It is not enough to predicate freedom of our own will, from whatever reason, if we have not sufficient grounds for predicating the same of all rational beings.  For as morality serves as a law for us only because we are rational beings, it must also hold for all rational beings; and as it must be deduced simply from the property of freedom, it must be shown that freedom also is a property of all rational beings.  It is not enough then to prove it from certain supposed experiences of human nature (which indeed is quite impossible, and it can only be shown a priori), but we must show that it belongs to the activity of all rational beings endowed with a will.  Now I say every being that cannot act except under the idea of freedom is just for that reason in a practical point of view really free, that is to say, all laws which are inseparably connected with freedom have the same force for him as if his will had been shown to be free in itself by a proof theoretically conclusive. [Footnote:  I adopt this method of assuming freedom merely as an idea which rational beings suppose in their actions, in order to avoid the necessity of proving it in its theoretical aspect also.  The former is sufficient for my purpose; for even though the speculative proof should not be made out, yet a being that cannot act except with the idea of freedom is bound by the same laws that would oblige a being who was actually free.  Thus we can escape here from the onus which presses on the theory. (Compare Butler’s treatment of the question of liberty in his “Analogy,” part I., ch. vi.)] Now I affirm that we must attribute to every rational being which has a will that it has also the idea of freedom and acts entirely under this idea.  For in such a being we conceive a reason that is practical, that is, has causality in reference to its objects.  Now we cannot possibly conceive a reason consciously receiving a bias from any other quarter with respect to its judgments, for then the subject would ascribe the determination of its judgment not to its own reason, but to an impulse.  It must regard itself as the author of its principles independent on foreign influences.  Consequently as practical reason or as the will of a rational being it must regard itself as free, that is to say, the will of such a being cannot be a will of its own except under the idea of freedom.  This idea must therefore in a practical point of view be ascribed to every rational being.

Of the Interest attaching to the Ideas of Morality

We have finally reduced the definite conception of morality to the idea of freedom.  This latter, however, we could not prove to be actually a property of ourselves or of human nature; only we saw that it must be presupposed if we would conceive a being as rational and conscious of its causality in respect of its actions, i. e., as endowed with a will; and so we find that on just the same grounds we must ascribe to every being endowed with reason and will this attribute of determining itself to action under the idea of its freedom.