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96 DESCARTES. worlds belongs to those standpoints which are valid with- out being ultimate truth ; on the pyramid of metaphysical knowledge it takes a high, but not the highest, place. We may not rest in it, yet it retains a permanent value in op- position to subordinate theories. It is in the right against a materialism which still lacks insight into the essen- tial distinction between mind and matter, thought and ex- tension, consciousness and motion ; it loses its validity when, with a full consideration and conservation of the dis- tinction between these two spheres, we succeed in bridging over the gulf between them, whether this is accomplished through a philosophy of identity, like that of Spinoza and Schelling, or by an idealism, like that of Leibnitz or Fichte. In any case philosophy retains as an inalienable possession the negative conclusion, that, in view of the heterogeneity of consciousness and motion, the inner life is not reducible to material phenomena. This clear and simple distinction, which sets bounds to every confusion of spiritual and ma- terial existence, was an act of emancipation ; it worked on the sultry intellectual atmosphere of the time with the puri- fying and illuminating power of a lightning flash. We shall find the later development of philosophy starting from the Cartesian dualism. Descartes himself looked upon the fundamental princi- ples which have now been discussed as merely the founda- tion for his life work, as the entrance portal to his cosmol- ogy. Posterity has judged otherwise ; it finds his chief work in that which he considered a mere preparation for it. The start from doubt, the self-certitude of the thinking ego, the rational criterion of certitude, the question of the origin of ideas, the concept of substance, the essential dis- tinction between conscious activity and corporeal being, and, also, the principle of thoroughgoing mechanism in the material world (from his philosophy of nature) — these are the thoughts which assure his immortality. The vesti- bule has brought the builder more fame, and has proved more enduring, than the temple : of the latter only the ruins remain ; the former has remained undestroyed through the centuries. I J