Representing… Yohann Kunders

Welcome to ‘Representing…’ in which a philosopher from a traditionally underrepresented group explains their research for a non-expert audience. In this edition Yohann Kunders introduces the Causal Exclusion problem in the Metaphysics of Mind.


Yohann Kunders is an MSc student at the University of Edinburgh. His supervisor is Jesper Kallestrup, and his interests include Metaphysics of Mind and Embodied Cognition.


The Causal Exclusion Problem

The hall of records has a special place for Collin Burns. On the 26th of April this year, he solved the standard 3x3x3 Rubik’s cube in exactly 5.25 seconds. It takes me about 20 minutes to finish a side! (And, no, I’m not going to tell you how long it takes me to finish the cube) But for all my deftness with the cube, I do love puzzles in all their forms, shapes and colors. It’s why I got into Philosophy of Mind. And at the moment I’m working on one that’s kept brows furrowed and fingers a-tapping for decades now. Here’s something to think about before I hit you with it:

  1. Thomas is rushing to leave his apartment on a Monday morning. No time for breakfast. He’s running late as it is. As he’s leaving he thinks, ‘I should eat something if I’m going to make it to lunch’. Quick dash back to the kitchen and he grabs a banana. What caused him to grab the banana?
  2. Suzy and Billy have skipped school to throw rocks at bottles. They’re going through some stuff, okay? Both spy a particularly delicious green Bailey’s bottle squatting on top of a nice flat piece of concrete. Perfect. Unaware of the other, each takes careful aim. Fire! Both rocks hit the bottle at exactly the same time and it shatters. What caused the bottle to break, Billy’s rock or Suzy’s?

The answer to the first question, you might say, is obvious. Thomas’ belief (that he should eat something) caused him to pick up the banana. Thoughts, beliefs and desires cause actions all the time. And most philosophers agree. (Why ‘most’ if the answer is so obvious? The dissenter’s reasons are tied in with Billy and Suzy’s bottle, but I feel obligated to let you know before you’re disappointed later. The only thing Philosophers can agree on is how systematically terrible they are, as a group, at agreeing with each other.)

The case of Billy and Suzy is strange, I’ll admit. If Billy had thrown his rock and Suzy hadn’t, the bottle still would’ve shattered. If Suzy has thrown hers and Billy hadn’t, again, the bottle still would’ve shattered. So it seems like both rocks caused the bottle to shatter. The breaking of the bottle was overdetermined – it had two causes!

Some philosophers argue that mental states (like Thomas’ belief) do not causally influence physical ones (like Thomas’ action). They do this to avoid the worry of overdetermination. Saying Thomas’ beliefs have causal powers, they argue, means saying mental causation is overdetermined. Just like Billy and Suzy’s bottle.

Wait. Hold up just a second, you crazy philosophers. Overdetermination requires two causes. Where’s the second event that causes Thomas to pick up the banana? As far as I can see, there’s only one – his belief! Ah, the philosophers say, there’s one

you can’t see – it’s sitting deep inside Thomas’ brain. We can tell two stories about Thomas’ action. A psychological story: Thomas believes he won’t make it to lunch without something to eat so he grabs a banana. And a physical story: Neurons fire in Thomas’ brain, sending signals to the muscles in his arms, causing him to pick up a banana. Two stories, two causes, overdetermination!

So we see the puzzle beginning to form. On the one hand, it’s absurd to think of actions being caused without neurons firing. We’re good people of physics and physiology, after all. But it’s equally absurd to think actions being caused without beliefs. Aren’t we good people of psychology as well?

Of course, you might answer, let’s embrace overdetermination. So what if behavior is overdetermined? The problem is that this is just as absurd an option as the previous ones – how often is it that fire is caused by a match and lightning both at the same time? It’s possible, but is it routine? Accepting two separate, independent causes can’t be our way out. We must be good people of logic too.

This is the causal exclusion problem. The more we go out of our way to say that beliefs cause actions, the more it sounds like those actions are overdetermined. And the more we go out of our way to say that neurons and muscles (and other physical things) cause actions, the more it sounds like mental states are useless.

‘Why bother with it at all?’ you’re probably thinking. Why not just wait for neuroscience to give us some answers? The mind is becoming less mysterious every day. Good point, I say, but this is a problem of metaphysics. There was nothing within Newton’s physics that could dismiss Hume’s skeptical worries. Kant, the metaphysician, had to step in and give Newtonian physics a defense against skepticism. Similarly, neuroscience cannot dismiss the logic of the exclusion problem. It’s a problem not because it says a belief doesn’t cause an action but because it says there’s no way a belief could cause an action at all.

The exclusion problem is relevant because how we conceive and talk about ourselves is at stake. A compromise in any direction to see it resolved has potentially dangerous implications. To say neurons don’t really cause actions means admitting the physical world isn’t causally closed. We might as well admit Casper exists. To say mental states don’t really cause actions is even worse. It would mean reducing thoughts, beliefs and desires to useless side effects, like Wittgenstein’s paper in the wind. “You sometimes see in a wind a piece of paper blowing about anyhow. Suppose the piece of paper could make the decision: ‘Now I want to go this way.’ I Say: ‘Queer, this paper always decides where it is to go and al1 the time it is the wind that blows it.’” (From Wittgenstein’s ‘Lectures on Freedom of the Will’)

There is another option; Jaegwon Kim, the man who first conceived of the problem in this way, suggests we identify mental events with physical ones. The problem disappears if we stop seeing the two as independent, and start seeing them as the same. Mental states simply are physical states. But this ‘they are the same’ argument has the same problem the ‘mental states don’t cause anything’ argument does. It reduces the human mind to a piece of paper blowing about in the wind.

This puzzle is a Rubik’s cube. And we need a Collin Burns.

Up steps Karen Bennett! She believes that the only way to tract the exclusion problem is to go after the idea of overdetermination. True cases of overdetermination, she argues, require two separate and independent causes (like Suzy’s rock and Billy’s rock). But how independent are mental and physical states? She doesn’t want to go the Kim way and say they are the same but neither does she want to say they’re as distinct as Billy’s rock from Suzy’s. Her ‘in-between’ position is called Compatibilism.

Compatibilism, in essence, is the idea that an event can have two distinct causes without being overdetermined, as long as the relationship between the causes is tight enough. Right off the bat, the Compatibilist is at a disadvantage. She must characterize the relationship between the mental and physical in just the right way. Lean too much to one side and her position can be likened to Kim’s. There is no difference between mental and physical states. Lean too much towards the other and she sounds like a spooky magician. Mental states don’t need neurons to cause physical actions.

My work at the moment revolves around a Compatibilist solution to the causal exclusion problem; using Karen Bennett’s arguments as a base to come at the exclusion problem from a new angle. It will by no means be an end to the discussion (one side, at most, of our Rubik’s cube). But I believe my work is a step in the right direction – ensuring our science of the mind is grounded in a stable metaphysics.


Would you like to be featured on ‘Representing…’ ?If you are, or have been, a student or faculty member from Edinburgh, and consider yourself to be a member of an underrepresented group, then please get in touch!

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