The three most common forms are non-reductive materialism, reductive materialism, and eliminative materialism. .
The most advanced form of materialism is non-reductive materialism. This type of materialism affirms that psychological properties can be exemplified even in an immaterial world. Mental states are not reducible to physical states. The nature of a mental state is determined by its relation to environmental stimuli, other mental states, and behavioral outputs. This materialism relies on the interaction of two primary causal attributions: .
"(a) Physical causations and (b) environmental determinism. This position insists that the human being is, in Aristotelian terminology, the conglomeration of material and efficient causes: Mind is cause by matter or physical substance it is made of and is causally affected by the material forces that constitute the flux of environmental events."" .
Basically the physical causes all metal events. And certain environmental conditions cause the organism to respond to a stimulus. There is a stimulus and then a response, which includes changes in brain states, etc, which then causes changes within an organism. Non-reductive materialists acknowledge difficulty in accounting for certain aspects of mental reality and leave open the possibility for psychical interpretations of mental events that exist and manifest apart from or are at least co-extensive with physical brain processes. "There is no such things as non-reductive materialism: It is merely a myth. The burden of proof lies on the shoulders of those materialists who wish to account for freedom within an entirely materialist framework."" .
Reductive materialism states that mental states exist and each mental state is identical to a type of physical state of the brain. Mental properties and/or states are reduced to or identical to brain properties and/or states. The mind is reducible to natural processes that can be translated into the language of math and physics.