Abstract

To understand Kant's moral theory, I argue, one must appreciate parallels with his philosophy of mathematics. Justified ethical judgments, as Kant understands them, are non-empirical judgments, but they are substantive nonetheless. So also for mathematical judgments, as Kant understands them. Each of these disciplines provides justified judgments that are, at once, substantive and non-empirical. Ethical and mathematical concepts share properties not enjoyed by prudential and physical concepts, I argue, features on which substantive, non-empirical reasoning depends. ;Many commentators, recent and long gone, have supposed there must be some sleight of hand involved in Kant's celebration of pure practical reason. Many have thought Kant simply abandoned his critical scruples upon turning to practical philosophy, pretending to accomplish there what he recognized could not be done in theoretical philosophy. Kant makes no such pretension, I argue. The ethicist's methods of justification are successful in the theoretical domain, for the important analogies lie between ethics and mathematics, not between ethics and metaphysics. ;Both the mathematician and the ethicist employ concepts that concern sensible form, not sensible content. This explains their success, for only if a concept concerns sensible form, can it be emptied of sensible content and still contribute to substantive judgment. Ethical and mathematical concepts differ from prudential and physical concepts in this respect. Prudential reasoning makes essential appeal to felt desires; prudential concepts when emptied of sensible content, truly are empty. Similarly, physical concepts, when emptied of sensible content, yield illegitimate metaphysical judgments, in Kant's view. ;Yet so far as my account treats ethical judgment as sensibly conditioned, it seems to conflict with Kant's contention that ethics is a product of pure reason. Kant makes the same contention concerning mathematics, however; each discipline is a product of pure reason, Kant insists, but each is sensibly conditioned. Kant does not consider these claims incompatible, and proper understanding of mathematical and ethical justification shows why