materialism, in philosophy, a widely held system of thought that explains the nature of the world as entirely dependent on matter, the fundamental and final reality beyond which nothing need be sought. Certain periods in history, usually those associated with scientific advance, are marked by strong materialistic tendencies. The doctrine was formulated as early as the 4th cent. BC by Democritus, in whose system of atomism all phenomena are explained by atoms and their motions in space. Other early Greek teaching, such as that of Epicurus and Stoicism, also conceived of reality as material in its nature. The theory was later renewed in the 17th cent. by Pierre Gassendi and Thomas Hobbes, who believed that the sphere of consciousness essentially belongs to the corporeal world, or the senses. The investigations of John Locke were adapted to materialist positions by David Hartley and Joseph Priestley. They were a part of the materialist development of the 18th cent., strongly manifested in France, where the most extreme thought was that of Julien de La Mettrie. The culminating expression of materialist thought in this period was the Système de la nature (1770), for which Baron d'Holbach is considered chiefly responsible. A reaction against materialism was felt in the later years of the 18th cent., but the middle of the 19th cent. brought a new movement, largely psychological in interpretation. Two of the modern developments of materialism are dialectical materialism and physicalism, a position formulated by some members of the Logical Positivist movement. Closely related to materialism in origin are naturalism and sensualism.
See D. M. Armstrong, Materialist Theory of the Mind (1968); P. M. Churchland, Scientific Realism and the Plasticity of the Mind (1979) and Matter and Consciousness (1984).