World --Another major theme is the world itself--specifically what can be known about it. A pre-existentialist writer, the novelist Fyodor Dostoyevsky, said that the universe does not make sense. There are no underlying patterns that can be perceived by everyone, on the basis of which everyone agrees: "This is what the world is all about." Life, and the world itself, are often unpredictable and capricious.All attempts to find or impose an order on the world must fail because no single human mind--nor all human minds together--can adequately perceive all possible facts, make sense of them, and put them into an ordered scheme. If there were such an order or scheme, it would mean that everything is determined as it is for the flower and the fish. Humans would not have free choice but would be fated to whatever course their lives take.
This inability to comprehend the world is compounded by individuals' inability to gain a thorough understanding of other people or even of themselves. The meanings of their own mental processes, emotions, and motivations are never entirely clear to them as they try to make sense of themselves and the larger and smaller worlds in which they live. If there is a standard of truth outside themselves, they must select it and commit themselves to it, though they are unable to prove the certainty of such a truth.
Limits --Another theme is that of limits. Individuals are thrust into existence for a short time only. They are caught in what existentialist theologian Karl Barth called "the boundary situation." They come into the world at a specific time, and they leave it at another specific time. About this there is no choice. Because the time is limited, there are urgent decisions to be made. People are free to make them on the basis of whatever facts they have available. But the facts themselves are a matter of choice. Individuals select the criteria by which they decide the course of their lives or particular undertakings.
Existence --The chief theme of Existentialism, of course, is existence itself. Flowers, animals, and stones all exist. But people exist in a different way. Individuals are unique--able to think about themselves and the world in which they find themselves and to make choices. They can choose because they are free, and the choices they make establish the future into which they project themselves.
