Existentialism is a philosophical position reflected in works of a group of nineteenth and twentieth century philosophers who, despite doctrinal differences, shared the belief that philosophical thinking begins with the human subject—not merely the thinking subject, but the acting, feeling, living human individual. Existentialist philosophy is the explicit conceptual manifestation of an existential attitude that recognizes the unresolvable confusion of the human world and begins with a disoriented individual facing a confused world that he cannot accept. Many existentialists have also regarded traditional systematic or academic philosophy, in both style and content, as too abstract and remote from concrete human experience.
Existentialism emerged as a movement in twentieth-century literature and philosophy, foreshadowed most notably by nineteenth-century philosophers Søren Kierkegaard and Friedrich Nietzsche, though it had forerunners in earlier centuries. Fyodor Dostoevsky and Franz Kafka also described existential themes in their literary works. Although there are some common tendencies amongst "existentialist" thinkers, there are major differences and disagreements among them (most notably the divide between atheistic existentialists like Sartre and theistic existentialists like Tillich); not all of them accept the validity of the term as applied to their own work.