All existentialists are concerned with ontology, the study of being. The point of departure is human consciousness and mental processes. In contrast to most previous philosophical systems, which maintain that an a priori essence precedes or transcends the individual existence of people of objects, the existentialists (which is what Sartre is) precedes essence. The significance of this for human beings is that the concept that a man has an essential self is shown to be an illusion. A man’s self is nothing except what he has become; at any given moment, it is the sum of the life he has shaped until then.
The “nothing” he begins with is thus the source of man’s freedom, for at each moment it is man’s will that can choose how to act or not to act. However, such a decision affects the future doubly… a man is or should be responsible for the consequences of his actions… and each actions necessarily excludes the other potential actions for the moment, and their consequences and thus at least partially limit the potentialities for future actions. By what standards then shud man make his decsions? Man’s mind cannot discern any meaning for this existence in the universe.
When he abandons his illusions he finds himself horrified by the absurdity of the human condition. The question of the existence of God for some cosmic purpose is irrelevant, accroding to Sarte and the atheistic existentialists… because even if He does exists (which they ususally deny), He does not reveal to men the meaning of their lives. Thus man must create a human morality in the absence of any know absolute values. Honesty with oneself is maybe, perhaps the major value common to existentialist thinking (my opinion). Sartre’s writngs describe the emotional anguish of trying to achieve it.
Sartre calls the “man of good faith” one who understands the human condition described above and fully accepts the responsibility of the freedom it entails. The “man of bad faith” accepts illusion… is deliberately hypocritical, or tries to use the excuse of good intentions to escape the responsibility of his actions, the ramifications of which obviously involve other people. The man of good faith judges a potential action by estimating the result if everyone.. not just himself… were to perform it…. yet despite the difficulty of choice, he doesn’t withdraw from life, but is engaged in the business of living with himself and other men.
Camus’s philosophical thinking started from similar assumptions, but he was not existentialist (to digress here a bit)… and disagreed publicly with Sartre on a number of issues (they were friends) particularly that of ends and means. Sartre had this troubled sympathy with Communism on the grounds that one must be ‘engage’, supporting the least undesirable of the inevitably flawed contemporary movements. After the Soviet invasion in Hungary in 1956, however, Sartre publicly announced his final disillusionment with Soviet communism.