In Chapter four of Candide, Voltaire gives full rein to his biting satire of the optimism promulgated by the mathematician and philosopher G. W. von Leibniz.
After meeting a beggar covered with sores, having lifeless eyes, a rotted nose and teeth that fall out with every racking cough of his wretched body, Candide is moved to give the poor creature a florin, whereupon the beggar hugs him. Candide is appalled to discover that this beggar is Dr. Pangloss. After Candide learns from him that Cunegonde is dead he exclaims, "Oh best of all possible worlds--after the philosophy of von Leibniz--, where are you?" Pangloss explains that he has contracted syphilis from Paquette who was infected, "a present given to her by a learned Franciscan friar," who in turn contracted it from another on back to a Jesuit who received it from a shipmate of Christopher Columbus. When Candide suggests that it has all stemmed from the devil, Pangloss contradicts him, saying,
Not at all....It was an indispensable element in the best of worlds, a necessary ingredient, becuase if Columbus, on an American island, hadn't caught that disease which poison the source of generation, ...and which is obviously opposed to the great goal of nature, we would now have neither chocolate nor cochineal.
In this passage, of course, Voltaire parodies von Leibniz's reasoning as well as the blind optimism of his philosophy that holds that since God has created the world, and God is all good, then the world, also, must be good. This attempt of Pangloss to explain evil in a world where all is good by suggesting that the evils have served a good purpose, the production of chocolate, for instance, is absurd.