Many commentators hold that in addition to the categorical imperative of morality, Kant also posits an objective law of non-moral practical rationality, 'the' Hypothetical Imperative. On this view, the appeal to the Hypothetical Imperative increases the dialectical options that Kantians have vis-a-vis Humean skepticism about the authority of reason, and it allows for a systematic explanation of the possibility of non-moral weakness of will. I argue that despite its appeal, this interpretation cannot be sustained: for Kant the only objective, universally (...) valid a priori principle of practical reason that governs transcendentally free agents is the moral law. All non-moral practical rules are mere “precepts” that lack genuine objectivity, certainty, and intersubjective validity. I suggest that for Kant the rejection of the possibility of non-moral practical laws plays an important part in his argument for the supreme rational authority of moral norms over prudential precepts of happiness. (shrink)