The Critique of Practical Reason · Immanuel Kant
REMARK.
Thus freedom and an unconditional practical law reciprocally imply each other. Now I do not ask here whether they are in fact distinct, or whether an unconditioned law is not rather merely the consciousness of a pure practical reason and the latter identical with the positive concept of freedom; I only ask, whence begins our knowledge of the unconditionally practical, whether it is from freedom or from the practical law? Now it cannot begin from freedom, for of this we cannot be immediately conscious, since the first concept of it is negative; nor can we infer it from experience, for experience gives us the knowledge only of the law of phenomena, and hence of the mechanism of nature, the direct opposite of freedom. It is therefore the moral law, of which we become directly conscious (as soon as we trace for ourselves maxims of the will), that first presents itself to us, and leads directly to the concept of freedom, inasmuch as reason presents it as a principle of determination not to be outweighed by any sensible conditions, nay, wholly independent of them. But how is the consciousness, of that moral law possible?
We can become conscious of pure practical laws just as we are conscious of pure theoretical principles, by attending to the necessity with which reason prescribes them and to the elimination of all empirical conditions, which it directs. The concept of a pure will arises out of the former, as that of a pure understanding arises out of the latter. 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 explained 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.
Text from Project Gutenberg, public domain in the United States.