Being and Nothingness that among them the work usually went unread. Being and Nothingness Being and Nothingness: An Essay on Phenomenological Ontology (), sometimes published with the subtitle 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
Being and Time of what a hammer "is" is not determined by a theoretical understanding of its presence, but by the fact that it is something we need at the moment we wish to do hammering. Only a "later" understanding might come to contemplate a hammer "as" an object. The total understanding of being results from an explication of the implicit knowledge of being that inheres in "Dasein". Philosophy thus becomes a form of interpretation, but since there is no external reference point outside being from which to begin this interpretation, the question becomes to know in which way to proceed with this