Objection 1: It would seem that there is no order among the powers of the soul. For in those things which come under one division, there is no before and after, but all are naturally simultaneous. But the powers of the soul are contradistinguished from one another. Therefore there is no order among them.
Objection 2: Further, the powers of the soul are referred to their objects and to the soul itself. On the part of the soul, there is not order among them, because the soul is one. In like manner the objects are various and dissimilar, as color and sound. Therefore there is no order among the powers of the soul.
Objection 3: Further, where there is order among powers, we find that the operation of one depends on the operation of another. But the action of one power of the soul does not depend on that of another; for sight can act independently of hearing, and conversely. Therefore there is no order among the powers of the soul.
On the contrary, The Philosopher (De Anima ii, 3) compares the parts or powers of the soul to figures. But figures have an order among themselves. Therefore the powers of the soul have order.
I answer that, Since the soul is one, and the powers are many; and since a number of things that proceed from one must proceed in a certain order; there must be some order among the powers of the soul. Accordingly we may observe a triple order among them, two of which correspond to the dependence of one power on another; while the third is taken from the order of the objects. Now the dependence of one power on another can be taken in two ways; according to the order of nature, forasmuch as perfect things are by their nature prior to imperfect things; and according to the order of generation and time; forasmuch as from being imperfect, a thing comes to be perfect. Thus, according to the first kind of order among the powers, the intellectual powers are prior to the sensitive powers; wherefore they direct them and command them. Likewise the sensitive powers are prior in this order to the powers of the nutritive soul.
In the second kind of order, it is the other way about. For the powers of the nutritive soul are prior by way of generation to the powers of the sensitive soul; for which, therefore, they prepare the body. The same is to be said of the sensitive powers with regard to the intellectual. But in the third kind of order, certain sensitive powers are ordered among themselves, namely, sight, hearing, and smelling. For the visible naturally comes first; since it is common to higher and lower bodies. But sound is audible in the air, which is naturally prior to the mingling of elements, of which smell is the result.
Reply to Objection 1: The species of a given genus are to one another as before and after, like numbers and figures, if considered in their nature; although they may be said to be simultaneous, according as they receive the predication of the common genus.
Reply to Objection 2: This order among the powers of the soul is both on the part of the soul (which, though it be one according to its essence, has a certain aptitude to various acts in a certain order) and on the part of the objects, and furthermore on the part of the acts, as we have said above.
Reply to Objection 3: This argument is verified as regards those powers among which order of the third kind exists. Those powers among which the two other kinds of order exist are such that the action of one depends on another.
Whether all the powers of the soul are in the soul as their subject?
Objection 1: It would seem that all the powers of the soul are in the soul as their subject. For as the powers of the body are to the body; so are the powers of the soul to the soul. But the body is the subject of the corporeal powers. Therefore the soul is the subject of the powers of the soul.
Objection 2: Further, the operations of the powers of the soul are attributed to the body by reason of the soul; because, as the Philosopher says (De Anima ii, 2), "The soul is that by which we sense and understand primarily." But the natural principles of the operations of the soul are the powers. Therefore the powers are primarily in the soul.
Objection 3: Further, Augustine says (Gen. ad lit. xii, 7,24) that the soul senses certain things, not through the body, in fact, without the body, as fear and such like; and some things through the body. But if the sensitive powers were not in the soul alone as their subject, the soul could not sense anything without the body. Therefore the soul is the subject of the sensitive powers; and for a similar reason, of all the other powers.
On the contrary, The Philosopher says (De Somno et Vigilia i) that "sensation belongs neither to the soul, nor to the body, but to the composite." Therefore the sensitive power is in "the composite" as its subject. Therefore the soul alone is not the subject of all the powers.
I answer that, The subject of operative power is that which is able to operate, for every accident denominates its proper subject. Now the same is that which is able to operate, and that which does operate. Wherefore the "subject of power" is of necessity "the subject of operation," as again the Philosopher says in the beginning of De Somno et Vigilia. Now, it is clear from what we have said above (Q[75], AA[2],3; Q[76], A[1], ad 1), that some operations of the soul are performed without a corporeal organ, as understanding and will. Hence the powers of these operations are in the soul as their subject. But some operations of the soul are performed by means of corporeal organs; as sight by the eye, and hearing by the ear. And so it is with all the other operations of the nutritive and sensitive parts. Therefore the powers which are the principles of these operations have their subject in the composite, and not in the soul alone.
