What is existentialism, the philosophy whose own thinkers fought over its name?

In 1945, the French Catholic philosopher Gabriel Marcel called Jean-Paul Sartre an "existentialist" to his face at a colloquium. Sartre said no. Weeks later, on October 29, 1945, he changed his mind and publicly adopted the label himself in a Paris lecture, a talk later published as Existentialism Is a Humanism, a short book that helped popularize existentialist thought. To complete the irony, Marcel, the very person who had coined the term, eventually rejected it too, preferring to call his own thought "Neo-Socratic" instead. And the philosophy they were arguing over? A family of views about the individual's struggle to live an authentic life despite the apparent absurdity of existence.

That tangled origin story fits a philosophy obsessed with exactly this kind of problem: how a person defines themselves. Sartre's central claim was that existence precedes essence: a person isn't born with some fixed nature waiting to be discovered, they simply exist first, and only define themselves afterward through what they actually do. As he put it in his famous lecture, "Man first of all exists, encounters himself, surges up in the world—and defines himself afterwards." He illustrated the opposite, inauthentic path with an unforgettable image: what he called bad faith, a waiter who is simply performing the role of "a waiter," however convincingly, rather than actually choosing who he is.

Albert Camus took the problem of meaning somewhere even darker. He argued that neither the world nor human beings are absurd on their own; absurdity only appears from the mismatch between the two, in the incompatibility between human beings and the world they live in. He pushed the logic to its most extreme conclusion in The Myth of Sisyphus, writing that "there is only one truly serious philosophical problem, and that is suicide."

Even the word's history turns out to be borrowed. Kierkegaard, often credited as existentialism's founder, most likely picked up the term "existential" not on his own but from the Norwegian poet and critic Johan Sebastian Cammermeyer Welhaven. From these tangled, contested beginnings, the ideas spread far beyond philosophy departments entirely, eventually shaping theology, drama, art, literature, and psychology.