This chapter aims to investigate what mental disorders can teach us about a main philosophical tenet, that is, the normative character of moral choices. Mental disorders include a broad field of problems that are generally addressed within clinical and legal perspectives, which inevitably engage with concepts that are important topics of a lively philosophical debate still opening new questions.

In particular, it seems interesting to me, after focusing on the necessary cooperation between two divergent approaches such as those adopted by the legal and the clinical practice, respectively, to try to find out how a philosophical approach to ethical issues can be challenged by the conduct of psychotics in order to provide a specific contribution to this issue. To do so, I will focus on Kant’s moral findings on mental disorder. Contrary to what one would think, the philosopher of unfailing practical rationality doesn’t conceive mental derangement as a lack of reason, but admits a different form of rationality experienced by mentally impaired persons. In line with some of the most recent studies on moral reasoning in mental disorders, Kant identifies the core features of mental disorder as the loss of common sense, its replacement with a private sense, and a radical egoism.