Commentaria in Summam contra Gentiles, Liber II

Since it has been shown that some spiritual substance is united to a body, Saint Thomas shows, in the last place, to what kind of body it is united ¹.

I. And he states this conclusion: To no other elementary body than the human is an intellectual substance united as form. But why he speaks only of the elementary body, he makes clear by saying that this is so because, concerning the heavenly bodies—namely, whether they are animated by an intellectual soul—it was shown above what Aristotle held; and that Augustine leaves this in doubt.

It is argued, however, thus. It is not united to a mixed body. Nor to a simple one ². Therefore, etc.

That it is not mixed is proved. For a mixed body possessing the most noble form, such as an intellectual substance, must be most temperate: since we see that mixed bodies have the more noble forms the more they attain to the temperament of the mixture; on account of which we see that the softness of flesh and the goodness of touch, which demonstrate an equality of complexion, are signs of a good intellect. But the complexion most equal is the complexion of the human body. Therefore, if an intelligible substance is united to a mixed body, that body will be of the same nature as the human body. Similarly, the form will be of the same nature as the human soul. Therefore, between that animal and man there will be no difference according to species.

Note that Saint Thomas wishes to conclude, from the identity of the nature of perfect bodies with intellectual substance, that the intellectual substances themselves are of the same nature, namely, that they are intellective souls: for, since form is proportioned to matter, where matters are of the same nature, the intellectual forms themselves must also be of the same nature, as exercising the same operations in a similar body. And thus it follows that each composite is of the same species. And consequently the intellectual substance itself is united to no other mixed body than the human one.

II. That it is not united to a simple body is argued first as follows. If some part of a simple body, say air, were animated by an intellectual soul, the whole air and any part of it would be animated: for a body of this kind is uniform in the whole and in its parts, since it is of one species, as is evident from the identity of its motion; for like things moved (namely, naturally) are owed like forms. But this is manifestly false, since no operation of life appears in it. Likewise neither in the other elements. Therefore, and so on.

Concerning what is said, that the whole air and any part of it are of the same nature and species, it must be noted that parts being of the same species as the whole can be understood in two ways. In one way, because they are certain things complete in species, to which the perfect ratio of a whole belongs, and by mere division they can become individuals of the same species as the whole itself. And thus the parts of an element are said to be of the same species as the whole element: for just as the whole air is air, so any part of air is air, and by mere division a part of air can be a per se individual of air. And this is common to every homogeneous whole. — In another way, because they belong to the same species by reduction to that to which the whole belongs, even though they themselves do not have the complete ratio of that species. And thus the parts of a heterogeneous whole are of the same species as the whole, as its principles, whether material or formal: for although neither flesh nor bone is a man, they nevertheless belong to the human species as material principles. Hence when Saint Thomas sometimes says that a homogeneous whole differs from a heterogeneous whole because the parts of the homogeneous have the species and form of the whole, but not the parts of the heterogeneous, this is understood according to the first way of having the same form and species; but not according to the second way.

III. Second. That substance would not have intellect alone. For it would be united to a body in vain, since it would have no operation through the body; nor, I say, would it understand or will, for these are not exercised through an organ of the body; nor move, for the elements do not move themselves, but their motions come from what generates them, and consequently they are not animate. — Nor would it have the other parts of the soul. For, since those are parts of certain organs, there would have to be a diversity of organs in the element, which is repugnant to its simplicity. — Therefore etc.

Third. The elements are bodies of lesser nobility in their species than mixed bodies, because they are closer to prime matter and consequently more in potency and less in complete act. And the intellective soul is the noblest form. Therefore etc. — The consequence is proved: because the nobler body has the nobler form.

Note that, when Saint Thomas said that the elements are less noble than mixed bodies, he added "according to species," because they are not less noble in every respect. For, as is said in IV Sent., d. xlvii, q. ii, a. 1, quª 1, ad 3, with regard to perfection of species, a mixed body is nobler than an element; but with regard to permanence of duration, on the contrary, a simple body is nobler than a mixed one.

3. Fourth. It would be necessary that bodies, the nearer they were to the elements, the closer they would be to life. But the opposite appears: for plants have less of life than animals, and yet they are nearer to the earth; and minerals, which are still nearer to the earth, have even less of life. Therefore, etc.

Attend to the fact that the foundation of this argument is that the closer something approaches to what is most perfect, the more perfect it is. And therefore, since the element, if it were granted an intellective soul, would have life most perfectly among lower animate things, it follows very well that the closer any body comes to the element, the more perfectly it has life.

