 Hume and Kant both believe that philosophy should offer a theory of morality’s foundation. When it comes to morality’s foundation, they seem to agree on two things. First, morality’s foundation cannot be found in religion. Second, it cannot be found in mind-independent facts about the world. Yet they disagree about the rest of the story. Hume locates the foundation of morality in human nature, primarily in our emotional responses to the behavior of our fellow human beings. By contrast, Kant locates the foundation of morality in the rational nature that we share with all possible finite rational beings. He argues that morality’s foundation lies in the “autonomy” of the rational will. Kant’s notion of autonomy is one of the more central, distinctive, and influential aspects of his ethics. He defines autonomy as “the property of the will by which it is a law to itself (independently of any property of the objects of volition)” (G 4:440). According to Kant, the will of a moral agent is autonomous in that it both gives itself the moral law (is self-legislating) and can constrain or motivate itself to follow the law (is self-constraining or self-motivating). The source of the moral law is not in the agent’s feelings or inclinations, but in her “pure” rational will, which Kant identifies as the “proper self” (G 4:461). A heteronomous will, on the other hand, is governed by something other than itself, such as an external force or authority.