Abstract
A number of philosophers have argued that causation is not an objective feature of the microphysical world but rather is a perspectival phenomenon that holds only between “coarse-grained” entities such as those that figure in the special sciences. This view seems to pose a problem for arguments for physicalism that rely on the alleged causal completeness of physics. In this paper, I address this problem by arguing that the completeness of physics has two components, only one of which is causal. These two components of completeness can be used in an argument for physicalism that is supported by strong inductive evidence even in the absence of microphysical causation.
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Notes
An anonymous referee pointed out some physicalists claim that physics provides a comprehensive account of all of reality (and not just empirical reality). However, as Daniel Stoljar notes: “Most physicalists do not mean that absolutely everything is physical or that every particular is physical or even that every property is physical. What they mean instead is (something like) every instantiated property is necessitated by some physical property” (2010, p. 5; see also pp. 29–38).
Of course, one may doubt whether this evidence (which, following Papineau, I take to concern the conservation of energy and the lack of non-physical forces and causes in living systems) is itself all that convincing. I shall not respond to this kind of concern in this paper. Rather, I am arguing that the absence of microphysical causation does not pose any additional problems for a (correctly construed) completeness-based argument for physicalism.
In earlier work (Haug 2009), I have argued that the completeness of physics has two components, but the second component I formulate there is somewhat different from the one I identify in this paper.
I owe the Mach references to Frisch (2014). As Frisch points out, although Russell repeated many of Mach’s arguments, Russell’s paper “at least in the English-speaking world, is much better known than Mach’s earlier critique” (ibid., p. 5).
As a result, the micro/macro distinction that is relevant to debates about the existence of microphysical causation is not based on the part/whole relation. In terms of a distinction made by Jaegwon Kim (1998, pp. 83ff.), the micro/macro distinction spans “orders” of states/properties, not mereological “levels.” Thanks to an anonymous referee for prompting me to clarify this point.
As we’ll soon seen, this statement arguably needs to be qualified so that only maximally determinate values of fundamental (or narrowly) physical quantities or variables automatically count as microphysical.
I will not address what makes a physical theory fundamental here. Some have suggested that the notion of grounding can be used to understand fundamentality (e.g., Rosen 2010, p. 112), while others claim that fundamentality is a basic notion that cannot be completely characterized in other terms (e.g., Wilson 2014, p. 560).
To take another example, Ney suggests that precisely described motions of individual dendrites are microphysical events, even though dendrites are not fundamental physical entities (2016, p. 150). Note that I assume Kim’s (1976) property-exemplification account of events, according to which events can be represented by an ordered triple \(\langle \hbox {O}\), P, \(\hbox {t}\rangle \), consisting of an object (or objects), O, instantiating a property (or relation), P, at time (or time-interval), t.
See, e.g, Price and Corry (2007, p. 4). In terms of Eric Funkhouser’s (2014) distinction between specification (the relation between determinables and determinates) and realization, macrophysical properties, on this view, are either multiply realizable broadly physical properties or multiply specifiable narrowly physical properties.
Here I am following Wilson’s (2003) usage of “nothing over and above,” according to which it is possible for one entity to be nothing over and above a numerically distinct entity.
It is thought that fundamental forces arise from constraints imposed by local gauge symmetries (Gross 1996). Perhaps to avoid the causal connotations of the word ‘force,’ contemporary physical theories tend to use the term ‘fundamental interaction.’ However, I will usually use the term ‘fundamental force’ below.
Note that this is logically stronger than the claim (*) that every physical event (that has a sufficient cause at all) has a physical sufficient cause, at least assuming that causation is transitive. For suppose causation is transitive, and suppose that there is some physical event that has only a non-physical sufficient cause at time t, which in turn has a physical sufficient cause prior to t. Then, (*) will be true, but causal completeness as formulated in the text will be false. For this point, see Lowe (2000, pp. 575, 576). I am indebted to Gibb (2013) for reminding me of Lowe’s paper.
For instance, given the right background conditions, a sharp pain is a sufficient cause of someone’s wincing, and a belief that it is sunny and a desire to go for a long run without getting a sunburn together are a sufficient cause of someone’s putting on sunscreen. See Bennett (2003, p. 281) for the claim that “causal sufficiency is only sufficiency in the circumstances [e.g., given various background conditions].” On a different point, I follow Papineau (2001, p. 33 n.5) in thinking that the “causal argument provides a schema that delivers physicalism for other special subjects [e.g., the biological or social] as readily as for the mental.” In other words, the causal argument is best understood as a “family of arguments” with different efficacy premises for different special science domains, rather than a single overarching argument (ibid., p. 6).