Reply to Objection 1: All the powers are said to belong to the soul, not as their subject, but as their principle; because it is by the soul that the composite has the power to perform such operations.
Reply to Objection 2: All such powers are primarily in the soul, as compared to the composite; not as in their subject, but as in their principle.
Reply to Objection 3: Plato's opinion was that sensation is an operation proper to the soul, just as understanding is. Now in many things relating to Philosophy Augustine makes use of the opinions of Plato, not asserting them as true, but relating them. However, as far as the present question is concerned, when it is said that the soul senses some things with the body, and some without the body, this can be taken in two ways. Firstly, the words "with the body or without the body" may determine the act of sense in its mode of proceeding from the sentient. Thus the soul senses nothing without the body, because the action of sensation cannot proceed from the soul except by a corporeal organ. Secondly, they may be understood as determining the act of sense on the part of the object sensed. Thus the soul senses some things with the body, that is, things existing in the body, as when it feels a wound or something of that sort; while it senses some things without the body, that is, which do not exist in the body, but only in the apprehension of the soul, as when it feels sad or joyful on hearing something.
Whether the powers of the soul flow from its essence?
Objection 1: It would seem that the powers of the soul do not flow from its essence. For different things do not proceed from one simple thing. But the essence of the soul is one and simple. Since, therefore, the powers of the soul are many and various, they cannot proceed from its essence.
Objection 2: Further, that from which a thing proceeds is its cause. But the essence of the soul cannot be said to be the cause of the powers; as is clear if one considers the different kinds of causes. Therefore the powers of the soul do not flow from its essence.
Objection 3: Further, emanation involves some sort of movement. But nothing is moved by itself, as the Philosopher proves (Phys. vii, 1,2); except, perhaps, by reason of a part of itself, as an animal is said to be moved by itself, because one part thereof moves and another is moved. Neither is the soul moved, as the Philosopher proves (De Anima i, 4). Therefore the soul does not produce its powers within itself.
On the contrary, The powers of the soul are its natural properties. But the subject is the cause of its proper accidents; whence also it is included in the definition of accident, as is clear from Metaph. vii (Did. vi, 4). Therefore the powers of the soul proceed from its essence as their cause.
I answer that, The substantial and the accidental form partly agree and partly differ. They agree in this, that each is an act; and that by each of them something is after a manner actual. They differ, however, in two respects. First, because the substantial form makes a thing to exist absolutely, and its subject is something purely potential. But the accidental form does not make a thing to exist absolutely but to be such, or so great, or in some particular condition; for its subject is an actual being. Hence it is clear that actuality is observed in the substantial form prior to its being observed in the subject: and since that which is first in a genus is the cause in that genus, the substantial form causes existence in its subject. On the other hand, actuality is observed in the subject of the accidental form prior to its being observed in the accidental form; wherefore the actuality of the accidental form is caused by the actuality of the subject. So the subject, forasmuch as it is in potentiality, is receptive of the accidental form: but forasmuch as it is in act, it produces it. This I say of the proper and "per se" accident; for with regard to the extraneous accident, the subject is receptive only, the accident being caused by an extrinsic agent. Secondly, substantial and accidental forms differ, because, since that which is the less principal exists for the sake of that which is the more principal, matter therefore exists on account of the substantial form; while on the contrary, the accidental form exists on account of the completeness of the subject.
Now it is clear, from what has been said (A[5]), that either the subject of the soul's powers is the soul itself alone, which can be the subject of an accident, forasmuch as it has something of potentiality, as we have said above (A[1], ad 6); or else this subject is the composite. Now the composite is actual by the soul. Whence it is clear that all the powers of the soul, whether their subject be the soul alone, or the composite, flow from the essence of the soul, as from their principle; because it has already been said that the accident is caused by the subject according as it is actual, and is received into it according as it is in potentiality.