In 1960 Sartre returned to philosophy, publishing the first volume of his Critique of Dialectical Reason. It represented essentially a modification of his existentialist ideas, or a philosophy that stresses the importance of the individual experience. The drift of Sartre's earlier work was toward a sense of the uselessness of life. In Being and Nothingness he declared man to be "a useless passion," forced to exercise a meaningless freedom. But after World War II, his new interest in social and political questions gave way to more optimistic and activist views.
Sartre believes wholeheartedly in the freedom of the will: he is strongly anti-deterministic about human choice, seeing the claim that one is determined in one’s choices as a form of self-deception to which he gives the label ‘bad faith’, a notion that plays an important role in Being and Nothingness . Although he rejects the idea that human beings have any essence, he takes the essence of human beings to be that they are free when he declares: “man is free, man is freedom” (p. 34). The word ‘freedom’ would have had a particularly powerful appeal for people recently freed from the Nazi Occupation. ‘Freedom’ is a word with extremely positive associations – hence its frequent appropriation by politicians who redefine it to suit their own purposes. Yet Sartre states that we are “condemned to be free” (p. 34), a deliberate oxymoron bringing out what he believes to be the great weight of responsibility accompanying human freedom.