Full Idea
Virtue is a purposive disposition, lying in a mean that is relative to us and determined by a rational principle, and by that which a prudent man would use to determine it.
Clarification
'Prudence' is Greek word 'phronesis', for which the translation 'practical reason' is nowadays preferred
Gist of Idea
Virtue is a purposive mean disposition, which follows a rational principle and prudent judgment
Source
Aristotle (Nicomachean Ethics [c.334 BCE], 1107a01)
Book Reference
Aristotle: 'Ethics (Nicomachean)', ed/tr. ThomsonJ A K/TredennickH [Penguin 1976], p.101
A Reaction
Presumably the last two are getting both the theory and the practice right. Are saying that virtues finds the appropriate mean, or that virtue IS the mean? Of what?