1 Philosophical Behaviorism
Philosophical (= Dispositional) Behaviorism takes for granted a distinction between mental predicates and non-mental ones.
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2 Functionalism
Functionalism is the claim: Functionalism Mental States are Functional States.
Functional states are states specified in terms of their relations to inputs, outputs, and other states.
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3 Reductive Materialism
Reductive Materialism is the claim: Mental States are Physical States.
Reductive Materialism identifies a mental state with a particular physical state. In that, it agrees with functionalism and behaviorism that all mental states confer certain dispositions on the thing that has these mental states. I.e., reductive materialism accepts (1). However, and this is where reductive materialism differs from functionalism, it is not enough for a creature to have the dispositions that certain counterfactuals are true; they must be true in virtue of the creature’s having a particular physical constitution. Here’s a different way of putting the same point: Reductive Materialism claims that, among all the possible realizers of the machine table associated with human psychology, only the realizers that have our physiology count as actually having mental states like pain.
4 Eliminative Materialism
Eliminative Materialism is the claim : There are no mental states.
Crucially, eliminative materialism does not say that we don’t talk using words like “pain”; we obviously do. But when we believe that there’s something out there that answers to this, we’re wrong. So eliminative materialism denies all three claims (1), (2), and (3).