Lecho asked:

Are Psychology and Materialism compatible?

Answer by Danny Krämer

This question boils down to the question of the relationship between psychology and the other natural sciences. Descartes famously argued, that body and mind must be two very different substances. But since the scientific revolution, it is difficult to defend some form of dualism. How should the two substances interact — and they for sure do, because I can consciously move my body by thinking about it — without contradicting the natural laws like the law of energy conservation? But it is also a difficult question how a materialist worldview can explain the mind. I will talk now about some materialist proposals. I start with the theories that I find rather unplausible and end with the one I think is the most promising.

First, there is eliminative materialism. This form of materialism argues, that the predicates of our folk psychology, like belief, wish or desire are empty. When we talk about the behaviour of other people, we explain their behaviour by reference to their beliefs and desires. The eliminative materialist says, there is nothing like a belief or a desire that can be identified by neurobiology. These concepts are like the concept of phlogiston. They are concepts of a bad theory and when we have a better theory we can drop these concepts altogether. So materialism is not compatible with folk psychology but with a psychology to come, the eliminativist argues. I think that is just a very bald speculation about the future of science. Today there is no reason to believe, that our best psychological explanations will not contain the concepts of our folk psychology. Most of psychology is belief-desire-psychology and neurobiology is not even close to explain the complex behaviour of human beings without the concepts of beliefs and desires.

The reductive materialist is something more liberal. He thinks there will be a theory reduction. Psychological predicates will be reduced to predicates of neurobiology and in the last instance to physics. What does this mean? Let’s take the predicate “pain”. The reductive materialist thinks that the predicate “pain” will be identified for example with the predicate “c-fibres firing”. Every time someone is in pain her c-fibres fire. Do this reduction with all psychological predicates and you have a reduction of psychology to neurobiology. Psychology and Materialism are compatible because the predicates of psychology are coreferential with some predicates of physics. But there are some problems with this proposal too. For example, pain may be realised in humans by firing of the c-fibres. But what about an octopus or a martian? They do not even have c-fibres but they may still be in pain — the octopus shows clearly pain behaviour if you hurt him. That is the so called argument from multiple realisations.

How to solve the problem? The most promising form of materialism is, I think, nonreductive materialism. That means you believe that everything supervenes over the material, i.e. if you destroy all matter there will be nothing left. But you do not think there must be some theory reduction to make this claim true and you can bring good reasons why some predicates cannot be reduced to physical predicates. I think the reason for that is, that most of the predicates we use are multiply realisable. Take the predicate “money”. Money can be made of paper, metal and even bits on a computer. Most of the money nowadays is virtual money. But if you destroy all computers and all the cash, there will be no money any more. Or take “pain”. Pain is realized in humans, let’s pretend, by firing c-fibres, in martians maybe by some organ made of silicon. These are predicates that are more abstract than for example a predicate of physical science. “Electron” only refers to electrons. But “money” can refer to paper, pieces of metal or bits in a computer. What counts here is not the material but the role the thing plays in a wider context, or like Aristotle would say its form. But still: destroy all matter and there will be no money and no pain whatsoever.

So all these forms of materialism argue that Psychology and Materialism are compatible, and I think, some form of nonreductive materialism is true.