Alhassanain(p) Network for Heritage and Islamic Thought

Alhassanain (p) Network for Islamic Heritage and Thought

The Dependence of Objects on Structure: Tailoring our Metaphysics to Fit the Physics

[1]

Steven French

Dept. of Philosophy

University of Leeds

www.alhassanain.org/english

Table of Contents

Abstract 3

1. Introduction 4

2. Meshing, Humility and Structural Realism 7

3. Dependence and Elimination 9

4. Eddington’s Two Tables and the Elimination of Everyday Objects 11

5. Metaphysical Manoeuvres 16

6. Ontic Structural Realism and the Elimination of Particles (as Objects) 23

7. Bringing Back the Bundle 25

Conclusion: Back to Composition 31

References 35

Notes 38

Abstract

The composition of objects is a much discussed issue in metaphysics. In this paper I look at various approaches to this issue in the context of two examples: the relationship between ‘everyday’ objects, such as tables, and their constituent physical entities, and the relationship between structures and objects, from the perspective of structural realism. My aims are first, to defend forms ofeliminativism in both cases, whereby one can still make statements about the entities to be eliminated (tables and objects, respectively); and second, to highlight some of the metaphysical moves that are available to thestructuralist in articulating their ontology. In doing so I hope also to indicate how metaphysics and the philosophy of science can be brought into a more productive relationship.

1. Introduction

The relationship between composite objects and their constituents can be approached from both physical and metaphysical directions. Some will insist on the priority of one such approach over the other but one of my aims in this paper is to urge that we need both to fully understand the nature of this relationship. In particular I will suggest that metaphysics presents a range of useful tools and techniques that we can pull down off the shelf, as it were. In this way I hope to contribute to a fuller appreciation of the inter-relationships between science, metaphysics and the philosophy of science, following recent suggestions byCallender (forthcoming),Chakravartty (2010), Hawley (2006a) and others.

The particular ontological standpoint from which I shall consider the above relationship is that of ‘ontic structural realism’ (OSR). This is a view which, it has been argued, meshes significantly with modern physics (Ladyman 1998; French andLadyman 2003;Ladyman and Ross 2007;Rickles et. al. 2006). My claim is that this will help shed new light on the compositional relationship and in that light I shall then examine the similarities between OSR and certain metaphysical accounts of objects that have recently been put forward, such as so-called ‘blobjectivism ’ andMereological Bundle Theory (MBT).

Let me begin then with a quick sketch of the composition of objects from a metaphysical perspective.

Part, Whole and Composition

Famously, vanInwagen approaches this issue in terms of three questions:

The General Composition Question (GCQ): Whatis composition?

The Special Composition Question (SCQ): In which cases is it true ofcertain objects thatthey compose something?

The Inverse Composition Question (ICQ): In which cases is it true ofan object that there are objects that composeit? (Inwagen 1990, pp. 39-48)

According to Hawley, GCQ has been comparatively neglected, following vanInwagen’s own suggestion that there is no way of answering it. However she points out that the criteria for a satisfactory answer to his question appear to be much stricter than for the other two and that by relaxing these requirements we may yet learn something interesting about composition (Hawley 2006b). What is required as an answer is a ‘principle of composition’ of the form ‘thex s composey iff ....’., where what follows theiff is a sentence containing nomereological terms. However, Hawley points out that ‘VanInwagen demands that an answer to the GCQ be not only a necessary truth but also something like a conceptual truth, to which counterexamples are inconceivable.’ (p. 5)That this is the case seems clear from vanInwagen’s consideration of a putative answer that he himself puts forward:

Thex s composey iff no two of thex s occupy overlapping regions of space andy occupies the sum of the regions of space occupied by thex s .

This fails, he thinks, because a counterexample is conceivable: he suggests that asceptic could insist that they could imagine an object which is not one of the things that thex s compose but which occupies the sum of the regions of space occupied by them. This is not the case for answers to either SCQ or ICQ, where thebiconditionals must be necessary truths but needn’t be conceptual truths. By relaxing vanIwagen’s requirement, Hawley maintains, we can open up some logical space for informative answers to GCQ, in the form of ‘a principle of composition which does not achieve a non-mereological analysis of ‘composition’ but which is nevertheless metaphysically necessary.’ (p. 6) Indeed, we might go further and drop the requirement that the answer be a necessary truth[2] . Doing so allows for different principles of composition for different kinds of things, by analogy with different criteria of identity (Hawley ibid.).

