Through the functioning of the soul, the moral and intellectual aspects of humanity are developed. Aristotle clearly stated the relationship between human insight and the senses in what has become a slogan of empiricism the view that knowledge is grounded in sense experience. It seemed to Aristotle that the individual's freedom of choice made an absolutely accurate analysis of human affairs impossible. The inherent limitations on practical science are made clear in Aristotle's concepts of human nature and self-realization. Aristotle's Nicomachean Ethics is an analysis of character and intelligence as they relate to happiness.
Moral virtue is an expression of character, formed by habits reflecting repeated choices.
A moral virtue is always a mean between two less desirable extremes. Intellectual virtues are not subject to this doctrine of the mean. Aristotle did not regard politics as a study of ideal states in some abstract form, but rather as an examination of the way in which ideals, laws, customs, and property interrelate in actual cases. He thus approved the contemporary institution of slavery but tempered his acceptance by insisting that masters should not abuse their authority, inasmuch as the interests of master and slave are the same. The Lyceum library contained a collection of 158 constitutions of the Greek and other states.