the effect, must be produced; hence, although freedom is not a
property of the will depending on physical laws, yet it is not for
that reason lawless; on the contrary it must be a causality acting
according to immutable laws, but of a peculiar kind; otherwise a
free will would be an absurdity. Physical necessity is a heteronomy of
the efficient causes, for every effect is possible only according to
this law, that something else determines the efficient cause to
exert its causality. What else then can freedom of the will be but
autonomy, that is, the property of the will to be a law to itself? But
the proposition: "The will is in every action a law to itself," only
expresses the principle: "To act on no other maxim than that which can
also have as an object itself as a universal law." Now this is
precisely the formula of the categorical imperative and is the
principle of morality, so that a free will and a will subject to moral
laws are one and the same.

On the hypothesis, then, of freedom of the will, morality together
with its principle follows from it by mere analysis of the conception.
However, the latter is a synthetic proposition; viz., an absolutely
good will is that whose maxim can always include itself regarded as
a universal law; for this property of its maxim can never be
discovered by analysing the conception of an absolutely good will. Now
such synthetic propositions are only possible in this way: that the
two cognitions are connected together by their union with a third in
which they are both to be found. The positive concept of freedom
furnishes this third cognition, which cannot, as with physical causes,
be the nature of the sensible world (in the concept of which we find
conjoined the concept of something in relation as cause to something
else as effect). We cannot now at once show what this third is to
which freedom points us and of which we have an idea a priori, nor can