For instance, many authors have taken issue with the causal exclusion principle, in effect arguing that it equivocates on the notion of overdetermination. On this view, only overdetermination between completely independent simultaneous sufficient causes is rare and unsuitable in an account of mental causation, while overdetermination between necessarily connected simultaneous sufficient causes (such as mental events and their physical realizers) is widespread and unproblematic. (See Sider 2003 for an example of this kind of view.) This dispute over the causal exclusion principle is related to the fact that the causal argument has been used for two different purposes: (i) to argue for physicalism of any kind (whether reductive or non-reductive) and (ii) to argue that non-reductive physicalism is an unstable position. I am sympathetic to this line of thought, but it raises the difficult question of whether the causal argument can be used to accomplish (i), while at the same time blocking (ii). I have addressed this question elsewhere (Haug 2009), but to avoid getting bogged down in complications that are mostly tangential to the main arguments in this paper, I will here assume that the causal argument supports reductive physicalism.
Vicente (2006, pp. 157, 161, 162) claims that Papineau’s argument implicitly depends on a force-based account of causation, according to which causation can be reduced to the “action of forces” (see, e.g., Bigelow and Pargetter 1990). Note that this simple reduction of causes to forces implies that causation occurs in the microphysical domain (since interactions involving the fundamental forces would be the basic causal processes to which all other causal processes were reduced). Thus, this defense of the causal completeness of physics runs afoul of the absence of microphysical causation. Ney claims that the conservation of energy forges the link between forces and causes by motivating the idea “that if some [causal] process takes place, there must have been some force present, something providing the energy for this process to occur” (2016, p. 143 n.7). However, the conservation of energy by itself does not support the converse claim that if some force is present, then a causal process also occurs. Note that, like Papineau, Ney sometimes uses the terms “force” and “cause” interchangeably (2016, pp. 144, 145).
As above, I have inserted the phrase “in non-living systems,” so that the simple inductive argument and the causal argument from physiology (to be discussed below) have distinct evidential bases, as Papineau claims. Ney’s formulation of causal completeness should be more precisely formulated, as I have above (see note 12).
Here is another statement of the simple inductive argument: “...[C]ontemporary physics has found sufficient physical causes for very many kinds of physical effects and has found no physical effects at all for which it is necessary (or even likely to turn out to be necessary) to invoke nonphysical causes. The success to date of current physics in finding sufficient physical causes for physical effects therefore provides inductive evidence that all physical events, including both unexamined physical events and examined-but-as-yet-unexplained physical events, have sufficient physical causes” (Melnyk 2003, p. 289, italics in original).
What if the universe turns out not to have a fundamental level? I believe that this does not immediately result in physicalism being a false or uninteresting doctrine. The physicalist can utilize a notion of “relative fundamentality.” If physicalism is true, then all entities that have physical effects are determined by physical entities such that any further determination of these entities is also by physical entities (see Montero 2006, p. 178).
Precedent for taking the completeness of physics to be partly a constitutive thesis comes from Lewis’s (1966) “explanatory adequacy of physics,” which, as noted above, claims that there is a “unified body of scientific theories... which together provide a true and exhaustive account of all physical phenomena.” This claim is partly constitutive in that the unity among the theories is spelled out in compositional terms. The theories are unified “in that they are cumulative: the theory governing any physical phenomenon is explained by theories governing phenomena out of which that phenomenon is composed and by the way it is composed out of them” (1966, p. 23).
Ney also claims that if (what I’m calling) the causal argument from physiology is to be fully convincing it “must concern microphysical causal processes” (2016, p. 150). For, in her view, this argument would need to rule out the existence of non-physical causes “affecting even the tiniest and most precisely described motion of particles” in living things (ibid.). I think that this concern is misguided. After all, if there are no microlevel causes, then there can hardly be non-physical causes at the microlevel, and the causal argument from physiology cannot be faulted for failing to rule them out. On a related note, although I agree with Ney that (if there is no microphysical causation) the simple inductive argument and the causal argument from physiology support a version of causal completeness that is substantively true only in the macrophysical domain, this needn’t be expressed by taking the conclusion of these arguments to be the (logically weaker) causal completeness of macro physics. Instead, we can continue to take the conclusion to be the causal completeness of physics, but simply note that if no microphysical events have causes, then this more general completeness claim is only vacuously true in the microphysical domain.
Here it matters whether multiply realizable entities like dendrites can be constitutive elements of microphysical events. If not, we can use some other event that is uncontroversially microphysical.
Here I agree with Robin Hendry’s skepticism “about how closely physics (as opposed to chemistry) has unified, or even been involved in, physiological explanation at the cellular level” (2010, p. 216).
