On the side of matter falls the manifold, given, empirical, contingent material of sense; on the side of form fall the unifying, _a priori_, synthetic, relational instruments of sensibility and thought. For Kant these latter are no mere abstractions, capable of being _distinguished_ by the mind; they differ from the matter of experience in nature, in function, and in origin. Upon this dualistic mode of conceiving the two factors depends the strength as well as the weakness of his position. To its perverting influence most of the unsatisfactory features of his doctrine of space and time can be directly traced. But to it is also due his appreciation of the new Critical problems, with their revolutionary consequences, as developed in the _Analytic_. Kant proceeds to argue: (_a_) that the distinction is between two elements of fundamentally different nature and origin. The matter is given _a posteriori_ in sensation; the form, as distinct from all sensation, must lie ready _a priori_ in the mind. (_b_) Kant also argues that form, because of its separate origin, is capable of being contemplated apart from all sensation. The above statements rest upon the unexpressed assumption that sensations have no spatial attributes of any kind.[377] In themselves they have only intensive, not extensive, magnitude.[378] Kant assumes this without question, and without the least attempt at proof.[379] The assumption appears in Kant’s writings as early as 1768 as a self-evident principle;[380] and throughout the _Critique_ is treated as a premiss for argument, never as a statement calling for proof. The only kind of supporting argument which is even indirectly suggested by Kant is that space cannot by itself act upon the senses.[381] This would seem to be his meaning when he declares[382] that it is no object, but only an _ens imaginarium_. “Space is no object of the senses.”[383] Such argument, however, presupposes that space can be conceived apart from objects. It is no proof that an extended object may not yield extended sensations. Kant completely ignores the possibility that formal relations may be given in and with the sensations. If our sensibility, in consequence of the action of objects upon it, is able to generate qualitative sensations, why, as Vaihinger very pertinently enquires,[384] should it be denied the power of also producing, in consequence of these same causes, impressions of quantitative formal nature? Sensations, on Kant’s view, are the product of mind much more than of objects. Why, then, may not space itself be sensational?[385] From the point of view of empirical science there is no such radical difference between cause and effect in the latter case as exists in the former. As Herbert Spencer has remarked,[386] Kant makes the enormous assumption