Physicalism

First published Tue Feb 13, 2001; substantive revision Tue May 25, 2021

Physicalism is, in slogan form, the thesis that everything is physical.The thesis is usually intended as a metaphysical thesis, parallel tothe thesis attributed to the ancient Greek philosopher Thales, thateverything is water, or the idealism of the 18th Century philosopherBerkeley, that everything is mental. The general idea is that thenature of the actual world (i.e. the universe and everything in it)conforms to a certain condition, the condition of being physical. Ofcourse, physicalists don’t deny that the world might containmany items that at first glance don’t seem physical —items of a biological, or psychological, or moral, or social, ormathematical nature. But they insist nevertheless that at the end ofthe day such items are physical, or at least bear an importantrelation to the physical.

1. Preliminaries

1.1 Terminology

Physicalism is sometimes known as ‘materialism’. Indeed,on one strand to contemporary usage, the terms‘physicalism’ and ‘materialism’ areinterchangeable. But the two terms have very different histories. Theword ‘materialism’ appears in English towards the end ofthe 17th century, but the word ‘physicalism’ wasintroduced into philosophy only in the 1930s byOtto Neurath (1931) andRudolf Carnap (1959/1932), both of whom were key members of the Vienna Circle, agroup of philosophers, scientists and mathematicians active in Viennaprior to World War II. While it is not clear that Neurath and Carnapunderstood physicalism in the same way, one thesis often attributed tothem (e.g. in Hempel 1949) is the linguistic thesis that everystatement is synonymous with (i.e. is equivalent in meaning with) somephysical statement. But materialism as traditionally construed is nota linguistic thesis at all; rather it is a metaphysical thesis in thesense that it tells us about the nature of the world. At least for thepositivists, therefore, there was a clear reason for distinguishingphysicalism (a linguistic thesis) from materialism (a metaphysicalthesis). Moreover, this reason was compounded by the fact that,according to official positivist doctrine, metaphysics is nonsense.Since the 1930s, however, the positivist philosophy that under-girdedthis distinction has for the most part been rejected—forexample, physicalism is not a linguistic thesis for contemporaryphilosophers—and this is one reason why the words‘materialism’ and ‘physicalism’ are now ofteninterpreted as interchangeable.

Some philosophers suggest that ‘physicalism’ is distinctfrom ‘materialism’ for a reason quite unrelated to the oneemphasized by Neurath and Carnap. As the name suggests, materialistshistorically held that everything was matter — where matter wasconceived as “an inert, senseless substance, in which extension,figure, and motion do actually subsist” (Berkeley, Principles ofHuman Knowledge, par. 9). But physics itself has shown that noteverything is matter in this sense; for example, forces such asgravity are physical but it is not clear that they are material in thetraditional sense (Lange 1865, Dijksterhuis 1961, Yolton 1983). So itis tempting to use ‘physicalism’ to distance oneself fromwhat seems a historically important but no longer scientificallyrelevant thesis of materialism, and related to this, to emphasize aconnection to physics and the physical sciences. However, whilephysicalism is certainly unusual among metaphysical doctrines in beingassociated with a commitment both to the sciences and to a particularbranch of science, namely physics, it is not clear that this is a goodreason for calling it ‘physicalism’ rather than‘materialism.’ For one thing, many contemporaryphysicalists do in fact use the word ‘materialism’ todescribe their doctrine (e.g. Smart 1963). Moreover, while‘physicalism’ is no doubt related to ‘physics’it is also related to ‘physical object’ and this in turnis very closely connected with ‘material object’, and viathat, with ‘matter.’

In this entry, I will adopt the policy of using both termsinterchangeably, though I will typically refer to the thesis we willdiscuss as ‘physicalism’. It is important to note, though,that physicalism (aka materialism) is often associated with a numberof further doctrines distinct from the one we will focus on; for adiscussion of some of these, see the supplement on:

Physicalism and Associated Doctrines

1.2 Historical Issues

Setting aside what it is properly called, the thesis of physicalism isoften described as an extremely old, even ancient, thesis. The firstsentence ofFriedrich Lange’sThe History of Materialism, which was the standard work on thesubject in the 19th century is: “Materialism is as old as philosophy,but not older” (1925, 3). What Lange has in mind is the pre-SocraticphilosopherDemocritus, who is usually thought of defending a kind of physicalism ormaterialism when he said or allegedly said, “all is atoms and thevoid.” This view casts a long shadow over subsequent formulations ofphysicalism. A position like that of Democritus was revived in theearly modern period just prior to Newton, by philosophers andscientists such asHobbes orGassendi. In the eighteenth century, French philosophers likeD’Holbach and La Mettrie thought of themselves as materialists (and would benow classified as physicalists) somewhat in the same way since theyheld that each human being is a complicated sort of machine. In thenineteenth century, whileKarl Marx’s ‘dialectical materialism’ is something different from themetaphysical thesis we will focus on, he nevertheless developed hissocial philosophy against the background of what we would callphysicalism; in fact, Marx’s doctoral dissertation was a comparison ofDemocritus andEpicurus. And in the twentieth century, analytic philosophers such as Smart and Lewis self-consciously defended their views in a way that acknowledges, as Lewis put it, “our intellectual ancestors” (1994, 293).

However, while there is certainly something in common here, theunderlying historical issues are extremely complicated, since theyinvolve subtle questions of scientific and philosophical change. Wewon’t discuss them in detail in this entry. It is worth emphasis,though, that we should be careful in lumping different people indifferent epochs together. The precise views they held are oftendifferent from one another. As we noted above, and as Lange himselfemphasises, Newton did not think that, even in the physical world, allis atoms and the void, since for him there are also forces such asgravity. It follows that any post-Newtonian philosophers who think ofthemselves as physicalists must have a different thesis in mind fromDemocritus.

1.3 A Framework for Discussion

In approaching the topic of physicalism, one may distinguish what Iwill callthe interpretation question fromthe truthquestion. The interpretation question asks:

What does itmean to say that everything isphysical?

The truth question asks:

Is ittrue to say that everything is physical?

There is obviously a sense in which the second question presupposes ananswer to the first — you need to know what a statement meansbefore you can ask whether it’s true — and so we willbegin with the interpretation question.

The interpretation question itself divides into two sub-questions,which I will callthe condition question andthecompleteness question. The condition question asks:

What does it mean to for something to bephysical?

The condition question holds fixed the issue of what it means foreverything to satisfy some condition, or to bear a relation tosomething that satisfies that condition, and asks insteadwhatis the condition,being physical, thateverything satisfies or bears a relation to. Notice that a parallelquestion could be asked of Thales: what is the condition,beingwater, that according to Thales, everything satisfies?

The completeness question asks:

What relation or relations must obtain betweeneverythingand the physical if physicalism is to be true?

In other words, the completeness question holds fixed the issue ofwhat it means for something to be physical, and asks instead whatrelation or relations obtain between everything and the physical ifphysicalism is true; in what sense, in other words, is physicalism acomplete thesis, a thesis that applies to everythingwhatsoever. Notice again that a parallel question could be asked ofThales: assuming we know what condition you have to satisfy to bewater, what does it mean to say that everything satisfies thatcondition?

Once again there is a sense in which the second question herepresupposes an answer to the first — you need to know what it isfor something to be physical in order to assess different proposalsabout the relation everything bears to the physical. Nevertheless, itis easier from a presentational point of view to discuss thecompleteness question first, leaving our answer to the conditionquestion for the moment impressionistic, and that will be ourprocedure.

2. The Completeness Question

How should we approach the completeness question? In the history ofattempts to answer this question, people have tended to adopt one oftwo strategies. One appeals to (what philosophers call)modalnotions, where a modal notion here means a notion connected topossibility and necessity, to what might or must be the case. Anotherappeals tonon-modal notions, that is, notions distinct fromideas about possibility and necessity. There is a wide variety of suchnotions, though perhaps the most obvious one isidentity inthe logical sense, according to which if x is identical to y, thenevery property of x is a property of y. This notion has consequencesfor possibility and necessity, but it is not itself modal. Othernon-modal notions includerealization, orgrounding,which we will consider below.

In practice, most formulations of physicalism includebothmodal and non-modal elements at some level. Proponents of modalformulations often end up appealing to something non-modal in thecourse of elaborating and defending their view. Non-modal versions areusually interpreted so that they have the same modal consequences asmodal versions. Nevertheless, the issue of whether to answer thecompleteness question by appealing to modal or non-modal ideas hasproved as controversial as any in the literature on what physicalismis (for overviews, see Rabin 2020, Elpidorou 2018a, Tiehen 2018). Inwhat follows, we will first look at an influential modal answer to thecompleteness question, which appeals tosupervenience, andthen turn to several non-modal alternatives.

2.1 Supervenience and Necessity Physicalism

The idea of supervenience has its origins in meta-ethics but wasimported into philosophy of mind mainly by Davidson 1970; for asurvey, seesupervenience. For our purposes, the general idea might be introduced via an exampledue to David Lewis of a dot-matrix picture:

A dot-matrix picture has global properties — it is symmetrical,it is cluttered, and whatnot — and yet all there is to thepicture is dots and non-dots at each point of the matrix. The globalproperties are nothing but patterns in the dots. They supervene: notwo pictures could differ in their global properties withoutdiffering, somewhere, in whether there is or there isn’t a dot(1986, p. 14).

This gives us one way to think about the basic idea of physicalism.The basic idea is that the physical features of the world are like thedots in the picture, and the psychological or biological or socialfeatures of the world are like the global properties of the picture.Just as the global features of the picture supervene on the dots, sotoo everything supervenes on the physical, if physicalism is true.

It is desirable to have a more explicit statement of physicalism, andhere too Lewis’s example gives us direction. He says that, inthe case of the picture, supervenience means that “no twopictures can be identical in the arrangement of dots but different intheir global properties”. Similarly, one might say that, in thecase of physicalism, no two possible worlds can be identical in theirphysical properties but differ, somewhere, in their mental, social orbiological properties. To weaken this slightly, we might say that ifphysicalism is the case atour world – that is, is true ofour universe and everything in it – then noother world canbe physically identical to our world without being identical to it inall respects. This suggests the following general account of whatphysicalism is (in the following formulation and in subsequent ones,we use “iff” to abbreviate “if and onlyif”):

(1): Physicalism is true at a possible worldw iff any worldwhich is a physical duplicate ofw is a duplicate ofwsimpliciter.

If physicalism is construed along the lines suggested in (1), we havean answer to the completeness question. The completeness questionasks: what relation does everything bear to the physical ifphysicalism is true? According to (1), the answer is that everythingmust supervene on the physical; or, to put it more technically, thereis no possible world which is identical to our world in every physicalrespect but which is not identical to it in a biological or social orpsychological respect. It will be useful to have a name forphysicalism so defined, so let us call itsuperveniencephysicalism.

Supervenience offers one modal formulation of physicalism, but it isworth taking note of a second modal formulation too. Suppose we saythat a propertyG is necessitated by a propertyFjust in case, in all possible worlds, if something isF thenit isG; in this sense, for example, being red necessitatesbeing colored, and being square necessitates having some extension inspace. This suggests a formulation of physicalism along the followinglines:

(2): Physicalism is true at a possible worldw iff everyproperty instantiated atw is necessitated by a physicalproperty.

What is the relation between physicalism so defined, which we mightcallnecessity physicalism, andsuperveniencephysicalism? At least if necessitation is understood as a sort ofentailment, then these are not equivalent; for discussion of thispoint, seesupervenience. However, (1) and (2) are clearly similar, in particular they aremodal formulations of physicalism. In what follows we will concentrateon supervenience physicalism, but what we will say will apply also tonecessity physicalism.

Supervenience physicalism was for many years the dominant version ofphysicalism; perhaps because of this, many different problems havebeen raised for it; some of these problems are discussed in thesupplement on:

Supervenience Physicalism: Further Issues

But the most influential objection to supervenience physicalism (andto modal formulations generally) is what might be calledthesufficiency problem. This alleges that, while (1) articulates anecessary condition for physicalism it does not provide a sufficientcondition. The underlying rationale is that, intuitively one thing cansupervene on another and yet be of a completely different nature. Touse Fine’s famous (1994) example, consider the difference betweenSocrates and his singleton set, the set that contains only Socrates asa member. The facts about the set supervene on the facts aboutSocrates; any world that is like ours in respect of the existence ofSocrates is like ours in respect of the existence of his singletonset. And yet the set is quite different from Socrates. This in turnraises the possibility that something might be of a completelydifferent nature from the physical and nevertheless supervene onit.

