This paper sheds light on Kant’s notion of autonomy in his moral philosophy by considering Kant’s critique of the rationalist theories of morality that Kant discussed in his lectures on practical philosophy from the 1760s to the time of the Groundwork. The paper first explains Kant’s taxonomy of moral theories and his perspective on the history of ethics. Second, it considers Kant's arguments against the two main variants of ‘rationalism’ as he construes it, that is, perfectionism and theological voluntarism, pointing (...) out the similarities to previous criticisms. Third, the paper argues that Kant’s discussion of the 'rationalist' views does not amount to an unqualified dismissal, but to an attempt at working out a novel rationalist position. Kant’s criticisms of rationalist views suggest that his project emerges from the failures of previous rationalism, with the aim to work out a rationalist view that can account for moral obligation by integrating insights from the theological conception. The combination of perfectionism and theological views yields the basic outline of the idea of autonomy, consisting in the lawgiving function of a rational will as a key to the legislation of a necessary law. (shrink)