Hume attempted to rear on Berkeley's position an impregnable citadel of skepticism. He accepted Berkeley's conclusion that we know nothing of matter, and then attempted to show that inferences based on ideas might be equally illusory. Hume attacked the validity of the reasoning process itself. He endeavored to show that there is no such thing as cause and effect in either the mental or the material world. Hume's _Treatise of Human Nature_ (1739-1740), in which these views are stated, is one of the world's epoch-making works in philosophy. Its conclusion startled the great German metaphysician Kant and roused him to action. The questions thus raised by Hume have never been answered to the satisfaction of all philosophers. Hume's skepticism is the most thoroughgoing that the world has ever seen; for he attacks the certainty of our knowledge of both mind and matter. But he dryly remarks that his own doubts disappear when he leaves his study. He avoids a runaway horse and inquires of a friend the way to a certain house in Edinburgh, relying as much on the evidence of his eyes and on the directions of his friend as if these philosophic doubts had never been raised. Historical Prose.--In carefully elaborated and highly finished works of history, the eighteenth century surpasses its predecessors. _The History of England_ by David Hume, the philosopher, is the first work of the kind to add to the history of politics and the affairs of state an account of the people and their manners. This _History_ is distinguished for its polished ease and clearness. Unfortunately, the work is written from a partisan point of view. Hume was a Tory, and took the side of the Stuarts against the Puritans. He sometimes misrepresented facts if they did not uphold his views. His _History_ is consequently read more to-day as a literary classic than as an authority. [Illustration: EDWARD GIBBON. _From the painting by Sir Joshua Reynolds_.] Edward Gibbon (1737-1794) is the greatest historian of the century. His monumental work, _The History of the Decline and Fall of the Roman Empire_, in six volumes, begins with the reign of Trajan, A.D. 98, and closes with the fall of the Eastern Roman Empire at Constantinople in 1453. Gibbon constructed a "Roman road" through nearly fourteen centuries of history; and he built it so well that another on the same plan has not yet been found necessary. E.A. Freeman says: "He remains the one historian of the eighteenth century whom modern research has neither set aside nor threatened to set aside." In preparing his _History_, Gibbon spent fifteen years. Every chapter was the subject of long-continued study and careful original research. From the chaotic materials which he found, he constructed a history remarkable as well for its scholarly precision as for the vastness of the field covered.