Commentaria in Summam contra Gentiles, Liber II

Having shown that the intellectual soul is immediately united to the body, it remains to show that it is whole in the whole and in every part¹. On this point Saint Thomas does two things: first, he establishes the proposition; second, he excludes certain objections².

I. As to the first point: since the conclusion has two parts, namely that the soul is in the whole and in every part, and that it is whole in those parts: first, he proves the first part; second, the second³.

He proves the first part. And first, that it is in the whole. The soul is the act of an organic body, not of one organ alone. Therefore it is in the whole, and not in one part only, according to its essence, according to which it is the form of the body. — The consequence is proved. Because a proper act must be in its proper perfectible.

That it is in all the parts is argued as follows. It is the form of the individual parts. Therefore it is in all the parts. — The consequence is proved: because an act is in that of which it is the act. — The antecedent, too, is proved: because otherwise it would not be the substantial form of such a body, but an accidental one; just as the form of a house, which is the form of the whole and not of the individual parts, is an accidental form. But this is false: rather, the soul is the substantial form of both the whole and the parts, since from it both the whole and the parts receive their species. This is evident from the fact that when it departs, neither the whole nor the parts remain of the same species: for the eye and flesh of a corpse are called by these names only equivocally. Therefore, etc.

In the proof of the antecedent, it must be noted that it is not inferred that if the soul is not the form of the parts of the body, then it is an accidental form, as though no accidental form were the form of the whole and of the parts — for this is false: whiteness is the form of the whole and of the parts, as is said here. Rather, it is because every form of a whole that is not the form of the parts is an accidental form. For as is said in the First Part, question 76, article 8, since a whole consists of its parts, the form of the whole that does not give esse to each of the parts of the body is a form that is composition and order, as is the form of a house. But such a form is an accidental form.

II. For the second part of the conclusion, Saint Thomas notes first that there is a twofold whole: namely, one according to quantity, and another according to the perfection of the essence. — Second, he notes that the first totality belongs to forms only per accidens, insofar as they are divided by the division of a quantified subject; but the second totality belongs to them per se. — Third, he notes that if there is some form which is not divided by the division of a subject, as is the case with the souls of perfect animals, only the second totality belongs to it, and not the first. And it is of this form that the conclusion speaks.

Note here that Saint Thomas holds not only the intellectual soul to be inextended, but also the souls of the more perfect animals, leaving it that the souls of the less perfect animals are extended and divisible. For the reason for this, see Prima Pars, question 76, article 8.

The second part of the conclusion is therefore proved by the example of whiteness, which, just as it is in the whole according to the entire rationale of whiteness, so also is it in the part. Therefore, similarly, the soul is in the whole and in the parts according to its whole essence. But there does not belong to it another kind of wholeness, namely that which is according to quantity. Therefore it must be said absolutely that it is whole in the whole, and whole in each part.

III. Concerning the totality of the soul's essence, a doubt arises. For as is said here, "whole" is said by relation to parts. Therefore that which is whole according to essence must have parts of essence. But the soul has no parts of essence, since it is a simple essence. Therefore it does not have totality of essence, so as to be able to be said to be whole in the whole and in each of the parts.

To this, according to the doctrine of Saint Thomas, a twofold answer can be given. First, that the parts of essence are twofold: some are real parts, really composing the essence, as matter and form are parts of a material essence; but others are parts of reason and of definition, as genus and difference. The soul, therefore, has parts of reason and of definition, but not real parts. And in this way it is understood here that the soul has the totality of essence, insofar as it has the parts of its definition, in the manner in which a definition belongs to the soul. — That it is to be understood thus is evident: for, speaking of whiteness, as to how it is whole in the whole and whole in any part, he says that it is present according to the whole ratio of whiteness in the whole and in the parts; where it is clear that by the totality of essence he understands the totality of the ratio.

