Against the Causal Exclusion of the Mental, and Against the Picture of Agency That Motivates It
(See tl;dr summary in the first reply below)
Participants in the Newcomb thread will know that a recurring pressure point in that discussion has been the apparent tension between two things most of us want to say: that an agent’s rational character is stable and legible enough for a perceptive predictor to anticipate their actions, and that the agent nonetheless faces genuinely open alternatives from their own practical standpoint. In the Newcomb thread, @Suny has pressed this tension from one side — insisting that the agent retains genuine freedom in front of the boxes, which means their choice must be independent of what the predictor has already done, and therefore two-boxing is rational. @Hypericin has pressed it from the other — accepting that the agent’s choice is determined by the same rational character the predictor read, embracing compatibilism, and one-boxing. I promised a thread that addresses this tension on its own terms, so here it is.
The question isn’t specific to the Newcomb problem. It’s the old question of whether we are free, sharpened by a challenge from the philosophy of mind that most discussions of free will don’t adequately engage with: Jaegwon Kim’s causal exclusion argument, which purports to show that if every physical event already has a sufficient physical cause, there’s no causal work left for rational agency to do. Getting clear on where that argument goes wrong, I’ll argue, is the key to dissolving the apparent tension between the legibility of rational character and the openness of practical deliberation.
I want to argue that your reasoning really does do something — that rational agency is a genuine causal power, irreducible to the physical processes that underlie it, even though it operates entirely within a physically closed world. No spooky stuff, no violations of physics. But getting there requires working through a serious challenge.
The Challenge: Does Physics Leave Room for the Mind?
The Hard Determinist’s Challenge
Here’s a familiar thought. Your brain is a physical system. When you deliberate about what to do — whether to take the job, whether to apologise, whether to study for the exam — your brain is in some physical state, and the laws of physics determine what physical state it transitions to next. By the time you experience yourself as “deciding,” the physics has already settled the matter. Your feeling of deciding is real enough as an experience, but it’s not doing any causal work. The real causes are physical: neurons, synapses, electrochemical signals, all governed by the same laws that govern falling rocks and orbiting planets.
This is the hard determinist picture. It’s intuitive, it’s scientifically respectable, and many smart people find it compelling. Sam Harris puts it bluntly: you don’t author your own thoughts. They simply appear in consciousness, produced by prior physical causes you neither chose nor control.
But there’s something deeply strange about this picture — something that becomes visible once you take it seriously as a guide to practical life rather than just as a theoretical claim.
The Practical Absurdity
Nobody actually lives this way. Harris himself deliberates about what arguments to make, revises his prose, and holds people responsible for their actions. The chess grandmaster doesn’t say: “My move is determined by my brain state, so I might as well push the first piece my hand touches.” The student doesn’t say: “Whether I study or not is already settled by prior physical causes, so I might as well watch Netflix.” These conclusions follow from the hard determinist picture, if taken as a guide to practical reasoning. But nobody draws them, not even hard determinists.
Why not? The standard answer is that the hard determinist picture is true but practically irrelevant. We can’t help deliberating, even if deliberation doesn’t really do anything. But I think this underestimates the problem. The issue isn’t just that we can’t stop deliberating. It’s that the hard determinist picture, taken seriously, makes deliberation pointless. And deliberation is manifestly not pointless. The student who studies does better on the exam. The grandmaster who calculates deeply plays better chess. The person who carefully weighs the pros and cons of the job offer makes a better decision. These aren’t just correlations. The studying produces the better performance, the calculation produces the better move. If you doubt this, consider: would you accept surgery from a surgeon who didn’t bother deliberating about where to cut, on the grounds that the outcome was already determined by physics?
So we have a tension. On one hand, physics seems to be causally complete. Every physical event has a sufficient physical cause. On the other hand, rational deliberation seems to be genuinely causally efficacious. Reasoning well actually produces better outcomes. How can both of these be true?
A quick aside before we go further. Someone might object: “But physics isn’t deterministic: quantum mechanics tells us that physical processes are fundamentally probabilistic.” This is true, but it doesn’t help. Physical causal closure doesn’t require that the laws be deterministic. It requires that the physical story be self-contained: that you never need to leave the level of physics to account for why any physical event happened, or why physical events have the probabilities they do. Probabilistic laws are still physical laws, and they leave no gaps for non-physical causes to slip into. Quantum indeterminacy gives you randomness, not freedom, and random noise is no more hospitable to rational agency than clockwork determinism is. The question of whether your reasoning does real causal work is equally pressing whether the underlying physics is deterministic or probabilistic.
