— Gottfried Leibniz, livro Discourse on Metaphysics
De quelque manière que Dieu aurait créé le monde, il aurait toujours été régulier et dans un certain ordre général. Mais Dieu a choisi celui qui est le plus parfait, c’est-à-dire celui qui est en même temps le plus simple en hypothèses et le plus riche en phénomènes...
Discours de métaphysique (1686); Leibniz famously tried to show that ours is the best of all possible worlds (see also Monadologie (53 & 54) below and compare Maimonides from Guide for the Perplexed (c. 1190), "Whatever is formed of matter receives the most perfect form possible in that species of matter.") These attempts were mercilessly parodied in Voltaire's Candide. Quotations from Voltaire's novel are often mistakenly attributed to Leibniz. Other statements by Leibniz upon the subject include these:
S'il n'y avait pas le meilleur (optimum) parmi tous les mondes possibles, Dieu n'en aurait produit aucun.
If there were no best among all possible worlds, God would not have created one.
Théodicée (1710)ː I. 8
I do not believe that a world without evil, preferable in order to ours, is possible; otherwise it would have been preferred. It is necessary to believe that the mixture of evil has produced the greatest possible good: otherwise the evil would not have been permitted.
The combination of all the tendencies to the good has produced the best; but as there are goods that are incompatible together, this combination and this result can introduce the destruction of some good, and as a result some evil.
Letter to Bourguet (late 1712)], as translated in The Shorter Leibniz Texts (2006) http://books.google.com/books?id=oFoCY3xJ8nkC&dq edited by Lloyd H. Strickland, p. 208