Abstract
In a recent paper, Barry Loewer attempts to defend Humeanism about laws of nature from a charge that Humean laws are not adequately explanatory. Central to his defense is a distinction between metaphysical and scientific explanations: even if Humeans cannot offer further metaphysical explanations of particular features of their “mosaic,” that does not preclude them from offering scientific explanations of these features. According to Marc Lange, however, Loewer’s distinction is of no avail. Defending a transitivity principle linking scientific explanantia to their metaphysical grounds, Lange argues that a charge of explanatory inadequacy resurfaces once this intuitive principle is in place. This paper surveys, on behalf of the Humean, three strategies for responding to Lange’s criticism. The ready availability of these strategies suggests that Lange’s argument may not bolster anti-Humean convictions, since the argument rests on premises that those not antecedently sharing these convictions may well reject. The three strategies also correspond to three interesting ways of thinking about relations of grounding linking Humean laws and their instances, all of which are consistent with theses of Humean supervenience, and some of which have been heretofore overlooked.
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Notes
As Maudlin points out, and as a referee helpfully reminds me, Humeans need to say something more about what this complete global physical state of the world includes, so as, roughly put, to preclude simply building the laws themselves into the global physical state. Maudlin’s proposal: “The intrinsic physical state of the world can be specified without mentioning the laws (or chances, or possibilities) that obtain in that world” (2007, p. 52). Note, too, that the two theses of Humeanism can come apart, which generates some subtleties. For example, one might accept the first thesis, taking the laws to supervene on the global physical state, without endorsing supervenience of this global physical state on separable qualitative states of, and some relevantly privileged relations linking, localized individuals. While my primary concern here is with supervening Humean laws, all the positions I will sketch are open to Humeans endorsing both theses.
If two worlds are isomorphic with respect to space–time structure and the distribution of qualities, then all the same facts hold in those worlds, with one caveat: someone sympathetic to this background picture might want to modify it slightly to allow for haecceitistic differences between the worlds.
Loewer’s terminology can be somewhat confusing, as it can seem to suggest that scientists are exclusively interested in “scientific” explanations, even though science may sometimes underwrite what Loewer classifies as “metaphysical” ones. Really, Loewer is gesturing towards a distinction between two answers we might give to a “why?” question, such as, when considering some ice, “Why is this sample of H2O solid?” One sort of answer, the metaphysical one, explains the fact that the ice is solid by citing more fundamental facts about, for instance, the present structural arrangement and attributes of the molecules in the sample. The other sort of answer, the scientific one, cites facts about the earlier temperature and features of some water sample and the changing environmental conditions, as well as some laws relating these facts to the present state of the sample.
Alternatively, Humeans may restrict local Humean facts to facts about point-sized individuals and take as their paradigmatic example Lange’s law that all sodium burns yellow, even though instances of that law are not, strictly speaking, among the local Humean facts. Then they can say the law and its instances have common grounds in the local Humean facts, using Lange’s transitivity principle to generate the conclusion that some local Humean facts both help scientifically explain and ground the law’s instances. In order to generate self-explanation, they need some additional principle, such as: whatever helps scientifically explain some fact helps scientifically explain the grounds of that fact, too.
Lange’s transitivity principle links explanations of distinct sorts (scientific and metaphysical explanations); note that it is distinct from any principle affirming the transitivity of a single kind of explanatory relation, such as metaphysical explanation—as I mentioned above, Lange may not affirm the transitivity of (partial) grounding, itself.
To clarify: the focus here is on circularity arising when laws themselves feature among our scientific explanantia. As I discuss in §5, related concerns can arise with explanatory appeals to metanomological facts, such as the fact that L is a law, as well.
