Understanding Physicalism
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Understanding Physicalism

Gregor M. Hörzer

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eBook - ePub

Understanding Physicalism

Gregor M. Hörzer

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Publisher
De Gruyter
Year
2020
ISBN
9783110688467

1 Introduction

1.1 The general aim of this book

This book is in a certain respect different from many other philosophical works. In most cases, the aim of a philosophical project is to argue for, or sometimes against, a particular thesis. This is not what I aim for here, at least not with regard to the main thesis under consideration: physicalism. Rather than trying to argue that physicalism is true, or that physicalism is false, I take a step back and focus on the question of how to best understand the thesis. The thesis is easy to express very roughly. Physicalism is the claim that everything is physical, or maybe more accurately, that there is nothing over and above the physical. However, spelling out the thesis in a more exact and rigorous manner is more difficult than one might expect.
Among contemporary philosophers, physicalism is one of the most widely accepted views in the philosophy of mind and metaphysics. According to a recent survey of Bourget and Chalmers (2014), the majority of philosophers accept or at least lean towards the view.1 Some (Gillett and Loewer 2001: ix) even take physicalism to be the Weltanschauung of much of contemporary philosophy. Moreover, most scientists, while not in general acquainted with the vast amount of philosophical literature and debates concerning the topic, would likely agree to something like the core idea because it is closely intertwined with our scientific worldview.
Given the pervasiveness of physicalism, one might think that it is perfectly clear, at least within the philosophical community, what exactly the thesis of physicalism amounts to. After all, it seems reasonable to assume that we need to understand the thesis we are concerned with in order to argue for or against its truth. It is thus somewhat surprising to note the great number and diversity of characterizations of the thesis proposed by authors writing on the topic, provided they offer a characterization at all. The question of how to best formulate the thesis of physicalism is all but settled. In fact, given the wide variety of characterizations, it may even seem that there is no single thesis of physicalism at all. Still, it is at least plausible that there is something like a minimal set of characteristics that different physicalist views have in common and that make up the core of what we might call ‘minimal physicalism’. Different physicalist views add further commitments to this core thesis of minimal physicalism. As we will see, there are also some views that are not to be considered proper physicalist views by our contemporary standards even though they are traditionally so-called.
In this book, I focus on how we should interpret the thesis of minimal physicalism in a way that enables us to distinguish the view from its traditional rivals, respects the current state of the relevant debates, and takes into account the intellectual ancestry of contemporary physicalist views. These views have two main origins: the metaphysical views of early modern materialists like Thomas Hobbes, who opposed their dualist and idealist rivals like René Descartes and Bishop George Berkeley, on the one hand, and the views regarding the privileged status of physics in the hierarchical picture of the sciences in the works of positivist thinkers like Rudolf Carnap (1931; 1932) and Otto Neurath (1931), who first introduced the term ‘physicalism’ into the philosophical landscape, on the other hand. Interestingly, while physicalism, as understood today, is a metaphysical thesis, Carnap and Neurath had an outspoken anti-metaphysical stance, so the conception associated with the term ‘physicalism’ shifted during the 20th century. Nevertheless, there is still a component in the understanding of contemporary physicalism that pays tribute to its ancestry.
The term ‘physicalism’ is often more narrowly understood to express a thesis about the mental domain only. However, I focus on a characterization of physicalism as a general thesis, or physicalism simpliciter. Nevertheless, the mental domain plays a major role in the case of the more general thesis as well, because it is arguably the domain that leads to the most substantial troubles when arguing for the truth of the thesis. As already mentioned, there are two rough-and-ready formulations of physicalism that can serve as a starting point for further inquiry into the question of how to spell out the thesis more precisely. We can either say that (i) physicalism is the thesis that everything is physical, or that (ii) physicalism is the thesis that there is nothing over and above the physical. On the basis of these two formulations, I distinguish and address three questions that need to be answered in order to fully understand the thesis of physicalism. First, drawing on formulation (i), I focus on the question of what it means to say that everything is physical, or, what entities physicalism is concerned with. Do physicalists really want to claim that everything whatsoever is physical, or is the claim restricted to certain categories of entities? A closely related question is what categories we need to explicitly quantify over in formulating the thesis of physicalism. I evaluate and adapt various candidate phrasings in order to develop one I consider suitable to capture what physicalism intuitively is concerned with. Second, again drawing on formulation (i), I move on to clarify what it means that everything is physical. In other words, having settled on a conception of what categories the thesis quantifies over and which entities it attributes being physical to, I provide an account of what it means for entities from these categories to be physical entities. This question has only relatively recently begun to receive the attention it deserves. I discuss the options available in the literature, reject the whole range of standard views, and develop an alternative account. Third, drawing on formulation (ii), I clarify what it means for an entity to be nothing over and above some other entity. Formulation (i) might suggest that the relation in question is identity, but it is widely accepted that a relation weaker than identity suffices for physicalism to be true. What is needed is a relation of metaphysical dependence that can plausibly serve to capture nothing-over-and-above-ness in a way that enables us to draw the boundary between physicalism and its pluralist rivals.