Fifth. In the elements there are the excellences of hot and cold, wet and dry. Therefore, etc. — The consequence is proved: because the life of all corruptible living things is destroyed through the excellence of contrariety, and consequently it is impossible for there to be life in them.

VI. Sixth. If certain parts of an element had substantial unities of their own endowed with cognition, touch would be assigned to them above all, since it is the sense that discerns hot and cold and the other contrarieties that corrupt, and it is present in all animals for preservation from corrupting things; because the parts of an element are corruptible, inasmuch as they possess contrariety, even though the element as a whole is incorruptible. But this sense cannot belong to a simple body: for the organ of touch must not have the contrarieties in act but in potency, which belongs only to tempered mixtures. Therefore, and so on.

Concerning this proposition of the Elements, that although they are incorruptible as a whole, yet the individual parts are corruptible, inasmuch as they possess contrariety, it must be noted that Saint Thomas does not say this as though the parts of an element possessed contrariety while the whole element did not; for this is false, since the qualities of the elements by which contrariety is attended to belong prior to the whole than to the parts, inasmuch as they follow upon the form of the element. Rather, he says this because, since the element possesses contrariety, by reason of which it is corruptible by its contrary; and since it is not corruptible as a whole, because, as is said in II Sent., d. xix, a. 2, ad 2, and de Malo, q. v, a. 5, ad 6, the elements are governed by the power of the heavenly body, by which their actions are regulated, therefore it is corruptible according to its parts.

It may also be said that the parts of an element have contrariety, but not the whole element, with respect to the exercise of contrariety. For although one element, speaking absolutely, is contrary to another by reason of the primary qualities, nevertheless one does not exercise contrariety against the other acting with respect to the whole—that is, toward its destruction—but only with respect to certain parts, in accordance with which the elements are transmuted into one another.

V. Seventh. In the elements no local motion that is from a soul appears, but only natural motion. Therefore, etc.—The consequence is proved. Because every living body is in some way moved locally according to soul: as is evident in the heavenly bodies, if they are animate; and in animals, both perfect and imperfect; and in plants, which are moved by the motion of growth and diminution, which are in some way according to place.

It must be known that the motions of increase and decrease, in themselves and primarily, are not local motions. For local motion is toward something extrinsic to the mobile thing, namely toward place, which is in the container and not in the contained; or, if it is toward an intrinsic "where," which is a certain relation consequent upon the containment of the contained by place, that "where" is nevertheless not quantity. But the motion of increase is toward a quantity intrinsic to the thing increased or diminished. — Consecutively, however, and secondarily, they are local motions: insofar as what through increase acquires greater quantity occupies a greater place than it occupied before; and acquiring lesser quantity through decrease, it occupies a lesser place than before. On account of this, Saint Thomas did not say absolutely that every living thing is moved locally by the soul, nor that the motions of increase and decrease are according to place: but he added something to each proposition in some way.

VI. But to all the arguments set out above it might be said that an intellectual substance is indeed not united to an element or a part of it as form, as the arguments prove; yet it is united to it as mover. Against this Saint Thomas argues.

First, concerning air. No part of air is of itself terminable. Therefore no determinate part of it can have its own proper motion, on account of which an intellectual substance would be united to it.

It must be noted that a part of air is said not to be terminable of itself, because, being a moist body, it flows until it is terminated by something extrinsic; and if it were separated from the whole, it would not be figurable in itself, so as to retain any figure from itself, but takes on various figures according as it is terminated by different bodies. From this it follows that, if left to itself with no other body interposed, it cannot be distinguished from the surrounding air. And since everything moved by its own motion has its own termini and its own figure distinct from every other, therefore a part of air cannot have any proper and singular motion naturally suited to it, in the way we say the heaven is moved naturally by the inclination of its form by an intelligence appropriated to it—although a part of air can be moved by an intelligence as by an agent wholly extrinsic and separate, one separating and dividing it from the rest of the air.

Second. It would follow that an intellectual substance, in moving, would not exceed some determinate part of some element: for the power of the moving substance must be limited to the movable body to which it is naturally united as its proper movable body. But this is ridiculous. And likewise that it would not exceed in moving any mixed body: namely, one of which it is not the form. Therefore, etc.

Third. Because, since elemental motions can be caused from other principles, it would be superfluous for intellectual substances to be united to the elements on account of motions of this kind.

VII. From these things is excluded the error of Apuleius and of certain Platonists, who say that demons are animals with an aerial body, etc. — Likewise the error of the pagans, who hold that the elements are animate. — Likewise also the error of those who say that angels and demons have bodies naturally united to them, of the nature of the higher and lower elements.