Happy Birthday: Jean-Paul Charles Aymard Sartre (21 June 1905 – 15 April 1980) was a French philosopher, playwright, novelist, screenwriter, political activist, biographer, and literary critic, considered a leading figure in 20th-century French philosophy and Marxism. Sartre was one of the key figures in the philosophy of existentialism (and phenomenology). His work has influenced sociology, critical theory, post-colonial theory, and literary studies. He was awarded the 1964 Nobel Prize in Literature despite attempting to refuse it, saying that he always declined official honours and that "a writer should not allow himself to be turned into an institution."

Sartre held an open relationship with prominent feminist and fellow existentialist philosopher Simone de Beauvoir. Together, Sartre and de Beauvoir challenged the cultural and social assumptions and expectations of their upbringings, which they considered bourgeois, in both lifestyles and thought. The conflict between oppressive, spiritually destructive conformity (mauvaise foi, literally, 'bad faith') and an "authentic" way of "being" became the dominant theme of Sartre's early work, a theme embodied in his principal philosophical work Being and Nothingness (L'Être et le Néant, 1943). Sartre's introduction to his philosophy is his work Existentialism Is a Humanism (L'existentialisme est un humanisme, 1946), originally presented as a lecture.

Sartre's primary idea is that people, as humans, are "condemned to be free". He explained, "This may seem paradoxical because condemnation is normally an external judgment which constitutes the conclusion of a judgment. Here, it is not the human who has chosen to be like this. There is a contingency of human existence. It is a condemnation of their being. Their being is not determined, so it is up to everyone to create their own existence, for which they are then responsible. They cannot not be free, there is a form of necessity for freedom, which can never be given up."

This theory relies upon his position that there is no creator, and is illustrated using the example of the paper cutter. Sartre says that if one considered a paper cutter, one would assume that the creator would have had a plan for it: an essence. Sartre said that human beings have no essence before their existence because there is no Creator. Thus: "existence precedes essence". This forms the basis for his assertion that because one cannot explain one's own actions and behaviour by referring to any specific human nature, they are necessarily fully responsible for those actions. "We are left alone, without excuse." "We can act without being determined by our past which is always separated from us."

Sartre maintained that the concepts of authenticity and individuality have to be earned but not learned. We need to experience "death consciousness" so as to wake up ourselves as to what is really important; the authentic in our lives which is life experience, not knowledge. Death draws the final point when we as beings cease to live for ourselves and permanently become objects that exist only for the outside world. In this way death emphasizes the burden of our free, individual existence. "We can oppose authenticity to an inauthentic way of being. Authenticity consists in experiencing the indeterminate character of existence in anguish. It is also to know how to face it by giving meaning to our actions and by recognizing ourselves as the author of this meaning. On the other hand, an inauthentic way of being consists in running away, in lying to oneself in order to escape this anguish and the responsibility for one's own existence."