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Explaining causal closure


The physical realm is causally closed, according to physicalists like me. But why is it causally closed, what metaphysically explains causal closure? I argue that reductive physicalists are committed to one explanation of causal closure to the exclusion of any independent explanation, and that as a result, they must give up on using a causal argument to attack mind–body dualism. Reductive physicalists should view dualism in much the way that we view the hypothesis that unicorns exist, or that the Kansas City Royals won the 2003 World Series: false, but not objectionable in any distinctively causal way. My argument turns on connections between explanation, counterfactuals, and inductive confirmation.

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  1. Kim (2005, p. 15).

  2. Kim (1973, 1976).

  3. I assume here that a universal generalization like (Closure) is the sort of thing that could be a law. But everything I say could be made compatible with alternative conceptions of laws, like the Tooley/Dretske/Armstrong view on which laws are relations among universals.

  4. See for instance Yablo (1992), Pereboom (2002), and Shoemaker (2007). Some nonreductive physicalists, like Fodor (1974), have held that although mental and physical properties are distinct, mental and physical events are identical. On the Kimian conception of events we are assuming, however, if mental and physical properties are distinct, it follows that mental and physical events must be distinct.

  5. The variables here range over true propositions, or facts. However, a similar notion of independent explanation could be formulated in terms of events.

  6. Lowe (2009) explores the prospects and limitations of using such counterfactuals to analyze ontological dependence, a non-causal but explanatory metaphysical determination relation. I do not mean to defend such an analysis here, I only mean to suggest that there is a close connection between metaphysical explanation and counterfactuals, just as there is a close connection between causation and counterfactuals even if the counterfactual analysis of causation fails.

  7. Kim (2005, pp. 39–40).

  8. Here, following Kim, the variables range over events.

  9. However, this leads to the familiar causal exclusion problem since P, being a physical state, has fully sufficient physical causes. Or so Kim argues.

  10. This version is taken from Papineau (2002) with minor adjustments. Besides Papineau, proponents of some sort of causal argument for physicalism (either reductive or nonreductive) include Smart (1959), Lewis (1966), Davidson (1970), Tye (1995) and (2009), Levine (2001), and Melnyk (2003). It is the single most influential argument for physicalism today.

  11. (C) says that all mental events are physical, while (P*) says that absolutely all events are physical. These claims are equivalent if we assume the via negativa approach, which defines “the physical” as the non-mental. Even if we do not assume this, treating (C) and (P*) as equivalent is harmless since proponents typically take the causal argument to generalize to all events.

  12. My analysis entails that explanatory overdetermination in general is problematic just when there are not independent sources of evidence for the different explainers. If a pair of simultaneous gunshots to the heart leave separate entrance wounds, this need not be an objectionable case of overdetermination—there is separate evidence for the efficacy of each shot. This is very different from the sort of overdetermination at issue in (P3), since mental and physical causes do not leave separate traces. Compare Kim (2005, p. 48) on this very point.

  13. See for instance Crisp and Warfield (2001), Sider (2003), and Schaffer (2003), who defend causal overdetermination.

  14. A non-Champion Royal event is one whose constitutive object is not a member of the 2003 World Series Champion Kansas City Royals. All actual events are thus non-Champion Royal events.

  15. In fact, I do think it is a logical possibility that the Royals could win the 2003 World Series while being epiphenomenal or causally redundant. An epiphenomenal Royals team could win all its games by virtue of the opposing team always forfeiting, for example, which plausibly requires the opponents to cause some effects (e.g. perhaps they announce their forfeiture to the umpires) but not the victorious Royals.

  16. I take this point to apply even to absences: either absences are causes and thus exist, or else they do not exist and so are not causes. I prefer the former view, but will not try to defend it here.

  17. Papineau (2001, p. 11).

  18. See Papineau (2002, p. 19), where it is made explicit that the specific physicalist conclusion Papineau is arguing for is that Kimian mental events are identical with physical events.

  19. See for instance Wright (2003, 2004), Davies (2004), McLaughlin (2003), Pryor (2004), Silins (2005), and Tucker (2010).

  20. Wright (2003).

  21. Cf. Pryor (2004) and Tucker (2010).

  22. Davidson’s (1970) and (1995) case for (Closure) appears to be a priori. The “pairing problem” discussed by Foster (1991, Chap. 6) and Kim (2005, Chap. 3) also potentially serves as the basis for an a priori defense.

  23. The second and third premises of the causal argument are supported by armchair considerations. If the argument is to rely on any empirical support, it must be support for its (Closure) premise.

  24. Melnyk (2003, pp. 289–290). See also Papineau (2001) and (2002, Chap. 1).

  25. Goodman (1955) is the classic contemporary discussion of the link. My arguments that follow are especially influenced by Lange (2000).

  26. Perhaps it also commits you to accepting a certain range of counterfactuals, but we can leave this open.

  27. Just which counterfactuals you must refrain from accepting will depend on your warranted background beliefs. I happen to know there are bits of copper warmer than my samples, but imagine a subject with the warranted (but false) belief that my samples are the warmest pieces of copper in the world. Such a subject could plausibly justifiably accept the inductive case even while accepting the counterfactual in question, holding that my samples wouldn’t have been conductive had they been warmer. For, by her lights, whether my samples would or wouldn’t have been conductive had they been warmer may well be irrelevant to the question of whether all actual copper is conductive, given her warranted but false view that no actual copper is so warm.

  28. A related possibility is to propose that being physical is a natural kind while being a non-Champion Royal event is not. But I can only see how this might help if it is supposed in addition that by virtue of being a natural kind, the property of being physical enters into explanatory relations, like lawful relations, while properties that aren’t natural kinds can’t do this. In other words, I can only see how this might help if it involves covertly supposing that (Closure)’s truth is explanatorily overdetermined.

  29. Sometimes the term “induction” is used broadly, to cover abduction as well as enumerative induction. In that case I concede that (Closure) is “inductively confirmed” by its positive instances, but insist that its positive instances confirm it only by first confirming (P*).

  30. Chalmers (1996), Jackson (1982).

  31. See for instance Tye (2009, Sect. 2.2), a section entitled “Why Consciousness Cannot be Physical,” which sets out familiar dualist arguments. It is immediately followed by a section (Sect. 2.3) entitled “Why Consciousness Must be Physical,” which defends a version of the causal argument.

  32. Jackson (1982) notably defends epiphenomenalism while Chalmers (1996) at least entertains it.

  33. Presumably God could know of this act of creation even if unicorns were epiphenomenal or causally redundant, and so what God tells us does not deductively entail ~(U-Closure).


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Thanks to William Beardsley, Sara Bernstein, Douglas Cannon, Carrie Figdor, Jaegwon Kim, Dan Korman, Geoffrey Lee, Aidan McGlynn, Paul Loeb, Gualtiero Piccinini, Ian Schnee, David Sosa, Ariela Tubert, Michael Tye, and Gene Witmer. Special thanks to Andrew Melnyk, and to John Heil, who oversaw the 2009 NEH Summer Seminar on Mind and Metaphysics, where an early version of the paper was presented.

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Correspondence to Justin Tiehen.

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Tiehen, J. Explaining causal closure. Philos Stud 172, 2405–2425 (2015).

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  • Physicalism
  • Causation
  • Counterfactuals
  • Induction
  • Explanation
  • Causal closure