We proceed to the fourth article thus:

1. It seems that grace is not in the soul's essence as its subject, but in one of its powers. For Augustine says (or another, in Hypognosticon 3): "grace is to the will, or free will, as a rider to his horse," and it was said in Q.88, Art.2, that the will, or the free will, is a power. It follows that grace is in a power of the soul as its subject.

2. Again, Augustine says (De Grat. et Lib. Arb.4): "a man's merits arise out of grace." But merit consists in action, and action proceeds from a power. It seems, then, that grace is a power of the soul.

3. Again, if the essence of the soul is the proper subject of grace, every soul which has an essence ought to be capable of receiving grace. But this is false, since it would follow that every soul was capable of receiving grace. Hence the essence of the soul is not the proper subject of grace.

4. Again, the soul's essence is prior to its powers, and what is prior can be conceived apart from that which depends on it. If grace were in its essence, therefore, we could conceive of a soul which possessed grace without possessing any part or any power, whether will, intellect, or anything of the kind. But this is impossible.

On the other hand: it is through grace that we are regenerated as sons of God. Now generation reaches the essence before it reaches the powers. It follows that grace is in the soul's essence before it is in its powers.

I answer: this question depends on the preceding question. If grace is the same as virtue, it must be in one of the soul's powers as its subject, since the proper subject of virtue is a power of the soul. But we cannot say that a power of the soul is the subject of grace if grace is not the same as virtue, because every perfection of a power of the soul has the nature of virtue, as we said in Qq.55, 56. Now grace is prior to virtue, and accordingly has a subject which is prior to the powers of the soul, such as the essence of the soul. Just as it is through the virtue of faith that a man partakes of the divine knowledge by means of the power of his intellect, and through the virtue of charity that he partakes of the divine love by means of the power of his will, so is it through regeneration or recreation of his soul's nature that he partakes of the divine nature by way of a certain likeness.

On the first point: just as the soul's essence is the source of the powers which are its principles of action, so is grace the source of the virtues which enter the powers of the soul, and move them to act. Hence grace is related to the will as a mover to a thing moved, which is the relation of a rider to his horse, not as an accident to its subject.

The answer to the second point is then clear. Grace is the principle of meritorious works through the medium of the virtues, just as the soul's essence is the principle of its vital operations through the medium of its powers.

On the third point: the soul is the subject of grace because it belongs to the species of the intellectual, or rational. But it is not on account of any of its powers that it belongs to this species. The powers of the soul are its natural properties, and are therefore consequential to its species. Because of its essence, the soul belongs to a different species from other souls, such as irrational animals and plants. That the human soul should be the subject of grace does not then imply that every soul should be so. A soul can be the subject of grace only if it is of a certain kind.

On the fourth point: since the powers of the soul are natural properties consequential to its species, a soul cannot exist without them. But supposing that it did exist without them, the soul would still be said to belong to the species of the intellectual, or rational, not as actually possessing such powers, but on the ground that its species was of the kind from which such powers are derived.