Reply Obj. 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 Obj. 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 Obj. 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. _______________________
SIXTH ARTICLE [I, Q. 77, Art. 6]
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.
Obj. 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.
Obj. 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.