Being and Nothingness: An Essay on Phenomenological Ontology (French: L’Être et le néant : Essai d’ontologie phénoménologique), sometimes subtitled A Phenomenological Essay on Ontology, is a 1943 book by the philosopher Jean-Paul Sartre, in which the author asserts the individual’s existence as prior to the individual’s essence (“existence precedes essence”) and seeks to demonstrate that free will exists. While a prisoner of war in 1940 and 1941, Sartre read Martin Heidegger’s Being and Time (1927). Heidegger’s work, an ontological investigation through the lens and method of Husserlian phenomenology (Edmund Husserl was Heidegger’s teacher), initiated Sartre’s own philosophical enquiry.
Though influenced by Heidegger, Sartre was profoundly sceptical of any measure by which humanity could achieve a kind of personal state of fulfilment comparable to the hypothetical Heideggerian re-encounter with Being. In Sartre’s account, man is a creature haunted by a vision of “completion”, what Sartre calls the ens causa sui, literally “a being that causes itself”, which many religions and philosophers identify as God. Born into the material reality of one’s body, in a material universe, one finds oneself inserted into being. Consciousness has the ability to conceptualize possibilities, and to make them appear, or to annihilate them. Being and Nothingness is considered Sartre’s most important philosophical work, original despite Sartre’s debts to Heidegger, and the most important non-fiction expression of Sartre’s existentialism. The book was popular among British students in the 1960s.