While there is more than one strand of communist theory, the most famous by far is Marxism, named for the German philosopher and economic theorist Karl Marx. Marx, together with Friedrich Engels, developed an economic and political theory that argued that history follows irrevocable laws and develops through a series of stages, stretching from primitive systems like feudalism through to the excesses of capitalism, and—eventually—to a communist utopia in which all social hierarchies will be eradicated and the state will wither away in favor of harmonious collectivism. To achieve this final stage of communism, Marx believed in a proletarian revolution and a “dictatorship of the proletariat” that would oversee the confiscation of private property and the formation of a planned, state-run economy. While Camus acknowledges some of the more appealing and humanitarian aspects of Marxist thought, he nevertheless criticizes Marx throughout The Rebel for the dangerously totalizing nature of his revolutionary philosophy.

Nihilism—which comes from the Latin word nihil, meaning “nothing”—is a philosophical movement that asserts the meaninglessness of existence and rejects all human morals and values as baseless. While forms of nihilism appeared at various points in European history, it became especially dominant during the 19th century, when it attracted the attention of philosophers like Søren Kierkegaard and Nietzsche.