The major theme of Candide, which is even included in the title of the book, is optimism. Only mentioned twice in the book, optimism in the 18th century referred to a philosophical position that the world is the best possible world because an omnipotent, benevolent God has chosen and created the best of all worlds. Philosopher Gottfried Wilhelm Leibniz was known for his optimism, seeking to reconcile the existence of evil in what must be a perfect world, and this philosophy is planted in Candide’s mind as a child by Pangloss, a philosopher and follower of Leibniz.

Optimism is problematic for Voltaire because it involves a degree of fatalism, wherein all events are predetermined and thus inevitable. This view undermines any free will humans might have in their lives, rendering them helpless to change the problems of society and the world, and forcing them to accept the way things are. The position of optimism likewise undermines those who seek to change situations for the better, for it posits that life is already at its best and any improvement is futile. Voltaire often mocks this belief through Pangloss. For example, after the earthquake in Lisbon, Pangloss comforts the locals at dinner, who are so distraught they are soaking their bread with their tears, by saying: “‘This is all for the best,’ he said.