How do Mental States cause Physical Effects?

Discussing the incompatibility of the Exclusion Problem.

Without contemplation, most of us presuppose that mental states cause physical effects. Assuming that thoughts, feelings and emotions can cause us to do actions in the physical world.

My feelings of thirst, and desire to resolve such thirst, can cause me to pour a drink, for example.

The Exclusion Problem is a worry for such an intuitive truth.

Put briefly, it is a worry for any forms of Property Dualism (be that Physicalist or Dualist in nature) which states that mental states or properties are not numerically identical (one and the same) as physical states or properties

For example, if you disagree that feelings of pain are just c fibres firing (physical parts of the brain,) then this is a problem that you must resolve.

The exclusion problem is inspired by Princess Elizabeth Of Bohemia’s Problem of Mental Causation, which asks how, if mental states are not present in the physical world, how they can cause physical effects, given physical effects are caused by something extended coming into contact with it.

Incompatible Truths.

The exclusion problem takes five facts that are intuitively true and illustrates that as a grouping, they are incompatible.

These truths being:

1 ) Mental Causal Efficacy:This states that mental states can have physical effects. As previously stated, this is an intuitive truth, illustrated through the fact we intuitively think that thoughts and emotions can cause physical effects. To illustrate another, feelings of pain can cause you to wince and say “ow.”

2) Physical Causal Closure:This is a scientific truth of physics which states that all physical effects as physical causes. Given this is an undisputed, and empirical fact of physics, it’s counterintuitive to refute such a claim.

3) Distinctness:This states that physical states and mental states are separate and distinct. Given we have previously presupposed property dualism: disagreeing that mental states are physical states, this must be an intuitive truth.

4) Non Overdetermination: This states that mental causes don’t overdetermine their effects.

An effect is overdetermined where it has more than one cause, where each cause would have been sufficient on its own to cause such an effect.

This is an intuitive truth, comparable to two snipers both simultaneously shooting someone and both bullets coming into contact with its victim at the same time. Theoretically, both bullets would have been sufficient on their own to cause the effect.

Although overdetermination is possible, it is inductively unlikely. It’s an intuitive truth that mental states don’t overdetermine their effects, given for this to be true; would require that every mental effect would have to consistently undergo the unlikely event of overdetermination. In the same way that it is unlikely that every sniper murder is overdetermined, it is unlikely that every mental effect reliably, every time, is overdetermined.

5) Exclusion:This states that no effect has more than one sufficient cause unless it is overdetermined. Given the definition of overdetermination given, this is an intuitive truth.

Overall, these five intuitive facts cannot all be true, given they’re incompatible. We presuppose that mental states have physical causes, but given physical causal closure; if they do, then they are overdetermined, but entail states don’t overdetermine their effects, so this is impossible.

To resolve this solution, Philosophers must deny one of these truths. This is a much disputed live debate amongst thinkers, which is still yet to be resolved.


Identity Theory

One solution is to deny our initial intuition that the mental and physical are not one and the same. Doing so refutes (3).

As established by Smart and Place, Identity theory does this by arguing that mental states and physical states are numerically identical. Illustrating type identity: arguing that mental states are physical states.

Thus, feelings of pain are just physical states in the brain (c — fibres firing,) they are one and the same thing (even if we are unaware of this fact).

The initial reasoning for favouring this view is the apparent correlations that have been discovered in neuroscience between mental states and physical states. For example, every time someone experiences pain, neuroscience has shown that c — fibres fire in the brain at the same time. Identity theorists explain this by arguing that pain and c — fibres firing are just the same thing.

If we accepted this, this would resolve the exclusion problem: given that mental states and physical states can both cause physical effects without overdetermination: given they are one and the same, and there is only one cause.

The issue with this proposal is that it cannot explain the apparent multiple realizability of mental states: given, mental states can occur in different physical states. Hilary Putnam argues for this proposal by illustrating that beings, such as Octopi, can experience pain even though they don’t have c — fibres firing. Given this is the case, they cannot be one and the same, and Identity theory appears false and is an unsatisfactory solution to the exclusion problem.


Karen Bennett discusses a solution which refutes (1). Epiphenomenalism resolves the debate by arguing that mental states cannot cause physical effects.

In fact, most radical forms of epiphenomenalism deny that mental states cause anything at all. They argue they are causally inefficacious, but exist and are grounded in the physical (such as the brain.

Of course, this would resolve the exclusion problem. But this appears an unsatisfactory solution, given most people find it intuitive that our thoughts and mental states can cause physical effects.

Refuting Exclusion and Non-Overdetermination

The most plausible solution to the exclusion problem is to deny (4) or (5).

Philosophers do so by adopting compatibilism, and arguing that mental states always overdetermine their effects, and this isn’t a problem when explaining mental efficacy.

Philosophers (Yablo, Shoemaker and others,) have argued for this by attempting to illustrate that the relationship between mental and physical causes is much more intimate and closer than the relationship between the two shooters in the sniper example.

For example, they may argue that mental causes supervene on physical ones, and as a consequence: it is impossible to have a physical cause without at the same time having a mental one.

This would resolve the exclusion problem, by arguing that although mental states overdetermine their effects, this isn’t a problem.

The issue with this proposal is that it is still widely debated amongst Philosophers, and still exists as a live debate.

For example, Jaegwon Kim asserts:

“the exclusion problem doesn’t go away when we recognize the two purported causes as in some way related to each other. As long as they are recognized as distinct events, each claiming to be the full cause of a single event, the problem remains.” (Mind in a Physical World 53).

Consequently, this solution would resolve the exclusion problem, but it is widely disputed whether it does.


  1. The exclusion problem is a prominent, live issue that remains widely debated and unresolved even today. It presents five intuitive truths which illustrate the difficulty of explaining how mental states can cause physical effects.
  2. Although there exist arguments which, if true, would resolve the problem, it is widely disputed whether any of the arguments are true, and consequently, none of them appear satisfactory.
  3. As a result, to hold the belief that mental states are not identical to physical states but instead are separate and distinct, you must deny one of these five intuitive truths.

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