The philosophical tradition emphasizeng human freedom, individual responsibility and the making of meaning in a universe that supplies none from outside. Its shared premise, in Sartre's formula, is that existence precedes essence: there is no human nature fixed in advance that tells a person what to be, and the absence of that instruction is the condition of freedom rather than a deficiency in it.
Kierkegaard and Nietzsche are the nineteenth-century forerunners — the first insisting that the decisive questions are faced in the first person and cannot be settled by system, the second describing the death of God and the consequent need to create values rather than receive them. Heidegger's Being and Time (1927) supplied the analytic vocabulary of authenticity, anxiety and being-toward-death that the French existentialists worked with, though he rejected the label and his conduct under the Nazi regime remains an unresolved problem for readers of the work.
The movement became a public phenomenon in post-war France. Sartre's Being and Nothingness (1943) argued that we are condemned to be free and responsible even for what we did not choose; Beauvoir turned the framework to the situation of women in The Second Sex (1949), producing the tradition's most consequential book and arguably its most rigorous ethics in The Ethics of Ambiguity; Camus refused the label while writing its best-known statements of the absurd. The Sartre-Camus break of 1952, over whether revolutionary violence could be justified by history, is the tradition's defining political quarrel.
Its political legacy is genuinely ambiguous. The same emphasis on situated freedom fed Fanon's anti-colonial writing and a strand of individualism indifferent to politics altogether. The standard objection is that a philosophy of radical choice supplies no criteria for choosing, leaving authenticity as a formal virtue compatible with almost any content.