In Western civilization, materialism is the oldest philosophical tradition. It reached its full classical form in the atomism of Democritus and Epicurus in the 4th century BCE. Epicurus argued that reality consisted of invisible and indivisible particles of free-falling matter called atoms randomly colliding in the void. Through materialism everything that happens is explained in terms of the law of nature.
Basically materialism is the idea that everything that exists is material, or physical. Many philosophers believe that something is material, if and only if it is spatial, extended in space. In Descartes' Meditation II, his view is that everything that is extended in space exists, anything else does not. Nothing exists but matter in motion. Materialists would agree that spirits, angel, ghosts, etc, do not exist. Materialism has been atheistic. This is a consequence of its premises. The belief that immaterial things do not exist, lead to believe that there is no God. If they were to be referenced to, they would be described strictly in the terms of nature. Materialism is not an empirical philosophy. It rests on assumptions that are metascientific not metaphysical in the Aristotelian sense. The assumptions of materialism reached beyond empirical science, though never beyond physical reality. Materialism can be said to conform to three theses:.
"(a) The identification thesis: Mind is identified as nothing more than physical states and processes of the brain and central nervous system. (b) The explanation thesis: All human and animal behavior is best and more fully explained by physicalistic interpretations "that is, through neurochemistry and neurophysiology. (c) The exclusion thesis: There are no powers or properties of the mind that no physical object or system can possess."" .
There are different forms of materialism. Materialists have always had a hard time explaining how materialism accounts for such phenomena as thoughts, beliefs, desires, intentions, and sensory experiences.