Aristotle devotes books 8-9 of the Nicomachean Ethics to friendship, distinguishing three kinds: a primary kind motivated by the other's character; and other kinds motivated by utility or pleasure. He takes up Plato's idea that one knows oneself better as reflected in another's eyes, as providing one of the benefits of friendship, and he also sees true friendship as modelled on true self-love. He further compares friendship with justice, and illustrates the ubiquity of friendship by referring to the way in which we help wayfarers as if they were kin (oikeion), a word he takes from...