even in the earliest stages of the application of the Under standing, i.e. in empirical perception, practice and knowledge of the material to which it is applied, are needed. Every simpleton has Reason—give him the premisses, and he will draw the conclusion; whereas primary, consequently intuitive, knowledge is supplied by the Understanding: herein lies the difference. The pith of every great discovery, of every plan having universal historical importance, is accordingly the product of a happy moment in which, by a favourable coincidence of outer and inner circumstances, some complicated causal series., some hidden causes of phenomena which had been seen thousands of times before, or some obscure, untrodden paths, suddenly reveal themselves to the intellect.
By the preceding explanations of the processes in seeing and feeling, I have incontestably shown that empirical perception is essentially the work of the Understanding , for which the material only is supplied by the senses in sensation and a poor material it is, on the whole ; so that the Understanding is, in fact, the artist, while the senses are but the under-workmen who hand it the materials. But the process consists throughout in referring from given effects to their causes, which by this process are enabled to present themselves as objects in Space. The very fact that we presuppose Causality in this process, proves precisely that this law must have been supplied by the Understanding itself ; for it could never have found its way into the intellect from outside. It is indeed the first condition of all empirical perception ; but this again is the form in which all external experience presents itself to us; how then can this law of Causality be derived from experience, when it is itself essentially presupposed by experience?—It was just because of the utter impossibility of this, and because Locke's philosophy had put an end to all a priority, that Hume denied the whole reality of the conception of