1.2 The line of argument in broad brushstrokes

With regard to the question of which entities physicalism is concerned with, I argue in chapter two (“I want it all”) that in order for physicalism to be true, the entities that must be physical are particulars like objects, for which I also use the term ‘individuals’, and maybe also events and facts. There are however some particulars physicalism is arguably not concerned with – those that are neither contingent nor causal entities. This restriction makes physicalism compatible with certain realist views about numbers, which, even if non-physical, are not to be considered a challenge for physicalism (cf. Melnyk 2003). I distinguish between different ways in which we attribute being physical to particulars, and argue that the way such entities are required to be physical derives from the relation between the property types these entities instantiate and physical property types. A mere claim of identity or metaphysical dependence of token instances of properties on instances of physical properties, at least without further commitments, is arguably not sufficient to capture the views of contemporary physicalists. While such a view rules out substance dualism, property dualists can also adopt it.
Physicalism rather requires that every property type instantiated by an individual is either a physical property type or metaphysically depends on physical property types, unless it is a property type that is necessarily instantiated by any individual whatsoever. I add the latter constraint to ensure that properties like being self-identical or being such that 2+2=4 need not be physical properties or metaphysically depend on physical properties in order for physicalism to be true. I further address different notions of fundamentality and their viability as alternatives to the notion of metaphysical dependence for characterizing physicalism, as considered by Wilson (2018), and their connection to Schaffer’s (2003) view according to which we have no clear evidence that there is a fundamental level. Moreover, I consider whether physicalism is to be considered compatible with the instantiation of haecceitistic properties, i. e. properties the instantiation of which requires the existence of a specific particular. Some explicitly exclude such properties from their framework in the first place (e. g. Chalmers 1996: 367), others claim that physicalism is incompatible with them (e. g. Hofweber 2005). I side with Chalmers in these regards, and argue that we do not need to worry much about haecceitistic properties in a physicalist framework. Furthermore, I discuss a much neglected aspect of physicalist claims, which is usually either completely neglected or brushed aside in a footnote: the explicit treatment of relations among individuals as an element of the physicalist thesis. Finally, I relativize the physicalist thesis to worlds. After all, we do not always want to only evaluate whether physicalism is true of our world. A physicalist thesis that is relativized to possible worlds enables us to address whether physicalism would be true if certain things were different than they actually are.
In chapter three (“Physical”), I discuss the question of how to understand the notion of a physical property. The most common view is to claim that physical properties are just those properties that are picked out by predicates of physics. This understanding immediately gives rise to a dilemma, however, first considered by Hempel (1980). Which physics is the relevant one: current or future physics? If it is current physics, then physicalism is very likely false, because current physics is probably incomplete and additional properties are going to be needed in the dependence base that would not count as physical on such a view. Melnyk (1997; 2003) tries to blunt this horn of the dilemma and accepts that physicalism as he construes it is likely false, but his arguments are unconvincing. One important reason, among others, is that if physicalism were indeed quite obviously false due to the incompleteness of physics, it cannot be the thesis that is most frequently challenged by using complex conceivability arguments like the zombie argument (Chalmers 1996; 2010) and the knowledge argument (Jackson 1982). If the relevant physics is future (or final, ideal) physics, then the thesis of physicalism lacks content because we do not know what future physics will be concerned with. We should also avoid defining ‘future physics’ as “the fundamental theory of everything”. Tying physicalism to that notion of future physics would make physicalism a trivially true thesis. Moreover, some have considered a situation in which future physicists incorporate predicates like ‘… is an immaterial soul’ into their theories. It seems odd to think that physicalism in such a case would turn out to be compatible with the existence of immaterial souls