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Immanuel Kant
69
The Critique of Practical Reason
But since a practical rule of pure reason in the first place as practical concerns the existence of an object, and in the second place as a practical rule of pure reason implies necessity as regards the exist- ence of the action and, therefore, is a practical law, not a physical law depending on empirical principles of determination, but a law of freedom by which the will is to be determined independently on anything empirical (merely by the conception of a law and its form), whereas all           that can occur of possible actions can only be empirical, that is, belong to the experience of physical nature; hence, it seems absurd to expect to find in the world of sense a case which, while as such it depends only on the law of nature, yet admits of the application to it of a law of freedom, and to which we can apply the supersensible idea of the morally good which is to be exhibited in it in concreto.