This is the order of nature and of justice, which whoever shall be willing to hold and to observe will fulfill the perfection of the active life. To which active life those three virtues are profitable (concerning which I have spoken what was commanded to be said, God granting it). For temperance, fortitude of soul, and justice are the spiritual action, without which that knowledge which seems to pertain to prudence avails nothing at all. For it will profit us nothing to have learned the things to be fulfilled, unless we earnestly strive to fulfill what we have learned. Therefore the strength of the soul, which is divided into appetite and reason, is aided by these four virtues (of which we have already long discoursed) toward fulfilling the perfection of good action and toward attaining the knowledge of hidden things.
By three of these—namely temperance, fortitude of soul, and justice—the appetite itself is formed, so that it may become action; but prudence illuminates reason, which is the keen edge of the mind, so that both reason may govern the appetite and the appetite may obey reason. For all virtue (as it pleased the ancients) is concerned with about three things: one of which lies in discerning what in each matter is true and genuine, which is the proper office of prudence, of which we shall see in its own place; the second, in that which restrains and tempers the disordered affections of the soul, which the Greeks call pathē, so that it may make all the appetites, which they call hormai, obedient to reason;
the third, that we may be willing to use those things by which we are joined together for the attaining of the fullness of their salvation and of our own. All which things seem to pertain to the office of the remaining three virtues: in which temperance and fortitude avail very much for restraining and bridling the perturbations of the soul, which perturbations some call passions, others call sicknesses. When these are moderated and composed by a certain law of temperance and fortitude, all the virtues reign in the man who is made subject to his Creator, without any contradiction of the vices.