after all (see Montero 1999: 192, who attributes the worry to Chomsky 1993; 1995). Poland (1994) and Dowell (2006b) bite the bullet, but their criteria for an acceptable incorporation of entities into physical theories are too weak. Furthermore, as long as we tie the notion of a physical property too tightly to any actual physical theory, we cannot account for the idea of alien physical properties, i. e. properties we would clearly count as physical if they were instantiated, but which are in fact never instantiated and thus not addressed by any actual world physics (Stoljar 2010: ch. 4). Thus, notions of the physical tied to some particular actual world physics would at most allow us to characterize physicalism for the actual world, rather than for arbitrary possible worlds.
An alternative account of the physical that has gained some popularity in recent years because it completely avoids Hempel’s dilemma is a view sometimes called the ‘via negativa’ (e. g. Montero 1999; Spurrett and Papineau 1999; Crook and Gillett 2001; Montero and Papineau 2005). The basic idea is to provide a negative characterization of the physical as the non-mental. However, defenders of such a view must be careful to avoid understanding the term ‘non-mental’ in a way that trivially rules out views that take mental properties to be identical to physical properties. Even if this concern can be accounted for, however, such an account makes it difficult to distinguish between a domain-specific physicalism about the mental and a general, non-domain-specific physicalism, because it is overly inclusive with regard to what counts as physical.
There are also some accounts which mix aspects of the different views discussed so far, conjoining a clause that ties the notion of the physical to one or another physical theory with a clause that rules out as physical certain entities, especially mental ones, on a priori grounds (e. g. Wilson 2006). In turn, such a view renders certain live panpsychist accounts conceptually incoherent, which is unacceptable. In fact, we should not rule out the identity of mental and physical entities at all, the only thing we should make sure is that we do not trivially include them by including mental predicates into our physical theories. Following Lewis (1983: 362 – 363), I even consider some versions of panpsychism (e. g. those that are a version of the identity theory) to be compatible with physicalism, so we need to be careful not to rule out too much. Furthermore, I discuss Howell’s (2013) neo-Cartesian account and Jackson’s (1998) account that tries to fix the reference by pointing at paradigmatic physical objects. However, I find both accounts wanting, because they also rule out certain views as false or even incoherent that cannot be so easily dismissed.
Instead, I argue for an often-overlooked account that draws to some extent on Jackson’s account, but does not run into the same problems. According to this view, physical properties are those which, broadly speaking, resemble paradigmatic properties of current physics in a certain respect, where the resemblance relation in question is a sameness-in-kind relation (for related views, see Nimtz and Schütte 2003: 419; Díaz-León 2008: 99). The underlying idea is closely connected to Strawson’s claim that “‘[p]hysical’ is a natural-kind term – it is the ultimate natural-kind term” (2008 [2003]: 20). This view of the physical is not susceptible to the first horn of Hempel’s dilemma because the ties to current physics are weak enough to be able to account for some as-of-yet unknown properties of future physics as well as physical properties alien to our world. Moreover, it is not susceptible to the second horn of Hempel’s dilemma either, because the connection to paradigmatic properties from current physics gives the theory the required content, and the account does not allow for dualism to sneak in through the back door. Finally, the view accounts for the intuition that physics is concerned with the entities it is concerned with because they are physical rather than that those entities are physical because physics is concerned with them.
In chapters four (“The bare necessities”) and five (“Higher Ground”), I address the last of the three questions, namely how to appropriately spell out nothing-over-and-above-ness or metaphysical dependence in the characterization of physicalism. In accordance with a view of metaphysics that focuses on questions regarding structure instead of merely on questions regarding existence (e. g. Schaffer 2009; Sider 2011), we need to address how everything else is linked to the physical in order to understand the thesis of physicalism. In chapter four, I focus on attempts to spell out metaphysical dependence in purely modal terms, and discuss the modal commitments physicalism comes along with. After the (at least partial) demise of traditional type identity theory (Place 