The central claim of Kant's political philosophy is that rational agents sharing a territory can justifiably be forced to live under a state; they have, in Kant's words, a duty of right to leave the state of nature. Perhaps something along these lines is entailed by any theory of state legitimacy, but the point raises special difficulties for Kant. He believes that rational agents have a right to freedom; that is, he believes that a rational agent's external freedom - her (...) ability to set and pursue ends for herself without being subject to the choices of others - can justifiably be restricted only for the sake of external freedom itself. To establish that human beings can be forced to join a civil condition, it will therefore not do to show that the state promotes security, prosperity or any other such value: Kant has to show that human beings living side by side need a state to be free. (shrink)