Nothingness, is primarily concerned with developing an original approach to the being of consciousness. Sartre's ontology resituates the Cartesian cogito in a complete system that provides a new understanding of negation and a dynamic interpretation of human existence. The article examines the role of consciousness, temporality and the relationship between self and others in the light of Sartre's arguments against "classical" rationalism. The conclusion suggests that Sartre's departure from modern foundationalism has "postmodern" implications that emerge in the areas of ontology, existential analytics and the ethics of human freedom.The purpose of this paper is to demonstrate that Jean-Paul Sartre's Being and Nothingness (L'être et le néant, 1943) responds in decisive ways to the Cartesian legacy in developing an original ontology that underlies the philosopher's commitment to existentialism. In arguing that Sartre is in dialogue with the rationalist tradition, we shall maintain that he is a "postcartesian," not primarily in the minimal sense of coming after René Descartes, but rather in the stronger sense of responding to the philosophical challenge of his "classical" predecessor. This stronger claim also means that Sartre sometimes adopts an adversarial relationship to Cartesian ontology. Our approach to Sartre's attempt to address the question of being will allow us to examine four integral concerns, namely, (i) the structure of consciousness as conscious being, (ii) the nature of temporality, (iii) the role of the cogito in clarifying the existence of other persons and (iv) the significance of freedom to "postmodern" accounts of the modern condition. These four concerns will be interrelated in a way that argues in favor of Sartre's distinctive contribution to existential phenomenology. I While early commentators on Sartre's work did not hesitate to discuss the influence of Descartes on Being and Nothingness, we might begin by reconsidering this influence from two different standpoints. First, Sartre's early philosophy 37