1 The full and final version appeared in: Kant on Moral Autonomy, ed. Oliver Sensen, Cambridge: Cambrdige University Press, 2013, pp. 193-211. Heiner F. Klemme Moralized nature, naturalized autonomy. Kant’s way of bridging the gap in the third Critique (and in the Groundwork) I. Posing the Problem In the Groundwork of the Metaphysics of Morals, Kant establishes the “principle of the autonomy of the will“ (GMS 4:433) as the “supreme principle of morality“ (GMS 4:440). This principle is unprecedented in the history of philosophy. Kant is the first philosopher to make a case for the seemingly paradoxial thesis that we are subject to the moral law just because we give it to ourselves. Kant connects this thesis of a self-imposed obligation that depends on rational will with a novel conception of motivation. By applying the moral law to our maxims, we not only recognize our duties. It is reason itself that causes a feeling of respect for the moral law in us. Without this feeling, we would lack a subjective motivation to fulfill our duties. The Kantian conception of duty and moral ought is characterized by the idea that our will is not determined by the knowledge of our duties and the feeling of respect. If we are willing to, we human beings can act in accordance with our duties. But we do not have to. Our freedom to decide for or against our duties is part of the condition humaine. 1 The principle of autonomy finds its counterpart in the principle of the heteronomy of the will. We act heteronomously every time we take the liberty to make an exception in observing the moral law in favor of our inclinations (cf. GMS 4:424). In doing so, we submit, in our volition, to the laws of natural causality (cf. GMS 4:433, 441). But if we privilege our private ends that are based on our sensible nature over reason, our actions have no inner moral value. At best, we are acting conformable to duty, but not in accordance with it. 1 See Klemme 2008.