These considerations seem to preclude us, when once we have recognised the ground of distinction between a world of experience and a world of things-in-themselves, from any attempt to overcome that absolute separation between the two worlds, which Kant's doctrine implies, by treating the organising subject of the world of experience as in any sense a product of things-in-themselves. Kant himself lends no countenance to any such attempt; but on further reflectionwe may begin to question whether the view, which Kant himself gives, of the relation between things-in-themselves and the matter of experience, or natura materialiter spectata--the view out of which the whole difficulty arises--is not itself open to the same charge of inconsistency as that method of escape from its consequences which we have examined. When we say that sensations, or phenomena in respect of their mere matter, are effects of things-in-themselves, we may exclude as carefully as possible all confusion of the things-in-themselves with the ascertainable material conditions, or formal causes, of feeling, but we cannot assert such a relation of cause and effect between the things and sensation without making the former a member of a relation which, as Kant himself on occasion would be ready to remind us, we have no warrant for extending beyond the world of experience, or for considering as independent of the intellectual principle of unity which is the condition of there being such a world. Causation has no meaning except as an unalterable connexion between changes in the world of our experience--an unalterableness of which the basis is the relation of that world throughout, with all its changes, to a single subject. That sensations therefore, the matter of our experience, should be connected as effects with things-in-themselves, of which all that can be said is that they belong to a world other than the world of our experience and are not relative to the subject to which it is relative, is a statement self-contradictory or at best unmeaning. (§ 41 ¶ 1)

That Kant should not have seen this merely goes to show that his own doctrine, being the gradual conquest of his later years, had not obtained full possession of his mind. The antithesis between the real and the work of thought had still such command over him that, after he had himself traced the agency of thought in all that gives the world of experience a definite character, h still could not help ascribing to this world, in terms of the knowable, a relation to an unknowable opposite; though that very relation, if it existed, would according to his own showing bring this unknowable opposite within that world (dependent on an intelligent subject) from which it is expressly excluded. (§ 41 ¶ 2)