(16) This article, together with the following four, find a parallel in I-II, 56, where the order is somewhat different. The treatment in both places is practically identical. Thomas' determination of the subject of virtue is one of his major contributions to the doctrine of the virtues in general. Indeed neither his predecessors nor his contemporaries approached this intricate question with the precision, coherence, or perspicuity evidenced in the Summa and in the articles of this Disputed Question.
Thomas has already proved that the virtues are immediately operative habits. From this it should be obvious that they do not reside in the essence of the soul, which operates only through its powers. In this regard, it is necessary to recall the distinction of the essence of the soul from its faculties: cf. I, 77, 1. Moreover, powers or faculties which are not indifferent as to good or bad operation, but completely determined to a single good, have no difficulty in performing their proper operations. Of this type are the external bodily members, the vegative powers, and the external senses: hence these cannot be the subject of virtue. Cf. Art. 1, Body, in the text, above. It remains, then, to consider but four powers of the soul, namely, the internal senses, the sense appetites, the will, and the intellect. This is the order followed by St. Thomas in Articles 3-7.
(17) Sacred Scripture locates virtues in various powers, e.g.: "God hath abolished the memory of the proud, and hath preserved the memory of them that are humble in mind." (Ecclus. 10/21): "My son, if thy mind be wise, my heart shall rejoice with thee" (Prov. 23/15); "Give me constancy in my mind, that I may despise him; and fortitude, that I may overthrow him." (Judith 9/14); "I am meek and humble of heart" (Matt. 11/29). In tradition, St. Augustine is concerned with proving that virtue is not in the body but in the soul, because the former is ruled by the latter. With St. Thomas clear and exact distinction is made of the subjects of all the virtues, and this distinction affords another penetration into the essence and grandeur of virtue. Virtue is seen as the power or faculty carried to its highest point of perfection. It is in the power an aptitude for or facility in action, a disposition for the best, i.e., for the full and complete realization of itself in action or in what is attained by means of action. Virtue, then is the great resource of life's activity.
(18) This question pertains largely to psychology, wherein its solution is found. Thus Father Brennan:
"As Aquinas points out, not all our powers are in need of habit, since some of them are disposed by their nature to operate well and successfully. Being determined to a single course of action or a single kind of stimulus, they are not in potentiality to many things. The eye, for example, sees light and nothing else. Its action is confined to the visual field, and the mode of its operation is fixed beforehand. This sort of determination is found in all our psychosomatic powers, where activity is impossible except through a material organ. Obviously, then, it is in the intellectual dimension that habit is properly lodged For here our powers are not determined to one. Light and sound, odor and tangibility, accident and substance are all so many objects of human understanding, just as any conceivable kind of good may attract the human will. And so, because our rational powers can act in indefinite ways, they have need of habit in order to act well in definite ways. Sense, for example, is directed to concrete and singular entities. Intellect, on the other hand, is directed to abstract and universal entities. Similarly, sensitive appetite is ordained to particular goods. Will, on the other hand, is ordained to good in general. While sense and sensitive appetite, therefore, do not require habits for their perfection, intellect and will can reach the operational excellence that is possible to them only through the acquisition of habits." Op. cit., pp. 265-66.
(19) "Substance, which is the subject of all accidents, receives some accidents through the medium of others, while others are caused by substantial principles by means of other accidents. Thus color is received through the medium of surface, while taste is caused from the principles of a mixed body by means of heat and cold. Hence the subject of an accident can be considered from two aspects. In one sense, it is the substance, which is the primary foundation for accidents; and under this aspect virtuous habits are not in powers as in their subject, but rather in the soul itself or in what is conjoined to it.
"In another sense, an accident through the medium of which another accident inheres in a substance is said to be the subject of the other accident, as surface is of color. And under this aspect, virtuous habits are said to be in the powers as in their subject; because habits are ordered to acts, and acts proceed from the essence of the soul by means of its powers." In III Sent. d. 33, q. 2, a. 4, sol 1 resp. ad 1.