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. Purpose and freedom The Sartrean claim is best understood in contrast to the scholastic thesis that essence precedes existence, i.e. a typical claim for this traditional thesis would be a human is essentially selfish, or that they are a rational being. To Sartre, "existence precedes essence" means that a personality is not built over a previously designed model or 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 obliged 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