The author seeks first to resolve the problem of the relative chronology of the Aristotelian Ethics: since only the Nicomachean Ethics presupposes the knowledge of Plato's Laws, the Eudemian Ethics must be prior, and must have its origin at a relatively early point in Aristotle's philosophical career. If the doctrines of the two Ethics are analyzed and compared in the light of this influence, an important difference can be seen between them. Whereas the Eudemian Ethics insist that virtue is based on nature, the Nicomachean Ethics see moral education as based on habit. The traces of this new conception are also visible in the treatment of other themes related to virtue, including reason, happiness, and friendship.