Claude Lefort (; ; 21 April 1924 – 3 October 2010) was a French philosopher and activist. He was politically active by 1942 under the influence of his tutor, the phenomenologist Maurice Merleau-Ponty (whose posthumous publications Lefort later edited). By 1943 he was organising a faction of the Trotskyist Parti Communiste Internationaliste at the Lycée Henri-IV in Paris. Lefort was impressed by Cornelius Castoriadis when he first met him. From 1946 he collaborated with him in the Chaulieu–Montal Tendency, so called from their pseudonyms Pierre Chaulieu (Castoriadis) and Claude Montal (Lefort). They published On the Regime and Against the Defence of the USSR, a critique of both the Soviet Union and its Trotskyist supporters. They suggested that the USSR was dominated by a social layer of bureaucrats, and that it consisted of a new kind of society as aggressive as Western European societies. By 1948, having tried to persuade other Trotskyists of their viewpoint, they broke away with about a dozen others and founded the libertarian socialist group Socialisme ou Barbarie. Lefort's text L'Expérience prolétarienne was important in shifting the group's focus towards forms of self-organisation. For a time Lefort wrote for both the journal Socialisme ou Barbarie and for Les Temps Modernes. His involvement in the latter journal ended after a published debate during 1952–4 over Jean-Paul Sartre's article The Communists and Peace. Lefort was for a long time uncomfortable with Socialisme ou Barbarie's "organisationalist" tendencies. In 1958 he, Henri Simon and others left Socialisme ou Barbarie and formed the group Informations et Liaison Ouvrières (Workers' Information and Liaison). In his academic career, Lefort taught at the University of São Paulo, at the Sorbonne and at the École des Hautes Études en Sciences Sociales (EHESS), being affiliated to the Centre de recherches politiques Raymond Aron. He has written on the early political writers Niccolò Machiavelli and Étienne de La Boétie and explored "the Totalitarian enterprise" in its "denial of social division... [and] of the difference between the order of power, the order of law and the order of knowledge". Biography Lefort studied at the Sorbonne. He became a Marxist in his youth under the influence of his teacher, Maurice Merleau-Ponty. From 1944, he belonged to the small French Trotskyite. In 1946, he met Cornelius Castoriadis who came to Paris from Greece. Right away, they formed a faction in the Trotskyist Parti Communiste Internationaliste called "Chaulieu–Montal Tendency", that left the