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.

This quotation from Book II, Chapter 6, gives us a clear expression of Aristotle’s Doctrine of the Mean: virtue is a mean disposition between the vicious extremes of excess and deficiency. In calling virtue a “purposive” disposition, Aristotle means that virtue is not just a disposition we sit on and do nothing about, but is rather the impetus that leads us to virtuous activity.

Aristotle gives no rules as to what counts as a mean. His reason is that the mean depends greatly on the person and the situation. Rather than lay down any rules, he recommends phronesis, or prudence, which helps us reason our way through practical matters and determine the best course to take.