Freedom for Sartre is the sine qua non of our species, our way of being in the world and our responsibility for the world. To contemplate the extent of what he believes freedom to be, and to require of us is to feel dizzy, to feel the physical sense of nausea that he argues is a mark of any honest interactions with the reality of the world. Sartre argues that, even when this appears not to be the case, that we are in fact each free, that we cannot exist in any other state:
Jean-Paul Sartre is a demoniacal philosopher of freedom. As Hakim writes, freedom is Sartre's main key to the understanding of man: through freedom, meaning enters into the world. We recall that he asserts that, at the start, man simply is. Thus the vocation of the Sartrean man is nothing else but the perpetual process of self-creation. Sartrean freedom is one which excuses no one.
Man is not free not to be free. The heavy burden of this freedom perpetually haunts man. An oft-quoted phrase encapsulates this burden: Man condemned to be free carries the whole world (http://www.geocities.com/sartresite/sartre_theses4.html).
Sartre is the most philosophical of these three writers: He is in fact the only one of the three who arguably should be called a philosopher at all while the other two are writers with a philosophical bent. It is thus in no way surprising that Sartre's concept of freedom is more complex, entangled in and supported by his understanding about the nature of knowledge and