L'Être et le Néant
Some philosophers argue that Sartre's thought is contradictory. Specifically, they believe that Sartre makes metaphysical arguments despite his claim that his philosophical views ignore metaphysics. Herbert Marcuse criticized "Being and Nothingness" for projecting anxiety and meaninglessness onto the nature of existence itself: "Insofar as Existentialism is a philosophical doctrine, it remains an idealistic doctrine: it hypostatizes specific historical conditions of human existence into ontological and metaphysical characteristics. Existentialism thus becomes part of the very ideology which it attacks, and its radicalism is illusory." In "Letter on Humanism", Heidegger criticized Sartre's existentialism: