actions: first, so far as he belongs to the world of sense, he finds
himself subject to laws of nature (heteronomy); secondly, as belonging
to the intelligible world, under laws which being independent of
nature have their foundation not in experience but in reason alone.

As a rational being, and consequently belonging to the
intelligible world, man can never conceive the causality of his own
will otherwise than on condition of the idea of freedom, for
independence of the determinate causes of the sensible world (an
independence which reason must always ascribe to itself) is freedom.
Now the idea of freedom is inseparably connected with the conception
of autonomy, and this again with the universal principle of morality
which is ideally the foundation of all actions of rational beings,
just as the law of nature is of all phenomena.

Now the suspicion is removed which we raised above, that there was a
latent circle involved in our reasoning from freedom to autonomy,
and from this to the moral law, viz.: that we laid down the idea of
freedom because of the moral law only that we might afterwards in turn
infer the latter from freedom, and that consequently we could assign
no reason at all for this law, but could only [present] it as a
petitio principii which well disposed minds would gladly concede to
us, but which we could never put forward as a provable proposition.
For now we see that, when we conceive ourselves as free, we transfer
ourselves into the world of understanding as members of it and
recognise the autonomy of the will with its consequence, morality;
whereas, if we conceive ourselves as under obligation, we consider
ourselves as belonging to the world of sense and at the same time to
the world of understanding.