What is the theme in Candide by Voltaire?

The grand theme of the novel is the human condition. Candide wonders, what is the best way to approach life? In the story, Candide has been educated in the system of optimism. It is all he knows, but if Candide had been a flat enough character to accept optimism, the book would be without hope. Instead, Candide doubts the philosophy of optimism and eventually rejects it.