One may bring out this objection further by considering positions inphilosophy which entail supervenience and yet deny physicalism. A goodexample isnecessitation dualism, which is an approach thatweaves together elements of both physicalism and its traditionalrival, dualism. On the one hand, the necessitation dualist wants tosay that mental facts and physical facts are metaphysicallydistinct—just as a standard dualist does. On the other hand, thenecessitation dualist wants to agree with the physicalist that mentalfacts are necessitated by, and supervene on, the physical facts. Ifthis sort of position is coherent, (1) does not articulate asufficient condition for physicalism. For if necessitation dualism istrue, any physical duplicate of the actual world is a duplicatesimpliciter. And yet, if dualism of any sort is true,including necessitation dualism, physicalism is false.

How to respond to the sufficiency problem? Some respond by denying thecoherence of the position that causes the problem. Necessitationdualism as we have just described it violates (what is known as)Hume’s dictum that there are no necessary connections betweendistinct existences. According to necessitation dualism, mental andphysical properties are metaphysically distinct, and yet arenecessarily connected. However, Hume’s dictum is itself a matterof controversy (see Jackson 1993, Stalnaker 1996, Stoljar 2010, andWilson 2005, 2010). Another approach appeals to a priori physicalismwhich will examine below (see Jackson 2006). But by far the mostcommon response has been to concede that the sufficiency problem showsthat supervenience formulation of physicalism is too weak (e.g. Kim1998), and to look for an alternative.

2.2 Identity Physicalism

Suppose then that (1) provides a necessary condition for physicalismbut not a sufficient condition; how might we strengthen it to make itmore plausible? The most obvious thing to do is to appeal to identity.Indeed, in the history of attempts to answer the completenessquestion, the appeal to identity predates the appeal to supervenience.Nevertheless, this version of physicalism— identityphysicalism as we may call it—runs into seriousproblems.

2.2.1. Token Physicalism

In fact there are two different versions of identity physicalism,type physicalism andtoken physicalism. Tokenphysicalism is the view that every particular thing in the world is aphysical particular. So the token physicalist says that physicalismshould be formulated in the following way:

(3): Physicalism is true at a possible worldw iff for everyparticular (object, event or process)x that exists atw, there is some physical particulary such thatx =y

But (3) offers neither necessary nor sufficient conditions forphysicalism. To see that it is not sufficient, consider the variety ofdualism usually calledproperty dualism. Property dualismsays that (a) every particular is a physical particular but (b) someparticulars (e.g. human beings) have psychological properties whollydistinct from any physical properties. The contrast here is withsubstance dualism. The substance dualist agrees with theproperty dualist that some particulars have psychological propertieswholly distinct from any physical properties, but they will add thatsuch particulars are themselves non-physical.

Token physicalism – physicalism according to (3) – is certainlyinconsistent with substance dualism. Substance dualism entails thatsome particulars are non-physical, token physicalism denies it. Buttoken physicalism is compatible with property dualism; indeed propertydualism entails that token physicalism is true. On the other hand,property dualism is usually understood as being inconsistent withphysicalism in any form. Hence token physicalism is not sufficient forphysicalism.

The problem that property dualism presents for token physicalism isnoteworthy in several respects. For one thing, it is similar to theproblem necessitarian dualism presents for supervenience physicalism,though necessitarian dualism can itself be developed either as a sortof property dualism or as a sort of substance dualism. For anotherthing, it brings out the important role properties rather thanparticulars play in the contemporary discussion of physicalism. If oneignores properties, the dispute between physicalism and dualism mayeasily be understood as the dispute between token physicalism andsubstance dualism; but once properties are factored in, things lookvery different.

Not only does (3) not provide a sufficient condition for physicalism,it does not provide a necessary condition either. Consider a social orlegal object such as the United States Court of Appeals for theSeventh Circuit. According to (3), if physicalism is true, there mustbe some physical object or particular for the court to be identicalwith. But intuitively, there is no such physical object. Nevertheless,physicalism might still be true. If so, token physicalism is notnecessary for physicalism. (Notice here that there is no parallelproblem for supervenience physicalism. It entails that the facts aboutcourt supervene on physical facts but not that there is any physicalobject that the court is identical with. For the classic presentationof this point, see Haugeland 1983).

2.2.2. TypePhysicalism

Turning now to type physicalism, this holds that every property (or atleast every property instantiated in the actual world) is identicalwith some physical property. So the type physicalist supposes thatphysicalism should be formulated in the following way:

(4): Physicalism is true at a possible worldw iff everyproperty instantiated atw is identical to a physicalproperty.

Unlike both token physicalism and supervenience physicalism, typephysicalismis sufficient for physicalism: if every propertyinstantiated in the actual world is identical with some physicalproperty, then dualism will be false in any of the versions we haveconsidered

However, while (4) provides a sufficient condition for physicalism, itdoes not provide a necessary condition. Consider again the UnitedStates Court of Appeals for the Seventh Circuit. If type physicalismis true, then every property that the court has (for example, having alegal power over lower courts) must be identical with some physicalproperty. But on the face of it, that is unlikely. Nevertheless,physicalism might still be true. If so, type physicalism is notnecessary for physicalism. (Notice again that there is no parallelproblem for supervenience physicalism. It entails that the propertyhaving a legal power over lower courts supervenes on physicalproperties, not that it is identical with a physical property.)

Another way to bring out the sense in which type physicalism is toostrong for physicalism is to focus on the possibility ofmultiplerealizability, as philosophers call it. This is roughly the ideathat physically very different creatures can nevertheless sharepsychological properties; seemultiple realizability. A major benefit of supervenience physicalism is that, as usuallyunderstood, it is consistent with this possibility. But typephysicalism is often thought of as not consistent with it, at least ifwe focus on instantiated psychological properties. If so, typephysicalism may be false while supervenience physicalism may betrue.

We have been assuming that supervenience physicalism is distinct fromtype physicalism. But it is worth noting that, there are ways tounderstand supervenience according to which this difference is lessobvious. The reason for this has to do with questions concerning thelogical (or Boolean) closure of the set of physical properties —ifP,Q andR are physical properties,which of the various logical permutations ofP,QandR are likewise physical properties? On some assumptionsconcerning closure and supervenience, supervenience physicalism(construed as a necessary truth) entails type physicalism; on otherassumptions, it doesn’t. But the problem is that the assumptionsthemselves are difficult to interpret and evaluate, and so the issueremains a difficult one. It is not necessary for our purposes tosettle the question concerning closure here. (For further discussionof these issues see Kim 1993, Bacon 1990, Van Cleve 1990, Stalnaker1996.)

2.3 Realization Physicalism

Our discussion of the completeness question has so far yieldednegative results: supervenience physicalism is too weak, typephysicalism is too strong, and token physicalism is both too weak andtoo strong. What seems to be required is an approach that, like themodal formulations we started with, entails the supervenience ofeverything on the physical, but unlike them avoids the sufficiencyproblem. One prominent idea along these lines appeals to a relationbetween properties distinct from both identity and supervenience,usually calledrealization. As in the case of identityphysicalism, there are two different versions ofrealizationphysicalism as we may call it; we will consider them in turn.

2.3.1 Second-order Physicalism

The first realization definition has been explored and defended inmost detail by Andrew Melnyk (see Melnyk 2003 and the referencestherein). For Melnyk, a propertyF realizes a propertyG if and only if (a)G is identical to asecond-order property, the property of having some property that has acertain causal or theoretical role; and (b)F is the propertythat plays the causal or theoretical role in question. We may callthis notion ‘second-order realization’ to distinguish itfrom a different notion of realization to be considered in a moment.This suggests:

(5): Physicalism is true at a possible worldw iff everyproperty instantiated atw is either a physical property oris second-order realized in a physical property.

Suppose we call physicalism so definedsecond-order realizationphysicalism orsecond-order physicalism for short; whatis the relation between it and supervenience physicalism?Supervenience physicalism does not entail second-order physicalismsince the fact that a propertyF supervenes on a propertyG does not entail thatF is a second-order property.

Does second-order physicalism entail supervenience physicalism? Theusual assumption is that it does, but, as Melnyk himself notes at onepoint (2003, p. 23), there is an issue here having to do with thedefinition of a second-order property, the property of having someproperty that has a certain causal or theoretical role. What are theproperties involved in spelling out these causal or theoretical roles?If physicalism is true at all, it must be true of these properties asmuch as any other properties. But then by second-order physicalism,these properties themselves will be either physical or realized byphysical properties. If the first option is taken, the second-orderphysicalist will stand revealed as holding a version of identityphysicalism (one level up, as it were), and thus will face themultiple realization objection. If the second option is taken, thesecond-order physicalist looks committed to an infinite regress, sincenow we have further properties realized by physical properties and,correlatively, further causal or theoretical roles. To avoid theregress, the second-order physicalist might say that these propertiessupervene on or are identical to physical properties. But now it hardto see the difference between the realization physicalist and theseother doctrines. (For some further discussion of this issue, seeElpidorou 2018a.)

2.3.2 Subset Physicalism

The second realization definition of physicalism has been developed byWilson 1999, 2011 and Shoemaker 2007. On this view, a propertyF realizes a propertyG if and only if (a)G has some set of causal powers or featuresS; (b)F has some set of causal powers or featuresS*; and(c)S is a subset ofS*. (We may call this notion‘subset realization’ to distinguish it from the differentnotion of realization just considered.) This suggests:

(6): Physicalism is true at a possible worldw iff everyproperty instantiated atw is either a physical property oris subset realized in a physical property.

Suppose we call physicalism so definedsubset realizationphysicalism orsubset physicalism for short; what isthe relation between it and supervenience physicalism? Superveniencephysicalism does not entail subset physicalism since the fact that apropertyG supervenes on a propertyF does notentail anything about their causal powers. For example, if causationis a macro-phenomenon as some philosophers have held it to be, it maybe thatF has no causal powers at all, whileG does.

Does subset realization physicalism entail supervenience physicalism?Well, there is a problem here too having to do with (what is sometimescalled) acausal theory of properties, that is, a theoryaccording to which the causal powers or features that a propertybestows on the things that have it are exhaustive of the nature ofthat property. Suppose that a causal theory is false. Then, inprinciple, one property might subset realize another and yet be quitedifferent from it in nature. And this in turn suggests that subsetphysicalism does not by itself entail supervenience physicalism. Ofcourse, one might respond by asserting that the causal theory is true.But to do that is controversial; indeed, even those philosophers whohold both a subset modeland a causal theory want toseparate out these two commitments (e.g. Shoemaker 2007; see alsoWilson 2011). Alternatively, one might respond by denying thatphysicalism entails supervenience in the first place, by saying that“lack of … supervenience is compatible with physicalism”(Wilson 2014, 255, see also Wilson 2011). But this too iscontroversial; as we saw above, most philosophers assume thatsupervenience is necessary for physicalism. Hence the status of thesubset approach remains controversial.

2.4 Grounding Physicalism

An influential recent approach to the completeness question that isdifferent from any we have considered so far focuses on the idea ofgrounding, something that has been extensively discussed recently inthe metaphysics literature (see, e.g., Fine 2001, Schaffer 2009, Rosen2010, Wilson 2014, Bennett 2017 and the essays in Correia andSchneider 2012). Intuitively, a propertyF is grounded in apropertyG just in caseF holds in virtue ofG, or the instantiation ofG explains theinstantiation ofF. This suggests:

(7): Physicalism is true at a possible worldw iff everyproperty instantiated atw is either a physical property oris grounded in a physical property.

Suppose we call physicalism so definedgrounding physicalism;what is the relation between it and supervenience physicalism?Supervenience physicalism does not entail grounding physicalism, sincethe fact that a propertyF supervenes on a propertyG does not entail thatF is grounded byG.

