During the lives of Johann Friedrich and his successor, Ernst August, Leibnitz remained in high favor and enjoyed in particular the friend ship of the *two Electresses,a Sophia, wife of Ernst August and daughter of Descartes' cor respondent, Elizabeth of the Palatinate, and her daughter, Sophia Charlotte, queen of Prus .sia. With the accession of the former's son, George Louis, afterward George I of England, to the dukedom he seems to have fallen into some disfavor, which, combined with the at tacks of Newton's partisans, did much to em bitter his last years.
Works.— In addition to his diplomatic and historical compositions, Leibnitz conducted an enormous scientific and philosophical corre spondence, but his busy life left little time for the production of philosophical works on a large scale. He preferred to make his ideas known piecemeal in correspondence and occa sional short essays on particular points. The one extended philosophical treatise published in his lifetime, the famous (Theodicy,' a de fense of natural theology against the sceptical attack of Bayle, is by general consent his poor est performance. (The far more important (New Essays on Human Understanding,> a penetrating criticism of the empiricism of Locke, remained in manuscript until 1765; the even more valuable 'Discourse on Meta physics,> composed in 1685 for Arnauld, was not printed until 1846. Even the famous 'Monadology,> the best known of his shorter philosophical essays, was only published in the original French by Erdmann in 1840). There is thus no such thing as an even approximately complete edition of the philosophical writings of Leibnitz. The best substitute available is afforded by the two editions of Gerhardt of the mathematical (Halle and Berlin 1850-63) and the philosophical works (Berlin 1875-90). But the recent publication by M. Couturat of a selection from the manuscript preserved at Han over (Opuscules et fragments inidits de Leib nitz, Paris 1903), has shown that many things of first rate importance have been passed over in Gerhardt's editions, and has thrown a wholly new light on the logical foundations of Leib nitz's system. Though the great majority of the Hanover manuscripts are still unprinted, it is already clear that Leibnitz had anticipated to a previously unsuspected extent many of the most important recent developments in both mathe matics and philosophy. Thus he had conceived the idea of projective geometry, and of the cal culus of extension, while he had completely worked out the main principles of the exact logic recreated nearly 200 years later by Boole.
Similarly the the apparently chi merical project of a universal ((characteristic,* or philosophical symbolism independent of spoken language, to which so much of Leibnitz's thought was devoted, has only been shown in the last few years by its approximate realization in the mathematical logics of Peano, Freje and others.
Philosophical System.— Leibnitz makes his first appearance as a philosopher with a settled system of his own in 1685 at the age of 39, in the 'Discourse on Metaphysics> composed for Arnauld. He had previously passed succes sively under several different influences. In youth he had been familiar with the traditional doctrines of the great schoolmen, particularly with the nominalist system of Duns Scotus, and had afterward been powerfully influenced by the new materialist and mechanical philosophy of nature as expounded by Hobbes and Gas sendi. During his stay in Paris he had been a profound student and acute critic of Car tesianism, and had subsequently, as we have seen, come into relations with Spinoza, who, however, failed from the first to satisfy him. At some time between 1675 and 1685 }kg had evidently further made a special study of Plato and Aristotle. The system of ideas at which he finally arrived bears traces of all these prepara tory studies. In its general character it is cor rectly described by the common statement that it represents a reaction against the exclusively mechanical interpretation of nature and mind and a return to the spiritualistic and teleological conceptions of the Platonic-Aristotelian philoso phy. Against the purely mechanical conception of extra-human nature assumed by Cartesian ism Leibnitz maintains that the explanation of mechanical routine itself has always in the last resort to be found in final casuality, in pur posive activity; against the Spinozistic concep tion of the illusoriness of all finite individual ity, which he sincerely regarded as fatal to re ligion, he insists upon the ultimate and absolute reality of individual finite existence. At the same time, Leibnitz's system is one of pure and consistent rationalism; he aims at ruining the mechanical philosophy by showing that it col lapses of itself when the attempt is made to think it out with rigorous consistency. Phys ical science is absolutely justified in demanding a mechanical explanation of all events without exception, but the very nature of mechanical explanation is such that it cannot be finally satisfactory, but demands a further metaphys ical explanation in terms of individual purposive activity to make it intelligible.