Significance and System: Essays on Kant's Ethics brings together central lines of thought in Mark Timmons's work on Kant's moral theory. The first part of the book concerns the interpretation and justification of the categorical imperative in which Timmons argues for a "differential roles" interpretation of the categorical imperative, according to which distinct formulations of this principle play different roles in the overall economy of Kant's ethics. In addition he offers a detailed interpretation of the analytic/synthetic distinction in Kant's ethics that plays a central role in Kant's justification of his supreme moral principle. In the second part, Timmons addresses questions about the relation between motive and rightness, arguing, for example, that contemporary Kantians have misunderstood that relation. This part also examines Kant's attempt in the Doctrine of Virtue to ground a system of ethical duties in the categorical imperative. In part three, Timmons turns to issues in Kant's psychology of moral evil, including the psychology of the devilish vices. Throughout Timmons combines interpretive insight with a critical eye in interpreting and criticizing Kant's ethical thought.