A loose title for various philosophies that emphasize certain common themes: the individual, the experience of choice, and the absence of rational understanding of the universe with a consequent dread or sense of absurdity in human life. The combination suggests an emotional tone or mood rather than a set of deductively related theses, and existentialism attained its zenith in Europe following the disenchantments of the Second World War. However, the first significant thinker to stress such themes was Kierkegaard, whose work is generally regarded as the origin of existentialism. Existentialist writing both reacts against the view that the universe is a closed, coherent, intelligible system, and finds the resulting contingency a cause for lamentation. In the face of an indifferent universe we are thrown back upon our own freedom. Acting authentically becomes acting in the light of the open space of possibilities that the world allows. Different writers who united in stressing the importance of these themes nevertheless developed very different ethical and metaphysical systems as a consequence. In Heidegger existentialism turns into scholastic ontology; in Sartre into a dramatic exploration of moments of choice and stress; in the theologians Barth, Tillich, and Bultmann it becomes a device for reinventing the relationships between people and God. Existentialism never took firm root outside continental Europe, and many philosophers have voiced mistrust of particular existentialist concerns, for example with being and non-being, or with the libertarian flavour of its analysis of free will.