Kim’s Challenge: The Exclusion Argument
The philosopher Jaegwon Kim sharpened this tension into what I think is the most powerful argument against the causal efficacy of the mental. The argument has a deceptively simple structure. I’ll lay it out in three steps.
Step 1: Physical causal closure. Every physical event that has a cause has a physical cause. When your arm moves, that movement has a complete physical explanation: signals from motor neurons, muscle contractions, and so on, all the way back to brain states governed by physical laws. There’s no point in the physical causal chain where a non-physical cause needs to intervene to keep things going. The physics is, as it were, self-contained.
This doesn’t mean physics can explain everything. It means that for any physical event — your arm moving, your vocal cords vibrating, your fingers typing — you can in principle trace a complete causal history that never leaves the physical level. No gaps, no mysterious interventions.
Step 2: Mental states depend on physical states. Your belief that it’s raining, your desire for coffee, your judgment that you should apologise; these mental states aren’t free-floating. They depend on what’s going on in your brain. (This is sometimes put by saying that mental states supervene on physical states. They depend on them, are realised by them, but aren’t reducible to them. If two people are in the exact same physical state down to the last atom, they’re in the same mental state. But the same mental state could be realised by different physical configurations.)
Step 3: The exclusion. Now here’s the punch. Suppose you deliberate about whether to apologise, conclude that you should, and then apologise. Your reason (the judgment that you should apologise) and your brain state (the neural configuration that realises that judgment) both seem to be causes of the same outcome (the apology). But the physical cause — the brain state — is already sufficient for the outcome, by Step 1. The physical causal chain doesn’t need any help from “reasons.” So what causal work is the reason doing? It seems to be excluded from the causal picture by the sufficiency of the physical cause.
Kim’s conclusion: if you want to maintain that the physical world is causally closed (Step 1), and that mental states depend on physical states (Step 2), then you must accept that mental causation is redundant. Your reasons don’t cause your actions. Your brain states do. The reasons are just along for the ride.
Why This Is Hard to Resist
The argument is powerful because each step is individually plausible:
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Denying Step 1 (physical causal closure) means accepting gaps in physics: places where non-physical causes intervene in physical processes. This is what old-fashioned Cartesian dualism required, and it faces the notorious problem of explaining how a non-physical mind could push physical matter around.
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Denying Step 2 (mental dependence on the physical) means accepting that mental states float free of the brain. It is a kind of dualism most people find implausible.
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Denying Step 3 (the exclusion) means accepting causal overdetermination: every action has two independent sufficient causes (one physical, one mental), like a person simultaneously shot by two bullets, each independently lethal. This is logically possible but seems extravagant and ad hoc if it holds for every single voluntary action.
So Kim’s argument doesn’t rest on any exotic premises. It follows from two claims that almost everyone accepts (physical closure and mental dependence on the physical) plus the reasonable principle that we shouldn’t multiply causes beyond necessity.
The Non-Accidentality Reply
I accept Steps 1 and 2. The physical world is causally closed, and mental states do depend on physical states. But I reject Step 3 — the conclusion that mental causation is therefore redundant. Here’s why.
Grant, for the sake of argument, that the physical story is causally closed. P₁ (the physical state of your brain before deliberation) determines P₂ (the physical state after deliberation) via the laws of physics. And M₂ (your decision) is realised by P₂. So far, so good. Kim’s premises are in place.
But now ask a question that the purely physical story cannot answer: why does P₂ happen to be a physical state that realises M₂?
Think about what’s happening. P₁ realises M₁ (your awareness of the situation, your assessment of the considerations, your rational grounds). And P₂ realises M₂ (your decision to act). The mental transition from M₁ to M₂ is rationally intelligible: given those grounds, that decision makes sense. It’s the kind of transition we recognise as good reasoning.
Now, the physical laws tell us that P₁ leads to P₂. But the physical laws don’t care about rational intelligibility. They govern the interactions of particles, the propagation of electrical signals, the dynamics of chemical reactions. There is nothing in the laws of physics that says: “when a brain state realises an awareness of rain, the next brain state must realise an intention to take an umbrella.” The laws just say: given these particular physical conditions, those particular physical conditions follow.
