We might have expected that in his critiques of theoretical and practical reason Kant would have started with an exposition of the nature of reason in general, and, after he had thus defined the _genus_, would have gone on to the explanation of the two _species_, showing how one and the same reason manifests itself in two such different ways, and yet, by retaining its principal characteristic, proves itself to be the same. But we find nothing of all this. I have already shown how inadequate, vacillating, and inconsistent are the explanations of the faculty he is criticising, which he gives here and there by the way in the “Critique of Pure Reason.” The _practical_ reason appears in the “Critique of Pure Reason” without any introduction, and afterwards stands in the “Critique” specially devoted to itself as something already established. No further account of it is given, and the use of language of all times and peoples, which is treated with contempt, and the definitions of the conception given by the greatest of earlier philosophers, dare not lift up their voices. In general, we may conclude from particular passages that Kant’s opinion amounts to this: the knowledge of principles _a priori_ is the essential characteristic of reason: since now the knowledge of the ethical significance of action is not of empirical origin, it also is an _a priori_ principle, and accordingly proceeds from the reason, and therefore thus far the reason is _practical_. I have already spoken enough of the incorrectness of this explanation of reason. But, independently of this, how superficial it is, and what a want of thoroughness it shows, to make use here of the single quality of being independent of experience in order to combine the most heterogeneous things, while overlooking their most essential and immeasurable difference in other respects. For, even assuming, though we do not admit it, that the knowledge of the ethical significance of action springs from an imperative lying in us, an unconditioned _ought_, yet how fundamentally different would such an imperative be from those universal _forms of knowledge_ of which, in the “Critique of Pure Reason,” Kant proves that we are conscious _a priori_, and by virtue of which consciousness we can assert beforehand an unconditioned _must_, valid for all experience possible for us. But the difference between this _must_, this necessary form of all objects which is already determined in the subject, and that _ought_ of morality is so infinitely great and palpable that the mere fact that they agree in the one particular that neither of them is empirically known may indeed be made use of for the purpose of a witty comparison, but not as a philosophical justification for regarding their origin as the same.