A mode of philosophy which emerged in the latter part of the nineteenth century and came into prominence in the middle part of the twentieth century. It foregrounds the perplexing condition of the modern subject who, in the absence of God, is forced to contend with the meaninglessness of life. This does not necessarily mean that existentialism is a secular philosophy, though largely speaking it is, because the absence of God can be understood to mean that humans have forsaken God or that God has forsaken humans (i.e. God still exists: He just does not involve Himself in human affairs). Both of the so-called âfathersâ of existentialism, SĂžren Kierkegaard and Nietzsche, Friedrich, start from this position and argue for a metaphysics of truth and freedom in response---authenticity thus replaces piety as the new condition for the righteous to aspire to. Instead of being true to God, one must rather be true to oneself, but this is difficult for two reasons: first, there is the apparent logical impossibility of the self knowing the self; second, there is the problem of knowing how one should act. In the early twentieth century, phenomenology confronted the question of how the subject makes sense of their world, and although it did not concern itself overly much with the metaphysical question of how one should act, it had a significant influence on existentialism all the same because of its account of apperception (derived from actant), which solves the first problem. The second problem, namely the question of how one should act preoccupied existentialismâs most important theorist Sartre, Jean-Paul and answering it effectively became his lifeâs work. Sartre popularized the term existentialism (which he borrowed from Gabriel Marcel, who first used it in the mid-1920s), in his short book Lâexistentialisme est un humanisme (1946), translated as Existentialism and Humanism (1948), which summarized and simplified his previous book, LâĂtre et le nĂ©ant (1943), translated as Being and Nothingness (1958), which is for many the definitive work on the subject. Sartreâs novels, particularly La NausĂ©e (1938), translated as Nausea (1959), are also taken to be important contributions to existentialism because they dramatize the situation of the subject confronted by the brute fact of existence. The label existentialism has also been applied to the work of both Heidegger, Martin and Jaspers, Karl, though neither of them accepted the term themselves. Further Reading: S. Earnshaw Existentialism: A Guide for the Perplexed (2006). T. Flynn Existentialism: A Very Short Introduction (2006). diaspora âą A basic introduction to existentialism.