The Federalist, written by “Publius” (Alexander Hamilton, John Jay, and James Madison) in 1787-1788 in defense of the proposed constitution of the United States, endorses a fundamental principle of political legitimacy: namely, “it is the reason of the public alone, that ought to control and regulate the government.” This essay argues that this principle—the rule of reason—may be traced back to Plato. Part I of the essay seeks to show that Plato's Statesman offers a clearer understanding of the rule of reason than his more famous Republic, and it also indicates how this principle gave rise to the ideal of constitutionalism, which was adopted and reformulated by Aristotle, Polybius, and Cicero, as well as moderns including Locke and Montesquieu. Part II argues that The Federalist agrees with Plato when it argues that popular sovereignty must be tempered by the rule of reason. A proper distance should be maintained between the people and the actual exercise of power in order that political decisions be based on reason rather than passion. The people must therefore act through a federal system divided between national government and state governments, and these governments must themselves possess separated powers which control each other by means of checks and balances. Indeed, federalism itself may be viewed as a modern counterpart of Plato's “art of weaving,” which unites naturally disparate and opposed parts of the city-state into a concordant whole. In declaring, “If men were angels, no government would be necessary,” The Federalist concedes that politics is the art of the possible. But statesmanship is not an exercise in pragmatism devoid of principles. Here “Publius” shares Plato's vision of politics as a “second sailing,” that is, an attempt to approximate the ideal of rational governance as far as possible in ordinary politics.