So virtue is a purposive disposition, lying in a mean that is relative to us and determined by a rational principle, by that which a prudent man would use to determine it.
There are two kinds of virtue: intellectual and moral. We learn intellectual virtues by instruction, and we learn moral virtues by habit and constant practice. We are all born with the potential to be morally virtuous, but it is only by behaving in the right way that we train ourselves to be virtuous. As a musician learns to play an instrument, we learn virtue by practicing, not by thinking about it.
Because practical circumstances vary a great deal, there are no absolute rules of conduct to follow. Instead, we can only observe that right conduct consists of some sort of mean between the extremes of deficiency and excess. For instance, courage consists in finding a mean between the extremes of cowardice and rashness, though the appropriate amount of courage varies from one situation to another.
An appropriate attitude toward pleasure and pain is one of the most important habits to develop for moral virtue. While a glutton might feel inappropriate pleasure when presented with food and inappropriate pain when deprived of food, a temperate person will gain pleasure from abstaining from such indulgence.
Aristotle proposes three criteria to distinguish virtuous people from people who behave in the right way by accident: first, virtuous people know they are behaving in the right way; second, they choose to behave in the right way for the sake of being virtuous; and third, their behavior manifests itself as part of a fixed, virtuous disposition.
Virtue is a disposition, not a feeling or a faculty. Feelings are not the subject of praise or blame, as virtues and vices are, and while feelings move us to act in a certain way, virtues dispose us to act in a certain way. Our faculties determine our capacity for feelings, and virtue is no more a capacity for feeling than it is a feeling itself. Rather, it is a disposition to behave in the right way.
We can now define human virtue as a disposition to behave in the right manner and as a mean between extremes of deficiency and excess, which are vices. Of course, with some actions, such as murder or adultery, there is no virtuous mean, since these actions are always wrong. Aristotle lists some of the principle virtues along with their corresponding vices of excess and deficiency in a table of virtues and vices. Some extremes seem closer to the mean than others: for instance, rashness seems closer to courage than to cowardice. This is partly because courage is more like rashness than cowardice and partly because most of us are more inclined to be cowardly than rash, so we are more aware of being deficient in courage.