This analogy is worth pursuing a little because it reveals what may be seen as a fundamental flaw with contemporary metaphysics. Thus Hawley notes that just as with a principle of composition, a criterion of identity is abiconditional with an identity claim on the left, and a correlated condition on the right. And just as conceivability can be allowed to undermine answers to GCQ, so in the case of the proposal that Leibniz’s Law and the Principle of Identity ofIndiscernibles jointly constitute a necessarily true criterion of identity, so someone could always say, ‘I think I can imagine two objects which share all their properties and yet are distinct’. The way forward, Hawley argues, is to allow both principles of composition and criteria of identity to be sort-relative. And of course, in the former case, such principles may vary both with the sort of object that is composed and the sort of objects doing the composing. Thus, to use an example I shall come back to later, a table might be said to have both legs and elementary particles as parts, but we might expect the relationship between legs and table to be different from that between particles and table (Hawley uses the example of a cat).

Hawley herself puts thissortal -relative notion of composition relation to work in an analysis of the classic example of the statue and the lump of clay but what is important for my purposes are two features of her discussion. First, as I indicated above, the stringent demand for conceivability-proof criteria of composition is revelatory of the problematic state of contemporary metaphysics. Such a demand and that of necessary truths immediately puts it in a difficult relationship with contemporary physics, since any metaphysical principles will have to be immune from contact with the relevant physical ones. (Of course, we do not need to go to the extremes of conceivability to rule out even vanIwagen’s own attempted answer to the GCQ: a light beam may be said to be composed of photons, yet photons do not ‘occupy’ (in the standard sense) regions of space.) Following Hawley’s analogy with identity, we might recall Hacking’sdefence of the Principle of Identity ofIndiscernibles through the admonition that bland metaphysical assertion of putative counter-examples was not enough (Hacking 1975). Hacking’s point was that we should not take the Principle to be undermined by conceiving of a world with, say, two indiscernible iron globes, since if such a conception is regarded in an appropriately robust manner (and this is contentious of course) it will include an appropriatespatio -temporal background, the inclusion of which effectively blocks the attempt to refute the Principle (unfortunately the specific way in which Hacking includes such a background fails). Blocking such bland assertions, or restraining conceivability, allows room for the development of metaphysical principles – of both composition and identity – that mesh with our physical picture of the world, even if they do not count as conceptual truths.

Secondly, as Hawley concludes, recognition that there might be a variety of compositional relations, each appropriate for particular sorts of objects, say, itself provides a new tool for metaphysics, and for metaphysically informed philosophy of physics. Even if one concludes that from the perspective of OSR composition might not be the right way to go, this is an important conclusion that is echoed byLadyman and Ross in their now classic excoriation of contemporary metaphysics:

‘It [the general composition relation] is supposed to be the relation that holds between the parts of any whole but the wholes [typically considered] are hugely disparate and the composition relations studied by the special sciences aresui generis . We have no reason to believe that an abstract composition relation is anything other than an entrenched philosophical fetish.’ (Ladyman and Ross 2007, p. 21)

Thus we might expect that in different scientific contexts, different composition relations will hold.

Before we move on to consider the kind ofstructuralist stanceLadyman and Ross adopt, however, there is a further issue to consider. In his discussion of SCQ, vanInwagen also sets out two desiderata that answers must satisfy, which I shallcharacterise as follows (ibid. p. 18):

Unitarity : the answers should be general and systematic;

Meshing: the answers should yield an ontology that conforms reasonably well to pre-theoretic and scientific beliefs.

In their recentdefence of ‘austere realism (which I shall be returning to below),Horgan andPotrc (2008), insist that ‘unitarity ’ should trump ‘meshing’, on the grounds that ‘… a metaphysical theory should keep to a minimum the unexplained facts that it posits.’ (p. 18) By analogy with physics, a metaphysical explanation of how certain objects compose others should ‘bottom out’ in general and systematic laws, rather than specific compositional facts that are themselves inexplicable. In particular it cannot be the case that there is ‘… a body of specific compositional facts that are collectively disconnected and unsystematic and are individually unexplainable.’(ibid., p. 19). This ontological arbitrariness would not be a result of Hawley’sprogramme but if metaphysics is to be appropriately naturalistic, it must allow for non-unitary and possiblysui generis answers to composition questions, asLadyman and Ross suggest[3] .

