Descartes
Sartre's existentialism shares its philosophical starting point with René Descartes: The first thing we can be aware of is our existence, even when doubting everything else (Cogito ergo sum). In Nausea, the main character's feeling of dizziness towards his own existence is induced by things, not thinking. This dizziness occurs "in the face of one's freedom and responsibility for giving a meaning to reality".[1] As an important break with Descartes, Sartre rejects the primacy of knowledge (a rejection summed up in the phrase "Existence precedes essence") and offers a different conception of knowledge and consciousness.
Husserl
Important ideas in Being and Nothingness build on Edmund Husserl's phenomenology. To both philosophers, consciousness is intentional, meaning that there is only consciousness of something. For Sartre, intentionality implies that there is no form of self that is hidden inside consciousness (such as Husserl's transcendental ego). An ego must be a structure outside consciousness, so that there can be consciousness of the ego.[2]
