In Hume, the empirical theory of knowing found a disciple who did not hesitate to affirm all that was involved in it. Locke said there was an outward world, and knowledge was its image. Berkeley said there was no material world; that knowledge was the reflection of God’s ideas. Hume said there was neither outer world nor inner; that there was nothing but impressions, sensations, ideas, in perpetual flow and flux. He claimed that all ideas which could not be resolved into impressions were false. He declared we could have no ideas of substance, because, if perceived by the eye, it must be a color; if by the ear, a sound; if by the palate, a taste. And because we could not think of substance as a color or a sound or a taste, we could therefore have no idea of it whatever. Belief in a permanent external world was rendered irrational by his theory of knowledge. Nothing is more vital and irrepressible than belief in one’s own existence, but even this could not be retained in accordance with the teachings of Hume’s philosophy. “Whence,” says he, “could the impression of the idea of self be derived? What impression could create this idea? This question it is impossible to answer without a manifest contradiction and absurdity, and yet it is a question that must necessarily be answered. For my part, when I enter most intimately into what I call myself, I always stumble upon some perception or other; heat or cold, light or shade, pain or pleasure. I cannot catch myself at any time without a perception, or observe anything but a perception. When my perceptions are removed at any time, as by sound sleep, so long am I insensible of myself, and may be said truly not to exist.” The sensational philosophy which promised so much, which appeared so eminently practical, that took to itself such an air of common sense as it got about obliterating innate ideas, was seen at length to be utterly impotent. It corresponded with absolutely nothing in heaven or in earth. The very impressions it admitted, passed through it like drops of water out of a fisherman’s net. Where the impressions came from or where they went to, it furnished no means of knowing. God and world and cause and law and self might be, but the human mind could never know whether they were or not. The human observer stood before a procession of images, sensations, perceptions going by like an unending circus troupe. In Hume may be traced the entire breakdown of empirical philosophy as a method for getting at the truth. He recognized this himself. “When I turn my eye inward,” he says, “I find nothing but doubt and ignorance.” “The understanding, when it acts alone, and according to its most general principles, entirely subverts itself, and leaves not the lowest degree of evidence in any proposition, either in philosophy or common life.” “We have, therefore, no choice left, but betwixt a false reason and none at all.” VII.