Materialism in philosophy is the view that everything that exists is either composed of matter or depends on matter for its existence. Materialism is generally contrasted with idealism, which holds that ideas are real and stresses the importance of the mind and soul. Materialists have generally believed that the only things that are real are the things that a person can perceive through his senses and that all events in the universe can be explained by scientific law. Basic to materialism is the denial of the existence of a God who directs the universe and of the immortality of the individual soul.

One of the earliest materialists was Democritus, a Greek philosopher who lived in the 4th century B.C. He taught that everything in the world is composed of minute bits of matter, which he named atoms, and that all events could be explained by the motion of the atoms in space. Similar views were taught by another Greek philosopher, Epicurus, and, in the Roman world, by Lucretius, notably in his poem De rerum natura ("On the Nature of Things").

During the Middle Ages the Christian world view, which is idealistic, rather than materialistic, was universally accepted in Europe, and it was not until the Renaissance period, beginning in about the 1400's, that materialism began to be revived in Western thought. During the next few centuries, materialism gained influence because of the rise of the modern physical sciences, which were concerned with explaining the world in terms of matter and motion. Materialism seemed the obvious philosophy through which men could organize the findings of the new science into a consistent view of the world.

By the 17th and 18th centuries, materialism was advocated by Thomas Hobbes, Pierre Gassendi, Julien de la Mettrie, and Baron Paul d'Holbach.

A reaction against materialism developed during the 18th and 19th centuries, particularly in the works of such idealistic philosophers as George Berkeley and Georg Hegel. After Hegel's death in 1831, however, materialism enjoyed a strong revival. This was due in part to the Industrial Revolution, which focused men's attention on the material conditions of life among the poor. It was concern with the material means of economic production, for example, that inspired Karl Marx to develop his philosophy of dialectical materialism, the official philosophy of Communism.

Science during the 19th century also tended to encourage materialism as a philosophy. Charles Darwin's theory of biological evolution, for example, led many people to believe that man does not possess a unique soul but is merely a more highly complex form of life that evolved from the lower animals and could be explained in terms of purely physical forces.

The physical forces with which science dealt were at first conceived of as mechanical, that is, as attractions or repulsions between bodies moving through space in accordance with fixed laws. Late in the 19th century and in the 20th century, however, the old idea of matter as a solid body gave way to a more complicated view of matter as energy or a field of force. New discoveries in physics have led a number of philosophers to prefer the broader term "naturalism" to describe the philosophy that the real world is the world of nature studied by science.