So the fact that the trajectory your brain follows happens to be a trajectory between physical states that realise rationally connected mental states — that the transition from P₁ to P₂ is non-accidentally a transition from “grounds for acting” to “acting on those grounds” — is something the physical story alone doesn’t explain.
But the point here is not merely that physics leaves a coincidence that cries out for a further explanation tacked on alongside the physical one. It’s that the physical facts themselves do their explanatory work, with respect to producing a rational action, in virtue of the mental properties they realise.
Consider a chess computer. At a particular moment, the machine’s transistors are in some specific configuration — call it E₁. The laws of electrodynamics determine that E₁ leads to E₂, a later transistor configuration that results in a signal being sent to move the bishop. The electronic story is causally complete. But now ask: why does E₁ lead to a bishop move specifically? The answer isn’t really about the particular voltages and current flows that constitute E₁. It’s that E₁ is a physical state that realises a particular stage in the execution of the chess algorithm — say, the point at which the minimax search and positional evaluation function have converged on the bishop move as optimal. E₁ produces a bishop-moving E₂ in virtue of realising that functional state.
You can see this clearly through the fact that the same functional state could be realised by very different physical hardware. A different chess engine, running on different chips with entirely different electrical properties, implementing the same algorithm (or even a different algorithm that converges on the same evaluation), would arrive at the same bishop move from the same functional state. The physical trajectories would differ in every electronic detail. What they’d share is the functional property: they all realise a state in which the algorithm has determined the bishop move to be optimal. What explains the convergence across physically diverse implementations isn’t any shared electronic feature. The electronics may be completely different. It’s the shared higher-level property: the functional state that the algorithm has reached.
Strip away the algorithmic description and you don’t just lose a useful gloss on the electronics. You lose the very thing in virtue of which E₁’s leading to E₂ is a case of executing a sound chess move rather than one arbitrary transistor state succeeding another. The higher-level description isn’t a supplementary explanation offered alongside the electronic one. It’s what the electronic trajectory operates through when the question is why the machine moved the bishop.
The same structure holds for rational agency. P₁, the fully specific physical state of your brain, is causally sufficient for P₂. The physics is complete. But P₁ produces an M₂-realising P₂ in virtue of being a realiser of M₁ (your rational grounds). And as with the chess case, the same rational assessment could in principle be carried by different neural configurations, or even by a very different kind of physical system altogether. What all those diverse realisers would have in common is that they would all lead to states realising M₂. What explains this convergence is not any specific feature of the physical trajectory but the mental-level property they share: they all realise M₁, and M₂ is what M₁ rationally calls for.
The physical story tells you that P₁ leads to this specific P₂. But there is the further fact that P₂ had to be such as to realise M₂, and this necessity doesn’t come from the physics. It comes from the fact that P₁ realises M₁ and M₂ is what M₁ rationally calls for. The physical trajectory had to land somewhere within the class of M₂-realising states, and what explains that “had to” is the rational connection at the mental level.
And this modal “had to” is not an abstract explanatory posit visible only to philosophers. In the case of a rational agent, it is the most familiar thing in the world: it is the agent’s own practical recognition that this is what needs to be done. The chess player moves the bishop because the position demands it. The student studies because the exam requires preparation. The person apologises because the situation calls for it. In each case, the agent does what they do because they recognise a rational requirement, and it is precisely this recognition, operating through its physical realisation, that explains why the physical trajectory had to be such as to realise that action rather than any other. The “had to” of rational necessity and the “had to” of the non-accidentality argument are one and the same: they are rational agency at work.
One important disanalogy between the chess engine and the human agent is worth flagging. The chess engine’s strategic structure was imposed from outside, by the programmer. So a physicalist might concede the explanatory point about the chess engine while insisting that it’s merely a useful description we impose for our own convenience. The claim I’m making about rational agency is stronger: the agent’s rational structure isn’t externally imposed. It is the agent’s own, cultivated through development, education, and the practices of holding one another responsible. It isn’t a convenient shorthand for underlying physics. It is a genuine form of causal organisation. But this stronger claim can wait because even the weaker chess-engine version of the point is enough to show that Kim’s exclusion argument fails even in the case of deterministic functional artefacts like chess engines.
What About Free Will? The Agent Isn’t Part of the Furniture
The causal exclusion argument isn’t just an abstract puzzle in the philosophy of mind. It connects directly to the oldest and most practical philosophical question: are we free to choose between alternative opportunities for action?