A second answer can be given: although "whole" is said by relation to its parts insofar as whole means composed of parts, yet insofar as whole is the same as perfect, it does not signify a relation to parts, but is said absolutely. And thus the soul is said to have totality of essence inasmuch as it has its essential perfection. And according to that it is in every part of the body and in the whole. We can draw this answer from the words of St. Thomas in Qu. de Anima, art. 10, where he says that totality of essence belongs even to simple essences, by reason of their perfection: because just as composites have a perfect species from the conjunction of their essential principles, so simple substances and forms have a perfect species through themselves — understand species here to mean entity and proper nature.

IV. As to the second point ⁴, four objections that might be raised against this determination are removed.

A first objection could be raised. The soul is indivisible. Therefore it cannot exist except in something indivisible. Therefore it is not in the whole body and in any part of it.

It is answered that the consequence would be true of an indivisible in the manner of a point having position within a continuum, but not of an indivisible by abstraction from the whole genus of continuum—that is, in the way the soul is indivisible, as is said in the Spiritualibus, article 4, ad 16.

2. The second objection may be this. That which is joined as a whole to one thing cannot be joined as a whole to another, separated from it. For it is evident that a body which is joined to the hand, entire in itself, is not joined to the foot. Therefore, if the soul is entire in the hand, it will not be able to be in the foot.

It is answered that the major premise is true of the conjunction of bodies, but not of the conjunction by which an incorporeal thing is joined to a body.

3. A third objection can be made. Form is proportionate to matter. But the soul is a simple form. Therefore simple matter corresponds to it, and not manifold matter. But the diverse parts of the body stand to one another as manifold matter. Therefore the soul is not the form of any part of the body.

It is answered that the soul, although it is simple in its essence, is nevertheless multiple in virtue and power, and is the principle of many operations: for the nobler and more perfect a form is, the greater its power. Now the soul is the noblest among inferior forms. And therefore it needs diverse organs to carry out its operations.

Two things must be noted here. The first is that matter exists not only for the esse of the form, but also for its operations. And therefore it must be proportioned not only to the esse of the form, but also to its operations: namely, such that it is apt for all the operations of the form to be exercised through that matter. Hence, although the soul is simple in essence, since it is nevertheless the principle of many operations, its matter must have a multiplicity of organs. And herein consists the answer given.

The second is that, although it is universally true that the nobler and more perfect a form is, the greater its power—for power follows the essence of a thing—it is not nevertheless universally true that the nobler and more perfect a form is, the more multiplied it is in powers and in diversity of operations. For if we suppose the heavenly bodies to be ensouled, their souls are more perfect than the human intellective soul; and yet they have only intellective powers, whereas the human soul has sensitive and vegetative ones as well. But this is true among the forms of corruptible things: for we see that the sensitive soul has vegetative and sensitive powers, while the vegetative has only vegetative ones; and again, the soul of man, besides the sensitive and vegetative, also has intellective powers. Therefore Saint Thomas did not say simply that the soul is the noblest among forms, but that it is the most noble among inferior forms. And in On Spiritual Creatures, article 4, where the same opinion is found, the comparison is made only among the forms of corruptible things, where it is said that in these corruptible things the more imperfect forms, which are of weaker power, have few operations; but the soul, since it is of greater and higher power, can be the principle of diverse operations.

4. A fourth objection could be raised, because Aristotle, in the Book on the Cause of the Movement of Animals, says that the soul is only in a certain principle of the body ⁵. Therefore it is not in every part.

It is answered that, since the soul exercises diverse operations through diverse powers, which are the acts of different parts of the body, it is said to be in one part only according to one power, but not in the others: although it is in all of them according to its essence. And for this reason Aristotle said, in the passage cited, that the soul is in only one part of the body: because there he was speaking of the motive power, according to which the soul is only in the heart, by which it moves the whole body. But he did not mean that it is in only one part according to its essence.

You have this matter most fully explained by Saint Thomas in the First Part ⁶, in the Questions on the Soul ⁷, and On Spiritual Creatures ⁸, and also in Book I of the Sentences ⁹. Therefore one need not dwell upon it any further.