The work that more than any other popularized the optimistic philosophy, not only in England but throughout Europe, was Alexander Pope's Essay on Man (1733-34), a rationalistic effort to justify the ways of God to man philosophically. As has been stated in the introduction, Voltaire had become well acquainted with the English poet during his stay of more than two years in England, and the two had corresponded with each other with a fair degree of regularity when Voltaire returned to the Continent.
Voltaire could have been called a fervent admirer of Pope. He hailed the Essay of Criticism as superior to Horace, and he described the Rape of the Lock as better than Lutrin. When the Essay on Man was published, Voltaire sent a copy to the Norman abbot Du Resnol and may possibly have helped the abbot prepare the first French translation, which was so well received. The very title of his Discours en vers sur l'homme (1738) indicates the extent Voltaire was influenced by Pope. It has been pointed out that at times, he does little more than echo the same thoughts expressed by the English poet. Even as late as 1756, the year in which he published his poem on the destruction of Lisbon, he lauded the author of Essay on Man. In the edition of Lettres philosophiques published in that year, he wrote: "The Essay on Man appears to me to be the most beautiful didactic poem, the most useful, the most sublime that has ever been composed in any language." Perhaps this is no more than another illustration of how Voltaire could vacillate in his attitude as he struggled with the problems posed by the optimistic philosophy in its relation to actual experience. For in the Lisbon poem and in Candide, he picked up Pope's recurring phrase "Whatever is, is right" and made mockery of it: "Tout est bien" in a world filled with misery!
Pope denied that he was indebted to Leibnitz for the ideas that inform his poem, and his word may be accepted. Those ideas were first set forth in England by Anthony Ashley Cowper, Earl of Shaftesbury (1671-1731). They pervade all his works but especially the Moralist. Indeed, several lines in the Essay on Man, particularly in the first Epistle, are simply statements from the Moralist done in verse. Although the question is unsettled and probably will remain so, it is generally believed that Pope was indoctrinated by having read the letters that were prepared for him by Bolingbroke and that provided an exegesis of Shaftesbury's philosophy. The main tenet of this system of natural theology was that one God, all-wise and all-merciful, governed the world providentially for the best. Most important for Shaftesbury was the principle of Harmony and Balance, which he based not on reason but on the general ground of good taste. Believing that God's most characteristic attribute was benevolence, Shaftesbury provided an emphatic endorsement of providentialism.
Following are the major ideas in Essay on Man: (1) a God of infinite wisdom exists; (2) He created a world that is the best of all possible ones; (3) the plenum, or all-embracing whole of the universe, is real and hierarchical; (4) authentic good is that of the whole, not of isolated parts; (5) self-love and social love both motivate humans' conduct; (6) virtue is attainable; (7) "One truth is clear, WHATEVER IS, IS RIGHT." Partial evil, according to Pope, contributes to the universal good. "God sends not ill, if rightly understood." According to this principle, vices, themselves to be deplored, may lead to virtues. For example, motivated by envy, a person may develop courage and wish to emulate the accomplishments of another; and the avaricious person may attain the virtue of prudence. One can easily understand why, from the beginning, many felt that Pope had depended on Leibnitz.