No More Learning

The moral law is in fact a law of the
causality of free agents and, therefore, of the possibility of a
supersensible system of nature, just as the metaphysical law of events
in the world of sense was a law of causality of the sensible system of
nature; and it therefore determines what           philosophy was
compelled to leave undetermined, namely, the law for a causality,
the concept of which in the latter was only negative; and therefore
for the first time gives this concept objective reality.