In part, postmodernism has its origin in the existentialism of the 19th and 20th centuries. The Danish theologian and philosopher Søren Kierkegaard (1813-1855) is generally regarded as the first existentialist. Kierkegaard had his life profoundly marked by the breaking of an engagement and by his discomfort with the formalities of the (Lutheran) Church of Denmark. In his understanding (as well as of others of the time, within a movement known as Pietism, influential mainly in Germany, but with strong precedence over the English Methodism of John Wesley) Lutheran theology had become overly intellectual, marked by a “Protestant scholasticism.”

Scholasticism was before this period a branch of Catholic theology, whose main representative was Thomas Aquinas (1225-1274). Thomas Aquinas argued against the theory of the double truth, defended by Muslim theologians of his time. According to this theory, something could be true in religion and not be true in the empirical sciences. Thomas Aquinas defended a classic concept of truth, used centuries earlier by Augustine of Hippo (354-430), to affirm that the truth could not be so divided. Martin Luther (1483-1546) made many criticisms of Thomas Aquinas, but ironically the methodological precision of the medieval theologian became quite influential in Lutheran theology of the 17th and 18th centuries. In Germany and the Nordic countries (Denmark, Finland, Iceland, Norway and Sweden) Lutheranism became the state religion after the Protestant Reformation of the 16th century, and being the pastor of churches in major cities became a respected and coveted public office.

It is against this intellectualism and this facility of being Christian that Kierkegaard revolts. In 19th century Denmark, all were born within the Lutheran Church, and being a Christian was the socially accepted position. Kierkegaard complained that in centuries past being a Christian was not easy, and could even involve life-threatening events. In the face of this he argued for a Christianity that involved an individual decision against all evidence. In one of his most famous texts he makes an exposition of the story in which the patriarch Abraham is asked by God to kill Isaac, his only son. Kierkegaard imagines a scenario in which Abraham does not understand the reasons of God, but ends up obeying blindly. In Kierkegaard’s words, Abraham gives “a leap of faith.”

This concept of blind faith, going against all the evidence, is central to Kierkegaard’s thinking, and became very influential in twentieth-century Christianity and even in other Western-established religions. Beyond the strictly religious aspect, Kierkegaard marked Western thought with the notion that some things might be true in some areas of knowledge but not in others. Moreover, its influence can be seen in the notion that the individual must make decisions about how he intends to exist, regardless of the rules of society or of all empirical evidence.

Another important existentialist philosopher of the 19th century was the German Friedrich Nietzsche (1844-1900). Like Kierkegaard, Nietzsche was also raised within Lutheranism but, unlike Kierkegaard, he became an atheist in his adult life. Like Kierkegaard, Nietzsche also became a critic of the social conventions of his time, especially the religious conventions. Nietzsche is particularly famous for the phrase “God is dead.” This phrase appears in one of his most famous texts, in which the Christian God attends a meeting with the other gods and affirms that he is the only god. In the face of this statement the other gods die of laughing. The Christian God effectively becomes the only god. But later, the Christian God dies of pity for seeing his followers on the earth becoming people without courage.

Nietzsche was particularly critical of how Christianity in his day valued features which he considered weak, calling them virtues, and condemned features he considered strong, calling them vices. Not just Christianity. Nietzsche also criticized the classical philosophy of Socrates, Plato, and Aristotle, placing himself alongside the sophists. The German philosopher affirmed that Socrates valued behaviors like kindness, humility, and generosity simply because he was ugly. More specifically, Nietzsche questioned why classical philosophers defended Apollo, considered the god of wisdom, and criticized Dionysius, considered the god of debauchery. In Greco-Roman mythology Dionysius (or Bacchus, as he was known by the Romans) was the god of festivals, wine, and insania, symbolizing everything that is chaotic, dangerous, and unexpected. Thus, Nietzsche questioned the apparent arbitrariness of the defense of Apollo’s rationality and order against the irrationality and unpredictability of Dionysius.

Nietzsche’s philosophy values courage and voluntarism, the urge to go against “herd behavior” and become a “superman,” that is, a person who goes against the dictates of society to create his own rules . Although he went in a different religious direction from Kierkegaard, Nietzsche agreed with the Danish theologian on the necessity of the individual to go against the conventions and the reason to dictate the rules of his own existence.

In the second half of the 20th century existentialism became an influential philosophical current, represented by people like Jean-Paul Sartre (1905-1980) and Albert Camus (1913-1960). Like their predecessors of the 19th century, these existentialists criticized the apparent absurdity of life and valued decision-making by the individual against rational and social dictates.