In 1710 Leibnitz published Th?odic?e a philosophical work intended to tackle the problem of evil in a world created by a good God. Leibnitz claims that the universe had to be imperfect, otherwise it would not be distinct from God. He then claims that the universe is the best possible without being perfect. Leibnitz is aware that this argument looks unlikely – surely a universe in which nobody is killed by floods is better than the present one, but still not perfect. His argument here is that the elimination of natural disasters, for example, would involve such changes to the laws of science that the world would be worse. In 1714 Leibnitz wrote Monadologia, which synthesized the philosophy of his earlier work, the Th?odic?e.
Much of the mathematical activity of Leibnitz’s last years involved the priority dispute over the invention of the calculus. In 1711 he read the paper by Keill in the Transactions of the Royal Society of London, which accused Leibnitz of plagiarism. Leibnitz demanded a retraction saying that he had never heard of the calculus of fluxions until he had read the works of Wallis. Keill replied to Leibnitz saying that the two letters from Newton, sent through Oldenburg, had given pretty plain indications whence Leibnitz derived the principles of that calculus or at least could have derived them.
Leibnitz wrote again to the Royal Society asking them to correct the wrong done to him by Keill’s claims. In response to this letter the Royal Society set up a committee to pronounce on the priority dispute. It was biased, not asking Leibnitz to give his version of the events. The report of the committee, finding in favor of Newton, was written by Newton himself and published as Commercium epistolicum near the beginning of 1713 but not seen by Leibnitz until the autumn of 1714. He learned of its contents in 1713 in a letter from Johann Bernoulli, reporting on the copy of the work brought from Paris by his nephew Nicolaus Bernoulli. Leibnitz published an anonymous pamphlet Charta volans setting out his side in which a mistake by Newton in his understanding of second and higher derivatives, spotted by Johann Bernoulli, is used as evidence of Leibnitz’s case.
The argument continued with Keill who published a reply to Charta Volans. Leibnitz refused to carry on the argument with Keill, saying that he could not reply to an idiot. However, when Newton wrote to him directly, Leibnitz did reply and gave a detailed description of his discovery of the differential calculus. From 1715 up until his death Leibnitz corresponded with Samuel Clarke, a supporter of Newton, on time, space, freewill, gravitational attraction across a void and other topics.
Leibnitz is described as a man of medium height with a stoop, broad-shouldered but bandy-legged, as capable of thinking for several days sitting in the same chair as of traveling the roads of Europe summer and winter. He was an indefatigable worker, a universal letter writer (he had more than 600 correspondents), a patriot and cosmopolitan, a great scientist, and one of the most powerful spirits of Western civilization. Leibnitz’s legacy may have not been quite what he had hoped for. It is ironical that one so devoted to the cause of mutual understanding should have succeeded only in adding to intellectual chauvinism and dogmatism. There is a similar irony in the fact that he was one of the last great polymaths – not in the frivolous sense of having a wide general knowledge, but in the deeper sense of one who is a citizen of the whole world of intellectual inquiry. He deliberately ignored boundaries between disciplines, and lack of qualifications never deterred him from contributing fresh insights to established specialisms. Indeed, one of the reasons why he was so hostile to universities as institutions was because their faculty structure prevented the cross-fertilization of ideas, which he saw as essential to the advance of knowledge and of wisdom. The irony is that he was himself instrumental in bringing about an era of far greater intellectual and scientific specialism, as technical advances pushed more and more disciplines out of the reach of the intelligent layman and amateur.