As a man with an idea, with a philosophical nostrum, Leibniz may be compared to Bishop Berkeley. There was never any more doubt that Leibniz was a Leibnitian than that Berkeley was a Berkeleian. But there is no comparison between the two men in the width of their range. About many things Berkeley never took the trouble to Berkeleianize. To take the most surprising instance of his neglect--he assured the world that his whole doctrine pointed to, and hung upon, theology. But what sort of a theology? He scarcely took the first steps in the formulation of it. He preferred to keep on defending and explaining his _esse est percipi_. With Leibniz it is wholly different; he carries his new torch into every corner, to illuminate the dark questions. The wide applicability of pre-established harmony might come home to its inventor as a rich surprise. The reflective historian will find it less[12] surprising, for he will suspect that the applications were in view from the start. What was Leibniz thinking of when the new principle flashed upon him? What was he _not_ thinking of? He had a many-sided mind. If the origins of the principle were complex, little wonder that its applications were manifold. Every expositor of Leibniz who does not wish to be endlessly tedious must concentrate attention on one aspect of Leibniz's principle, and one source of its origin. We will here give an account of the matter which, we trust, will go most directly to the heart of it, but we will make no claims to sufficient interpretation of Leibniz's thought-processes. Leibniz, then, like all the philosophers of the seventeenth century, was reforming scholasticism in the light of a new physical science. The science was mathematical in its form, mechanistical in its doctrine, and unanswerable in its evidence--it got results. But it was metaphysically intractable, and the doctrines of infinite and finite substance which it generated furnish a gallery of metaphysical grotesques; unless we are to except Leibniz; his system is, if nothing else, a miracle of ingenuity, and there are moments when we are in danger of believing it. It is a natural mistake for the student of seventeenth-century thought to underestimate the tenacity of scholastic Aristotelianism. Descartes, we all know, was reared in it, but then Descartes overthrew it; and he had done his work and died by the time that Leibniz was of an age to philosophize at all. We expect to see Leibniz starting on his shoulders and climbing on from there. We are disappointed. Leibniz himself tells us that he was raised in the scholastic teaching. His acquaintance with Descartes's opinions was second-hand, and they were retailed to him only that they might be derided. He agreed, like an amiable youth, with his preceptors.