Can mental things cause physical things?

Anomalous monism is a theory in the philosophy of mind. The philosopher Donald Davidson argues that mental things must have a physical ontology (that is, must exist as/be part of a physical thing) because only physical things can cause other physical things (see my earlier post on identity theory  for a reminder of why this is). Davidson gives the following argument for why mental things must have a physical ontology. He argues that (a) mental things causally interact with physical things (I have a desire to open my door so I put my keys in the lock); that (b) all causal interactions depend on law; and that (c) all laws are physical. Therefore mental things must have a physical description.

Anomalous monism differs from functionalism in so far as it states that mental things cannot be reduced to physical things. It is, however, still a physicalist theory, because it states that mental things have a physical description. In other words, if a pain occurs, so too does c-fibre firing, because pain and c-fibres are two properties of the same thing. The physical description (c-fibre firing) is what causally interacts with physical things (when I move my hand from a hot stove, it is c-fibres which cause this).

First, it is worth going over the concept of causality. What does it mean for a to cause b? Well, when we say that a causes b, what we mean is that in every case where there is an a, there is also a b. Every time I put my foot on the pedal of the brakes of my car, the car stops. Pressure on the brake pedal causes the car to stop. What this means is that a is sufficient in bringing about b. If there was an a without a b, then we would quickly begin to doubt that a causes b (or, as Marianne points out in the lecture, we might reasonably conclude that only some a‘s cause b).


But if, as Davidson argues, mental things cannot causally interact with other mental things because causality depends on a physical law, then how do we explain the relation between things like desires and intentions? I might have a desire to cross the road; and then I might have an intention to cross the road. Or I might have a memory that x, and then a belief that p.

The answer, according to Davidson, is explained by the principle of charity. The principle of charity states that whenever we interpret the thoughts and beliefs of others, we attribute an intrinsic rationality to them. So whenever I notice somebody pulling out an umbrella, I believe that they are doing so because of some or other rational belief, i.e. that it is raining. But this is not the same as a physical law, which must be true in (almost) every case. It is possible that the belief that it is raining caused this person to pull out an umbrella, but it is also possible that any other number of beliefs caused them to pull out an umbrella. It could be because it was a Tuesday, or because they were wearing yellow. Therefore the relation between a belief and an intention (or mental thing a and mental thing b) is not a causal relation (law).

It is because we are charitable in our attribution of rationality to the beliefs of others that we usually interpret them correctly. But this does not mean that beliefs cause intentions or other mental things, only that our interpretation of them in others is usually correct. What really causes an intention, according to Davidson, is the physical description of that mental thing (belief p, for instance) – and it must be this physical description, because the relation between mental things is not a causal relation.

But Davidson’s argument faces a considerable problem. If, as he argues, pain has a physical property by which it causally interacts with other physical things, then it is c-fibres firing that cause my hand to move from the stove. But if this is true, then pain has no role to play in bringing about my hand moving from the stove, unless pain and C-fibres are the same thing – bringing us back full circle to the problem of identity theory.


*This post is a written run through of a lecture given by Marianne Talbot at the University of Oxford, which you can watch here.


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