It is now necessary to make a formal definition of virtue or excellence, starting with the determination of its genus (the class of things to which it belongs), and following with a determination of its differentia or species (the point or points which distinguish it from other members of its class).
Since the human soul is conditioned by three factors — emotions (feelings), capacities, and dispositions (characteristics) — it is evident that virtue must be one of these. Emotions include such things as anger, appetite, fear, confidence, envy, pity, and any other state of mind that involves pleasure or pain.
Capacities are our faculties for experiencing emotions. Dispositions are the conditions or states of character in which we are in regard to emotions (e.g., we say that one has a bad disposition where anger is concerned if he tends to become excessively or insufficiently angry, and has a good disposition toward anger if he consistently feels the appropriate amount of anger).
Virtue is something for which men are called good or bad or for which they are praised or blamed. Since one is not called good or bad on the basis of his emotions, it is clear that virtue is not an emotion. Furthermore, virtues are the result of some kind of choice but a man does not exercise his will (i.e., make a choice) when he experiences such emotions as anger or fear. It is also clear that virtue is not a capacity, since a man is not praised or blamed for having the ability to experience certain feelings. A human being receives his capacities from nature, but nature does not cause him to develop into a good or bad man. Therefore, since virtues and vices are not emotions or capacities, they must belong to the genus known as dispositions or characteristics.