In Nicomachean Ethics, Aristotle offers a solution to the problem of motivating morality based on his distinction between three types of friendship. I consider Aristotle's argument in detail, placing it in a context of similar concerns about the question of why we ought to be moral that ranges from Socrates' discussion of the ring of Gyges in Plato's Republic to Wittgenstein's distinction between internal and external rewards and punishments for action in Tractatus Logico-Philosophicus. Contrary to J.O. Urmson's conclusion that Aristotle's (...) discussion of the highest form of friendship is an editorial insertion in Book VIII of the Ethics, I attempt to show, by filling in the necessary steps in Aristotle's inference, that the treatment of friendship is an integral part of what Aristotle considers a complete moral philosophy. According to the interpretation that I propose, Aristotle's account of being worthy of the highest form of friendship is indispensable to his explanation of an internally rewarding reason for being moral. (shrink)