difference between six and twelve, but how imperfect is our notion of the difference between six millions and twelve millions.[75:1] All human consciousness being of these two materials, impressions and ideas, the answer to the question, What knowledge have we of an external world, resolved itself into this, that there were certain impressions and ideas which we supposed to relate to it--further we knew not. When we turn, according to this theory, from the external world, and, looking into ourselves, ask what certainty we have of separate self-existence, we find but a string of impressions and ideas, and we have no means of linking these together into any notion of a continuous existence. Such is that boasted thing the human intellect, when its elements are searched out by a rigid application of the sceptical philosophy of Hume. Not a thing separate and self-existent, which was, and is, and shall continue; but a succession of mere separate entities, called in one view impressions, in another ideas.[76:1] It may make this brief sketch more clear, to notice a circumstance in the history of philosophy, which, perhaps, serves better in an incidental manner to mark the boundaries of the field of Hume's inquiry, than many pages of discursive description. The transcendentalists took him up as having examined the materials solely, on which pure reason operates; not pure reason itself. They said that he had examined the classes of matter which come before the judge, but had omitted to describe the judge himself, the extent of his jurisdiction, and his method of enforcing it. They maintained, that all these things, which with Hume appeared to be the constituent elements of philosophy, were nothing but the materials on which philosophy works,--that to presume them to be of service presupposed a reason which could make use of them,--that Hume himself, while thus speculating and telling us that his mind consisted but of a string of ideas, left behind by certain impressions, was himself making use of that pure reason which was in him before the ideas or impressions existed, and was through that power adapting the impressions and ideas to use. He characterized his system as "an attempt to introduce the experimental method of reasoning into moral subjects:" but they said that there was another and a preliminary matter of inquiry--the faculty, to speak popularly, which suggested what experiments should be made, and judged of their results.