The surpassing of the Logic of the abstract concept and the achievement of that of the concrete concept or pure concept or idea, was realized in other ways, primarily by a sort of reduction to the absurd of empiricist and mathematical Logic, in the scepticism which was its result. This reduction to the absurd, this final scepticism, is to be observed in the movement of English philosophy, beginning with Locke or even with Hobbes, to Hume. Locke, starting from perception as his presupposition, derived all ideas from experience, with the sole instrument of reflection; and rejecting innate ideas and looking upon others as more or less arbitrary, he preserved some objectivity to mathematical ideas alone, which relate to what are called primary qualities. Berkeley denies objectivity even to the primary qualities. All concepts, naturalist and mathematical alike, are for him abstract concepts and to that extent without truth. The only truth is the "idea," which means here nothing but sensation or the representation of the individual. His Logic is not empiricist, because it is in no respect Logic. At the most it is an Æsthetic substituted for and given as Logic. It is true, notwithstanding his complete denial of universals--of empirical and abstract, no less than of philosophic, which he never even mentions--that he deludes himself into thinking that he has overcome scepticism; and it is true also that he laid the foundations of a spiritualist and voluntarist conception of reality, which in our opinion should be preserved and adopted by modern thought. But this proves only that his philosophy does not wholly agree with his Logic, and not that his Logic is not the complete denial of the concept and of thought. The logical consequence of Berkeley could not, then, be anything but the scepticism of David Hume, who shakes the very foundation upon which the whole of the science of nature rests, namely, the principle of causality. [Sidenote: _Exact science and Kant. The concept of the category._]