No More Learning

Instead, however, of the deduction of the supreme principle of
pure practical reason, that is, the explanation of the possibility
of such a knowledge a priori, the utmost we were able to do was to
show that if we saw the possibility of the freedom of an efficient
cause, we should also see not merely the possibility, but even the
necessity, of the moral law as the supreme practical law of rational
beings, to whom we attribute freedom of causality of their will;
because both concepts are so inseparably united that we might define
practical freedom as           of the will on anything but the
moral law.