Physicalism, supervenience, and monism

Abstract

Physicalism is standardly construed as a form of monism, on which all concrete phenomena fall under one fundamental type. It is natural to think that monism, and therefore physicalism, is committed to a supervenience claim. Monism is true only if all phenomena supervene on a certain fundamental type of phenomena. Physicalism, as a form of monism, specifies that these fundamental phenomena are physical. But some argue that physicalism might be true even if the world is disorderly, i.e., not ordered by supervenience relations in the way commonly supposed (Montero in J Philos 110:92–110, 2013; Leuenberger in Inquiry 57:151–174, 2014; Montero and Brown in Topoi 37(3):523–532, 2018; Zhong in Philos Stud 178(5):1529–1544, 2021). Unless these authors intend to challenge the claim that physicalism is a type of monism—a claim so central to the dialectic in philosophy of mind that rejecting it risks changing the subject—they are committed to challenging a supervenience requirement for monism. We argue that monism entails that there are substantial supervenience relations among concrete phenomena: relations that would not obtain in a disorderly world. Our argument thus has implications for debates about physicalism and supervenience, and sheds light on an under-discussed issue: what is implied by classifying a theory in the philosophy of mind as a form of monism? We also argue that physicalism’s commitment to monism creates problems for via negativa physicalism, on which the physical is characterized negatively.

Addendum: grounding and supervenience

We have argued that monism is committed to a “nothing over and above” claim, or something similar. Such claims are sometimes expressed in terms of (metaphysical) grounding. For example, the “nothing over and above” claim associated with physicalist monism is sometimes expressed as the claim that all truths (at least, all truths about the concrete world) are fully grounded in physical (or physical*) truths.³⁶ Grounding is widely held to entail metaphysical necessitation, that is, supervenience (Fine, 2012; Rosen, 2010). Given that widely held view, the claim that all truths are grounded in physical (or physical*) truths implies a further commitment to a supervenience claim such as PSV.

However, that the widely accepted connection between grounding and supervenience has been disputed. Arguments for what is sometimes termed “contingent grounding” have been developed by Leuenberger (2014) and Skiles (2015). Thus, those arguments might appear to threaten our claims about monism, physicalism, and supervenience. In this addendum, we will consider those arguments. We will argue that they do not undermine our claims.

Skiles (2015) argues for grounding contingentism, which holds that a fact P can be grounded in a set of facts Γ but without supervening on Γ. He bases his argument largely on counterexamples to grounding necessitarianism, which holds that if Γ grounds P, then P supervenes on Γ. One type of counterexample begins with the idea that an ordinary composite object is grounded in its parts (Conee & Sider, 2005, p. 68). Skiles then considers rearrangements of those parts, modeled on the ship of Theseus:

Let ‘‘o’’ pick out a particular tuna sandwich. Suppose that in an earlier epoch, the existence of o is grounded in an arrangement of its parts, the as (call this arrangement ‘‘Γ’’). At a later epoch, one of the as (call it ‘‘a₁’’) is sloughed off and replaced with a duplicate (call it ‘‘b₁’’). There is now a sandwich composed of b₁, a₂, … a_n: this sandwich (call it ‘‘o₁’’) is presumably identical to o. Suppose this process of gradual replacement repeats so that eventually in a later epoch, we are left with two sandwiches: one (call it ‘‘o_n’’) identical to o and composed of b₁, b₂, ..., b_n, but also another sandwich (call it ‘‘o_R’’, for replacement) composed of a₁, a₂, ..., a_n and placed in the same arrangement, Γ, they were in when they composed o in the earlier epoch. Finally, o is destroyed, leaving o_R unscathed. Although all the facts in Γ obtain during this later epoch, [o exists] does not; hence although the existence of o was grounded in these facts about its parts, they do not necessitate o’s existence. (Skiles, 2015, p. 722)

Skiles’s case is a counterexample to grounding necessitarianism only if the latter is viewed as a local doctrine about a particular part of reality being grounded in another part of reality. His case doesn’t challenge global necessitarianism, however, which is all we need for our purposes. SV is a form of global supervenience. It says that any possible world that is a minimal n-duplicate of the actual world is a duplicate simpliciter of actual world. If successful, Skiles’s argument would show only that grounding does not entail certain local supervenience claims. The same is true of Skiles’s other counterexamples to grounding necessitarianism. Indeed, Skiles acknowledges the point, noting that, “grounding contingentism is…compatible with the global supervenience of every fact on the fundamental facts” (Skiles, 2015, p. 738).³⁷ We shouldn’t infer from the failure of local necessitation that global necessitation fails any more than we should infer from the fact that someone can stand without a foot on the ground that they can stand without any feet on the ground.³⁸

Let us turn to Leuenberger’s argument. His “main target” (Leuenberger, F, p. 155) is the following claim, where ‘Γ’ is the set of facts that grounds fact A, ‘<’ denotes the grounding relation, ‘□’ is a metaphysical necessity operator, ‘O(A)’ and ‘O(Γ)’ “express that A obtains and that all members of Γ obtain, respectively” (Leuenberger, 2014, p. 154):

Entailment Necessarily, if Γ < A then □(O(Γ) -> O(A)). (Leuenberger, 2014, p. 155).

Leuenberger presents two arguments against Entailment. We will focus on the one that is most relevant to present concerns.³⁹

That argument concerns physicalism, which, he notes, entails that all facts, including phenomenal facts, are grounded in actual physical facts. As an example of a phenomenal fact, he mentions ‘Red’: “the fact that I am having a red experience” (Leuenberger, 2014, p. 157). In his view, it is conceivable, and therefore possible, that all actual physical facts obtain but Red does not. And that, he claims, is compatible with the physicalist claim that Red is grounded in the actual physical facts.

