Materialism is a philosophical monism asserting that matter is the fundamental substance of nature, with all phenomena, including mental states and consciousness, being results of material interactions. This directly contrasts with idealism, which posits consciousness as fundamental. Closely related to physicalism—a modern evolution incorporating broader physical entities like energy and spacetime—both views hold that the universe is solely matter-energy in motion, and consciousness is a property of complex material systems.

Its historical roots trace back to ancient Greece, with Leucippus and Democritus in the 5th century BCE establishing classical atomism, a concept later refined by Epicurus to explain all existence, including the mind, as atoms moving in a void, introducing the concept of clinamen for atomic interactions. Despite historical dominance by idealism, influential materialist thinkers such as Lucretius, Baruch Spinoza, and Karl Marx continuously advanced these naturalistic explanations, providing a foundational challenge to supernatural doctrines and significantly shaping modern scientific thought.