On the causal completeness of physics

February 15, 2026 | 1,643 words | 8min read

Paper Title: On the causal completeness of physics

Link to Paper: https://philpapers.org/rec/VICOTC

Date: 2006

Paper Type: Philosophy, Physicalism

Short Abstract: The overdetermiantion argument is the most commonly used argument in favour of physicalism, it relises o nthe assumption of the causaul lcosure of physics, this paper investiagtes jsutifaction for this assumptions.

1.Introduction: The Overdetermination Argument and the Closure Principle

The strongest current argument for physicalism is the exclusion or overdetermination argument, especially since older arguments based on the unification of all sciences have been undermined. Following ideas like those of Jerry Fodor, many philosophers now believe that the special sciences cannot be fully reduced to physics, so there is no clear epistemological reason to think everything is physical. As a result, defenders of physicalism rely on an ontological argument: anything that causally interacts with the physical world must itself be physical. This argument is particularly aimed at the mind, since mental events appear to cause physical effects, but it can be extended to any domain whose properties seem to have physical consequences.

The overdetermination argument consists basically of three premises, namely:

(i) the principle of the causal closure of the physical (CCP): every physical effect (i.e. caused event) has physical sufficient causes;

(ii) causal efficacy of the ‘dubious’: dubious events cause changes in the physical world;

(iii) no overdetermination: there is no dubious/physical causal overdetermination.

And the conclusion is that

(iv) dubious events are physical events.

Although many philosophers claim CCP is supported by contemporary physics, it is not itself a stated physical law. Two main justifications are considered: first, that CCP functions as a methodological principle supported inductively by the success of physics in explaining physical phenomena without appeal to non-physical causes; and second, that it is grounded in physical laws, especially conservation laws.

The conlusion will be, that CCP is not justified a priori but might be seen as an inductively supported generalization.

2. Causal Closure of the Physical as a Guiding Principle

Can the causal closure of the physical (CCP) be understood as a guiding or heuristic principle in science, similar to what Thomas Kuhn called “symbolic generalizations”?

Like laws such as F = ma, the CCP is highly general and sets a research agenda by instructing physicists to look for physical causes of physical effects. In that sense, it functions like a schematic principle guiding scientific practice, and it has appeared across different historical frameworks, from Epicurus’ atomism to Gottfried Wilhelm Leibniz’ dynamics.

However, unlike Kuhn’s examples, the CCP does not seem definitional or quasi-tautological; it is not analytically true, since non-physical causation is at least conceivable.

The principle appears to have a dual character: it can be seen either as an a priori methodological commitment reflecting physics’ aspiration to explanatory completeness, or as an a posteriori, inductively supported generalization about how the world actually is.

2.1 Causal Closure of the Physical as a Guiding Principle with A Priori Justification

One strategy to ground CCP is, strong reductionism: if everything must ultimately be explainable in purely physical terms, then only physical properties and causes exist. But this assumes classical reductionism, which is controversial and if physicalism is already presupposed, CCP cannot be used non-circularly to argue for it.

A second strategy claims that because physics is the “basic” science describing the bottom layer of reality, it must be explanatorily comprehensive. Yet this too is challenged. Emergentists argue that even if physics studies the lowest level, higher-level entities can emerge with genuine downward causal powers that physics cannot fully explain. Meanwhile, philosophers such as Nancy Cartwright and John Dupré reject the idea that physics is metaphysically basic at all. They defend a pluralistic view in which sciences describe different aspects of reality, and physical laws apply only within limited domains rather than universally.

The overall conclusion is that CCP is very difficult to justify a priori: it cannot rely on reductionism without circularity, it does not follow simply from physics being “basic,” and even the claim that physics is basic is itself open to dispute.

2.2 Causal Closure of the Physical as a Guiding Principle with A Posteriori Justification

In this view, past cases show that physical events are either uncaused or caused only by other physical events; apparent non-physical causes have either been reinterpreted as physical or dismissed as spurious. This makes the inductive strategy more promising than an a priori one, especially given the long success of physics since figures like Gottfried Wilhelm Leibniz.

However, the historical record complicates matters: belief in CCP has often coincided with belief in conservation laws, suggesting the principle may depend on them rather than on pure induction. Moreover, emergentist thinkers such as Stuart Kauffman argue that complex systems (like living organisms) exhibit downward causation, where higher-level wholes constrain and influence lower-level physical processes. Similar ideas are developed by John Dupré and Nancy Cartwright, who deny that physics has the universal empirical support required for CCP.

