In his relations with his fickle admirer, Frederick the Great, and with others of his fellow-thinkers, he and they painfully brought home to freethinkers the lesson that for them as for all men there is a personal art of life that has to be learned, over and above the rectification of opinion. But he and the others wrought immensely towards that liberation alike from unreason and from bondage which must precede any great improvement of human things. Voltaire's constant burden was that religion was not only untrue but pernicious, and when he was not dramatically showing this of Christianity, as in his poem La Ligue (1723), he was saying it by implication in such plays as Zaïre (1732) and Mahomet (1742), dealing with the fanaticism of Islam; while in the Essai sur les moeurs (1756), really a broad survey of general history, and in the Siècle de Louis XIV, he applied the method of Montesquieu, with pungent criticism thrown in. Later, he added to his output direct criticisms of the Christian books, as in the Examen important de Milord Bolingbroke (1767), and the Recherches historiques sur le Christianisme (? 1769), continuing all his former lines of activity. Meanwhile, with the aid of his companion the Marquise du Chatelet, an accomplished mathematician, he had done much to popularize the physics of Newton and discredit the scientific fallacies of the system of Descartes; all the while preaching a Newtonian but rather agnostic deism. This is the purport of his Philosophe Ignorant, his longest philosophical essay. [991] The destruction of Lisbon by the earthquake of 1755 seems to have shaken him in his deistic faith, since the upshot of his poem on that subject is to leave the moral government of the universe an absolute enigma; and in the later Candide (1759) he attacks theistic optimism with his matchless ridicule. Indeed, as early as 1749, in his Traité de la Métaphysique, written for the Marquise du Chatelet, he reaches virtually pantheistic positions in defence of the God-idea, declaring with Spinoza that deity can be neither good nor bad. But, like so many professed pantheists, he relapsed, and he never accepted the atheistic view; on the contrary, we find him arguing absurdly enough, in his Homily on Atheism (1765), that atheism had been the destruction of morality in Rome; [992] on the publication of d'Holbach's System of Nature in 1770 he threw off an article Dieu: réponse au Système de la Nature, where he argued on the old deistic lines; and his tale of Jenni; or, the Sage and the Atheist (1775), is a polemic on the same theme. By this time the inconsistent deism of his youth had itself been discredited among the more thoroughgoing freethinkers; and for years it had been said in one section of literary society that Voltaire after all "is a bigot; he is a deist!" [993]