Others, however, differentiate these virtues in respect of their matters, and it is in this way that Aristotle assigns the reason for their connection (Ethic. vi, 13).  Because, as stated above (Q. 58, A. 4), no moral virtue can be without prudence; since it is proper to moral virtue to make a right choice, for it is an elective habit.  Now right choice requires not only the inclination to a due end, which inclination is the direct outcome of moral virtue, but also correct choice of things conducive to the end, which choice is made by prudence, that counsels, judges, and commands in those things that are directed to the end.  In like manner one cannot have prudence unless one has the moral virtues:  since prudence is “right reason about things to be done,” and the starting point of reason is the end of the thing to be done, to which end man is rightly disposed by moral virtue.  Hence, just as we cannot have speculative science unless we have the understanding of the principles, so neither can we have prudence without the moral virtues:  and from this it follows clearly that the moral virtues are connected with one another.

Reply Obj. 1:  Some moral virtues perfect man as regards his general state, in other words, with regard to those things which have to be done in every kind of human life.  Hence man needs to exercise himself at the same time in the matters of all moral virtues.  And if he exercise himself, by good deeds, in all such matters, he will acquire the habits of all the moral virtues.  But if he exercise himself by good deeds in regard to one matter, but not in regard to another, for instance, by behaving well in matters of anger, but not in matters of concupiscence; he will indeed acquire a certain habit of restraining his anger; but this habit will lack the nature of virtue, through the absence of prudence, which is wanting in matters of concupiscence.  In the same way, natural inclinations fail to have the complete character of virtue, if prudence be lacking.

But there are some moral virtues which perfect man with regard to some eminent state, such as magnificence and magnanimity; and since it does not happen to all in common to be exercised in the matter of such virtues, it is possible for a man to have the other moral virtues, without actually having the habits of these virtues—­provided we speak of acquired virtue.  Nevertheless, when once a man has acquired those other virtues he possesses these in proximate potentiality.  Because when, by practice, a man has acquired liberality in small gifts and expenditure, if he were to come in for a large sum of money, he would acquire the habit of magnificence with but little practice:  even as a geometrician, by dint of little study, acquires scientific knowledge about some conclusion which had never been presented to his mind before.  Now we speak of having a thing when we are on the point of having it, according to the saying of the Philosopher (Phys. ii, text. 56):  “That which is scarcely lacking is not lacking at all.”