Leuenberger’s argument can be formalized as follows:

• 1. Possibly, physicalism is true and Red obtains as a non-fundamental fact.

• 2.

  Necessarily, there are no physical facts Γ such that □(O(Γ)—> O(Red)).

• 3. Necessarily, if physicalism is true, then for every non-fundamental fact A there are physical facts Γ such that Γ < A.

From these premises, it follows (even in a very weak modal logic) that it is not necessary that for all Γ, if Γ < Red then □(O(Γ) —> O(Red)), and hence that Entailment has a false instance. (Leuenberger, 2014, p. 157)

Unlike Skiles’s argument, Leuenberger’s might, if convincing, threaten our contention that grounding of the sort to which monists are committed entails a supervenience claim such as SV (though as we will explain, this is not entirely clear). However, his argument is not convincing. Consider premise 1. That premise says (or immediately entails) that there is a possible world in which the only fundamental facts are physical and yet Red obtains. But the latter is precisely the sort of claim that dualists deny. In the context of the debate over what physicalism requires, such a claim cannot be asserted without independent support—support that should be convincing to a neutral party, that is, to someone who is neither committed to physicalism nor committed to non-physicalism. But Leuenberger provides no such independent support.

Leuenberger considers a variant of the foregoing objection to his premise 1. He labels that variant “the objection from dualism” and suggests that the objection is dialectically problematic. He does not make his basis for that suggestion entirely clear, but the gist of it seems to be that to resist his argument against Entailment, one would have to be “saddle[d]…with a commitment to the falsity of physicalism” (Leuenberger, 2014, p. 158). But that is not so. One need not assume that physicalism is false in order to object that premise 1 is dialectically inapt. That dialectical concern about premise 1 can be raised by someone who is neutral regarding physicalism’s truth or falsity.⁴⁰

A similar problem arises for premise 2. That premise asserts a claim that is hotly contested in the mind–body literature. It requires substantial independent support. Leueberger fails to satisfy that requirement. Instead, he merely asserts that it is conceivable for the physical facts to obtain while Red does not that this conceivability suggests the corresponding possibility, and that “we have no particular reason to think that the appearance of possibility is misleading in this case” (Leuenberger, 2014, p. 157). But as he concedes, “it is hard to substantiate these claims, and flesh out a modal epistemology to back up one’s modal claim” (Leuenberger, 2014, p. 158). Further, in the context of the debate over what physicalism requires, the plausibility of those claims—claims that physicalists reject—cannot be simply taken for granted.

Leuenberger considers an objection in the vicinity of that dialectical concern. But once again, he mischaracterizes it, labeling it “the objection from necessitarianism” and suggesting that it rests on a controversial “necessitarian” doctrine, on which “metaphysical possibility is just logical compatibility with the laws of nature” (Leuenberger, 2014, p. 158). But the dialectical concern rests on no such doctrine. Instead, the concern is that he bases premise 2 on claims that are, in the context of the mind–body debate, not merely contentious but centrally disputed—and that he does so without providing anything close to sufficient justification.

Leuenberger gives one further argument that is worth considering. He argues that physicalism is compatible with the possibility of zombies. He develops that argument in response to an objection to the compatibility of his premises 1 and 2, but it could as easily be seen as an independent argument against Entailment. The argument involves the following variant Kripke’s creation metaphor, which we discussed above, in Sect. 3:

In the actual world, God had put all the physical facts in place by the end of day seven. This was enough to make it the case that Red obtains. God henceforth left the world alone. In world w_b, God on day eight ensured that in the region occupied by my brain, a non-physical fundamental property, to be called ‘chromaplasm’, is instantiated. Chromaplasm makes visual phenomenology disappear. In w_b, I do not have a red experience, i.e. Red does not hold. (Leuenberger, 2014, p. 160)

As Leuenberger (2014, p. 160) notes, physicalism is not true of w_b “because of the presence of chromaplasm”. And yet, he claims, physicalism is true of the actual world, as he describes it.

Since in the actual world God only created physical facts and then retired, physicalism is true. All the actual fundamental facts are physical, after all, and that seems to be sufficient condition for the truth of physicalism. Hence Red is grounded by some class of physical facts. (Leuenberger, 2014, p. 161)

However, that argument faces at least two problems. First, it is dialectically problematic in the same way that his premises 1 and 2 are. In describing his variant of Kripke’s creation myth, he asserts that God’s creating the physical facts “was enough to make it the case that Red obtains”. But in the context of the mind–body debate, the claim that creating the physical facts suffices to create phenomenal facts such as Red cannot be simply asserted. Second, the supervenience claim to which physicalists are arguably committed includes a minimality condition: any world that is a minimal physical* duplicate of our world is a duplicate simpliciter of our world.⁴¹ Although w_b is a physical duplicate of the actual world, it is not a minimal physical duplicate, due to the presence of chromoplasm. This is important, because the minimality condition reflects an important feature of the grounding claim: the phenomenal fact Red is fully grounded in certain physical conditions and the fact that nothing else is added. So, the scenario Leuenberger describes is not one where the physicalist’s grounding claim is true while her supervenience claim fails.

Thus, neither Skiles's argument nor Leuenberger’s argument establish the compatibility of physicalist’s grounding claim with the denial of her supervenience claim.