Late in his life, after his revolutionary work in epistemology, Kant first presented his mature moral philosophy in Foundations of the Metaphysics of Morals. Here, Kant developed his influential idea that human beings as rational agents are “autonomous,” or have the capacity for moral self-government. For Kant, autonomy means that, as rational beings, people set the own standards of conduct, as distinct from the demands made by their desires, and are able to decide and act on these standards. On the basis of a complex argument, Kant concluded that autonomy is possible only if the will is guided by a supreme principle of morality that he called the “categorical imperative.” Kant viewed this imperative as the product of reason and as the basis for determining moral duties. He expressed it in three basic formulations.