Both self determinism and existentialism consider that human beings have free will. Self determinism is sometimes linked with theologians such as Thomas Aquinas, it accepts determinism and free will, therefore it is a position held by the compatibilists as opposed to incompatibilists who believe that free will and determinism are incompatible. If we take Sartre as a representative of existentialism (however there is theistic and atheistic existentialism) we might interpret his believe in humans freedom to be incompatible with determinism, therefore he might be seen to hold a libertarian theory of free will. Libertarianism is the position of those who believe that free will and determinism are incompatible, and thus humans action is neither predictable nor caused by certain physiological or psychological causes. Self determinism accepts determinism. According to it human actions and choices are determined by internal causes which might include desires, emotions, believes and also inherited factors and enviromentally caused factors. Existentialism does not accept determinism of any kind. Man is creator of his actions and choices. Their believe in free will is based on indeterminism. Thus they are rightly called libertarianists. For compatibilism and incompatibilism see wikipedia free encyclopedia: " free will".
I hpe this will help!
Existentialism is a philosophy and postmodernism was an art form/movement
Behaviorism is the theory that animal and human behavior is explained without appeal to feeling or thought. The difference is that existentialism is a theory emphasizing the existence of a person as a free agent developing through acts of the will.
Nihilism claims that there is no meaning or purpose in life. Existentialism claims that there is meaning and purpose in your life inso far as you determine it for yourself.
existentialism is a freedom of choice
this sounds like a paper topic... they are extremely different... do some research!
Existentialism does not play into atheism.
Søren Kierkegaard was the first existentialism philosopher, so be the founder.
Existentialism and realism share a common element in that the "self" is a major focus
It does no such thing ! You may want to read about philosophy to learn what existentialism is.
Atheists have friends like anyone else; existentialism is irrelevant.
Existentialist epistemology is, like most existentialism, based on personal choice - i.e. a choice to believe.