Science tells us that ordinary solid objects are in fact nothing but empty space; it is only the repelling force of electrons that make things feel solid. I.e., physical objects are “reducible” to atoms of mostly empty space, or are “nothing but” that. Similarly, materialists suggest that the mind will similarly be reducible to “nothing but” physical particles.
Supervenience and Reductionism
Dualism makes suggestions that this will be difficult, if not impossible. One way of going for the materialist is called “supervenience”. A painting supervenes on the paint particles, and thus is not reducible to just the paint particles; the arrangement of the paint particles give rise to a higher order effect.
There are three reasons to think that materialism might be true:
1. Cause and effect; the closed nature of the universe
2. The success of materialism in science
3. There is a close link between brain and mind
However, a specific theory of how it works is still being debated. The main theories of materialism follow:
The first materialist theory. The view that all brain events are just behavior. Your feeling of fear is just the behavior of screaming, running away, etc, and nothing more than that. If true, this would make theory of mind easy to observe and study. As noted above, material things can be observed and has led to the success of science.
There are two problems with this theory that has led it to be almost completely dropped.
1. Many thoughts are an interconnected web of thoughts. Your feeling of “fear of bears” also involves beliefs that the bear will eat you, that being eaten will hurt, that you don’t want to be eaten, etc. All of these beliefs are behind the feeling of “fear of bears”, and are not describable in terms of just behavior.
2. More importantly, behaviorism leaves out the subjective experience. To know you’re in pain you don’t look in the mirror and see yourself wincing, you just feel the pain itself, directly. Behaviorism does not account for first-person experience.
As a result, behaviorism is almost completely abandoned today. It was replaced by:
This theory says that a mind event is identical to a brain event. Pain just is a certain pattern of firing neurons. It is important to be clear: it doesn’t say that a certain firing of neurons causes pain, but that pain is identical to the firing of certain neurons in the same way that water is identical to H20. I.e., you can’t have the one without the other. Two problems:
1. Certain beliefs are actually a web of beliefs with logical inference between them. Your belief that it is wet outside might be inferred from a set of other beliefs: that it rained recently, that rain causes wetness, and so on. So each belief is actually a web of beliefs with logical relations between them. But if mind states are literally just neurons firing, then there can clearly be no logical relationship between firing neurons. What does it mean to say that there is a logical relation between electrons firing over here, and electrons firing over there?
2. Multiple realizability: it is logically conceivable that there are aliens with completely different brain neurons other than us, but yet still feel pain. Or that artificial intelligence at some point in the future may gain consciousness. If so, then clearly mind states cannot be identical to certain brain states.
As a result, identity theory fell out of favor, and was replaced by:
It doesn’t matter what a knife is made out of, as long as it has the properties of being hard and being able to be sharpened. Otherwise, it can be made out of metal, wood, etc. So this idea is that mental states serve a certain function, and unlike identity theory, they do not have to be an organic brain per se. So the mental event “pain” serves the function of indicating to the being that some part of the body is injured. But this could be a human brain, a computer brain, an alien brain, etc. This theory also provides an answer to the dualist conceivability argument (outlined above): that we can coherently imagine the mind separate from the brain is because the mind fulfills certain functions but does not have to be made out of a brain (just like the knife doesn’t have to be made out of metal).
Burden of Proof
So it seems that materialism has a lot going for it, and it is only a matter of time before science can finally understand the mind in purely materialistic terms. However, purposeful intent in the universe is often swept under the “rug of the mind” by materialists, and thus when it comes to the mind itself and all its purposefulness, it may be inexplicable in materialist terms.
Materialism of the mind has not won out, and the debate is still live. Materialism in philosophy of mind is fashionable, but it’s arguments have not been decisively proven.