This paper attempts to shed light on Kant’s notion of autonomy in his moral philosophy by considering the extent to which he presents a similar doctrine in his theoretical philosophy, where he strikingly claims (e.g., in the Prolegomena) that the understanding prescribes laws to nature. It argues that even though there are important points of difference between the cases of theoretical legislation of the laws of nature and autonomy in moral philosophy, their extensive parallels make a strong, even if not (...) definitive case in favor of the Prolegomena forming at least an important part of the explanation of the emergence of autonomy in the Groundwork. In addition, the comparison proves instructive insofar as it reveals deep structural parallels between Kant’s theoretical and practical philosophy regarding his conception of laws. (shrink)