Being and Nothingness (1943) is the most comprehensive and far-reaching statement of Jean-Paul Sartre’s philosophy. It is subtitled: “An Essay on Phenomenological Ontology.”

Phenomenology is the study of how phenomena present or appear in consciousness. Ontology is the study of being. Thus, phenomenological ontology can be defined as the study of the nature of being of phenomena as they present in consciousness.

What is Being? What is Nothingness? How are they related? For Sartre, Being is objective, it is what is. Being is in-itself. Existence, on the other hand, has a subjective quality in relation to human reality. Existence refers to the fact that some individual or thing is present in the world.

Sartre distinguishes between two types of Being: “Being-in-itself” (être-en-soi) and “Being-for-itself” (être-pour-soi). Being-in-itself is non-conscious Being, the Being of existing things or objects of consciousness. Being-for-itself is conscious Being, which is conscious of what it is not.

Being-for-itself is conscious of itself. Indeed, consciousness can exist only as engaged in a being conscious of itself. Being-for-itself is consciousness of objects, and can be the object of its own consciousness; i.e. it is conscious that it is conscious of objects. Consciousness also includes self-consciousness.

Sartre emphasizes that “all consciousness is consciousness of something.” This is an ontological proof of what appears in consciousness. If consciousness can only be consciousness of something other than itself, then what appears in consciousness must already exist.

Sartre distinguishes between two type of consciousness: unreflective consciousness, and reflective consciousness.

Unreflective consciousness is seen in the pre-reflective cogito of Descartes (i.e. the statement “I think, therefore I am” says that I think, but not that I think about myself.) Unreflective consciousness is conscious of its consciousness, but does not attempt to become its own object.

Reflective consciousness, on the other hand, is conscious of its lack in relation to Being other than itself. Reflective consciousness can also be called moral consciousness, because it reveals values. Values can be determined by the Being-for-itself, in that the Being-for-itself sees what is lacking in relation to itself.

Because consciousness can conceive of a lack of Being, Being-for-itself is also the nihilation of Being-in-itself. Being-for-itself brings Nothingness into the world, because Being-for-itself judges other beings by seeing what it is not. Being-for-itself nihilates itself, and becomes its own Nothingness.

Nothingness is a state of non-being. Nothingness does not itself have Being, but is sustained by Being. Sartre disagrees with Hegel that Being and Nothingness are opposite, or are opposed as thesis and antithesis respectively. Sartre says that Nothingness is the contradiction, and not the opposite, of Being. Nothingness is logically subsequent to Being.

Sartre notes that Kierkegaard described anguish in the face of what the individual lacks as anguish in the face of freedom, and that Heidegger considered anguish as the apprehension of Nothingness. For Kierkegaard, anguish is consciousness of freedom, whereas fear is dread of something in the world.

Sartre agrees with both Kierkegaard and Heidegger, that anguish is the recogniton by the Self of the possibility of making choices, and that anguish is the discovery of Nothingness as future possibility. For Sartre, anguish is the discovery that the Self faces Nothingness in the past and the future, that the Self may nihilate itself, because nothing relieves the Self of the responsibility for making choices, and nothing guarantees the validity of the values that are chosen by the Self.

Flight from anguish toward reassuring myths is an attitude that Sartre calls “bad faith.” Religious or psychological beliefs which try to impose order or meaning on human existence, or which try to make us the passive subject of external forces, are an example of “bad faith,” because they are an attempt to escape the responsibility for making free choices. Through bad faith, we may seek to deny the responsible freedom of Being-for-itself. Bad faith consists in hiding the truth from ourselves. Sincerity is the antithesis of bad faith.

How is Being related to Space and Time? For Sartre, geometrical space, or the reciprocity of spatial relations, is Nothingness. The statement that “I know where I am” means that “I know where I am not.” Space is a Nothingness, and is seen in terms of the For-itself’s free project to organize relations between external objects.

Temporality is the process by which Being-for-itself continuously nihilates Being-in-itself. The Past is what is no longer. The Past is not nothing, the Past is what the For-itself has been. The Past is no longer for-itself, the Past is in-itself. The For-itself is sustained in being by the In-itself. The Present is Being-for-itself. The Future is revealed to the For-itself as that which the For-itself is not yet. The Future is the Being projected by the For-itself, because the For-itself is perpetually apprehending itself as unachieved in relation to it.

Being and Nothingness is remarkable for Sartre’s willingness to confront Nothingness as part of human reality. Nothingness for us is non-existence, negation, nihilation. Sartre argues for accepting personal responsibility, despite the absence of a determining principle that would guarantee objective certainty. He also argues that consciousness of Being means consciousness of Nothingness. For Sartre, we are our own Nothingness, and we bring Nothingness into the world. Sartre confronts Nothingness, and embraces it as part of human reality.