Reply to Objection 3: As the Philosopher says (Phys. ii, text. 89; Ethic. vii, 8), the end is, in practical matters, what the principle is in speculative matters. Consequently diversity of ends demands a diversity of virtues, even as diversity of active principles does. Moreover the ends are objects of the internal acts, with which, above all, the virtues are concerned, as is evident from what has been said (Q[18], A[6]; Q[19], A[2], ad 1; Q[34], A[4]).
Whether habits are divided into good and bad?
Objection 1: It would seem that habits are not divided into good and bad. For good and bad are contraries. Now the same habit regards contraries, as was stated above (A[2], OBJ[1]). Therefore habits are not divided into good and bad.
Objection 2: Further, good is convertible with being; so that, since it is common to all, it cannot be accounted a specific difference, as the Philosopher declares (Topic. iv). Again, evil, since it is a privation and a non-being, cannot differentiate any being. Therefore habits cannot be specifically divided into good and evil.
Objection 3: Further, there can be different evil habits about one same object; for instance, intemperance and insensibility about matters of concupiscence: and in like manner there can be several good habits; for instance, human virtue and heroic or godlike virtue, as the Philosopher clearly states (Ethic. vii, 1). Therefore, habits are not divided into good and bad.
On the contrary, A good habit is contrary to a bad habit, as virtue to vice. Now contraries are divided specifically into good and bad habits.
I answer that, As stated above (A[2]), habits are specifically distinct not only in respect of their objects and active principles, but also in their relation to nature. Now, this happens in two ways. First, by reason of their suitableness or unsuitableness to nature. In this way a good habit is specifically distinct from a bad habit: since a good habit is one which disposes to an act suitable to the agent's nature, while an evil habit is one which disposes to an act unsuitable to nature. Thus, acts of virtue are suitable to human nature, since they are according to reason, whereas acts of vice are discordant from human nature, since they are against reason. Hence it is clear that habits are distinguished specifically by the difference of good and bad.
Secondly, habits are distinguished in relation to nature, from the fact that one habit disposes to an act that is suitable to a lower nature, while another habit disposes to an act befitting a higher nature. And thus human virtue, which disposes to an act befitting human nature, is distinct from godlike or heroic virtue, which disposes to an act befitting some higher nature.
Reply to Objection 1: The same habit may be about contraries in so far as contraries agree in one common aspect. Never, however, does it happen that contrary habits are in one species: since contrariety of habits follows contrariety of aspect. Accordingly habits are divided into good and bad, namely, inasmuch as one habit is good, and another bad; but not by reason of one habit being something good, and another about something bad.
Reply to Objection 2: It is not the good which is common to every being, that is a difference constituting the species of a habit; but some determinate good by reason of suitability to some determinate, viz. the human, nature. In like manner the evil that constitutes a difference of habits is not a pure privation, but something determinate repugnant to a determinate nature.
Reply to Objection 3: Several good habits about one same specific thing are distinct in reference to their suitability to various natures, as stated above. But several bad habits in respect of one action are distinct in reference to their diverse repugnance to that which is in keeping with nature: thus, various vices about one same matter are contrary to one virtue.
Whether one habit is made up of many habits?
Objection 1: It would seem that one habit is made up of many habits. For whatever is engendered, not at once, but little by little, seems to be made up of several parts. But a habit is engendered, not at once, but little by little out of several acts, as stated above (Q[51], A[3]). Therefore one habit is made up of several.
Objection 2: Further, a whole is made up of its parts. Now many parts are assigned to one habit: thus Tully assigns many parts of fortitude, temperance, and other virtues. Therefore one habit is made up of many.
Objection 3: Further, one conclusion suffices both for an act and for a habit of scientific knowledge. But many conclusions belong to but one science, to geometry, for instance, or to arithmetic. Therefore one habit is made up of many.
On the contrary, A habit, since it is a quality, is a simple form. But nothing simple is made up of many. Therefore one habit is not made up of many.
I answer that, A habit directed to operation, such as we are chiefly concerned with at present, is a perfection of a power. Now every perfection should be in proportion with that which it perfects. Hence, just as a power, while it is one, extends to many things, in so far as they have something in common, i.e. some general objective aspect, so also a habit extends to many things, in so far as they are related to one, for instance, to some specific objective aspect, or to one nature, or to one principle, as was clearly stated above (AA[2],3).
If then we consider a habit as to the extent of its object, we shall find a certain multiplicity therein. But since this multiplicity is directed to one thing, on which the habit is chiefly intent, hence it is that a habit is a simple quality, not composed to several habits, even though it extend to many things. For a habit does not extend to many things save in relation to one, whence it derives its unity.
Reply to Objection 1: That a habit is engendered little by little, is due, not to one part being engendered after another, but to the fact that the subject does not acquire all at once a firm and difficultly changeable disposition; and also to the fact that it begins by being imperfectly in the subject, and is gradually perfected. The same applies to other qualities.
Reply to Objection 2: The parts which are assigned to each cardinal virtue, are not integral parts that combine to form a whole; but subjective or potential parts, as we shall explain further on (Q[57], A[6], ad 4; SS, Q[48]).
Reply to Objection 3: In any science, he who acquires, by demonstration, scientific knowledge of one conclusion, has the habit indeed, yet imperfectly. And when he obtains, by demonstration, the scientific knowledge of another conclusion, no additional habit is engendered in him: but the habit which was in him previously is perfected, forasmuch as it has increased in extent; because the conclusions and demonstrations of one science are coordinate, and one flows from another.