From The Writer’s Almanac:
It’s the birthday of philosopher Søren Kierkegaard (books by this author), born in Copenhagen (1813), the son of a wealthy wool merchant who left his son enough money to be financially independent for the rest of his life. Kierkegaard rarely left Copenhagen, but he enjoyed going to the theater, taking carriage rides out into the country, and chatting with people he met, including servants and laborers, whom wealthy people would ordinarily ignore.
Kierkegaard is widely considered the father of existential philosophy. His work touched not only philosophy, but also theology, psychology, literary criticism, and fiction. He also came up with two concepts that are commonplace to us today: One is “subjectivity,” the idea that we all perceive the world — and “truth” — differently; and the other is the “leap of faith,” that faith is not possible without doubt. One must doubt the existence of God to have faith in the existence of God. Belief without doubt is just credulity. He published several books at his own expense, including Either/Or (1843), Works of Love (1847), and The Sickness Unto Death (1849). Kierkegaard was unknown outside of Denmark until the early 20th century, when his work was discovered by European writers and philosophers. He influenced writers like Henrik Ibsen, Franz Kafka, and Albert Camus.