soul is neither a sensible nor a material thing. Consequently, it is impossible for man and animal to be a soul using a body, and not a thing composed of body and soul.

Again. It is impossible that there be one operation of things diverse in being. And in speaking of an operation being one, I refer not to that in which the action terminates, but to the manner in which it proceeds from the agent: for many persons rowing one boat make one action on the part of the thing done, which is one, but on the part of the rowers there are many actions, for there are many strokes of the oar. For it follows that things differing in forms and powers differ in action, since action is consequent upon form and power. Now, though the soul has a proper operation in which the body has no share (namely, intelligence), there are nevertheless certain operations common to it and the body, such as fear, anger, sensation, and so forth; for these happen by reason of a certain transmutation in a determinate part of the body, which proves that they are operations of the soul and body together. Therefore, from the soul and body there must result one thing, and they have not each a distinct being.

According to the opinion of Plato, this argument may be rebutted. For it is not impossible for mover and moved, though different in being, to have the same act, because the same act belongs to the mover as that from which it is, and to the moved as that in which it is. (Aristotle, Physics 3.3.) Therefore, Plato held that the aforesaid operations are common to the soul and body, namely, so that they are the soul’s as mover and the body’s as moved.

But this cannot be. For as the Philosopher proves in On the Soul 2: sensation results from our being moved by exterior sensibles. (Aristotle, On the Soul 2.5, 416b32–33; 417b19–20.) Therefore, a man cannot sense without an exterior sensible, just as a thing cannot be moved without a mover. Consequently, the organ of sense is moved and passive in sensing, but this is owing to the external sensible. And that by which it is passive is the sense, which is proved by the fact that things devoid of sense are not passive to sensibles by the same kind of passion. Therefore, sense is the passive power of the organ. Consequently, the sensitive soul is not as mover and agent in sensing, but as that by which the patient is passive. And this cannot have a distinct being from the patient. Therefore, the sensitive soul has not a distinct being from the animate body.

Further. Although movement is the common act of mover and moved, yet it is one operation to cause movement and another to receive movement; hence we have two predicaments, action and passion. (Aristotle, Categories, ch. 2, 1a29–b2; ch. 4, 1b26–2a3.) Accordingly, if the sensitive soul is in the position of agent in sensing, and the body in that of patient, the operation of the soul will be other than the operation of the body. Consequently, the sensitive soul will have an operation proper to it: and therefore it will have its proper subsistence. Hence when the body is destroyed, it will not cease to exist. Therefore, sensitive souls even of irrational animals will be immortal: which seems improbable. And yet it is not out of keeping with Plato’s opinion. But there will be a place for inquiring into this further on. (Ch. 82.)

Moreover. The movable does not derive its species from its mover. Consequently, if the soul is not united to the body except as mover to movable, the body and its parts do not take their species from the soul. Therefore, at the soul’s departure, the body and its parts will remain of the same species. Yet this is clearly false: for flesh, bone, hands, and like parts are so called only equivocally after the soul’s departure, (Aristotle, On the Parts of Animals 1.1.) since none of these parts retains its proper operation that results from the species. Therefore, the soul is not united to the body merely as mover to movable, or as man to his clothes.

Further. The movable does not have being through its mover, but only movement. Consequently, if the soul be united to the body merely as its mover, the body will indeed be moved by the soul, but will not have being through it. But in the living thing to live is to be. (Aristotle, On the Soul 2.4, 415b13–14.) Therefore, the body would not live through the soul.

Again. The movable is neither generated through the mover’s application to it nor corrupted by being separated from it, since the movable depends not on the mover for its being, but only in the point of being moved. If, then, the soul be united to the body merely as its mover, it will follow that neither in the union of soul and body will there be generation, nor corruption in their separation. And thus death, which consists in the separation of soul and body, will not be the corruption of an animal, which is clearly false.

Further. Every self-mover is such that it is in it to be moved and not to be moved, to move and not to move. (Aristotle, Physics 8.4, 254b14–26.) Now the soul, according to Plato’s opinion, moves the body as a self-mover. (Plato, Phaedrus 245c–e.) Consequently, it is in the soul’s power to move the body and not to move it. Therefore, if it be united to it merely as mover to movable, it will be in the soul’s power to be separated from the body at will, and to be reunited to it at will: which is clearly false.

That the soul is united to the body as its proper form is proved thus. That by which a thing, from being potentially, is made an actual being, is its form and act. Now the body is made by the soul an actual being from existing potentially, since to live is the being of a living thing. (Aristotle, On the Soul 2.4, 415b13–14.) But the seed before animation is only a living thing in potency, and is made an actually living thing by the soul. Therefore, the soul is the form of the animated body.

Moreover. Since both being and operation belong neither to the form alone, nor to the matter alone, but to the composite, being and action are ascribed to two things, one of which is to the other as form to matter; for we say that a man is healthy in body and in health, and that he is knowing in knowledge and in his soul, in which knowledge is a form of the soul knowing, and health of the healthy body. Now “to live” and “to sense” are ascribed to both soul and body, for we are said to live and sense both in soul and body, but by the soul as by the principle of life and sensation. Therefore, the soul is the form of the body.

Further. The whole sensitive soul has to the whole body the same relation as part to part. Now part is to part in such a way that it is its form and act, for sight is the form and act of the eye. Therefore, the soul is the form and act of the body.