Materialism is the view that the only thing that exists is matter; if anything else, such as mental events, exists, then it is reducible to matter. "Materialism" has also frequently been understood to designate an entire scientific, "rationalistic" world view, particularly by religious thinkers opposed to it and also by Marxists. It is typically contrasted both with dualism and with phenomenalism (which is also called idealism), and like those theories, has had a long history with many varieties and many distinguished proponents.
The varieties of materialism
The history of materialism
Ancient Greek philosophers like Parmenides, Epicurus, and even Aristotle may be called materialists. Later on, the materialist tradition was represented by Thomas Hobbes and Pierre Gassendi, in opposition to Rene Descartes' attempts to provide the natural sciences with dualist foundations. Later materialists were Denis Diderot and other French enlightenment thinkers, as well as Ludwig Feuerbach.
Karl Marx and Friedrich Engels, turning the idealist dialectics of Georg Hegel "upside down", provided materialism with a view on processes of quantitative and qualitative change called dialectical materialism, and with a materialist account of the course of history, known as historical materialism.
In recent years, Paul Churchland and Patricia Churchland have advocated an extreme form of materialism, eliminative materialism, which holds that mental phenomena simply do not exist at all--that talk of the mental is a reflection of a totally spurious "folk psychology" that simply has no basis in fact, something like the way that folk science speaks of demon-caused illness.