Thus the moral law induces a stupendous change. It changes the transcendent use of reason into the immanent use. And in result reason itself becomes, by its ideas, an efficient cause in the field of experience.
HUME AND SCEPTICISM
It may be said of David Hume that he initiated the attack on pure reason. My own labours in the investigation of this subject were occasioned by his sceptical teaching, for his assault made them necessary. He argued that without experience it is impossible to know the difference between one thing and another; that is, we can know a priori, and, therefore, the notion of a cause is fictitious and illusory, arising only from the habit of observing certain things associated with each in succession of connections.
On such principles we can never come to any conclusion as to causes and effects. We can never predict a consequence from any of the known attributes of things. We can never say of any event that it must necessarily have followed from another; that is, that it must have had an antecedent cause. And we could never lay down a rule derived even from the greatest number of observations. Hence we must trust entirely to blind chance, abolishing all reason, and such a surrender establishes scepticism in an impregnable citadel.
Mathematics escaped Hume, because he considered that its propositions were analytical, proceeding from one determination to another, by reason of identity contained in each. But this is not really so, for, on the contrary, they are synthetical, the results depending ultimately on the assent of observers as witnesses to the universality of propositions. So Hume's empiricism leads inevitably to scepticism even in this realm.
My investigations led me to the conclusion that the objects with which we are familiar are by no means things in themselves, but are simply phenomena, connected in a certain way with experience. So that without contradiction they cannot be separated from that connection. Only by that experience can they be recognised. I was able to prove the objective reality of the concept of cause in regard to objects of experience, and to demonstrate its origin from pure understanding, without experimental or empirical sources.
Thus, I first destroyed the source of scepticism, and then the resulting scepticism itself. And thus was subverted the thorough doubt as to whatever theoretic reason claims to perceive, as well as the claim of Hume that the concept of causality involved something absolutely unthinkable.
GOOD AND EVIL
By a concept of practical reason, I understand the representation to the mind of an object as an effect possible to be produced through freedom. The only objects of practical reason are good and evil. For by "good" we understand an object necessarily abhorred, the principle of reason actuating the mind in each case.
In the common use of language we uniformly distinguish between the "good" and the "pleasant," the "evil" and the "unpleasant," good and evil being judged by reason alone. The judgment on the relation, of means to ends certainly belongs to reason. But "good" or "evil" always implies only a reference to the "will," as resolved by the law of reason, to make something its object.