Why derive a just constitution from an imaginary contract rather than a real one? One reason is practical: It’s often hard to prove historically, in the distant history of nations, that any social contract ever took place. A second reason is philosophical: Moral principles can’t be derived from empirical facts alone. Just as the moral law can’t rest on the interests or desires of individuals, principles of justice can’t rest on the interests or desires of a community. The mere fact that a group of people in the past agreed to a constitution is not enough to make that constitution just.
