Chapter one sets up the main argument of the book by defining moral realism and metaphysical naturalism in ways appropriate to Kant’s philosophy. After reviewing contemporary definitions, I define moral realism as a claim that moral principles, properties, and objects are independent of the moral agent at either the empirical or transcendental level; I contrast it with moral idealism as agent-dependence and differentiate this position from constructivism. And while Kant employs an anti-naturalist methodology by emphasizing transcendental argument, the role of the a priori, and the dual perspectives of practical and theoretical reason, a focus on nature in space and time provides a benchmark for a possible metaphysical naturalism within which to fit ethics. The extent to which Kant is a realist or naturalist depends on assessing the particular elements of his ethics, which I identify and explain: the value of particular chosen ends, particular moral duties or norms, the value of humanity as end in itself, the highest good and the postulates of practical reason, moral obligation, the moral law itself, practical reason itself, and freedom of choice.