Does grounding physicalism entail supervenience physicalism? Somephilosophers suppose it does (e.g. Rosen 2010) and so for themgrounding physicalism would entail supervenience physicalism. Butothers suppose it does not (e.g. Schaffer 2009) which raises thequestion of whether a thesis such as (7) by itself provides an accountof physicalism, or whether some compromise between it and (1) wouldhave to be reached.

Even if grounding physicalism entails supervenience physicalism, thereare further issues about it that have been raised. One problemconcerns abstract objects, i.e., entities apparently not located inspace and time, such as numbers, properties and relations, orpropositions. However, since this problem seems a general problem forall kinds of physicalism, we will discuss it below.

A second problem for grounding physicalism is that the notion ofgrounding is itself controversial in some quarters. Wilson (2014), forexample, points out that grounding per se is similar to superveniencein that it leaves open many of the questions philosophers of mind areinterested in, viz., whether the mental exists, whether it is reducedto the physical, and whether it is causally efficacious. She concludesthat grounding “cannot do the work” that its proponentswant it to do (2014, 542). One might respond that this depends on whatwork grounding physicalism is supposed to do; indeed, it may be afeature rather than a bug that grounding leaves these things open. Butwhatever is the truth about this, there is no doubt that the precisecontours of the grounding relation are yet to be made out. Hence, theproper assessment of grounding physicalism is at this point a bitunclear (for some further discussion, see, e.g., Berker 2018 andSchaffer 2016).

2.5 Fundamentality Physicalism

The final answer to the completeness question we will consider focuseson the idea of a fundamental property, which is a notion discussedextensively in David Lewis’s metaphysics, and the literaturethat follows on from it. On Lewis’s view, a fundamental orperfectly natural property is a special kind of property, one that is,as he says, “not at all disjunctive, or determinable, ornegative. They render their instances perfectly similar in somerespect. They are intrinsic; and all other intrinsic propertiessupervene on them” (2009, 204). This suggests the followingformulation of physicalism:

(8): Physicalism is true at a possible worldw iff everyfundamental property instantiated atw is a physicalproperty.

Suppose we call physicalism so definedfundamentalityphysicalism; what is the relation between it and superveniencephysicalism? Supervenience physicalism does not entail fundamentalityphysicalism, since the fact that a propertyF supervenes on apropertyG does not entail that either property isfundamental. Nevertheless, it is reasonable to think thatfundamentality physicalism entails supervenience physicalism,especially in the light of Lewis’s comment about superveniencejust quoted.

How plausible is (8) as an account of physicalism? One objectionconcerns the notion of a fundamental property quite generally. For atleast some philosophers, Lewis’s ideas about fundamentality are, as hehimself puts it, a throwback to medieval metaphysics (Lewis 1983).Another objection is that physicalism on this view seems empiricallyspeculative, since it seems to entail that there is a fundamentallevel in the world; if so, definitions in terms of grounding may dobetter (Schaffer 2003). Whatever is the truth about these objections,it is an interesting historical fact that Lewis defines physicalismtwice-over. He defines it as supervenience physicalism (as we sawabove) and also as fundamentality physicalism. There is no suggestionin his work that these are in any sense in tension (for furtherdiscussion, see Stoljar 2015). This underscores the point madeearlier, namely, that in practice all versions of physicalism, andhence any answer to the completeness question, will include modal andnon-modal elements.

3. Varieties of Physicalism

We have been considering various answers to the completeness question,namely, what it means to say that everything is physical. At thispoint, it is worth considering two issues associated with completenessthat have not so far been brought to the surface, and which suggestdifferent varieties of physicalism. The first is whether physicalisminvolves a kind of reductionism; the second is whether physicalisminvolves what philosophers call a priori entailment or deducibility.

3.1 Reductive and Non-reductive Physicalism

The main problem in assessing whether a physicalist must be areductionist is that there are various non-equivalent versions ofreductionism.

One idea is tied to the notion of conceptual or reductive analysis.When philosophers attempt to provide an analysis of some concept ornotion, they often try to provide a reductive analysis of the notionin question, i.e. to analyze it in other terms. Applied to thephilosophy of mind, this notion might be thought of entailing the ideathat every mental concept or predicate is analyzed in terms of aphysical concept or predicate. A formulation of this idea is (9):

(9): Reductionism is true iff for each mental predicateF,there is a physical predicateG such that a sentence of theform ‘x isF iffx isG’ is analytically true.

While one occasionally finds in the literature the suggestion thatphysicalists are committed to (9) in fact, no physicalist since beforeSmart (1959) has (unqualifiedly) held anything like it. Adapting Ryle(1949), Smart supposed that in addition to physical expressions thereis a class of expressions which are topic-neutral, i.e. expressionswhich were neither mental nor physical but when conjoined with anytheory would greatly increase the expressive power of the theory.Smart suggested that one might analyze mental expressions intopic-neutral (but not physical) terms, which in effect means that aphysicalist could reject (9).

A different notion of reduction derives from the attempts ofphilosophers of science to explain intertheoretic reduction. Theclassic formulation of this notion was given by Ernest Nagel (1961).Nagel said that one theory was reduced to another if you couldlogically derive the first from the second together with what hecalled bridge laws, i.e., laws connecting the predicates of thereduced theory (the theory to be reduced) with the predicates of thereducing theory (the theory to which one is reducing). Here is aformulation of this idea, where the theories in question arepsychology and neuroscience:

(10): Reductionism is true iff for each mental predicateFthere is a neurobiological predicateG such that a sentenceof the form ‘x isF iffx isG’ expresses a bridge law.

Once again, however, there is no reason at all why physicalists needto accept that reductionism is true in the sense of (10). We notedearlier that the possibility of multiple realization renders typephysicalism implausible; something similar is true in this case. Manydifferent neurobiological processes (whether in our own species or adifferent one) could underlie the same psychological process —indeed, given science fiction, even non-neurobiological processesmight underlie the same psychological process. If so, (10) seems to befalse. (For a classic presentation of multiple realization andreductionism, see Fodor 1974, but for an alternative view, see Kim1993).

A third notion of reductionism is more metaphysical in focus thaneither the conceptual or theoretical ideas reviewed so far. Accordingto this notion, reductionism means that the properties expressed bythe predicates of (say) a psychological theory are identical to theproperties expressed by the predicates of (say) a neurobiologicaltheory — in other words, this version of reductionism is inessence a version of type physicalism or the identity theory. As wehave already seen, however, since a physicalism need not be a typephysicalism, it need not be reductionism in this metaphysical senseeither

A final notion of reductionism that needs to be distinguished from theprevious three concerns whether mental statements followapriori from non-mental statements. Here is a statement of thissort of idea,

(11): Reductionism is true iff for each mental predicateFthere is non-mental predicateG such that a sentence of theform “ifx isF thenx isG” isa priori.

What (11) says is that if reductionism is true,a prioriknowledge alone, plus knowledge of the physical or non-mental truthswill allow one to know the mental truths. This question is usuallydebated in the context of another, viz., the question ofaposteriori anda priori physicalism. So we now turn tothat question.

3.2A Priori andA Posteriori Physicalism

We have been assuming that supervenience is necessary for physicalism,even if it is not sufficient. But what follows from supervenience? Onething that is usually thought to follow is that the physical truths ofthe world entailall the truths; hence physicalism is true atall (12) is true

(12): The physical truths entail all the truths.

Now suppose thatS is a statement which specifies thephysical nature of the actual world andS* is a statementwhich specifies the total nature of the world. (It might be thatneitherS norS* are expressible in languages we canunderstand, but let us set this aside.) Then physicalism tells us inaddition that that:

(13): S entailsS*

Another way to say this is to say that if supervenience physicalism istrue, the following conditional is necessarily true:

(14): IfS thenS*

Indeed, this is a general feature of supervenience physicalism: if itis true then there will always be a necessary truth of the form of(14).

Now, if (14) is necessary the question arises whether it isapriori, i.e. knowable independent of empirical experience, orwhether it isa posteriori, i.e. knowable but notindependently of empirical experience. Traditionally, every statementthat was necessary was assumed to bea priori. However, sinceKripke’sNaming and Necessity (1980), philosophers havebecome used to the idea that there are truths which are both necessaryanda posteriori. Accordingly many recent philosophers havedefended aposteriori physicalism: the claim that statementssuch as (14) are necessary anda posteriori (cf. Loar 1997).Moreover, they have used this point to try to disarm many objectionsto physicalism, including those concerning qualia and intentionalitythat we will consider below. Moreover, as we have just noted, somephilosophers have suggested that the necessarya posterioriprovides the proper interpretation of non-reductive physicalism.

The appeal to the necessarya posteriori is on the surface anattractive one, but it is also controversial. One problem arises fromthe fact that Kripke’s idea that there are necessary andaposteriori truths can be interpreted in two rather differentways. On the first interpretation — I will call it thederivation view — while there are necessaryaposteriori truths, these truths can be deriveda priorifrom truths which area posteriori and contingent. On thesecond interpretation — I will call it the non-derivation view— there arenon-derived necessarya posterioritruths, i.e. necessary truths which are not derived from anycontingent truths (or anya priori truths for that matter).The problem is that when one combines the derivation view with theclaim that (14) is necessary anda posteriori, one encountersa contradiction. If the derivation view is correct, then there is somecontingent anda posteriori statementS# thatlogically entails (14). However, ifS# logically entails (14)then (since ‘IfC, then ifA thenB’ is equivalent to ‘IfC &A, thenB’) we can infer that the following isboth necessary anda priori:

(15): IfS &S# thenS*.

One the other hand, if physicalism is true, andS summarizesthe total nature of the world thenS#is already implicitly included in S. In otherwords, (15) is simply an expansionof (14). But if (15) is just an expansion of (14), then if (15) isa priori, (14) must also bea priori. But that meansour initial assumption is false: (14) is not a necessaryaposteriori truth after all (see Jackson 1998).

How might ana posteriori physicalist respond to thisobjection? The obvious response is to reject the derivation view ofthe necessarya posteriori in favor of the non-derivationview. But this is just to say that if one wants to defendaposteriori physicalism, one will have to defend thenon-derivation view of the necessarya posteriori. However,the non-derivation view is controversial, so it is not something thatwe can hope to solve here. (For discussion, see Byrne 1999, Chalmers1996, 1999, Jackson 1998, Loar 1997, Lewis 1994, Yablo 1999, and thepapers in Gendler and Hawthorne 2004)

4. The Condition Question

Earlier we distinguished two interpretative questions with respect tophysicalism, the completeness question and the condition question. Sofar we have been concerned with the completeness question. I turn nowto the condition question, the question of what it is for something(an object, an event, a process, a property) to be physical.

This issue has received less attention in the literature than thequestions we have been studying so far. But it is just as important.Without any understanding of what the physical is, we can have noserious understanding of what physicalism is. After all, what does itmean to say that everything is physical, as opposed to chemical orfinancial. (The point here is quite general: if Thales says thateverything is water, we don’t understand what he says unless hesays something about what water is. The physicalist is in the sameboat.)

4.1 The Theory and Object Conceptions of the Physical

So what is the answer to the condition question? If we concentrate forsimplicity on the notion of a physical property, we can discern twokinds of answers to this question (see Stoljar 2001, Stoljar 2010,Tiehen 2018). The first ties the notion of a physical property to anotion of a physical theory, for this reason we can call it thetheory-based conception of a physical property:

The theory-based conception:
A property is physical iff it is the sort of property that physicaltheory tells us about.

According to the theory-based conception, for example, if physicaltheory tells us about the property of having mass, then having mass isa physical property. (The theory-based conception bears some relationto the notion of physical1 discussed in Feigl 1967; more explicitdefense is found in Smart 1978, Lewis 1994, Braddon-Mitchell andJackson 1996, and Chalmers 1996.)

The second kind of answer ties the notion of a physical property tothe notion of a physical object, for this reason we can call it theobject-based conception of a physical property:

The object-based conception:
A property is physical iff it is the sort of property had byparadigmatic physical objects and their constituents.

According to the object-based conception, for example if paradigmaticphysical objects such as rocks or planets are solid or are located inspace or have mass, then the property of being solid or located inspace or having mass is a physical property. (The best examples ofphilosophers who operate with the object-conception of the physicalare Meehl and Sellars 1956 and Feigl 1967; more recent defense is tobe found in Jackson 1998.)

