Both in historical debates and in recent discussions, the Guise of the Good Thesis represents a genuine dogma of rationalism in moral philosophy. Many influential commentators have maintained that Kant belongs in that camp, even that he “explicitly endorses” the Thesis. Attributing the Thesis to Kant, however, faces scarce textual support and amounts to a dubious understanding of the relationship of Kant’s moral philosophy to previous rationalist views. I suggest that, in Kant’s view, the Thesis only applies to the determination (...) of the will through the moral law. The principle that prior rationalists regarded as descriptive acquires in Kant’s terms a normative status. (shrink)