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. 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 . . . 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 toward 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. . . . 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. And, when we say that man is responsible for himself, we do not mean that he is responsible only for his own individuality, but that he is responsible for all men. The word "subjectivism" is to be understood in two senses, and our adversaries play upon only one of them. Subjectivism means, on the one hand, the freedom of the individual subject and, on the other, that man cannot pass beyond human subjectivity. It is the latter which is the deeper meaning of existentialism. When we say that man chooses himself, we do mean that every one of us must choose himself; but by that we also mean that in choosing for himself he chooses for all men. For in effect, of all the actions a man may take in order to create himself as he wills to be, there is not one which is not creative, at the same time, of an image of man such as he believes he ought to be. . . . Our responsibility is thus much greater than we had supposed, for it concerns mankind as a whole. . . .

I am thus responsible for myself and for all men, and I am creating a certain image of man as I would have him to be. In fashioning myself I fashion man.

--Jean-Paul Sartre, "Existentialism Is a Humanism" (The Age of Analysis, Morton White, pp. 124-126)

[T]he spatio-temporal object always manifests itself through an infinity of aspects and is, at bottom, only the ideal unity of this infinity. As for meanings, or eternal truths, they affirm their transcendence in that the moment they appear they are given as independent of time, whereas the consciousness which apprehends them is, on the contrary, individuated through and through in duration. Now we ask: when a reflective consciousness apprehends the I Think, does it apprehend a full and concrete consciousness gathered into a real moment of concrete duration? The reply is clear: the I is not given as a concrete moment, a perishable structure of my actual consciousness. On the contrary, it affirms its permanence beyond this consciousness and all consciousnesses, and--although it scarcely resembles a mathematical truth--its type of existence comes much nearer to that of eternal truths than to that of consciousness.

. . .

[I]t seems to me that one can make the following statements:

First, the I is an existent. It has a concrete type of existence, undoubtedly different from the existence of mathematical truths, of meanings, or of spatio-temporal beings, but no less real. The I gives itself as transcendent.

Second, the I proffers itself to an intuition of a special kind which apprehends it, always inadequately, behind the reflected consciousness.

Third, the I never appears except on the occasion of a reflective act. In this case, the complex structure of consciousness is as follows: there is an unreflected act of reflection, without an I, which is directed on a reflected consciousness. The latter becomes the object of the reflecting consciousness without ceasing to affirm its own object (a chair, a mathematical truth, etc.). At the same time, a new object appears which is the occasion for an affirmation by reflective consciousness, and which is consequently not on the same level as the unreflected consciousness (because the latter consciousness is an absolute which has no need of reflective consciousness in order to exist), nor on the same level as the object of the reflected consciousness (chair, etc.). This transcendent object of the reflective act is the I.

Fourth, the transcendent I must fall before the stroke of phenomenological reduction. The Cogito affirms too much. The certain content of the pseudo-"Cogito" is not "I have consciousness of this chair," but "There is [emphasis added] consciousness of this chair." This content is sufficient to constitute an infinite and absolute field of investigation for phenomenology [the logos of phenomena].

--Jean-Paul Sartre, The Transcendence of the Ego, pp. 49-50, 52-54