Kant's "Grundlegung zur Metaphysik der Sitten" (1785) expounded a moral system based on the categorical imperative, one formulation of which is: "Act only according to that maxim through which you can at the same time will that it become a universal law." Rational agents must act on "principles of pure rational agency," writes Moore; that is, principles that regulate all rational agents. But Williams distinguished between thinking and acting. To think rationally is to think in a way compatible with belief in the truth, and "what it takes for one to believe the truth is the same as what it takes for anyone else to believe the truth," writes Moore. But one can "act" rationally by satisfying one's own desires (internal reasons for action), and what it takes to do that may not be what it takes for anyone else to satisfy theirs. Kant's approach to treating thinking and acting alike is wrong, according to Williams.