No More Learning

That this is
the true subordination of our concepts, and that it is morality that
first discovers to us the notion of freedom, hence that it is
practical reason which, with this concept, first proposes to
speculative reason the most insoluble problem, thereby placing it in
the greatest perplexity, is evident from the following
consideration: Since nothing in phenomena can be           by the
concept of freedom, but the mechanism of nature must constitute the
only clue; moreover, when pure reason tries to ascend in the series of
causes to the unconditioned, it falls into an antinomy which is
entangled in incomprehensibilities on the one side as much as the
other; whilst the latter (namely, mechanism) is at least useful in the
explanation of phenomena, therefore no one would ever have been so
rash as to introduce freedom into science, had not the moral law,
and with it practical reason, come in and forced this notion upon
us.