Do these conceptions characterize the same class of properties? Thereare a number of different possibilities here, but one that hasreceived some attention in the literature is that physical theory onlytells us about the dispositional properties of physical objects, andso does not tell us about the categorical properties, if any, thatthey have — a thesis of this sort has been defended by a numberof philosophers, among them Russell (1927), Armstrong (1968),Blackburn (1992) and Chalmers (1996). Hence, if physical objects dohave categorical properties, those properties will not count asphysical by the standards of the theory conception. On the other hand,there seems no reason not to count them as physical in some sense orother. If that is right, however, then the possibility emerges thatthe theory- and the object-conceptions characterize distinct classesof properties.

A further distinction that can be made here, and which cross-cuts thetheory/object distinction, is between a more narrow and a more broadconception of a physical property (see Chalmers 2015). A narrowconception counts as a physical property only those within arestricted range. On the theory conception, for example, these mightthe properties expressed by fundamental physics. A broader conceptioncounts as physical property any property which is either a property inthe narrow sense (a narrow physical property, as we might call it) orelse bears the right kind of relation to narrow physical properties,for example, is definable in terms of them, or is grounded in them.There are lots of complications here, partly because there aredifferent ways of restricting the narrow class, and different ways ofextending such a class. Here we will understand the theory and objectconceptions in a narrower rather than a broad way.

4.2 Circularity

Along with the concepts of space, time, causality, value, meaning,truth and existence, the concept of the physical is one of the centralconcepts of human thought. So it should not be surprising that anyattempt to come to grips with what a physical property is will becontroversial. The theory and object conceptions are no different:each has provoked a number of different questions and criticisms. Inthe remainder of our discussion of the condition question, I willreview some main ones.

To begin with, one might object that both conceptions are inadequatebecause they are circular, i.e., both appeal to the notion ofsomething physical (a theory or an object) to characterize a physicalproperty. But how can you legitimately explain the notion of one sortof physical thing by appealing to another?

However, the response to this is that circularity is only a problem ifthe conceptions are interpreted as providing a reductive analysis ofthe notion of the physical. But there is no reason why they should beinterpreted in that way. After all, we have many concepts that weunderstand without knowing how to analyze (cf. Lewis 1970). So thereseems no reason to suppose that either the theory or object conceptionis providing anything else but a way of understanding the notion ofthe physical.

The point here is an important one in the context of the conditionquestion. Earlier we said that the condition question was perfectlylegitimate because it is legitimate to ask what the condition of beingphysical is that, according to physicalism, everything has. But thislegitimate question should not be interpreted as the demand for areductive analysis of the notion of the physical. Consider Thalesagain: it is right to ask Thales what he means by ‘water’— and in so doing demand an understanding of the notion of water— but it is wrong to demand of him a conceptual analysis ofwater.

4.3 Hempel’s dilemma

One might object that any formulation of physicalism which utilizesthe theory-based conception will be either trivial or false. CarlHempel (cf. Hempel 1969, see also Crane and Mellor 1990) provided aclassic formulation of this problem: if physicalism is defined viareference to contemporary physics, then it is false — after all,who thinks that contemporary physics is complete? — but ifphysicalism is defined via reference to a future or ideal physics,then it is trivial — after all, who can predict what a futurephysics contains? Perhaps, for example, it contains even mental items.The conclusion of the dilemma is that one has no clear concept of aphysical property, or at least no concept that is clear enough to dothe job that philosophers of mind want the physical to play.

One response to this objection is to take its first horn, and insistthat, at least in certain respects contemporary physics really iscomplete or else that it is rational to believe that it is (cf. Smart1978, Lewis 1994 and Melnyk 1997, 2003). There is an element of truthin this. It may be rational to believe that contemporary science istrue, even if not that it is complete. Nevertheless, it also seemsmistaken todefine physicalism with respect to the physicsthat happens to be true in this world. The reason is that whether aphysical theory is true or not is a function of the contingent facts;but whether a property is physical or not is not a function of thecontingent facts. For example, consider medieval impetus physics.Medieval impetus physics is false (though of course it might not havebeen) and thus it is irrational to suppose it true. Nevertheless, theproperty of having impetus — the central property that objectshave according to impetus physics — is a physical property, anda counterfactual world completely described by impetus physics wouldbe a world in which physicalism is true. But it is hard to see how anyof this could be right if physicalism were defined by reference to thephysics that we have now or by the physics that happens to be true inour world. (For development of this point, and for a dilemma that issimilar to Hempel’s but which casts the issue in modal ratherthan temporal terms, see Stoljar 2010; for discussion, see Baltimore2013, Fiorese 2016)

A different response to Hempel’s dilemma is that what it shows,if it shows anything, is that a particular proposal about how todefine a physical property — namely, via reference to physics ata particular stage of its development — is mistaken. But fromthis one can hardly conclude that we have no clear understanding ofthe concept at all. As we have seen, we have many concepts that wedon’t know how to analyze. So the mere fact — if indeed itis a fact — that a certain style of analysis of the notion ofthe physical fails does not mean that there is no notion of thephysical at all, still less that we don’t understand thenotion.

One might object that, while these remarks are perfectly true, theynevertheless don’t speak to something that is right aboutHempel’s dilemma, namely, that for the theory-conception to becomplete one needs to know what type of theory a physical theory is.Perhaps one might appeal here to the fact that we have a number ofparadigms of what a physical theory is: common sense physical theory,medieval impetus physics, Cartesian contact mechanics, Newtonianphysics, and modern quantum physics. While it seems unlikely thatthere is anyone factor that unifies this class of theories,perhaps there is a cluster of factors — a common or overlappingset of theoretical constructs, for example, or a shared methodology.If so, one might maintain that the notion of a physical theory is aWittgensteinian family resemblance concept. However, whether this isenough to answer the question of what kind of theory a physical theoryis remains to be seen. (For further discussion of Hempel’sdilemma, see the papers in Elpidorou 2018a.)

4.4 The panpsychism problem

Hempel’s dilemma against the theory-conception is similar to anobjection that one often hears propounded against theobject-conception (cf. Jackson 1998). Consider a version ofpanpsychism according to which all the physical objects of ouracquaintance are conscious beings just as we are. (For furtherdiscussion and different versions of this view, seePanpsychism.) Would physicalism be true in that situation? It seems intuitivelynot; however, if physicalism is defined via reference to theobject-conception of a physical property then it is hard to see whynot. After all, according to that conception, something is a physicalproperty just in case it is required by a complete account ofparadigmatic physical objects. But this makes no reference to thenature of paradigmatic physical objects, and so allows thepossibility that physicalism is true in the imagined situation.

One thing to say in response to this objection is that the merepossibility of panpsychism cannot really be what is at issue here. Forpanpsychism per se is not inconsistent with physicalism (cf. Lewis1983). After all, the fact that there aresome consciousbeings is not contrary to physicalism — why then should thepossibility thateverything is a conscious being be contraryto physicalism? If so, what is at issue in the objection is notpanpsychism so much as the possibility that the paradigms or exemplarsin terms of which one characterizes the notion of the physical mightturn out to be radically different from what we normally assume in aquite specific sense — they might turn out to be in someessential or ultimate respect mental.

Once the problem is put like that, however, the panpsychism problemlooks similar to a problem that arises in general whenever one onetries to understand or define a concept in terms of paradigmaticobjects which fall under it, viz., that these definitions have certainsort of empirical presuppositions that might turn out to be false.Suppose one tried to define the concept red in terms of similarity toparadigmatic red things, such as blood. Pursuing this strategy commitsone to the idea that the belief that blood is red is a piece of commonknowledge shared among all those who are competent with the term. Butthat seems wrong — someone who thought that blood was greenwould be mistaken about blood but not about red. Now this problem is adifficult problem, however — and this is the crucial point forour purposes — the problem is also a quite general problem; itarises because of the paradigm style of definition. So to that extent,the concept of the physical does not seem to be any worse off than theconcept of red, the panpsychism problem notwithstanding. (Fordiscussion of the general strategy see Lewis 1997)

Of course, one would reject this entire line of thought if onerejected its starting point, viz., that panpsychism is consistent withphysicalism. Wilson (2006, 78–9), for example, suggests thatwhile physicalism is consistent with the view that some consciousbeings exist, it is not consistent with the view that some fundamentalconscious beings exist, and it is this last claim that is definitiveof panpsychism. But in fact even that is consistent with physicalism,though admittedly of an unusual sort. To illustrate, imagine a worldin which the fundamental properties are both mental and physical. Thatis certainly a far-fetched scenario but it doesn’t seem to beimpossible. Would physicalism be true in such a world? It is hard tosee why not; at least it may be true at that world that any physicalduplicate of it is a duplicatesimpliciter. Would panpsychismlikewise be true at such a world? Again, it is hard to see why not,since the fundamental properties instantiated at such a world aremental, though of course they are also physical.

4.5 The via negativa

One idea that often emerges in the context of Hempel’s dilemmaand the panpsychism problem, but deserves separate treatment, is theso-called Via Negativa (see e.g. Montero and Papineau 2005, Wilson2006, Fiorese 2016).

The simplest way to introduce the Via Negativa is to interpret it as adefinition of the notion a physical property something like this:F is a physical property if and only ifF is anon-mental property. But there are many reasons to resist such adefinition. Take vitalism. Vitalism isn’t true, but it mighthave been true; there is no contradiction in it for example. Soimagine a world in which plants and animals instantiate the keyproperty associated with vitalism, viz., élan vital. It seemsreasonable to say that in that case plants and animals instantiate aproperty that is non-physical, i.e. élan vital is not physical.And yet one should not say on this account that plants and animalsinstantiate a mental property, i.e., élan vital is not mental.In short, élan vital is neither mental nor physical. But theVia Negativa as stated cannot accommodate that fact.

One might try to meet this objection by revising the Via Negativa sothat what is intended is only a partial definition along these lines:F is a physical property only ifF is non-mental. Evenso problems remain. As we have seen élan vital causes a problembecause it is neither mental nor physical. But there might beproperties that are both mental and physical. Consider a version ofthe identity theory according to which being in pain just is c-fibersfiring. If we suppose that such a theory is true, is the property ofbeing in pain then mental or physical? Both presumably; but this couldnot be true on the Via Negativa construed as a definition of what aphysical property is, even a partial definition. For if a property ismental and physical, then, given the Via Negativa, it will be bothmental and non-mental which (of course) it can’t be! Nowobviously, there are good questions about whether an identity theoryalong these lines is or could be true, but regardless of whether it istrue, it should not be ruled out simply because of a proposal abouthow to define the words in which it is stated.

Alternatively, one might try to meet the objection by adopting whatWilson 2006 calls the ‘no fundamental mentality’constraint. On this interpretation, what proponents of the ViaNegativa have in mind is thatF is a physical property only ifF is not fundamentally mental, where in turn to be ‘notfundamentally mental’ is most naturally understood as entailingthat ifF is a fundamental property then it is non-mental. Thisversion of the view avoids the problem about having c-fibers sincepresumably that property is not fundamental. But once again problemsremain. Take the world we considered above at which the fundamentalproperties are both mental and physical; in effect, what applies toc-fibers firing (if the identity theory is true) applies to thefundamental properties instantiated at this world. As I said, thisscenario is far-fetched, but it doesn’t seem to be impossible,and it is certainly not impossible simply as a matter of thedefinition of the words. And yet it would be impossible for thatreason if the ‘no fundamental mentality’ version of theVia Negativa were true.

Of course, to raise these problems for the Via Negativa is not to denythat there is something right about it. For example, when we think ofproperties that would falsify physicalism we do often think of*certain* mental properties, e.g., the distinctive properties ofectoplasm or ESP. However, this fact—that certain mentalproperties would, if instantiated, falsify physicalism—can becaptured without defining the physical in general as the non-mental. Abetter way would be to require, of any spelling out of the notion ofthe physical, whether it be the object-based account or thetheory-based account, that it respect that fact that some(uninstantiated) mental properties are non-physical.

