Absurdism is an idea commonly associated with existentialism. Beginning in the 19th century, mainly through the influence of Soren Kierkegaard, religion was often described as absurd because it could not be justified on rational principles; rather, it was considered as based on what Kierkegaard called "a leap of faith." In their discussions of consciousness, Martin Heidegger and Jean Paul Sartre described the human consciousness as facing an apparently absurd world--absurd because it finds itself at the crossroads of Being and Nothingness, baffled by the meaninglessness of the human condition. Sartre's ideas of absurdity, anguish, and disgust are expressed in his plays and novels, especially in Nausea (1938; Eng. trans., 1949). A philosophical basis for the modern theater of the absurd has been established by other existentialists, such as Albert Camus, Karl Jaspers, and Gabriel Marcel.