The key challenge is that the same scientific record used to support CCP inductively can also be interpreted as evidence for emergence and downward causation. Thus, the claim that CCP is straightforwardly supported by empirical evidence is controversial and requires deeper analysis, possibly by examining its connection to conservation laws and the history of science.

3. Causal Closure of the Physical and Physical Law

A second strategy for justifying the causal closure of the physical (CCP): is grounding it in physical laws rather than defending it purely a priori or inductively.

Although no physical law directly entails CCP, the proposal is to argue in two steps:

1. that causation can be reduced to a specific kind of process;
2. that only physical magnitudes can realize that process.

Two major reductive accounts of causation are introduced:

1. defended by John Bigelow and Robert Pargetter (and also used by David Papineau), identifies causation with the action of forces.
2. The other explains causation as the transfer or exchange of conserved quantities.

Both reduce causation to concrete physical processes. However, to support CCP, it is not enough to reduce causation; one must also show that only physical processes can instantiate these causal relations.

3.1 Forces

David Papineau’s influential attempt to ground the causal closure of the physical (CCP) in physics uses the conservation of energy.

Papineau traces modern belief in CCP back to Hermann von Helmholtz’s defense of universal energy conservation and to developments in neurophysiology and biochemistry, which failed to find evidence for vital or mental forces. As physics and biology increasingly explained phenomena in terms of a limited set of physical forces, non-physical forces became empirically unnecessary.

Papineau’s strategy has three key components:

1. physical effects involve variations in conserved quantities such as energy.
2. causation consists in the action of forces.
3. there is inductive evidence that only physical forces are responsible for such variations.

This does not yield one sweeping argument for physicalism, but rather a set of stronger, domain-specific exclusion arguments (e.g., that bodily movements have sufficient neurophysiological causes). These local arguments are often more powerful than an appeal to CCP in general.

Still, each step of Papineau’s framework can be challenged. Emergentists may question whether all physical effects involve conserved quantities, whether causation really reduces to forces (as argued by John Bigelow and Robert Pargetter), or whether the empirical record truly rules out non-physical but energy-conserving forces. Thus, even this physics-based grounding of CCP remains philosophically contestable.

3.2 Conserved Quantity Accounts

Conserved quantity (CQ) theories of causation, developed by Wesley Salmon and Phil Dowe, provide an alternative way to ground the causal closure of the physical (CCP).

CQ theories define causation as the exchange or transfer of conserved quantities (such as mass-energy, momentum, or charge). If physical effects are understood as variations in conserved physical quantities, and conservation laws guarantee that such quantities cannot change without corresponding counter-changes, then it appears to follow that every physical effect must have a physical cause. This approach improves on force-based accounts by offering a clearer characterization of what counts as a “physical effect.”

However, the strategy is not decisive. CQ theories are philosophically controversial, and they do not by themselves rule out the possibility of non-physical conserved quantities (for example, some hypothetical “odd-energy”). An anti-physicalist could claim that physical changes are mediated by exchanges involving such non-physical quantities, even if ordinary energy conservation still appears intact from the standpoint of physics. In response, the physicalist must again rely on inductive evidence: there is no empirical trace of such non-physical conserved quantities, and physics successfully explains changes purely in terms of recognized physical magnitudes.

4. Conclusions

Two approaches have been examined, for the justification of CCP:

1. Heuristic or methodological approach: The CCP is not an a priori truth but may serve as an inductively supported guiding principle in physics. Its status is that of a reliable methodological rule rather than a directly stated law.
2. Law-based or supervenience approach: The CCP can be grounded in physics itself, proceeding in two steps.

Grounding CCP in conservation laws and reductive theories of causation places it on firmer empirical footing than purely a priori arguments. Yet it cannot deductively exclude non-physical causes; it ultimately depends on inductive support and on the continued success of physical theory.

The main challenges to this second approach come from the anti-physicalist side: they may question whether all causation is captured by these processes, or whether non-physical forces or conserved quantities could exist. Yet, there appears to be strong inductive evidence against such non-physical interventions evidence, which makes the CCP a reasonable default assumption.

Finally, while the CCP provides the basis for general overdetermination arguments for physicalism, these arguments can be strengthened by domain-specific exclusion arguments. These use the same inductive evidence that supports the CCP but apply it to particular domains, making the case against dualist or emergentist causes more robust. Importantly, even if the law-based grounding of the CCP were to fail, there remains enough direct inductive support to justify the principle.

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