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.
Objection 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.
Objection 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.
Objection 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.
On the contrary, It is stated in Ethic. i, 13 that "there are two kinds of virtue: some we call intellectual; some moral."
I answer that, Reason is the first principle of all human acts; and whatever other principles of human acts may be found, they obey reason somewhat, but in various ways. For some obey reason blindly and without any contradiction whatever: such are the limbs of the body, provided they be in a healthy condition, for as soon as reason commands, the hand or the foot proceeds to action. Hence the Philosopher says (Polit. i, 3) that "the soul rules the body like a despot," i.e. as a master rules his slave, who has no right to rebel. Accordingly some held that all the active principles in man are subordinate to reason in this way. If this were true, for man to act well it would suffice that his reason be perfect. Consequently, since virtue is a habit perfecting man in view of his doing good actions, it would follow that it is only in the reason, so that there would be none but intellectual virtues. This was the opinion of Socrates, who said "every virtue is a kind of prudence," as stated in Ethic. vi, 13. Hence he maintained that as long as man is in possession of knowledge, he cannot sin; and that every one who sins, does so through ignorance.
Now this is based on a false supposition. Because the appetitive faculty obeys the reason, not blindly, but with a certain power of opposition; wherefore the Philosopher says (Polit. i, 3) that "reason commands the appetitive faculty by a politic power," whereby a man rules over subjects that are free, having a certain right of opposition. Hence Augustine says on Psalm 118 (Serm. 8) that "sometimes we understand [what is right] while desire is slow, or follows not at all," in so far as the habits or passions of the appetitive faculty cause the use of reason to be impeded in some particular action. And in this way, there is some truth in the saying of Socrates that so long as a man is in possession of knowledge he does not sin: provided, however, that this knowledge is made to include the use of reason in this individual act of choice.
Accordingly for a man to do a good deed, it is requisite not only that his reason be well disposed by means of a habit of intellectual virtue; but also that his appetite be well disposed by means of a habit of moral virtue. And so moral differs from intellectual virtue, even as the appetite differs from the reason. Hence just as the appetite is the principle of human acts, in so far as it partakes of reason, so are moral habits to be considered virtues in so far as they are in conformity with reason.
Reply to Objection 1. Augustine usually applies the term "art" to any form of right reason; in which sense art includes prudence which is the right reason about things to be done, even as art is the right reason about things to be made. Accordingly, when he says that "virtue is the art of right conduct," this applies to prudence essentially; but to other virtues, by participation, for as much as they are directed by prudence.
Reply to Objection 2. All such definitions, by whomsoever given, were based on the Socratic theory, and should be explained according to what we have said about art (ad 1).
The same applies to the Third Objection.
Reply to Objection 4. Right reason which is in accord with prudence is included in the definition of moral virtue, not as part of its essence, but as something belonging by way of participation to all the moral virtues, in so far as they are all under the direction of prudence.
Source: Summa Theologica (New Advent)