2. Meshing, Humility and Structural Realism.

Prioritising ‘meshing’ overunitarity might satisfy our naturalist hankerings (cf Ladyman and Ross’s ‘Principle of Naturalistic Closure’; op. cit.) but it faces a well-knownproblem, that of theunderdetermination of metaphysics by physics. An example of this arises in precisely the context that Hawley introduces as an analogy with composition, namely issues of identity in physics. Here two metaphysical packages are equally natural in the quantum context, namely that which regards quantum objects as individuals and that which takes them to be non-individuals (French and Krause 2006). This is an example of the presentation of an array of metaphysical ‘facts’ about which we can have no knowledge and towards which we are urged to adopt an attitude of ‘metaphysical humility’ (Langton ref). An obvious response is to adopt a less humble stance by eliminating from our adopted ontology as many of such facts as we can, and my claim (defended elsewhere; French forthcoming), is thatOntic Structural Realism is more effective in this regard than other current forms of realism.

There has already been a lot written about OSR (for a recent summary see French andLadyman forthcoming) so I here I will only sketch the position.

Structuralism in general can becharacterised in this context as urging a shift in ontological focus from objects to structures. It has a long history, entwined with that of twentieth century physics and is exemplified in the works ofDuhem ,Poincaré , Cassirer, Russell,Eddington , and Born, among others. It is multiply motivated, with the two most significant being the desire to overcome the Pessimistic Meta-Induction, or, more generally, to address the problem of theory change byfocussing on the commonalities offered by the relevant structures presented by the theories; and the concern to respond to the metaphysical implications of modern physics, and, for example, undercut the above example of metaphysicalunderdetermination , by adopting a structure oriented ontology.

Famously this view comes in two forms, which can be expressed in slogan form as follows:

Epistemic Structural Realism (ESR): All that weknow is structure

This form maintains a form of agnosticism about the ‘objects’ that are assumed to exist ‘behind thestructure ( see Worrall 1989; recent ref?) and in doing so retains considerable humility (French forthcoming).

Ontic Structural Realism (OSR): All that thereis , is structure

This urges areconceptualisation of physical objects via structure and acharacterisation of that structure via the resources deployed in physics such as group theory (Ladyman 1998; French andLadyman 2003;Ladyman and Ross 2007; French 2006). It also comes in two variants:

Eliminativist OSR: as the name suggests this attempts to eliminate objects entirely, infavour of the appropriate structures, so that at best putative ‘objects’ come to be seen as mere ‘nodes’ in the structure or as dependent upon that structure (I shall be touching on this notion of dependence below).

Non-Eliminativist OSR: this incorporates a ‘thin’ notion of object, whose identity is given contextually via the relations of the structure. Thus Saunders has developed a notion of ‘weakdiscernibility ’ along these lines that is applicable to fermions (Saunders 2006); its extension to bosons by Muller andSeevinck is more contentious (Muller andSeevinck 2009; seeLadyman andBigaj 2010 for a useful discussion of the issues).

These positions have been much discussed and I shall not run through the criticisms or the responses here (see French andLadyman forthcoming). Both offer a stance that is less humble that either Worrall’s or other forms of realism, and both offer new insights into the compositional relationships assumed to hold between certain physical entities (see alsoLadyman , this volume). Let us now begin to consider these relationships in the context of exploring answers to the following questions: What is the relationship between everyday objects and the entities posited by physics? And: What is the relationship between those entities and the structure towards which the advocate of OSR adopts his realist stance?

