The proposition that existence precedes essence () is a central claim of existentialism, which reverses the traditional philosophical view that the essence (the nature) of a thing is more fundamental and immutable than its existence (the mere fact of its being). To existentialists, human beings—through their consciousness—create their own values and determine a meaning for their life because the human being does not possess any inherent identity or value. That identity or value must be created by the individual. By posing the acts that constitute them, they make their existence more significant.
The idea originates from a speech by F. W. J. Schelling delivered in December 1841. Søren Kierkegaard was present at this occasion and the idea can be found in Kierkegaard's works in the 19th century, but was explicitly formulated by philosopher Jean-Paul Sartre in the 20th century. The three-word formula originated in his 1945 lecture "Existentialism Is a Humanism", though antecedent notions can be found in Heidegger's Being and Time.
As a result, for Sartre, "existence precedes essence" not only defines and determines his own existential thinking or interpretation of existentialism, but also any thinking or philosophising that declares itself to be existential. Despite Sartre's later efforts to distance himself and his thinking from this remark and its consequences, it has become the most quoted, repeated, and cited description of existentialism and any non-theistic existential thought.
Purpose and freedom
The Sartrean claim is best understood in contrast to the scholastic thesis that essence precedes existence; a typical claim for this traditional thesis would be that a human is essentially selfish, or that they are essentially a rational being.
To Sartre, "existence precedes essence" means that a personality is not built from a previously designed model or for a precise purpose, because it is the human being who chooses to engage in such enterprise. While not denying the constraining conditions of human existence, he answers to Spinoza who affirmed that people are determined by what surrounds them. Therefore, to Sartre an oppressive situation is not intolerable in itself, but once regarded as such by those who feel oppressed the situation becomes intolerable. So by projecting my intentions onto my present condition, "It is I who freely transform it into action". When he said that "the world is a mirror of my freedom", he meant that the world obliges me to react, to overtake myself. It is this overtaking of a present constraining situation by a project to come that Sartre names transcendence. He added that "we are condemned to be free".
To claim that existence precedes essence is to assert that there is no such predetermined essence to be found in humans, and that an individual's essence is defined by the individual through how that individual creates and lives his or her life. As Sartre puts it in his Existentialism is a Humanism: "man first of all exists, encounters himself, surges up in the world – and defines himself afterwards".
Choice and sedimentation
Jonathan Webber interprets Sartre's usage of the term essence not in a modal fashion, i.e. as necessary features, but in a teleological fashion: "An essence is the relational property of having a set of parts ordered in such a way as to collectively perform some activity". For example, it belongs to the essence of a house to keep the bad weather out, which is why it has walls and a roof. Humans are different from houses because unlike houses they don't have an inbuilt purpose: they are free to choose their own purpose and thereby shape their essence, therefore their existence precedes their essence.
Sartre is committed to a radical conception of freedom: nothing fixes our purpose but we ourselves, our projects have no weight or inertia except for our endorsement of them. Simone de Beauvoir, on the other hand, holds that there are various factors, grouped together under the term sedimentation, that offer resistance to attempts to change our direction in life. Sedimentations are themselves products of past choices and can be changed by choosing differently in the present, but such changes happen slowly. They are a force of inertia that shapes the agent's evaluative outlook on the world until the transition is complete.