4.6 Structuralist Approaches

Another idea about how to define the physical that has becomeprominent in recent times is a structuralist approach to thephysical.

One way to introduce the structuralist approach is to see it as adevelopment of the theory conception formulated above. On the theoryview, a property is physical just in case it is tied in the right wayto a physical theory. One problem that arises for such a view, as wehave seen, is what ‘physical theory’ is supposed to meanhere. For the structuralist (at least in the context;‘structuralism’ can mean many different things), aphysical theory is one that employs a restricted vocabulary. Oneparticularly frank version of this sort of view is suggested byRussell 1927; on this view, the vocabulary in question is restrictedto logical or mathematical vocabulary. Contemporary philosophers adopta less restricted view according to which the vocabulary is eitherlogical or mathematical or causal or nomological (i.e. pertaining tolaws) or some combination of these (see Alter 2016, Chalmers 2020,Goff 2017; for criticism see Stoljar 2020). In effect, proposals likethis provide a topic-neutral conception of the physical, and hence atopic-neutral conception of physicalism.

An attractive feature of this approach is that it provides an answerto Hempel’s dilemma and similar problems. Physics may indeedchange over time, but according to the structuralist, any physicaltheory must be restricted to this sort of vocabulary. Hence we canappeal to the notion of a physical theory to formulate a version ofphysicalism on which everything supervenes on or is realised by or isgrounded in physical properties that can be expressed in that limitedvocabulary. (Here structuralism about the physical draws support fromstructural realism in philosophy of science, a position to which it isin some ways quite similar; see, e.g.Structural Realism)

However, a problem for structuralism (developed in Stoljar 2020) isthat, while placing restrictions of this sort on the notion of aphysical theory helps with Hempel’s dilemma, it also seemsoverly stringent. Physical theories on the face of it tell you lots ofthings about the physical world which are not topic-neutral, forexample, about mass, energy, electrons, protons and a myriad otherthings. The idea that we can capture all of this using a language thatemploysonly logical/mathematical or causal/nomic vocabularymay seem an overly ambitious one.

While there are problems with structuralist approaches to thephysical, as with the Via Negativa, there is also something rightabout it. We have noted one idea in philosophy of science that issimilar to the structuralist approach to the physical, namely,structural realism. A different idea that philosophers of science haveemphasised a lot in recent literature is that physicists and otherscientists often construct mathematical models of the systems they areinterested in; moreover, they often focus on the mathematicalproperties of these models themselves (see, e.g. Weisberg 2013).Perhaps a structuralist approach to such mathematical models isplausible. Nevertheless, structuralism about the physical is a thesis,not about these mathematical models, but about the target systems thatthese models correspond to, and it precisely this that causes theproblem.

4.7 Physicalism as an Attitude

In view of the difficulties posed by Hempel’s dilemma andrelated problems, some philosophers have explored the interesting ideathat to be a physicalist is not to hold some thesis or belief –that is, to hold something that may be true or false – but israther to adopt a kind of attitude or stance. As Alyssa Ney (2008, p.9, see also Van Fraassen 2002) develops this “attitudinal”view, for example, “physicalism is an attitude one takes to formone’s ontology completely and solely according to what physicssays exists”.

Now, as with other ideas we have looked at, there is certainlysomething right about the attitudinal view. As we will see below,contemporary physicalists are often methodological naturalists, andmethodological naturalists may well hold the attitude Ney describes.Nevertheless, there is a major problem for the view, viz., that on theface of it holding this sort of attitude is neither necessary norsufficient for being a physicalist.

To see it is not necessary, consider such ancient philosophers asDemocritus or Lucretius. These philosophers are physicalists, or atleast are usually classified that way, i.e., since they held thedoctrine traditionally called ‘materialism’. But they didnot hold the attitude Ney describes, either implicitly or explicitly,for physics (at least identified sociologically) did not exist intheir day at all.

In response, one might adjust the attitudinal view so that the‘physics’ towards which one holds the relevant attitude isnot identified sociologically, but is instead understood as a certainsort of theory considered in the abstract. But then further problemsarise. First, it is now difficult to see the difference betweenholding the relevant attitude and simply believing a thesis. If oneresolves to be guided in one’s ontology by the truth of aparticular theory, how is that different from just believing thetheory? Second, if one holds an attitude toward a particular theory,Hempel’s dilemma seems to arise again though in a slightlydifferent form. For which physical theory is meant? If one meanscurrent physics, as in fact Ney suggests, then one might argue thatthis is not an attitude that physicalists should reasonably hold,since current physics is incomplete; and if one means ideal physics,it is hard to see what the content or nature of the attitude is.

To see that the attitude is not sufficient, imagine a situation inwhich physics postulates properties or objects which are like thosepostulated by traditional dualists; as Ney puts it imagine “itis the year 3000 AD and physicists have been forced to introduceirreducible mental entities into their theory.” (2008, p. 12).In such a situation, a person might hold the attitude Ney describes,and yet intuitively not be a physicalist.

In response, Ney agrees that this is a possibility but points out,first, it would still be reasonable to criticize the people who holdthe attitude – for example, on the grounds that those who hold adifferent attitude might have arrived at correct ontology more quickly– and, second, that it doesn’t follow that the attitudedefinitive of physicalism is identical to the attitude definitive ofdualism. (The ideas underlying this second point are (a) if one adoptsthe attitudinal view about physicalism then one should in fairnessadopt it about dualism as well; and (b) that from the fact that twoattitudes coincide in a possible situation it does not follow thatthey are identical.) However, while both these suggestions might betrue, it is hard to see them as responding to the basic point thatperson who holds the attitude Ney describes in the imagined situationis not correctly described as a physicalist. In principle, after all,such a person may be criticized in many ways; moreover, the fact thatholding a particular attitude is not sufficient for being aphysicalist does not entail that doing so is necessary for being adualist.

5. The Case Against Physicalism

Having provided an answer to the interpretation question, I now turnto the truth question: is physicalism (as we have interpreted it sofar) true? I will first discuss three reasons for supposing thatphysicalism is not true. Then I will consider the case forphysicalism.

5.1 Qualia and Consciousness

The main argument against physicalism is usually thought to concernthe notion of qualia, the felt qualities of experience. The notion ofqualia raises puzzles of its own, puzzles having to do with itsconnection to other notions such as consciousness, introspection,epistemic access, acquaintance, the first-person perspective and soon. However the idea that we will discuss here is the apparentcontradiction between the existence of qualia and physicalism.

Perhaps the clearest version of this argument is Jackson’sknowledge argument; seequalia: the knowledge argument. This argument asks us to imagine Mary, a famous neuroscientistconfined to a black and white room. Mary is forced to learn about theworld via black and white television and computers. However, despitethese hardships Mary learns (and therefore knows) all that physicaltheory can teach her. Now, if physicalism were true, it is plausibleto suppose that Mary knows everything about the world. And yet —and here is Jackson’s point — it seems she does not knoweverything. For, upon being released into the world of color, it willbecome obvious that, inside her room, she did not know what it is likefor both herself and others to see colors — that is, she did notknow about the qualia instantiated by particular experiences of seeingcolors. Following Jackson (1986), we may summarize the argument asfollows:

P1. Mary (before her release) knows everything physical there is toknow about other people.

P2. Mary (before her release) does not know everything there is toknow about other people (because she learns something about them onbeing released).

Conclusion. There are truths about other people (and herself) thatescape the physicalist story.

Clearly this conclusion entails that physicalism is false: for ifthere are truths which escape the physicalist story how can everythingsupervene on the physical? So a physicalist must either reject apremise or show that the premises don’t entail theconclusion.

There are many possible responses to this argument, but here I willbriefly mention only three. The first isthe abilityhypothesis due to Lawrence Nemerow (1988) and developed anddefended by David Lewis (1994). The ability hypothesis follows Ryle(1949) in drawing a sharp distinction between propositional knowledgeor knowledge-that (such as ‘Mary knows that snow iswhite’) and knowledge-how (such as ‘Mary knows how to ridea bike’), and then suggests that all Mary gains is the latter.On the other hand, P2 would only be true if Mary gained propositionalknowledge.

A second response appeals to the distinction betweena priorianda posteriori physicalism. As we saw above, the crucialclaim ofa posteriori physicalism is that (13) — i.e.the claim thatS entailsS* — isaposteriori. Since (13) isa posteriori, you would needcertain experience to know it. But, it is argued, Mary has not had(and cannot have) the relevant experience. Hence she does not know(13). On the other hand, the mere fact that Mary has not had (andcannot have) the experience to know (13) does not remove thepossibility that (13) is true. Hencea posteriori physicalismcan avoid the knowledge argument. (It is an interesting question whichpremise of the knowledge argument is being attacked by this response.The answer depends on whether (13) is physical or not: if (13) isphysical, then the response attacks P1. But if (13) is not physical,the response is that the argument is invalid.).

A third response is to distinguish between various conceptions of thephysical. We saw above that potentially the class of propertiesdefined by the theory-conception of the physical was distinct from theclass of properties defined by the object-conception. But thatsuggests that the first premise of the argument is open tointerpretation in either of two ways. On the other hand,Jackson’s thought experiment only seems to support the premiseif it is interpreted in the one way, since Mary learns by learning allthat physicaltheory can teach her. But leaves open thepossibility that one might appeal to the object-conception of thephysical to define a version of physicalism which evades the knowledgeargument.

One of the most lively areas of philosophy of mind concerns the issueof which if any of these responses to the knowledge argument will besuccessful. (See the papers in Ludlow, Nagasawa, and Stoljar 2004. SeealsoQualia: The Knowledge Argument) The ability response raises questions about whether know-how isgenuinely non-propositional (cf. Lycan 1996, Loar 1997 and Stanley andWilliamson 2001), and about whether it gets the facts right to beginwith (Braddon Mitchell and Jackson 1996). As againstaposteriori physicalism, it has been argued both that it rests ona mistaken approach to the necessarya posteriori (Chalmers1996, 1999, Jackson 1998), and that the promise of the idea ischimerical anyway (cf. Stoljar 2000). The third response raisesquestions about the distinction between the object and the theoryconception of the physical and associated issues about dispositionaland categorical properties, and also about the relation betweenphysicalism on the one hand, and a related view, sometimes calledRussellian monism. SeeRussellian monism, as well as Chalmers 1996, Lockwood 1992, Stoljar 2000, 2001, Montero2010, 2015)

5.2 Meaning and Intentionality

Philosophers of mind often divide the problems of physicalism intotwo: first, there are the problems of qualia, typified by theknowledge argument; second, there are problems of intentionality. Theintentionality of mental states is their aboutness, their capacity torepresent the world as being a certain way. One does not simply think,one thinksof (orabout) Vienna; similarly, one doesnot simply believe, one believesthat snow is white. Just asin the case of qualia, some of the puzzles of intentionality derivefrom facts internal to the notion, and from the relation of thisnotion to the others such as rationality, inference and language; seeIntentionality. But others derive from the fact that it seems difficult to square thefact that mental states have intentionality with physicalism. Thereare a number of ways of developing this criticism but much recent workhas concentrated on a certain line of argument that Saul Kripke hasfound in the work of Wittgenstein (1982; see alsoPrivate Language).

Kripke’s argument is best approached by first considering whatis often called a dispositional theory of linguistic meaning.According to the dispositional theory, a word means what it does— for example, the word ‘red’ means red —because speakers of the word are disposed to apply to word to redthings. Now, for a number of reasons, this sort of theory has beenvery popular among physicalists. First, the concept of a dispositionat issue here is clearly a concept that is compatible withphysicalism. After all, the mere fact that vases are fragile and sugarcubes are soluble (both are classic examples of dispositionalproperties) does not cause a problem for physicalism, so why shouldthe idea that human beings have similar dispositional properties?Second, it seems possible to develop the dispositional theory oflinguistic meaning so that it might apply also to intentionality.According to a dispositional theory of intentionality, a mentalconcept would mean what it does because thinkers are disposed toemploy the concept in thought in a certain way. So a dispositionaltheory seems to hold out the best promise of a theory ofintentionality that is compatible with physicalism.

