The most remarkable thing in the whole search for truth, is that anybody after Hume should have attempted to find it with Hume’s principles. Yet the two best known writers who have lived in England since Hume’s day, have rested their dogmatic doctrines on the foundations laid by the sensational philosophers. Hume’s impressions and ideas became John Stuart Mill’s permanent possibilities of sensation and feeling, and Herbert Spencer’s vivid and faint manifestations of the unknowable. In our time Herbert Spencer has undertaken the herculean task of explaining matter and mind, time and space, society and morals; of showing what they are and what they are not, by the same principles which Hume himself demonstrated to be incapable of explaining anything. Spencer’s units of knowledge are vivid and faint manifestations of the Unknown. How the unknowable remains unknown, after vividly and faintly manifesting itself, we are not told. Mr. Spencer’s vivid and faint manifestations of the unknown are old acquaintances with new names. Locke knew them as impressions and sensations. Berkeley recognized them as ideas of sense and imagination. John Stuart Mill was on speaking terms with them as permanent possibilities of sensation and feeling. Mr. Spencer gives them another baptism and another name. He calls them vivid and faint manifestations of the unknowable. While they have been changed in name, however, it must not be supposed that they have undergone any change in nature or character. They stand apart, the one from the other, just the same as ever. They are just as foreign to the mind, where they vividly and faintly manifest themselves, as were the impressions of John Locke. They flare and flicker, rise and fall, like the jack-o’-lantern lights of legend and tale. One light is not of a piece with any other light. The lights follow one another in such quick succession, first vivid, then faint, that one cannot tell from the momentary flames and flashes what is intended to be advertised. That something is trying, by various pyrotechnic displays, to get itself revealed seems to be evident. But there is such hurry on the part of the something that makes the manifestations, such a disorderly whirl and changing of lights, that the observer is totally bewildered; and, being under the necessity of making some account to himself as to their meaning, concludes that they are vivid and faint illuminations of the unknowable. Hume’s procession of sensations and ideas has by Spencer been converted into the fire-works of the unknowable. With Hume’s physiological theory, the mind could know nothing but its own sensations. Spencer’s vivid and faint manifestations of the unknowable are equally as incapable of furnishing any rational basis for belief in mind or matter, law or cause, self or God. To ask the human mind to believe the encyclopedic, dogmatic system of philosophy he addressed to it, after insisting that all our knowledge is but the sum