The 20th century brought with it upheavals that produced a series of conflicting developments within philosophy over the basis of knowledge and the validity of various absolutes. With classical certainties thought to be overthrown, and new social, economic, scientific, ethical, and logical problems, 20th-century philosophy was set for a series of attempts variously to reform, preserve, alter, abolish, previously conceived limits.
Philosophy of science, philosophy of mathematics, and epistemology furthered seemingly antagonistic tendencies in accounting for consciousness and its objects, as expressed in the profound differences between analytic philosophy and phenomenology, both of which had foundations in place at the beginning of the century. Advances in relativity, quantum, and nuclear physics, cybernetics, genetics, and linguistics, rich literary output, and the emergence of the motion picture as an art form greatly enriched philosophical subject matter. Just as profoundly, historical events such as the World Wars, the Russian Revolution, the near collapse of European parliamentary democracy in the 1930s and 1940s, the Holocaust, the use of atomic weapons on Imperial Japan, continued colonial violence, the foundation of the United Nations, the elaboration of new doctrines of human rights, the Vietnam War, the failure of revolutionary sentiment in 1968, the collapse of the Soviet Union and its client states, continuing inequities in global development and civil society, the resurgence of "fundamental" religious identity in "Christian", Jewish, Islamic, and Hindu contexts, and seemingly irrepressible if intermittent genocidal activity called into question many philosophical doctrines on human rationality and created ever sharper demands on moral, political philosophy, and philosophy of religion.
This article takes philosophy not in the more general sense of a system of belief or ideology but as a tradition that generally requires a degree of more or less formalized study (although autodidacts have not been excluded) and a degree of institutional recognition in the form of work incorporated into subsequent formalized teaching in university education. Articles referenced here are expected to substantiate standing by demonstrating either of the above criteria.