and its organs. Reference to external conditions, though seldom explicit in these writers, who imagined they could appeal to an introspection not revealing the external world, was pervasive in them; as, for instance, where Hume made his fundamental distinction between impressions and ideas, where the discrimination was based nominally on relative vividness and priority in time, but really on causation respectively by outer objects or by spontaneous processes in the brain.
Hume it was who carried this psychological analysis to its goal, giving it greater simplicity and universal scope; and he had also the further advantage of not nursing any metaphysical changeling of his own to substitute for the legitimate offspring of human understanding. His curiosity was purer and his scepticism more impartial, so that he laid bare the natural habits and necessary fictions of thought with singular lucidity, and sufficient accuracy for general purposes. But the malice of a psychology intended as a weapon against superstition here recoils on science itself. Hume, like Berkeley, was extremely young, scarce five-and-twenty, when he wrote his most incisive work; he was not ready to propose in theory that test of ideas by their utility which in practice he and the whole English school have instinctively adopted. An ulterior test of validity would not have seemed to him satisfactory, for though inclined to rebellion and positivism he was still the pupil of that mythical