Hegel's great "Aufhebung"and the Marxian dialectic is simplified in English as the triad thesis - antithesis - synthesis. This does not capture Hegel's sense that the third stage rises up and overcomes the conflict and poses a new thesis in an unending succession.

In Heidegger, Being or unchanging eternal essence becomes lower-case being (dasein), the human condition of being thrown into the world and having to make decisions ("Dezisions") that Heidegger characterizes as Destruktion.

In Sartre's freedom, Heidegger's idea of Destruktion in a willed decision, the Hegelian dialectical "negation," becomes the "annihilation" of possibilities, which are thereby condemned to "nothingness."

Since the death of God, there is no reason to justify such decisions, no absolute values. The freedom to choose, to make oneself by one's willed actions, is therefore absurd. We are "condemned to this freedom," Sartre argued.

Freedom has no essence. It is not subject to any logical necessity.

For the for-itself, to be is to nihilate the in-itself which it is. Under these conditions freedom can be nothing other than this nihilation. It is through this that the for-itself escapes its being as its essence; it is through this that the for-itself is always something other than what can be said of it."

[I am] condemned to exist forever beyond my essence, beyond the causes and motives of my act. I am condemned to be free.

(Being and Nothingness, p.438-9)

Freedom "is a choice of its being but not the foundation of its being. . . . This choice is absurd, not because it is without reason but because there has never been any possibility of not choosing oneself. . . . It is absurd in this sense—that the choice is that by which all foundation and all reasons come into being, that by which the very notion of the absurd receives its meaning."

(Being and Nothingness, p.479)

Freedom without Values is Absurd (Continental Existentialism).
Values without Freedom are Worthless (British Utilitarianism).

When we think of God as the creator, we are thinking of him, most of the time, as a supernal artisan. Whatever doctrine we may be considering, whether it be a doctrine like that of Descartes, or of Leibnitz himself, we always imply that the will follows, more or less, from the understanding or at least accompanies it, so that when God creates he knows precisely what he is creating. Thus, the conception of man in the mind of God is comparable to that of the paper-knife in the mind of the artisan: God makes man according to a procedure and a conception, exactly as the artisan manufactures a paper-knife, following a definition and a formula. Thus each individual man is the realization of a certain conception which dwells in the divine understanding. In the philosophic atheism of the eighteenth century, the notion of God is suppressed, but not, for all that, the idea that essence is prior to existence; something of that idea we still find everywhere, in Diderot, in Voltaire and even in Kant. Man possesses a human nature; that "human nature," which is the conception of human being, is found in every man; which means that each man is a particular example of a universal conception, the conception of Man. In Kant, this universality goes so far that the wild man of the woods, man in the state of nature and the bourgeois are all contained in the same definition and have the same fundamental qualities. Here again, the essence of man precedes that historic existence which we confront in experience

Atheistic existentialism, of which I am a representative, declares with greater consistency that if God does not exist there is at least one being whose existence comes before its essence, a being which exists before it can be defined by any conception of it. That being is man or, as Heidegger has it, the human reality. What do we mean by saying that existence precedes essence? We mean that man first of all exists, encounters himself, surges up in the world—and defines himself afterwards.

Walter Kauffman, the translator or Nietzsche, saw a great (anti-) parallel between Sartre and a passage in Beyond Good and Evil (below)

If man as the existentialist sees him is not definable, it is because to begin with he is nothing. He will not be anything until later, and then he will be what he makes of himself. Thus, there is no human nature, because there is no God to have a conception of it. Man simply is. Not that he is simply what he conceives himself to be, but he is what he wills, and as he conceives himself after already existing—as he wills to be after that leap towards existence. Man is nothing else but that which he makes of himself. That is the first principle of existentialism. And this is what people call its "subjectivity," using the word as a reproach against us. But what do we mean to say by this, but that man is of a greater dignity than a stone or a table? For we mean to say that man primarily exists—that man is, before all else, something which propels itself towards a future and is aware that it is doing so. Man is, indeed, a project which possesses a subjective life, instead of being a kind of moss, or a fungus or a cauliflower. Before that projection of the self nothing exists; not even in the heaven of intelligence: man will only attain existence when he is what he purposes to be. Not, however, "what he may wish to be. For what we usually understand by wishing or willing is a conscious decision taken—much more often than not—after we have made ourselves what we are. I may wish to join a party, to write a book or to marry—but in such a case what is usually called my will is probably a manifestation of a prior and more spontaneous decision. If, however, it is true that existence is prior to essence, man is responsible for what he is. Thus, the first effect of existentialism is that it puts every man in possession of himself as he is, and places the entire responsibility for his existence squarely upon his own shoulders.

("Existentialism is a Humanism," in Existentialism from Dostoevsky to Sartre, ed. Walter Kaufmann, pp.289-292)