Lewis describes natural properties and relations as “fundamental,” and he also sometimes uses the language of “reduction,” which may seem to suggest that he is committed to, or at least motivated by, a background picture on which some local Humean facts are prior grounds of other facts, even if official statements of his Humean doctrine (cf. 1986, 1994a) merely invoke supervenience. Ned Hall directs me to the following passage, however:
Imagine a grid of a million tiny spots—pixels—each of which can be made light or dark. When some are light and some are dark, they form a picture, replete with interesting intrinsic gestalt properties. The case evokes reductionist comments. Yes, the picture really does exist. Yes, it really does have those gestalt properties. However, the picture and the properties reduce to the arrangement of light and dark pixels. They are nothing over and above the pixels. They make nothing true that is not made true already by the pixels. They could go unmentioned in an inventory of what there is without thereby rendering that inventory incomplete. And so on.
Such comments seem to me obviously right. The picture reduces to the pixels. And that is because the picture supervenes on the pixels: there could be no difference in the picture and its properties without some difference in the arrangement of light and dark pixels. Further, the supervenience is asymmetric: not just any difference in the pixels would matter to the gestalt properties of the picture. And it is supervenience of the large upon the small and many. In such a case, say I, supervenience is reduction. (Lewis 1994b, p. 294.)
Here, Lewis clearly states that reduction, in his sense, just is asymmetric supervenience of the sort familiar from his doctrine of Humean supervenience—he, at least, means nothing stronger.
For the sake of completeness, it is worth noting that Humeans somewhat sympathetic to groundless Humeanism could, at least in theory, deny instances ground and evade Lange’s criticism while still retaining some of the grounding relations described by that thesis: they could grant that C grounds the laws but reject relations of grounding between the local Humean facts and C, or they instead could allow that the local Humean facts help ground C but reject relations of grounding between C and the laws. The key would be to motivate the move from supervenience commitments to grounding claims in one case but not the other.
While those convinced of the futility of attempts at interlevel or intertheoretic reduction—I have in mind views discussed by Fodor (1974), Nagel (1998), and Batterman (2002), among others—may be more open to these sorts of examples, the force of such cases is not tied to such non-reductive metaphysical convictions.
Since Loewer characterizes scientific explanations as “typically” explaining the fact that some event occurred at a time by citing a fact about the state of the world at a different time (2012, p. 131), someone might resist the suggestion that this example counts as a case—or at least a typical case—of scientific explanation in Loewer’s sense. The more crucial point, though, is that this seems to be an example of some sort of top-down non-grounding explanation compatible with a bottom-up direction of grounding. (Note also that Lange’s favored example of scientific explanation—explaining the color of a flame by citing a law plus the fact that the burning substance is sodium—does not involve appeal to any earlier states of the world, either.)
As Bernhard Nickel and Alex Silk have emphasized to me, however, this sort of consideration will not be universally compelling, for one might insist that a general fact, such as the fact that all hydrogen atoms have mass m, can be genuinely explanatory only if it is not even partly grounded in its particular instances.
Loewer, for instance, claims that Humean laws “explain by unifying” (1996, p. 113). Thanks to Ned Hall for many helpful discussions of related points.
A referee suggests that even these Humeans might still want to insist that metanomological facts, such as the fact that it is a law that all sodium burns yellow, can scientifically explain such generalizations, including the laws themselves—I touch on this issue in §5.
But contrarian Humeans who have reservations about this consequence (cf. Lange 2009, p. 301) should join their more traditional counterparts in reevaluating the transitivity principle and the principle that no fact can help explain itself—and, as already noted, Humeans have other reasons to be wary of these principles.
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Acknowledgments
I am especially grateful to Ned Hall, Zeynep Soysal, and an anonymous referee for this journal. My thanks, also, to Jeffrey McDonough, Bernhard Nickel, Alexander Prescott-Couch, Mark Richard, Bradford Skow, Elanor Taylor, and Kate Vredenburgh; many helpful discussants at Harvard University, including members of the 2013–2014 Harvard M&E Workshop, and at the University of Birmingham; and participants in John Heil’s 2013 NEH Metaphysics and Mind Summer Seminar at Washington University in St. Louis. Work on this paper was supported, in part, by the National Endowment for the Humanities, although views expressed here do not necessarily represent those of the Endowment.
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Miller, E. Humean scientific explanation. Philos Stud 172, 1311–1332 (2015). https://doi.org/10.1007/s11098-014-0351-7
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DOI: https://doi.org/10.1007/s11098-014-0351-7