Here’s the connection. If the physical story is complete and the mental story is redundant, then a natural conclusion follows: since the prior physical state of the world (P₁) fully determines the outcome (P₂, and hence M₂), the agent couldn’t have done otherwise. The past was fixed, the laws are fixed, and together they fix the outcome. Your deliberation was a passenger, not a driver.
This is essentially van Inwagen’s Consequence Argument for incompatibilism, and it’s the same reasoning that motivates hard determinism: since everything you do is determined by prior physical states and the laws of nature, you never really had a choice.
Both hard determinists and a certain kind of libertarian accept this reasoning. The hard determinist concludes: we’re not free. The contra-causal libertarian concludes: since we are free, something must break the physical chain: there must be some point where the agent’s will intervenes from outside the causal order.
I think both are wrong, and wrong for the same reason. They share a picture of the agent that is fundamentally mistaken.
Imagine you’re standing at a bus station. One bus has already departed. You didn’t catch it, and that’s settled. It’s now part of the past, beyond your power to change. The question “what should I do?” now operates within the constraints left by that settled fact.
Hard determinism and contra-causal libertarianism both conceive of the agent’s own rational character on the model of the departed bus — as part of the fixed past that constrains the agent from outside. On this picture, the chain P₁→P₂→M₂ is a set of settled facts bearing down on the agent, and the agent either submits to them (hard determinism) or somehow breaks free of them (contra-causal libertarianism).
But this picture smuggles in a fundamental confusion. The agent is not part of their own circumstances. My rational character (which includes my capacity to weigh reasons, my cultivated dispositions, my practical judgment) is not a feature of the landscape I must navigate. It is me, the one doing the navigating.
When I say “I could have done otherwise,” I don’t mean that the past could have been different. I mean that I could have exercised my capacities differently. Consider J. L. Austin’s famous example from his essay “Ifs and Cans”: the golfer who misses a putt and says “I could have made that.” They don’t mean: “in some other possible world with a different past, a different version of me would have made it.” They mean: right here, with this green, this ball, this distance; I had the skill to sink it, and I didn’t. The circumstances were fine. I fell short.
This only makes sense if we distinguish, within the total situation, between the circumstances the agent faces (the layout of the green, the distance to the hole, the wind; all of these are genuinely fixed, external constraints) and the agent who faces them (whose capacities and their exercise are precisely what’s at issue). The hard determinist lumps the agent’s rational character in with the circumstances, treats it as one more fixed antecedent condition, and then observes that, given all of that, the outcome was determined. Of course it was! You’ve included the agent’s actual exercise of their capacities among the fixed conditions. But the agent isn’t a fixed condition of their own action. They’re the one acting.
The contra-causal libertarian makes the same mistake in reverse. Seeing that the agent-plus-circumstances determines the outcome, they conclude that freedom requires the agent to somehow act independently of their own rational character, injecting an element of indeterminacy that breaks the chain. But an action disconnected from the agent’s rational character isn’t a freer action. It’s a random one. The chess grandmaster whose move bears no intelligible connection to their assessment of the position hasn’t exhibited superior freedom; they’ve had a seizure.
What Makes the Past Settled?
There’s a further point worth pausing on. What makes the past settled, and what therefore makes it belong to the agent’s fixed circumstances rather than to what remains open for them to determine, is the fact that it is past.
This matters because the hard determinist’s argument depends on the fixity of the past: since P₁ is fixed, and the laws are fixed, P₂ follows, and the agent is powerless. But consider what you’re doing when you say “the past is fixed.” You are drawing a line between what is settled and what remains open. You are placing yourself at a temporal vantage point from which some things are behind you and beyond your reach and other things are ahead of you and up to you. You are, in short, deliberating, occupying precisely the practical standpoint of an agent situated in time, facing alternatives, determining what to do.
Someone who says “the past is fixed, therefore your deliberation is powerless” is in a peculiar position. The very act of advancing that argument, marshalling considerations, drawing a conclusion, presenting it as something we ought to accept, presupposes the practical standpoint it claims to undermine.
