  Unfortunately, it is far from obvious that this is what Socrates means. He does not actually say in the Republic that knowledge of the forms freely motivates beneficence. In fact, he says eight times that the philosophers in the ideal city will have to be compelled to rule and do their part in sustaining the perfectly just city (473d4, 500d4, 519e4, 520a8, 520e2, 521b7, 539e3, 540b5). It is possible to understand this compulsion as the constraint of justice: the philosophers rule because justice demands that they rule. But Socrates himself suggests a different way of characterizing the compulsion. He suggests that the compulsion comes from a law that requires those who are educated to be philosophers to rule. Moreover, this characterization better fits Socrates’ insistence that the philosophers are the best rulers because they prefer not to rule even while they are ruling (520e–521b, with 519c and 540b). For on this account, the philosophers’ justice alone does not motivate them to rule; rather, their justice motivates them to obey the law, which justly compels them to rule (E. Brown 2000).