Chapter 90 — That an intellectual substance is united as a form to no other than the human body

Since it has been proved (Ch. 68.) that a certain intellectual substance (namely, the human soul) is united to a body as its form, it remains for us to ask whether any intellectual substance can be united as form to any other body. Indeed, as regards heavenly bodies, we have shown above (Ch. 70.) what was Aristotle’s opinion as to their being animated with an intellective soul, and that Augustine leaves the question unsolved. Therefore, the present inquiry must be confined to elemental bodies.

That an intellectual substance is not united as form to any elemental body save that of man is evidently clear. For were it united to some other, it would be united either to a mixed or to a simple body. But it cannot be united to a mixed body, because that body, in respect of its genus, would have to surpass other mixed bodies in evenness of temperament, since we see that mixed bodies have forms so much the more noble the nearer they approach to an even temperament. Thus, if that which has a most noble form (such as an intellectual substance) be a mixed body, it must have a most even temperament. For this reason we find that a soft flesh and a delicate touch are signs of a keen understanding. (Aristotle, On the Soul 2.9, 421a22–26.) Now the most even temperament is that of the human body. Consequently, if an intellectual substance be united to a mixed body, the latter must have the same nature as the human body. Moreover, its form would be of the same nature as the human soul if it were an intellectual substance. Therefore, there would be no specific difference between that animal and man.

Again, neither can an intellectual substance be united as form to a simple body, such as air, water, fire, or earth. For each of these bodies is similar in the whole and in the parts, since a part of air has the same nature and species as the whole air, for it has the same movement, and the same applies to the others. Now like movers have like forms. Accordingly, if any part of any one of the aforesaid bodies (air, for instance) be animated with an intellectual soul, for the same reason the whole air and all its parts will be animated. But this is seen clearly to be false, because there is no sign of vital operations in the parts of the air or of other simple bodies. Therefore, an intellectual substance is not united as form to any part of the air or of similar bodies.

Again. If an intellectual substance be united as form to one of the simple bodies, it will have either an intellect only, or it will have other powers (for instance, those which belong to the sensitive or to the nutritive part, as in man). If it have the intellect only, there is no use in its being united to the body. For every form of a body exercises a proper operation through the body. And the intellect has no operation pertaining to the body, except insofar as it moves the body: because understanding is not an operation that can be exercised by an organ of the body; nor is willing, for the same reason. Again, the movements of the elements are from natural movers—namely, their generators—and they do not move themselves. Therefore, it does not follow that they are animated because they have movement. If, on the other hand, the intellectual substance, which is supposed to be united to an element or to a part of one, have other parts of the soul, since these parts are parts of certain organs, it follows that we shall find diversity of organs in the body of the element. But this is inconsistent with its simplicity. Therefore, an intellectual substance cannot be united as form to an element or to a part of one.

Moreover. The nearer a body is to prime matter, the less noble it is, according as it is more in potency and less in complete act. Now the elements are nearer than mixed bodies to prime matter, since they are the proximate matter of mixed bodies. Consequently, the elemental bodies are less noble than mixed bodies as to their species. Therefore, since the more noble bodies have more noble forms, it is impossible that the noblest form of all, which is the intellective soul, be united to the bodies of the elements.

Again. If the elemental bodies or any parts of them were animated by the noblest kind of soul, which is the intellective soul, it would follow that the more akin a body is to the elements, the nearer it approaches to life. Now this does not appear to be the case, but rather the contrary: for plants have less of life than animals, and yet they are more akin to earth; while minerals, which are still more akin, have no life at all. Therefore, an intellectual substance is not united as form to an element or to a part of one.

Further. Exceeding contrariety is destructive of life in all corruptible movers: for excessive heat or cold, wet or dryness, are fatal to animals and plants. Now these contraries exceed especially in the elemental bodies. Therefore, life cannot possibly be in them. Therefore, it is impossible for an intellectual substance to be united to them as their form.

Moreover. Although the elements are incorruptible as a whole, each of their parts is corruptible as having contrariety. If, therefore, some parts of the elements have cognitive substances united to them, it seems that the power of discerning corruptives should especially be ascribed to them. Now this is the sense of touch, which discriminates between hot and cold and like contraries: and for this very reason it is in all animals, as though it were necessary for preservation from corruption. But this sense cannot possibly be in a simple body, since the organ of touch needs to have contraries not actually but potentially, and this is the case only in mixed and tempered bodies. Therefore, it is not possible that any parts of the elements be animated with an intellective soul.

Again. Every living body has some kind of local movement proceeding from its soul: for the heavenly bodies (if indeed they be animated) (See the beginning of this chapter.) have a circular movement; perfect animals a progressive movement; oysters a movement of expansion and contraction; plants a movement of increase and decrease—all of which are kinds of local movement. Whereas in the elements there is no sign of movement proceeding from a soul, but only such as is natural. Therefore, they are not living bodies.

If, however, it be said that although an intellectual substance be not united as a form to an elemental body or part thereof, yet it is united to it as its mover, the first is impossible if applied to the air. For, since a part of the air has no bounds of its own, no determinate part of the air can have its own proper movement on account of which an intellectual substance be united to it.

Moreover. If an intellectual substance be naturally united to a body as a mover to its proper movable, the motive power of that substance must be confined to the movable body to which it is naturally united; since the power of every proper mover does not, in moving, go beyond its proper movable. Now it seems absurd to say that the power of an intellectual substance does not, in moving, exceed a determinate part of an element, or some mixed body. Therefore, it seems that an intellectual substance must not be said to be naturally united to an elemental body as its mover, unless it be united to it also as its form.

Again. The movement of an elemental body can proceed from other principles besides an intellectual substance. Therefore, this movement is not a sufficient reason for intellectual substances to be naturally united to elemental bodies.

By this is excluded the opinion of Apuleius and certain Platonists, who asserted that the demons are animals with an aerial body, a rational mind, passive in soul, and eternal in duration, and that of certain heathens who held the elements to be animated (and thus they offered them divine worship). (Cf. ch. 49.) Again, the opinion is refuted of those who said that angels and demons have bodies naturally united to them, which respectively partake of the nature of the higher or lower elements.

Separate substances