Existentialism at the beginning of the 19th centuryMajor themesDue to the diversity of positions associated with existentialism, the term is impossible to define precisely. Certain themes common to virtually all existentialist writers can, however, be identified. The term itself suggests a major theme: the emphasis on concrete individual existence and, therefore, on subjectivity, individual freedom and choice. Moral individualism Most philosophers since Plato hold that the highest ethical good is the same for all; to the extent that one approaches moral perfection, one resembles other morally perfect individuals. The 19th-century Danish philosopher SørenKierkegaard, who was the first writer to call himself existential, reacted against this tradition by insisting that the highest good of the individual is to find one's own vocation. As he wrote in his diary: “I must find a truth that is true for me. . . the idea for which I can live or die. Other existentialist writers have echoed Kierkegaard's belief that one must choose one's own path without the aid of universal, objective standards. Against the traditional view that moral choice involves an objective judgment of right and wrong, existentialists argue that no objective, rational basis can be found for moral decisions. The 19th century German philosopher Friedrich Nietzsche further asserted that the individual must decide which situations should be considered moral situations. that personal experience and acting on one's beliefs are essential to arriving at the truth. Thus, the understanding of a situation by a person involved in that situation is greater than that of a detached and objective observer. This emphasis on the individual agent's perspective also made existentialists suspicious of systematic reasoning. Kierkegaard, Nietzsche, and other existentialist writers were deliberately unsystematic in the exposition of their philosophies, preferring to express themselves in aphorisms, dialogues, parables, and other literary forms. However, despite their anti-rationalist stance, most existentialists cannot be considered irrationalists in the sense that they deny any validity to rational thought. They argued that rational clarity is desirable whenever possible, but that life's most important questions are not accessible to reason or science. Furthermore, they argued that even science is not as rational as is commonly assumed. Nietzsche, for example, claimed that the scientific hypothesis of an ordered universe is essentially a useful fiction. Choice and Commitment Perhaps the most important theme in existentialist writings is that of choice. The chief distinction of humanity, in the eyes of most existentialists, is the freedom to choose.