Jean-Paul Sartre (1905-80), the name most associated with existentialism, was a leading literary figure, public intellectual, and political activist in mid-20th century France. He initially became famous for dwelling on things like nausea and absurdity.
Sartre propounded one of the most extravagant voluntarisms ever conceived, grounded in a novel, atheistic metaphysics rather than the extreme supernaturalism that has usually supported such views. “[N]o limits to my freedom can be found except freedom itself…. [F]or human reality, to be is to choose oneself; nothing comes to it either from the outside or from within which it can receive or accept…. Man… is wholly and forever free” (Being and Nothingness, pp. 439-441). We are “condemned” to freedom, are free even in prison, were never freer than during the Nazi occupation, and so on. For my own contrasting view, see Freedom and Free Will; Freedom Without Sovereignty; Choice, Deliberation; Structural Causality, Choice; Brandomian Choice.
Later, he developed a theory of what he called totalization. “If dialectical Reason exists, then, from the ontological point of view, it can only be a developing totalisation, occurring where the totalisation occurs, and, from the epistemological point of view, it can only be the accessibility of that totalisation to a knowledge which is itself, in principle, totalising in its procedures.” (Critique of Dialectical Reason, p. 47). This sounds like a nightmare of the sort of bad old metaphysical Hegelianism that would swallow everything, completely opposed to Hegel’s own acute sensitivity to context and the essential role of mediation.
What is common to Sartre’s notions of freedom and totalization is their inflationary character. This is not a sound basis for anything.