Aristotle agrees with Plato that virtue requires the cooperation of the rational and the non-rational parts of the soul, and that the virtuous person is always better off than the non-virtuous, even though virtue alone is not sufficient for happiness. To strengthen Plato’s argument for this claim, he offers a more detailed account of the nature of happiness, and of the relation between virtue and happiness. Since happiness is the supreme human good, it should be identified with rational activity in accordance with virtue in a complete life, in which external circumstances are favourable. A virtue of character is the appropriate agreement between the rational and the non-rational parts of the soul, aiming at fine action (i.e., action that promotes the common good). This requirement of appropriate agreement distinguishes virtue from continence (mere control of the rational over the non-rational part). To show that a life of virtue, so defined, promotes the agent’s happiness, Aristotle argues that one’s own happiness requires the right kind of friendship with others, in which one aims at the good of others for their own sake.