I think that further evidence for the conservation of energy (and thus support for the argument from fundamental forces) that is compatible with the absence of microphysical causation comes from Emmy Noether’s first theorem (1918), which shows, roughly, that any global symmetry of a physical system corresponds to a conservation law. In particular, the fact that fundamental physical laws are time-symmetric corresponds to the fact that energy is conserved.
Note that even Ney accepts this. As she writes, “... although there are certainly still open questions in the foundations of quantum mechanics, we possess enough good physical explanations of these microscopic processes to rule out the need to postulate special forces. I am not suggesting that the argument for physicalism today is weak because of controversy in the foundations of quantum mechanics” (2016, p. 151). Rather, Ney is only pointing out that these “good physical explanations” do not follow from the completeness of macrophysics.
Thanks to anonymous referee for raising this objection.
It may be a mistake to appeal to a principle of determinative/generative exclusion in developing this objection since the notion of determination/generation arguably has causal connotations (e.g., asymmetry) that, according to selective causal skepticism, must be avoided at the microphysical level. The most natural exclusion principle to offer instead of one that appeals to determination/generation would claim that there cannot be more than one sufficient condition for a given event at a given time. But, as I discuss below, only np (or np together with the fundamental dynamical laws) is literally sufficient for e; bp is only sufficient for e given certain background conditions. So, this principle generates competition between bp and np only by conflating two distinct senses of ‘sufficiency.’ Further, even setting this aside, the existence of one sufficient condition for an event at a given time does not seem to exclude the existence of another sufficient condition for that event at that time (see Ney 2016, 1 p. 59 for a similar point).
It would take some work to show this in detail, but I take it as uncontroversial that, on any adequate account of “nothing over and above-ness,” if Y is nothing over and above X, then Y is not wholly distinct from and not independent of X. For example, being red is realized by, and hence, nothing over and above, being scarlet. As a result, being red is not wholly distinct from being scarlet (to be scarlet is, in part, to be red), and being red is not independent of being scarlet (something cannot be scarlet without also being red).
In these quotations, I have replaced instances of the word ‘production’ (and related words) with instances of ‘determination/generation.’
As Loewer notes: “Once we realize that local [determination/generation] is not a basic relation but supervenes on the total state that literally [determines/generates] subsequent states, we can think of [macrophysical] events [such as bp] as picking out features of that [total] state that are involved in, though not completely, the [determination/generation] of the effect” (2007, p. 254).
Kim has also claimed that the “fundamental rationale” for both the determinative/generative and causal exclusion principles is “essentially the same” (2001, p. 277), and in more recent work he has claimed that the causal exclusion principle is “virtually an analytic truth with not much content” (Kim 2005, p. 51). I think that a strong argument can be made that only a principle like the original principle of determinative/generative exclusion (i.e., a principle that rules out only more than one “wholly distinct or independent” generative source or sufficient cause at a given time) is close to being analytic. This is because of the notion of overdetermination at issue: the “genuine cases of overdetermination” that are ruled out by the principle involve only wholly distinct or independent sufficient causes (or generative sources). (See Árnadóttir and Crane 2013, p. 257.) But, as discussed above, bp and np do not violate the original principle of determinative/generative exclusion.
If there is no good rationale for this version of the strengthened principle of determinative/generative exclusion, and if any rationale for the causal exclusion principle would also be a rationale for this strengthened principle (see previous note), then this raises the worry that the causal exclusion principle (as stated above) is also unmotivated. I have two things to say in response. First, since causal sufficiency is only one kind of “generative relation,” there may be good reason to think that there is competition between two putative simultaneous sufficient causes that does not carry over to the generalized version of the strengthened principle of determinative/generative exclusion. Second, it may turn out that the causal exclusion principle, as stated above, is unmotivated and that even reductive physicalists should acknowledge that there are counterexamples to it. (See Haug 2010 for an argument for this.) But, a qualified causal exclusion principle that rules out only multiple wholly distinct or independent sufficient causes may still be true. Whether this qualified exclusion principle can be used in a sound argument for physicalism raises complications that I cannot discuss here (see Haug 2009).
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Acknowledgements
Some ideas in this paper are based on work that I completed while holding a Scholar’s Award from the National Science Foundation (SES-0957221). I am grateful for this support, and I also thank two anonymous referees for comments that improved the paper.
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Haug, M.C. No microphysical causation? No problem: selective causal skepticism and the structure of completeness-based arguments for physicalism. Synthese 196, 1187–1208 (2019). https://doi.org/10.1007/s11229-017-1519-4
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DOI: https://doi.org/10.1007/s11229-017-1519-4