Now moral virtue is so called from mos in the sense of a natural or quasi-natural inclination to do some particular action. And the other meaning of mos, i.e. custom, is akin to this: because custom becomes a second nature, and produces an inclination similar to a natural one. But it is evident that inclination to an action belongs properly to the appetitive power, whose function it is to move all the powers to their acts, as explained above (Q. 9, A. 1). Therefore not every virtue is a moral virtue, but only those that are in the appetitive faculty.
Reply Obj. 1: This argument takes mos in the sense of custom.
Reply Obj. 2: Every act of virtue can be done from choice: but no virtue makes us choose aright, save that which is in the appetitive part of the soul: for it has been stated above that choice is an act of the appetitive faculty (Q. 13, A. 1). Wherefore a habit of choosing, i.e. a habit which is the principle whereby we choose, is that habit alone which perfects the appetitive faculty: although the acts of other habits also may be a matter of choice.
Reply Obj. 3: "Nature is the principle of movement" (Phys. ii, text. 3). Now to move the faculties to act is the proper function of the appetitive power. Consequently to become as a second nature by consenting to the reason, is proper to those virtues which are in the appetitive faculty. ________________________
SECOND ARTICLE [I-II, Q. 58, Art. 2]
Whether Moral Virtue Differs from Intellectual Virtue?
Objection 1: It would seem that moral virtue does not differ from intellectual virtue. For Augustine says (De Civ. Dei iv, 21) "that virtue is the art of right conduct." But art is an intellectual virtue. Therefore moral and intellectual virtue do not differ.
Obj. 2: Further, some authors put science in the definition of virtues: thus some define perseverance as a "science or habit regarding those things to which we should hold or not hold"; and holiness as "a science which makes man to be faithful and to do his duty to God." Now science is an intellectual virtue. Therefore moral virtue should not be distinguished from intellectual virtue.
Obj. 3: Further, Augustine says (Soliloq. i, 6) that "virtue is the rectitude and perfection of reason." But this belongs to the intellectual virtues, as stated in Ethic. vi, 13. Therefore moral virtue does not differ from intellectual.
Obj. 4: Further, a thing does not differ from that which is included in its definition. But intellectual virtue is included in the definition of moral virtue: for the Philosopher says (Ethic. ii, 6) that "moral virtue is a habit of choosing the mean appointed by reason as a prudent man would appoint it." Now this right reason that fixes the mean of moral virtue, belongs to an intellectual virtue, as stated in Ethic. vi, 13. Therefore moral virtue does not differ from intellectual.