Kripke’s argument is designed to destroy that promise. (In fact,Kripke’s argument is designed to destroy considerably more thanthis: the conclusion of his argument is a paradoxical one to theeffect that there can be no such a thing as a word’s having ameaning. However, we will concentrate on the aspects of the argumentthat bear on physicalism.) In essence his argument is this. Imagine asituation in which (a) the dispositional theory is true; (b) the word‘red’ means red for a speaker S; and yet (c) the speakermisapplies the word — for example, S is looking at a white thingthrough rose-tinted spectacles and calls it red. Now, in thatsituation, it would seem that S is disposed to apply ‘red’to things which are (not merely red but)either-red-or-white-but-seen-through-rose-tinted-spectacles. But then,by the theory, the word ‘red’ means (not red but)either-red-or-white-as-seen-through-rose-tinted-spectacles. But thatcontradicts our initial claim (b), that ‘red’ means red.In other words, the dispositional theory, when combined with a trueclaim about the meaning of word, plus a truism about meaning —that people can misapply meaningful words — leads to acontradiction and is therefore false.

How might a physicalist respond to Kripke’s argument? As withthe knowledge argument, there are many responses but here I willmention only two. The first response is to insist that Kripke’sargument neglects the distinction betweena priori andaposteriori physicalism. Kripke often does say that according tothe dispositionalist, one should be able to ‘read off’truths about meaning from truths a physicalist can accept. (For aproposal like this, see Horwich 2000.) One problem with this proposalis, as we have seen, that its background account of the necessarya posteriori is controversial. As we saw,aposteriori physicalists are committed to what we called thenon-derivation view about necessarya posteriori truths. Butthe non-derivation view has come under attack in recent times.

The second response is to defend the dispositional theory againstKripke’s argument. One way to do this is to argue that theargument only works against a very simple dispositionalism, and that amore complicated version of such a theory would avoid these problems.(For a proposal along these lines, see Fodor 1992 and the discussionin Braddon-Mitchell and Jackson 1996). A different proposal is toargue that Kripke’s argument underestimates the complexity inthe notion of a disposition. The mere fact that in certaincircumstances someone would apply ‘red’ to white thingsdoes not mean that they are disposed to apply red to white things— after all, the mere fact that in certain circumstancessomething would burn does not mean that it is flammable in theordinary sense. (For a proposal along these lines see Hohwy 1998, andHeil and Martin 1998)

As with the knowledge argument, the issues surrounding Kripke’sargument are very much wide open. But it is important to note thatmost philosophers don’t consider the issues of intentionality asseriously as the issue of qualia when it comes to physicalism. Indifferent vocabularies, for example, both Block (1995) and Chalmers(1996) distinguish between the intentional aspects of the mind orconsciousness, and the phenomenal aspects or qualia, and suggest thatit is really the latter that is the central issue. As Chalmers notes(1996; p. 24), echoing Chomsky’s famous distinction, theintentionality issue is aproblem, but the qualia issue is amystery.

5.3 Numbers and Abstracta

A third problem, which we mentioned briefly above, isthe problemof abstracta (Rabin 2020). This concerns the status withinphysicalism of abstract objects, i.e., entities apparently not locatedin space and time, such as numbers, properties and relations, orpropositions.

To see the problem, suppose that abstract objects, if they exist,exist necessarily, i.e., in all possible worlds. If physicalism istrue, then the facts about such objects must either be physical facts,or else bear a particular relation (grounding, realisation) to thephysical. But on the face of it, that is not so. Can one really saythat 5+7=12, for example, is realised in, or holds in virtue of, somearrangement of atoms and void? Or can one say that it itself is aphysical fact or a fundamental physical fact? If not, physicalism isfalse: the property of being such that 5+7=12 obtains the actual worldbut is neither identical to, nor grounded in or realized by, anyphysical property. (Sometimes the problem of abstracta is formulatedas concerning, not abstract objects such as numbers or properties, butthe grounding or realization facts themselves; see, e.g, Dasgupta2015. We will set this aside here.)

There are a number of responses to this problem in the literature; foran overview, see Rabin 2020, see also Dasgupta 2015 and Bennett 2017;for more general discussion of physicalism and abstracta, see Montero2017, Schneider 2017, and Witmer 2017.

One response points out that, while the problem of abstracta confrontsmany different versions of physicalism, it does not arise forsupervenience physicalism. After all, since numbers exist in allpossible worlds, facts about them trivially supervene on the physical;any world identical to the actual world in physical respects will beidentical to it in respect of whether 5+7=12, because any world at allis identical to the actual world in that respect! But the difficultyhere is that supervenience physicalism seems, as we saw above, tooweak anyway. Indeed, one might think that the example of abstracta issimply a different way to bring out that it is too weak.

Another option is to adopt a version of nominalism, and deny theexistence of abstracta entirely. The problem with this option is thatdefending nominalism about mathematics is no easy matter, and in anycase nominalism and physicalism are normally thought of as distinctcommitments.

A third view, which seems more attractive than either of the twomentioned so far, is to expand the notion of a physical property thatis in play in formulations of physicalism. For example, one mighttreat the properties of abstract objects astopic-neutral insomething like the sense discussed in connection with Smart andreductionism above (see section 3.1). Topic-neutral properties havethe interesting feature that, while they themselves are not physical,but are capable of being instantiated in what is intuitively acompletely physical world, or indeed what is intuitively a completelyspiritual world or a world entirely made of water. If so, it becomespossible to understand physicalism so that the reference to‘physical properties’ within it is understood morecorrectly as ‘physical or topic-neutral properties’.

A final response to the problem does not expand the notion of thephysical as much as it restricts the scope of physicalism toproperties of a certain sort. One suggestion along these lines hasbeen made by a number of writers (e.g. Rabin 2020, following Dasgupta2015) in the context of grounding physicalism, though perhaps theunderlying idea can be extended to other varieties as well. Theysuggest that grounding physicalism, which we formulated above as (7),should be revised to take the following form:

(7*): Physicalism is true at a possible worldw iff everygroundable property instantiated atw is either aphysical property or is grounded in a physical property.

Here, a property is groundable just in case it is apt for beinggrounded, i.e. it is the sort of property that can be either groundedor not. Ordinary psychological properties are presumably in thisclass. If grounding physicalism is true, they are grounded in physicalproperties, whereas if it is false, they are not grounded in physicalproperties; either way, they are groundable properties. Butmathematical properties and the properties of abstracta more generallymight in at least some instancesnot be groundable, they mayfail to be properties that are apt for being grounded. If so, we havean alternative solution to the problem of abstracta: (7*) permits thatsome properties of abstracta are not grounded in the physical, so longas they are ungroundable.

5.4 Methodological Issues

The final argument I will consider against physicalism is of a moremethodological nature. It is sometimes suggested, not that physicalismis false, but that the entire ‘project of physicalism’— the project in philosophy of mind of debating whetherphysicalism is true, and trying to establish or disprove its truth byphilosophical argument — is misguided. This sort of argument hasbeen mounted by a number of writers, but perhaps its most vocaladvocate has been Noam Chomsky (2000; see also Searle 1992, 1999).

It is easiest to state Chomsky’s criticism by beginning with twopoints about methodological naturalism. In general it seems rationalto agree with the methodological naturalists that the best hope for atheoretical understanding of the world is by pursuing the methodswhich are typical of the sciences. It would then seem rational as aspecial case that our best hope for a theoretical understanding ofconsciousness or experience is by pursuing the methods of the sciences— by pursuing, as we might put it, the naturalistic project withrespect to consciousness. So Chomsky’s first point is that it isrational to pursue the naturalistic project with respect toconsciousness.

Chomsky’s second point is that the physicalist project inphilosophy of mind is on the face of it rather different from thenaturalistic project. In the first place, the physicalist project is,as we have noted, usually thought of a piece of metaphysics. But thereis nothing obviously metaphysical about the naturalistic project, itsimply raises questions about what we can hope to explain. In thesecond place, the physicalist project is normally thought of as beingamenable to philosophical argument, whereas it is unclear wherephilosophical argument (if this is different from scientific argument)would enter the naturalistic project. In short, there doesn’tseem anything particularly ‘philosophical’ about thenaturalistic project — it simply applies the methods of scienceto consciousness. But the physicalist project is central to analyticphilosophy.

It is precisely at the place where the physicalist project departsfrom the naturalistic project that Chomsky’s criticism begins totake shape. For insofar as it is different from the naturalisticproject, there are a number of ways in which the physicalist projectis questionable. First, it is hard to see what the project might be— it is true that throughout the history of philosophy andscience one encounters suggestions that one might find out about theworld in ways that are distinct from the ones used in the sciences,but these suggestions have always been rather obscure. Second, it ishard to see how this sort of project could recommend itself tophysicaliststhemselves — such a project seems to be adeparture from methodological naturalism but most physicalists endorsemethodological naturalism as a matter of fact. On the other hand, ifthe physicalist project does not depart from the naturalistic project,then the usual ways of talking and thinking about that project arehighly misleading. For example, it is misleading to speak of it as apiece of metaphysics as opposed to a piece of ordinary science.

In sum, Chomsky’s criticism is best understood as a kind ofdilemma. The physicalist project is either identical to thenaturalistic project or it is not. If it is identical, then thelanguage and concepts that shape the project are potentially extremelymisleading; but if it is not identical, then there are a number ofways in which it is illegitimate.

How is one to respond to this criticism? In my view, the strongestanswer to Chomsky accepts the first horn of his dilemma and suggeststhat what philosophers of mind are really concerned with is thenaturalistic project. Now, of course, what concerns them is not somuch the details of the project — that would not distinguishthem from working scientists. Rather they are concerned with what thenature of the project and what its potential limits might be.

This theme might be developed in several ways, but one well-knowndevelopment of it has been suggested by Thomas Nagel (1983) andBernard Williams (1985). According to them, any form of scientificinquiry will at least be objective, or will result in an objectivepicture of the world. On the other hand, we have a number of arguments— the most prominent being the knowledge argument — whichplausibly show that there is no place for experience or qualia in aworld that is described in purely objective terms. If Nagel andWilliams are right that any form of scientific inquiry will yield adescription of the world in objective terms, the knowledge argument isnothing less than a negative argument to the effect that thenaturalistic project with respect to consciousness will notsucceed.

If what is at issue is the limits of the naturalist project, why isthe debate so often construed as a metaphysical debate rather than adebate about the limits of inquiry? In answer to this question, weneed to sharply divorce the background metaphysical framework withinwhich the problems of philosophy of mind find their expression, andthe problems themselves. Physicalism is the background metaphysicalassumption against which the problems of philosophy of mind are posedand discussed. Given that assumption, the question of the limits ofthe naturalistic projectjust is the question of whetherthere can be experience in a world that is totally physical.Nevertheless, when properly understood, the problems that philosophersof mind are interested in are not with the framework themselves, andto that extent are not metaphysical. Thus, the common phrase‘metaphysics of mind’ is misleading.

6. The Case for Physicalism

Having considered one side of the truth question, I will turn finallyto the other: what reason is there for believing that physicalism istrue?

The first thing to say when considering the truth of physicalism isthat we live in an overwhelmingly physicalist or materialistintellectual culture. The result is that, as things currently stand,the standards of argumentation required to persuade someone of thetruth of physicalism are much lower than the standards required topersuade someone of its negation. (The point here is a perfectlygeneral one: if you already believe or want something to be true, youare likely to accept fairly low standards of argumentation for itstruth.)

However, while it might be difficult to assess dispassionately thearguments for or against physicalism, this is still something weshould endeavor to do. Here I will review two arguments that arecommonly thought to establish the truth of physicalism. What unitesthe arguments is that each takes something from the physicalistworld-picture which we considered previously and tries to establishthe metaphysical this of physicalism.

The first argument is (what I will call)The Argument from CausalClosure. The first premise of this argument is the thesis of theCausal Closure of the Physical — that is, the thesis that everyevent which has a cause has a physical cause. The second premise isthat mental events cause physical events — for example wenormally think that events such as wanting to raise your arm (a mentalevent) cause events such as the raising of your arm (a physicalevent). The third premise of the argument is a principle of causationthat is often called the exclusion principle (Kim 1993, Yablo 1992,Bennett 2003). The correct formulation of the exclusion principle is amatter of some controversy but a formulation that is both simple andplausible is the following:

Exclusion Principle
If an evente causes evente*, then there is noevente# such thate# is non-supervenient one ande# causese*.

