From the very beginning , existentialism defined itself as a philosophy of ambiguity. It was by affirming the irreducible character of ambiguity that Kierkegaard opposed himself to Hegel , and it is by ambiguity that, in our own generation, Sartre , in Being and Nothingness , fundamentally defined man, that being whose being is not to be, that subjectivity which realizes itself only as a presence in the world , that engaged freedom , that surging of the for-oneself which is immediately given for others.
The essential freedom, the ultimate and final freedom that cannot be taken from a man, is to say No. This is the basic premise in Sartre 's view of human freedom: freedom is in its very essence negative, though the negativity is also creative.
One does wish that Sartre would pause for a while to regroup his forces. The man really does write too much.