In proportion as an historical matter is of import to human kind, in that proportion does it spring not from apparent—let alone material—causes, but from some hidden revolution in the human spirit. To pretend an examination of the secret springs whence the human mind is fed is futile. The greater the affair, the more directly does it proceed from unseen sources which the theologian may catalogue, the poet see in vision, the philosopher explain, but with which positive external history cannot deal, and which the mere historian cannot handle. It is the function of history to present the outward thing, as a witness might have seen it, and to show the reader as much as a spectator could have seen—illuminated indeed by a knowledge of the past—and a judgment drawn from known succeeding events. The historian answers the question, “_What_ was?” this or that. To the question, “_Why_ was it?” if it be in the spiritual order (as are all major things), the reader must attempt his own reply based upon other aptitudes than those of historic science. It is the neglect of this canon which makes barren so much work upon the past. Read Gibbon’s attempt to account for “why” the Catholic Church arose in the Roman Empire, and mark his empty failure. [Footnote: It is true that Gibbon was ill equipped for his task because he lacked historical imagination. He could not grasp the spirit of a past age. He could not enter into any mood save that of his master, Voltaire. But it is not only true of Gibbon that he fails to explain the great revolution of A.D. 29-304. No one attempting that explanation has succeeded. It was not of this world.] Mark also how all examination of the causes of the French Revolution are colored by something small and degraded, quite out of proportion to that stupendous crusade which transformed the modern world. The truth is, that the historian can only detail those causes, largely material, all evident and positive, which lie within his province, and such causes are quite insufficient to explain the full result. Were I here writing “Why” the Reformation came, my reply would not be historic, but mystic. I should say that it came “from outside mankind.” But that would be to affirm without the hope of proof, and only in the confidence that all attempts at positive proof were contemptible. Luckily I am not concerned in so profound an issue, but only in the presentation of the thing as it was. Upon this I now set out. With the close of the Middle Ages two phenomena appeared side by side in the society of Europe. The first was an ageing and a growing fatigue of the simple mediæval scheme; the second was a very rapid accretion of technical power.