Ægis fortissima virtus — “Virtue is the strongest shield.”
Virtue, according to Aristotle, the prince of the Peripatetics, is a habit acquired in mediocrity, consisting in a mean between two extremes. By "mediocrity" mentioned in the above definition is understood the middle point between two extremes, one of which is excess and the other deficiency. It should be understood that the virtue discussed here is ethical virtue—that is, moral virtue. We know well that there are other virtues belonging to the intellect, such as knowledge and wisdom. As for the virtues that concern the perfection of what we call the moral powers, there are many, just as there are many virtues in a precious stone or in an herb. However, for the present this book considers four principal virtues, namely: Prudence, Temperance, Fortitude, and Justice.