[1] p. 312, note [Introduction to the Treatise of Human Nature] [2] See pp. 327 and 375 [Book I, part I., sec. II. and part III. sec. II.] [3] p. 310 [Introduction to the Treatise of Human Nature] [4] p. 318 [Book I, part I., sec. III.] ‘Ideas’ that cannot be so represented must be explained as mere words. 196. All, then, that Hume could find in his mind, when after Locke’s example he ‘looked into it,’ were, according to his own statement, feelings with their copies, dividing themselves into two main orders--those of sensation and those of reflection, of which the latter, though results of the former, are not their copies. The question, then, that he had to deal with was, to what impressions he could reduce those conceptions of relation--of cause and effect, substance and attribute, and identity--which all knowledge involves. Failing the impressions of sensation he must try those of reflection, and failing both he must pronounce such conceptions to be no ‘ideas’ at all, but words misunderstood, and leave knowledge to take its chance. The vital nerve of his philosophy lies in his treatment of the ‘association of ideas’ as a sort of process of spontaneous generation, by which impressions of sensation issue in such impressions of reflection, in the shape of habitual propensities,’ [1] as will account, not indeed for there being--since there really are not--but for there seeming to be, those formal conceptions which Locke, to the embarrassment of his philosophy, had treated as at once real and creations of the mind. [1] Pp. 460 and 496 [Book I, part III., sec. XIV. and part IV., sec. II.] Hume, taken strictly, leaves no distinction between impressions of reflection and of sensation.