No More Learning

The question then, "How a categorical imperative is possible," can be answered to this extent, that we can assign the only hypoth- esis on which it is possible, namely, the idea of freedom; and we can also discern the necessity of this hypothesis, and this is sufficient for the practical exercise of reason, that is, for the           of the validity of this imperative, and hence of the moral law; but how this
Immanuel Kant
279
Fundamental Principles of the Metaphysic of Morals
hypothesis itself is possible can never be discerned by any human reason.