Historically, philosophy falls into three large periods: classical (Greek and Roman) philosophy, which was concerned with the ultimate nature of reality and the problem of virtue in a political context; medieval philosophy, which in the West is virtually inseparable from early Christian thought; and, beginning with the Renaissance, modern philosophy, whose main direction has been epistemology.Classical Philosophy
The first Greek philosophers, the Milesian school in the early 6th cent. B.C., consisting of Thales, Anaximander, and Anaximenes, were concerned with finding the one natural element underlying all nature and being. They were followed by Heraclitus, Pythagoras, Parmenides, Leucippus, Empedocles, Anaxagoras, and Democritus, who took divergent paths in exploring the same problem.
Socrates was the first to inquire also into social and political problems and was the first to use the dialectical method. His speculations were carried on by his pupil Plato, and by Plato's pupil Aristotle, at the Academy in Athens. Roman philosophy was based mainly on the later schools of Greek philosophy, such as the Sophists, the Cynics, Stoicism, and epicureanism. In late antiquity, Neoplatonism, chiefly represented by Plotinus, became the leading philosophical movement and profoundly affected the early development of Christian theology. Arab thinkers, notably Avicenna and Averroës, preserved Greek philosophy, especially Aristotelianism, during the period when these teachings were forgotten in Europe.
Scholasticism, the high achievement of medieval philosophy, was based on Aristotelian principles. St. Thomas Aquinas was the foremost of the schoolmen, just as St. Augustine was the earlier spokesman for the church of pure belief. The Renaissance, with its new physics, astronomy, and humanism, revolutionized philosophic thought. René Descartes is considered the founder of modern philosophy because of his attempt to give the new science a philosophic basis. The other great rationalist systems of the 17th cent., especially those of Baruch Spinoza and G. W. von Leibniz, were developed in response to problems raised by Cartesian philosophy and the new science. In England empiricism prevailed in the work of Thomas Hobbes, John Locke, and David Hume, as well as that of George Berkeley, who was the outstanding idealist. The philosophy of Immanuel Kant achieved a synthesis of the rationalist and empiricist traditions and was in turn developed in the direction of idealism by J. G. Fichte, F. W. J. von Schelling, and G. W. F. Hegel.
The romantic movement of the 18th cent. had its beginnings in the philosophy of J. J. Rousseau; its adherents of the 19th cent. included Arthur Schopenhauer and Friedrich Nietzsche, as well as the American transcendentalists represented by Ralph Waldo Emerson. Opposed to the romanticists was the dialectical materialism of Karl Marx. The evolutionary theories of Charles Darwin profoundly affected mid-19th-century thought. Ethical philosophy culminated in England in the utilitarianism of John Stuart Mill and in France in the positivism of Auguste Comte. Pragmatism, the first essentially American philosophical movement, was founded at the end of the 19th cent. by C. S. Peirce and was later elaborated by William James and John Dewey.
The transition to 20th-century philosophy essentially came with Henri Bergson. The century has often seen a great disparity in orientation between Continental and Anglo-American thinkers. In France and Germany, major philosophical movements have been the phenomenology of Edmund Husserl and the existentialism of Martin Heidegger and Jean-Paul Sartre. Positivism and science have come under the scrutiny of Jürgen Habermas of the Frankfurt School; he has argued that they are driven by hidden interests. Structuralism, a powerful intellectual movement throughout the first half of the 20th cent., defined language and social systems in terms of the relationships among their elements.
Beginning in the 1960s arguments against all of Western metaphysics were marshaled by poststructuralists; among the most influential has been Jacques Derrida, a wide-ranging philosopher who has pursued deconstruction, a program that seeks to identify metaphysical assumptions in literature and psychology as well as philosophy. Both structuralism and poststructuralism originated mostly in France but soon came to influence thinkers throughout the West, especially in Germany and the United States.
Major concerns in American and British philosophy in the 20th cent. have included formal logic, the philosophy of science, and epistemology. Leading early figures included G. E. Moore, Bertrand Russell, and Ludwig Wittgenstein; Anglo-American philosophy was later exemplified by logical positivists like Rudolph Carnap. In their close attention to problems of language, the logical positivists, influenced by Wittgenstein, in turn influenced the work of W. V. O. Quine and others in the philosophy of language. Later Anglo-American philosophers turned increasingly toward ethics and political philosophy, as in John Rawls' work on the problem of justice.