The conclusion of the argument is the mental events are supervenienton physical events, or more briefly that physicalism is true. For ofcourse, if the thesis of Causal Closure is true then behavioral eventshave physical causes, and if mental events also cause behavioralevents, then they must supervene on the physical if the exclusionprinciple is true.

The Argument from Causal Closure is perhaps the dominant argument forphysicalism in the literature today. But it is somewhat unclearwhether it is successful. (For some discussion see,Mental Causation). One response for the anti-physicalist is to reject the second premiseand to adopt a version of what is called epiphenomenalism, the viewthat mental events are caused by, and yet do not cause, physicalevents. The argument against this position is usually epistemological:if pains don’t cause pain behavior how can it be that yourtelling me that you are in pain gives me any reason for supposing youare? It might seem that epiphenomenalists are in trouble here, but asa number of recent philosophers have argued, the issues here are veryfar from being settled (Chalmers 1996, Hyslop 1999). The crucial pointis that the causal theory of evidence is open to seriouscounterexamples so it is unclear that it can be used againstepiphenomenalism effectively.

A different sort of response is to reject the causal principles onwhich the argument is based. As against the exclusion principle, forexample, it is often pointed out that certain events areoverdetermined. The classic example is the firing squad: both thefiring by soldier A and by soldier B caused the prisoner’s deathbut since these are distinct firings, the exclusion principle isfalse. However, while this line of response is suggestive, it is infact rather limited. It is true that the case of the firing squadrepresents an exception to the exclusion principle — anexception that the principle must be emended to accommodate. But isdifficult to believe that it represents an exception that can bewidespread. A more searching response is to reject the very idea ofcausal closure on the grounds, perhaps, that (as Bertrand Russell(1917) famously argued) causation plays no role in a mature portrayalof the world. Once again, however, the promise of this response ismore imagined than real. While it is true that many sciences do notexplicitly use the notion of causation, it is extremely unlikely thatthey do not imply that various causal claims are true.

The second argument for physicalism is (what I will call)TheArgument from Methodological Naturalism. The first premise ofthis argument is that it is rational to be guided in one’smetaphysical commitments by the methods of natural science. Lyingbehind this premise are the arguments of Quine and others thatmetaphysics should not be approached in a way that is distinct fromthe sciences but should rather be thought of as continuous with it.The second premise of the argument is that, as a matter of fact, themetaphysical picture of the world that one is led to by the methods ofnatural science is physicalism. The conclusion is that it is rationalto believe physicalism, or, more briefly that physicalism is true.

The Argument from Methodological Naturalism has received somewhat lessattention in the literature than the Argument from Causal Closure. Butit seems just as persuasive — in fact, rather more so. For howmight one respond? One possibility is to reject its first premise. Butthis is not something that most people are attracted to (or at leastare attracted to explicitly.)

The other possibility is to reject its second premise. However, ifphysicalism can be clearly stated — admittedly, this is a big‘if’ — it is not terribly clear what this wouldamount to or what the motivation for it would be. In the first place,our earlier discussion shows that physicalism is not inconsistent withexplanatory autonomy of the various sciences, so that one should notreject physicalism merely because one can’t see how to reducethose sciences to others. In the second place, while it is perfectlytrue that there are examples of non-physicalist approaches to theworld — vitalism in biology is perhaps the best example —this is beside the point. The second premise of the Argument fromMethodological Naturalism does not deny that other views are possible,it simply says that physicalism is the most likely view at the moment.Finally, one might be inclined to appeal to arguments such as theknowledge argument to show that physicalism is false, and hence thatmethodological naturalism could not show that physicalism is false.However, this suggestion represents a sort of confusion about theknowledge argument. As we saw above, if successful the knowledgeargument suggests, not simply that physicalism is false but that anyapproach to the world that is compatible with methodologicalnaturalism is false. But if that is so, it is mistaken to suppose thatthe knowledge argument gives one any reason to endorseanti-physicalism if that is supposed to be a position compatible withmethodological naturalism.

