 A crucial move in Kant’s argument is his claim that a rational will cannot act except “under the Idea” of its own freedom (G 4:448). The expression “acting under the Idea of freedom” is easy to misunderstand. It does not mean that a rational will must believe it is free, since determinists are as free as libertarians in Kant’s view. Indeed, Kant goes out of his way in his most famous work, the Critique of Pure Reason, to argue that we have no rational basis for believing our wills to be free. This would involve, he argues, attributing a property to our wills that they would have to have as ‘things in themselves’ apart from the causally determined world of appearances. Of such things, he insists, we can have no knowledge. For much the same reason, Kant is not claiming that a rational will cannot operate without feeling free. Feelings, even the feeling of operating freely or the “looseness” Hume refers to when we act, cannot be used in an a priori argument to establish the CI, since they are empirical data.