This isn’t just a debater’s trick. It reveals something about the concept of the “fixed past” itself. The distinction between past and future, between what is settled and what remains open, doesn’t appear in physics. The equations of fundamental physics describe trajectories through state space with no privileged direction of time. They don’t mark any point as “now” or any portion of the trajectory as “done.” The settledness of the past is inseparable from the temporal perspective of a deliberating agent within the world. It is the perspective of someone for whom the departed bus is genuinely beyond reach while the next bus is still catchable. Strip away that perspective and you don’t have a “fixed past” constraining a powerless agent. You have a trajectory through state space, with no privileged temporal direction and no one to be constrained.
Putting It Together
Here’s the positive picture. You are a rational agent: a being whose cultivated capacity for reasoning shapes what you do. This capacity is realised physically: it is embodied in the structure and states of your brain. The physical trajectory your brain follows is causally closed. Every physical state has a sufficient physical cause, and no physical law is violated.
But the physical story, while complete on its own terms, doesn’t explain why your brain’s trajectory non-accidentally tracks rationally connected mental states. That explanation comes from the rational level: your grounds made your decision intelligible, and this rational connection is what makes the physical trajectory non-accidentally a trajectory between realisers of good reasoning rather than a trajectory between realisers of random noise.
When you deliberate and act on your conclusions, your rational assessment is genuinely causally efficacious not by violating physics but by being the rational structure that the physical trajectory expresses. The agent acts within a causally closed physical system simply by being the kind of organised system whose higher-level structure shapes which physically possible trajectory the system follows.
This isn’t unique to minds. Consider why a particular DNA sequence reliably produces a functioning heart. Every step (e.g. protein folding, cell differentiation, tissue formation, etc.) has a complete biochemical explanation. The chemistry is causally closed. But if you ask why this sequence of chemical reactions is, non-accidentally, a sequence that produces a working heart, the answer requires the biological level. The organism is a teleologically organised system whose functional structure constrains which of the countless chemically possible trajectories the molecules actually follow. The chemistry explains each step; the biology explains why the steps add up to a heart rather than a tumour.
A rational agent is that kind of system too — but one whose organising structure is rational rather than merely biological. Your cultivated capacity for reasoning shapes which physically possible trajectory your brain follows, in the same way that biological organisation shapes which chemically possible trajectory the developing embryo follows. In both cases, the higher-level structure operates entirely through the lower-level processes, violating no laws. And in both cases, it does explanatory work the lower level alone cannot do.
And when you say “I could have done otherwise,” you’re not right because the past could have been different or because some non-physical force might have intervened, but because you — your rational capacities, your skill, your practical judgment — are not part of the fixed furniture of your circumstances. You are the agent who navigates those circumstances, and the reactive attitudes that structure practical life (regret when you fall short, pride when you succeed, blame and praise from others) target precisely this: the gap between having a capacity and exercising it well. That gap is where your freedom lives.
Where This Goes
This thread will develop these arguments further as discussion proceeds. Among the questions I expect to address:
- Unactualised capacities: What does it mean to say “I could have done otherwise” if the physical past determines the outcome? How do we properly analyse the general abilities that ground responsibility?
- The reactive attitudes: Praise, blame, regret, and pride aren’t just responses to independently existing capacities. They’re partially constitutive of those capacities through scaffolding the development and exercise of practical rationality.
- Teleological organisation: What makes a rational agent different from a thermostat or a chess computer? The answer involves the kind of substance the agent is: a teleologically organised being whose rational structure is genuinely its own, not an externally imposed programme.
For those coming from the Newcomb thread: the position I’ve defended there, that the agent’s rational deliberation is genuinely causally upstream of the predictor’s action, rests on the foundations laid out here. If rational agency is a genuine causal power, then the Newcomb predictor’s sensitivity to the agent’s rational grounds is sensitivity to something causally real, not to an epiphenomenal shadow. I’d encourage Newcomb-specific discussion to continue in that thread, where it has plenty of momentum already, and to keep this thread focused on the underlying questions about rational agency, causal exclusion, and free will. Cross-references between the two threads are of course welcome since the arguments feed into each other.
I’m looking forward to the discussion.
I’ll be drawing on work by G. E. M. Anscombe, J. L. Austin, M. R. Ayers, P. F. Strawson, Robert Kane, Anthony Kenny, Susan Wolf and others as the thread develops. The specific arguments here are developed in more detail in two unpublished manuscripts (“Autonomy, Consequences and Teleology,” 2009, and “The Problem of Free Will, Determinism and Responsibility,” 2018/2021).