Bibliography

Alter, T., 2016, ‘The Structure and Dynamics Argumentagainst Materialism’,Noûs, 50(4): 794–815.
Armstrong, D., 1968,A Materialist Theory of the Mind,London: Routledge.
Bacon, J., 1990, ‘Van Cleve Versus Closure’,Philosophical Studies, 58: 239–242.
Baltimore, J., 2013, ‘Stoljar’s Twin-physicsWorld’,Philosophia, 41: 127–136.
Bennett, K., 2003, ‘Why the Exclusion Problem SeemsIntractable and How, Just Maybe, to Tract it’,Noûs, 37(3): 471–497.
–––, 2017,Making Things Up, Oxford:Oxford University Press.
Berkeley, G., 1710,Principles of Human Knowledge,London: Penguin, 2004.
Berker, S., 2018, ‘The Unity of Grounding’,Mind, 127(507): 729–777.
Blackburn, S., 1992, ‘Filling in Space’,Analysis, 50(2): 60–65.
Block, N., 1980, ‘Troubles with Functionalism’, in N.Block (ed.),Readings in the Philosophy of Psychology, Volume1, Cambridge, MA: Harvard University Press, 1980, pp.268–306.
–––, 1995, ‘On a Confusion About aFunction of Consciousness’,Behavioral and BrainSciences, 18(2): 227–287.
Block, N., and Stalnaker, R., 1999, ‘Conceptual Analysis,Dualism and the Explanatory Gap’,Philosophical Review,108(1): 1–46.
Boyd, R., 1980, ‘Materialism Without Reductionism: WhatPhysicalism Does not Entail’, in N. Block (ed.),Readings inthe Philosophy of Psychology Volume 1, Cambridge, MA: HarvardUniversity Press, 1980, pp. 76–106
Braddon-Mitchell, D., and Jackson, F., 1996,Philosophy ofMind and Cognition, Oxford: Blackwell.
Broad, C.D., 1925,The Mind and Its Place in Nature,London: Routledge and Kegan Paul.
Byrne, A., 1993,The Emergent Mind, Ph.D. Dissertation,Philosophy Department, Princeton University.
–––, 1999, ‘Cosmic Hermeneutics’, inJ. Tomberlin (ed.),Philosophical Perspectives, 13:347–83.
Carnap, R, 1932/33 ‘Psychology in Physical Language’,in A.J. Ayer (ed.),Logical Positivism, New York: The FreePress, 1959, pp. 165–198.
Chalmers, D., 1996,The Conscious Mind, New York: OxfordUniversity Press
–––, 1999, ‘Materialism and theMetaphysics of Modality’,Philosophy and PhenomenologicalResearch, 59: 473–493.
–––, 2002,Philosophy of Mind: Contemporaryand Classical Readings, New York: Oxford University Press
–––, 2002a, ‘Consciousness and its Placein Nature’, in Chalmers 2002, pp. 102–142.
–––, 2015, ‘Panpsychism andPanprotopsychism’ in T. Alter and Y. Nagasawa (eds.),Consciousness in the Physical World: Perspectives on RussellianMonism, New York: Oxford University Press, pp. 246–276..
–––, 2020, ‘Spatiotemporal functionalism v.the Conceivability of Zombies’,Noûs, firstonline 28 April 2020. doi:10.1111/nous.12331
Chomsky, N., 1994b, ‘Noam Chomsky’, in S. Guttenplan(ed.),A Companion to the Philosophy of Mind, Oxford:Blackwell, pp. 153–167.
–––, 1995, ‘Language and Nature’,Mind, 104(413): 1–61.
–––, 2000,New Horizons in the Study ofLanguage and Mind, Cambridge: Cambridge University Press.
Correia, F and Schneider, B (eds.), 2012,MetaphysicalGrounding: Understanding the Structure of Reality, Cambridge:Cambridge University Press.
Crane, T. and Mellor, D.H., 1990, ‘There is no Question ofPhysicalism’,Mind, 99: 185–206.
Daly, C. 1997, ‘What are Physical Properties?’,Pacific Philosophical Quarterly, 79(3): 196–217.
Dasgupta, S. 2015, ‘The Possibility of Physicalism’,Journal of Philosophy, 111: 557–592.
Davidson, D. 1970 . ‘Mental Events’, in D. Davidson,Essays on Actions and Events, Oxford: Oxford UniversityPress, pp. 207–223.
Descartes, R., 1641,Meditations on First Philosophy, inCottinghamet al. (eds.),The Philosophical Writings ofRene Descartes, Cambridge: Cambridge University Press, 1985.
Dijksterhuis, E.J., 1961,The Mechanization of theWorld-Picture, Oxford: Clarendon.
Dowell, J.L., 2006a, ‘Formulating the Thesis ofPhysicalism’,Philosophical Studies, 131(1):1–23.
–––, 2006b, ‘Physical: Empirical notMetaphysical’,Philosophical Studies, 131(1):25–60.
Elpidorou, A., 2018a, ‘Introduction: The Character ofPhysicalism’,Topoi: An International Review ofPhilosophy, 37(3): 435–455.
––– (ed.), 2018b, ‘Special Issue: TheCharacter of Physicalism’,Topoi: An International Review ofPhilosophy, 37(3).
Feigl, H., 1967, ‘The “Mental” and the“Physical”’, Minneapolis: University of MinnesotaPress, 370–497.
Feinberg, G., 1966, ‘Physics and the Thales Problem’,Journal of Philosophy, 63: 5–16.
Field, H., 1972, ‘Tarski’s Theory of Truth’,Journal of Philosophy, 69: 347–75.
–––, 1992, ‘Physicalism’, in J.Earman (ed.),Inference, Explanation and Other Frustrations,Berkeley: University of California Press, pp. 271–292.
Fine, K., 1994, ‘Essence and Modality’, in JamesTomberlin (ed.)Philosophical Perspectives 8: Logic andLanguage, 1: 1–16.
–––, 2001, ‘The Question ofRealism’,Philosophers’ Imprint, 1:1–30.
Fiorese, R., 2016, ‘Stoljar’s Dilemma and ThreeConceptions of the Physical: A Defence of the Via Negativa’,Erkenntnis, 81: 201–229.
Fodor, J.A., 1974, ‘Special Sciences: Or, The Disunity ofScience as a Working Hypothesis’, reprinted in J. Fodor,Representations, Cambridge, MA: MIT Press, 1981.
–––, 1992,A Theory of Content and OtherEssays, Cambridge, MA: MIT Press
Foster, J., 1982,The Case for Idealism, London:Routledge
–––, 1991,The Immaterial Self: A Defence ofthe Cartesian Dualist Conception of Mind, London: Routledge.
Gendler, T. and Hawthorne, J., 2004,Conceivability andPossibility, Oxford: Oxford University Press
Gillet, C. and Loewer, B., 2001,Physicalism and ItsDiscontents, Cambridge: Cambridge University Press.
Goff, P., 2017,Consciousness and Fundamental Reality,New York: Oxford University Press
Haugeland, J., 1983, ‘Weak Supervenience’,American Philosophical Quarterly, 19: 93–103.
Hawthorne, J., 2002, ‘Blocking Definitions ofMaterialism’,Philosophical Studies, 110(2):103–113
Hellman, C., 1985, ‘Determination and Logical Truth’,The Journal of Philosophy, 82(11): 607–616.
Hempel, C. 1949, ‘The Logical Analysis of Psychology’,in H. Feigl and W. Sellars (eds.),Readings in PhilosophicalAnalysis, New York: Appleton-Century-Crofts, 1949, pp.373–384; reprinted in N. Block (ed.),Readings in thePhilosophy of Psychology, Volume 1, Cambridge: Harvard UniversityPress, 1980, pp. 14–23.
–––, 1969, ‘Reduction: Ontological andLinguistic Facets’, in S. Morgenbesser,et al. (eds.),Essays in Honor of Ernest Nagel, New York: St Martin’sPress, pp. 179–199.
–––, 1980, ‘Comments on Goodman’sWays of Worldmaking’,Synthese, 45:139–199.
Hohwy, J., 1998,Meaning as Use, Ph.D Dissertation,Australian National University.
Horgan, T., 1983, ‘Supervenience and Microphysics’,Pacific Philosophical Quarterly, 63: 29–43.
–––, 1993, ‘From Supervenience toSuperdupervenience: Meeting the Demands of a Material World’,Mind, 102(408): 555–586.
Horwich, P., 2000,Meaning, Oxford: Oxford UniversityPress.
Hyslop, A., 1999, ‘Methodological Epiphenomenalism’,Australasian Journal of Philosophy, 78(1): 61–70.
Jackson, F., 1982, ‘Epiphenomenal Qualia’,Philosophical Quarterly, 32: 127–36.
–––, 1986, ‘What Mary Didn’tKnow’,Journal of Philosophy, 83: 291–5.
–––, 1998,From Metaphysics to Ethics: ADefense of Conceptual Analysis, Oxford: Clarendon.
–––, 1993, ‘Armchair Metaphysics’,in J. Hawthorne and M. Michael (eds.),Philosophy in Mind,Amsterdam: Kluwer, pp. 23–42.
Jackson, F., and Pettit, P., 1992, ‘In Defense ofExplanatory Ecumenism’,Economics and Philosophy, 8:1–21.
Kim, J., 1993,Mind and Supervenience, Cambridge:Cambridge University Press.
–––, 1998,Mind in a Physical World,Cambridge: Cambridge University Press.
–––, 2005,Physicalism, Or Something NearEnough, Princeton: Princeton University Press.
Kripke, S., 1980,Naming and Necessity, Cambridge, MA:Harvard University Press.
–––, 1982,Wittgenstein on Rules and PrivateLanguage: An Elementary Exposition, Oxford: Basil Blackwell.
Lange, F., 1865,A History of Materialism, London:Routledge, 1925.
Latham, N., 2001,‘Substance Physicalism’, in C.Gillett and B. Loewer (eds.),Physicalism and ItsDiscontents, Cambridge: Cambridge University Press, pp.152–171.
Leuenberger, S., 2008, ‘Ceteris AbsentibusPhysicalism’, in D. Zimmerman (ed.),Oxford Studies inMetaphysics, Oxford: Oxford University Press, pp.145–170.
Lewis, D., 1970, ‘How to Define Theoretical Terms’,Journal of Philosophy, 67: 427–46.
–––, 1983, ‘New Work for a Theory ofUniversals’,Australasian Journal of Philosophy, 61(4):343–377.
–––, 1986,On the Plurality of Worlds,Oxford: Blackwell.
–––, 1994, ‘Reduction of Mind’, inS. Guttenplan (ed),A Companion to the Philosophy of Mind,Oxford: Blackwell, pp. 412–431.
–––, 1997, ‘Naming the Colours’,Australasian Journal of Philosophy, 75: 325–342.
Loar, B., 1997, ‘Phenomenal States’, in N. Block,et al. (eds.),The Nature of Consciousness: PhilosophicalDebates, Cambridge, MA: MIT Press.
Lockwood, M., 1989,Mind, Brain and Quantum, Oxford:Basil Blackwell.
Ludlow, P., Nagasawa, Y. and Stoljar, D., 2004,There’ssomething about Mary: Essays on Phenomenal Consciousness and FrankJackson’s Knowledge Argument, Cambridge, MA: MITPress.
Lycan, W., 1996,Consciousness and Experience, Cambridge,MA: MIT Press.
McLaughlin, B., 1992, ‘The Rise and Fall of BritishEmergentism’, in A. Beckermannet al. (eds.),Emergence or Reduction?, Berlin: De Gruyter, pp.49–93.
Maudlin, T., 1996, ‘On the unification of physics’,Journal of Philosophy, 93: 129–144.
Meehl, P.E. and Sellars, W.S., 1956, ‘The Concept ofEmergence’, in H. Feigl and M. Scriven (eds.),TheFoundations of Science and the Concepts of Psychology andPsychoanalysis (Minnesota Studies in the Philosophy of Science:Volume 1), Minneapolis: University of Minnesota Press, pp.239–252.
Melnyk A., 1997, “How To Keep The ‘Physical’ inPhysicalism”,Journal of Philosophy, 94:622–637.
–––, 2003,A Physicalist Manifesto:Thoroughly Modern Materialism, Cambridge: Cambridge UniversityPress
Montero, B., 1999, “The Body Problem”,Noûs,33(2): 183–200.
–––, 2010, “A Russellian Response theStructuralist Argument Against Physicalism”,Journal ofConsciousness Studies, 17(3–4): 70–83.
–––, 2013, “Must Physicalism imply thesupervenience of the mental on the physical?”,Journal ofPhilosophy, 110(2): 93–110.
–––, 2015, “Russellian Physicalism”,in T. Alter and Y. Nagasawa (eds.),Consciousness in the PhysicalWorld: Perspectives on Russellian Monism New York: OxfordUniversity Press, pp. 209–223.
–––, 2017, “Should Physicalists FearAbstracta?”,Journal of Consciousness Studies,24(9–10): 40–49.
Montero, B. and Papineau, D., 2005, “A defense of the ViaNegativa Argument for Physicalism”,Analysis, 65(3):233–237.
Nagel, E., 1961,The Structure of Science, New York:Harcourt, Brace and World.
Nagel, T., 1974, ‘What is it like to be a bat’,Philosophical Review, 4: 435–50.
–––, 1983,The View from Nowhere, NewYork: Oxford.
Nemirow, L., 1988, ‘Physicalism and the Cognitive Role ofAcquaintance’, in W. Lycan (ed.),Mind and Cognition,Oxford: Blackwell, pp. 490–499.
Neurath, O, 1931, ‘Physicalism: The Philosophy of the ViennaCircle’, in R.S. Cohen, and M. Neurath (eds.),PhilosophicalPapers 1913–1946, Dordrecht: D. Reidel Publishing Company,1983, pp. 48–51.
Ney, A., 2008, ‘Physicalism as an Attitude’,Philosophical Studies, 138: 1–15.
Papineau, D., 1996,Philosophical Naturalism, Oxford:Blackwell.
Paull, R. C., and Sider, T., 1992, ‘In Defense of GlobalSupervenience’,Philosophical and PhenomenologicalResearch, 52: 833–854.
Poland, J., 1994,Physicalism: The PhilosophicalFoundations, Oxford: Clarendon.
Putnam, H., 1975, ‘Philosophy and our mental life’, inH. Putnam,Mind, Language and Reality: Philosophical Papers,Volume 2, Cambridge: Cambridge University Press, pp. 291–303.
Rabin, G., 2020, ‘Fundamentality Physicalism’,Inquiry, first online 02 Jan2020. doi:10.1080/0020174X.2019.1688177
Rosen, G., 2010, ‘Metaphysical Dependence: Grounding andReduction’, in B. Hale and A. Hoffman (eds.),Modality:Metaphysics, Logic and Epistemology, Oxford: Oxford UniversityPress, pp. 109–36
Russell, B., 1917, ‘On the Notion of Cause’, in B.Russell,Mysticism and Logic, London: Penguin, 1963, pp.180–208.
–––, 1927,The Analysis of Matter,London: Kegan Paul.
Ryle, G., 1949,The Concept of Mind, London:Routledge.
Schaffer, J., 2003, ‘Is There a Fundamental Level’,Noûs, 37(3): 298–517
–––, 2009, ‘On What Grounds What’,in D. Chalmers, D. Manley, R. Wasserman (eds.),Metametaphysics, New York: Oxford University Press,pp. 247–383
–––, 2016, ‘Ground Rules: Lessons fromWilson’, in K. Aizawa and C. Gillett (eds.),ScientificComposition and Metaphysical Ground, London: Palgrave, pp.143–70.
Schiffer, S., 1987,Remnants of Meaning, Cambridge, MA:MIT Press.
Schneider, S., 2017, “Does the Mathematical Nature ofPhysics Undermine Physicalism?”,Journal of ConsciousnessStudies, 24(9–10): 7–39.
Searle, J., 1992,The Rediscovery of the Mind, Cambridge,MA: MIT Press.
–––, 1998,Mind, Language and Society:Philosophy in the Real World, New York: Basic Books.
Shoemaker, S., 1994, ‘Phenomenal Character’,Noûs, 28: 21–38.
–––, 2007,Physical Realization,Oxford: Oxford University Press.
Smart, J.J.C., 1959, ‘Sensations and Brain Processes’,reprinted in D. Rosenthal (ed.),Materialism and the Mind-BodyProblem, Indianapolis: Hackett, 1987.
–––, 1978, ‘The Content ofPhysicalism’,Philosophical Quarterly, 28:239–41.
Smith, M., and Stoljar, D., 1998, ‘GlobalResponse-Dependence and Noumenal Realism’,The Monist,81(1): 85–111.
Stanley, J., and Williamson, T., 2001, ‘Knowing How’.Journal of Philosophy, 98: 411–444
Stalnaker, R., 1996, ‘Varieties of Supervenience’,Philosophical Perspectives, 10: 221–241.
Steward, H., 1996,The Ontology of Mind, Oxford:Clarendon.
Stoljar, D., 1996, ‘Nominalism and Intentionality’,Noûs, 30(2): 261–281.
–––, 2000, ‘Physicalism and the NecessaryA Posteriori’,Journal of Philosophy, 97(1):33–54.
–––, 2001, ‘Two Conceptions of thePhysical’,Philosophy and Phenomenological Research,62: 253–281.
–––, 2001a, ‘The Conceivability Argumentand Two Conceptions of the Physical’,PhilosophicalPerspectives, 15: 393–413.
–––, 2010,Physicalism, New York:Routledge.
–––, 2015,‘Lewis on Experience andMaterialism’, in B. Loewer and J. Schaffer (eds.),ACompanion to David Lewis, Oxford: Wiley-Blackwell,pp. 519–532.
–––, 2020, ‘Chalmers v Chalmers’,Noûs, first online 29 April2020. doi:10.1111/nous.12334
Stroud, B., 1986, ‘The Physical World’,Proceedings of the Aristotelian Society, 87:263–277.
Tiehen, J., 2018, ‘Physicalism’,Analysis,78: 537–551.
Van Cleve, J., 1990, ‘Supervenience and Closure’,Philosophical Studies, 58: 225–283.
Van Fraassen, B., 2002,The Empirical Stance, New Haven:Yale University Press.
Weisberg, M., 2013,Simulation and Similarity: Using Models toUnderstand the World, Oxford: Oxford University Press.
Williams, B., 1985,Ethics and the Limits of Philosophy,London: Fontana.
Wilson, J., 1999, ‘How Superduper does a PhysicalistSupervenience need to be?’,Philosophical Quarterly,49: 33–52.
–––, 2005, ‘Supervenience-basedformulations of Physicalism’,Noûs, 39(3):426–459.
–––, 2006, ‘On Characterizing thePhysical’,Philosophical Studies, 131:61–99.
–––, 2010, ‘What is Hume’s Dictumand Why Believe it’,Philosophy and PhenomenologicalResearch, 80: 595–637.
–––, 2011, ‘Non-reductive Realization andthe Powers-based sub-set strategy’,The Monist, 94:121–154.
–––, 2014, ‘No work for a Theory ofGrounding’,Inquiry, 57: 1–45.
Witmer, D.G., 2017, ‘Platonistic Physicalism withoutTears’,Journal of Consciousness Studies,24(9–10): 72–90.
–––, 2018, ‘Physicality forPhysicalists’,Topoi, 37(3): 457–472.
Yablo, S., 1992, ‘Mental Causation’,ThePhilosophical Review, 101: 245–280.
–––, 1999, ‘Concepts andconsciousness’,Philosophy and PhenomenologicalResearch, 59: 455–464.
Yolton, R., 1983,Thinking Matter, Minneapolis:University of Minnesota Press.

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Acknowledgments

The author would like to thank Hossein Ameri, Tim Bayne, Rich Cameron,Brian Garrett, Robert Pasnau, Stewart Saunders, Jessica Wilson, andparticularly David Chalmers for their help in constructing this entry.In addition, the author and editors would like to thank two readers,Joshua R. Stern and Greg Stokley, for discovering numeroustypographical errors on an earlier version. Their volunteer effortswere entirely unsolicited and very much appreciated.

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