While a prisoner of war in 1940/1941 Sartre read Martin Heidegger's Being and Time, an ontological investigation through the lens and method of Husserlian phenomenology (Husserl was Heidegger's teacher). Reading Being and Time initiated Sartre's own enquiry leading to the publication in 1943 of Being and Nothingness whose subtitle is 'A Phenomenological Essay on Ontology'. Sartre's essay is clearly influenced by Heidegger though Sartre was profoundly skeptical of any measure by which humanity could achieve a kind of personal state of fulfillment comparable to the hypothetical Heideggerian re-encounter with Being. In his much gloomier account in Being and Nothingness, man is a creature haunted by a vision of "completion", what Sartre calls the ens causa sui, and which religions identify as God. Born into the material reality of one's body, in an all-too-material universe, one finds oneself inserted into being (with a lower case "b"). Consciousness is in a state of cohabitation with its material body, but has no objective reality; it is nothing ("no thing"). Consciousness has the ability to conceptualize possibilities, and to make them appear, or to annihilate them.  Introduction
In the introduction, Sartre sketches his own theory of consciousness, being and phenomena through criticism of both earlier phenomenologists (most notably Husserl and Heidegger) as well as idealists, rationalists and empiricists. According to him one of the major achievements of modern philosophy has been to free us of the kinds of dualism that set the existent up as having a "hidden" nature as with Kant's noumenon; Phenomenology has removed "the illusion of worlds behind the scene."
Based on an examination of the nature of phenomena, he describes the nature of two aspects of being, being-in-itself and being-for-itself. While being-in-itself is something that can only be approximated, a sort of being that can only be imagined as itself if it is imagined without a witnessing consciousness, being-for-itself is the being of consciousness.  Part 1 Chapter 1: The origin of negation
When we go about the world, we have expectations which are often not fulfilled. For example, Pierre is not at the café where we thought we would meet him, so there is a negation, a void, a nothingness, in the place of Pierre. When looking for Pierre his lack of being there becomes a negation; everything he sees as he searches the people and objects about him are "not Pierre." So Sartre claims "It is evident that non-being always appears within the limits of a human expectation."   Part 1 Chapter 2: Bad faith
Bad faith or "Self-Deception", as translations vary, can be understood as the guise of existing as a character, individual or person who defines himself through the...