Being and Nothingness
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.