1956; Smart 1959) due to arguments from multiple realizability (Putnam 1975b [1967]) as well as due to modal considerations (Kripke 1980: 148 – 155), the candidate relation that has dominated the literature for almost the last half century is the relation of supervenience (e. g. Kim 1993d [1984]; 1993e [1987]; McLaughlin 1995) and the related necessitation relation. Supervenience relations feature prominently in many attempts to formulate physicalism, either explicitly or implicitly (e. g. Lewis 1983; Chalmers 1996; Jackson 1998). However, in order to preserve the contingency of physicalism, the ties between metaphysical dependence and supervenience have to be weaker than one might initially expect. Nevertheless, physicalism clearly entails some supervenience claim. After all, the central arguments against the view are all based on the idea that such an entailment holds, and thinking otherwise does not properly respect one of the basic presumptions that virtually all advocates and adversaries of the thesis agree upon.
Over the years, philosophers have started to realize that supervenience and necessitation, being purely modal notions, fail to account for the idea that metaphysical dependence is more than mere necessary co-variation of property instantiation. Rather, it requires that the dependent properties are instantiated because the properties they depend upon are instantiated. In order to account for this difference between physicalism and its pluralist rivals, some have considered adding an explanatory component to the notion of supervenience, resulting in what Horgan (1993) calls ‘superdupervenience’. However, depending on how we understand the notion of being explanatory, this may bring in an unwanted epistemic component into a so far purely metaphysical thesis. I discuss a variety of different lines of argument for the claim that purely supervenience-based notions of are too coarse-grained, and are thus unable to distinguish between cases of dependence and cases of mere modal co-variation. Relatedly, purely modal accounts fail to distinguish physicalism from some nonstandard versions of dualism, including certain versions of emergentism. I elaborate on the question whether such views are coherent. These considerations are closely tied to a metaphysical principle called ‘Hume’s dictum’: the claim that there are no necessary connections between distinct entities. The coherency of the views in question depends on what notion of distinctness is expressed. I draw on the discussion of notions of distinctness by Stoljar (2007; 2010) and Wilson (2010), and argue that the notion of distinctness involved is best understood as a notion of metaphysical independence or failure of metaphysical dependence. So understood, the views in question are most likely coherent, and a purely modal account of physicalism fails, as already indicated by a number of independent considerations.
In chapter five, I focus on more fine-grained accounts of metaphysical dependence that go beyond the purely modal realm. Recently, metaphysicians have begun to focus on the relation of Grounding to account for metaphysical dependence (Fine 2001; 2012; Correia 2005; Schaffer 2009), and a number of authors (e. g. Schaffer 2009; Dasgupta 2014) have proposed that it is the relation of dependence required for physicalism, while others remain skeptical (Melnyk 2016; Wilson 2018). Grounding is supposed to be a generic relation of metaphysical dependence that accounts for metaphysical structure and priority in a wide variety of different cases. Facts are usually taken to be the proper relata of the Grounding relation, although other sorts of entities have been considered as well (e. g. Schaffer 2009). Moreover, advocates of Grounding typically consider it to be an ‘explanatory’ relation (Fine 2001: 15), but the kind of explanation these authors seem to have in mind has little to do with how we usually understand the term. Finally, the notion of Grounding is often claimed to be primitive, which means that it cannot be analyzed in other terms (Fine 2001; 2012; Schaffer 2009), although some have considered doing so (Correia 2013).
I discuss the relation of Grounding, or at least a close cousin that relates properties, and investigate how Grounding is linked to other even more fine-grained relations that have been proposed as alternatives to supervenience in the literature. In particular, some have suggested that the relation of metaphysical dependence most well-suited to the task of formulating the thesis of physicalism is the realization relation. Melnyk (2003) has proposed a detailed account of physicalism employing a version of the realization relation based on the notion of a higher-order property. Wilson (1999; 2011) and Shoemaker (2007) have provided an alternative account of physical realization that is based on a s...

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