 Throughout his moral works, Kant returns time and again to the question of the method moral philosophy should employ when pursuing these aims. A basic theme of these discussions is that the fundamental philosophical issues of morality must be addressed a priori, that is, without drawing on observations of human beings and their behavior. Kant’s insistence on an a priori method to seek out and establish fundamental moral principles, however, does not always appear to be matched by his own practice. The Metaphysics of Morals, for instance, is meant to be based on a priori rational principles, but many of the specific duties that Kant describes, along with some of the arguments he gives in support of them, rely on general facts about human beings and our circumstances that are known from experience.