3. Dependence and Elimination

Consider, as an exemplar of an ‘everyday’ object, the table at which I am sat. An obvious answer to the first of the above questions in this case would be to say that the table is somehow dependent upon the relevant assembly of physical entities (whether these are taken to be particles, fields, strings or whatever). However, asCorreia notes, in his useful survey (2008), the term ‘dependence’, as deployed in metaphysics, covers a whole family of properties and relations. Broadly speaking, it is typically taken to denote some form of ‘non-self-sufficiency’:

‘A dependent object … is an object whose ontological profile, e.g. its existence or its being the object that it is, is somehow derivative upon facts of certain sorts – be they facts about other particular objects or not.’ (ibid., p. 1013)

One can then distinguish two forms: existential and essential dependence (ibid; Lowe 2005). Existential dependence obtains when the existence of the object requires that a condition of a certain sort be met; essential dependence obtains where the object would not be the object that it is had a condition of a certain sort not been met (Correia op cit., p. 1014).

Taking existential dependence first, its denial captures the following intuition:

object a could have existed even if objectb did not

and if this is the case, we can say thata is ontologically independent ofb . Thus my table could have existed even if the chair on which I am sitting did not, and in this sense is independent of it. However, my table could not have existed if its constituent particles/fields/strings/whatever did not, and in this sense is existentially dependent upon them (ibid., p. 1015). The relevant modality here is understood as metaphysical, rather than logical or conceptual, and one can read the sense of dependence here in terms of ‘rigid necessitation’, so that the table rigidly necessitates its specific constituent particles.Sortal considerations enter with ‘generic necessitation’, in the sense that my table generically necessitates the existence of fermions.

Similar considerations apply to essential dependence, so one can distinguish ‘rigid essential involvement’, such that, for some relation, x is essentially related by that relation to y, and ‘rigid essential necessitation’, whereby x is essentially such that it exists only if y does (ibid., p. 1017), together with their generic counterparts. Leaving aside concerns as to the relationship between existential and essential dependence (ibid.), a further useful notion here is that of ‘explanatory dependence’, in forms such as ‘ifx exists, then this is in virtue of the existence ofy ’ and ‘ifx exists, then this is in virtue of some feature ofy ’ (ibid., p. 1020).

Returning now to the initial idea that dependence involves non-self-sufficiency, not all of the notions of dependence currently in play possess the appropriate feature of derivative-ness , or fundamentality. So, x rigidly necessitating y does not imply that the existence of x is derivative upon or less fundamental than that of y, for rigid necessitation is not asymmetric (ibid., p. 1023). Thus, take Socrates and his life, for example: Socrates’ life depends on the existence of Socrates and vice versa, yet Socrates and his life are not identical since they each possess properties (weighing so many kg, being so many years long) that the other does not (Lowe 2005). Moving to the essentialist notion and that of explanatory dependence may help, because if the obtaining of y is essential to x, then the identity of x may be said to be derivative upon y, and likewise, if the existence of x is objectively explained by y, then the existence of x is less fundamental than y (Correia op. cit., p.1023). Thus if the solidity of my table is explained by the Pauli Exclusion Principle, or, more fundamentally, the anti-symmetry of the relevant wave-functions and the role of Permutation Invariance, then the existence of that solidity can be said to be less fundamental than, or derivative upon, those features associated with symmetry. More generally, we might capture the asymmetry involved here by asserting thatx is dependent upony, iff the identity ofx is dependent on the identity ofy (Lowe 2005).

As we shall indicate later, the notion of essential dependence, with its articulation in terms of identity, can be usefully applied in thestructuralist context. Sticking with tables for the moment, an obvious issue is whether the dependence of the table on its constituent physical entities entails the elimination of the table as an element of our ontology. In general terms, the answer is surely not, since we can imagine two things as being dependent upon one another without either being eliminated infavour of the other. Indeed, asCorreia has noted above, x existentially rigidly necessitating y does not entail that x should be eliminated infavour of y. However, in the case of explanatory dependence, if all the facts about x hold in virtue of and are explained by facts about y, then we can certainly mount a case that x is at best derivative upon y, or may even be eliminable infavour of y. A similar conclusion can be pushed from the claim that x essentially rigidly necessitates y so that the identity of x is dependent upon y. Not surprisingly perhaps, these conclusions have been resisted and in what follows I shall consider two examples of this resistance – one historical, one current – in order to indicate how one might respond to them in a way that is relevant to our overall discussion.

4.Eddington’s Two Tables and the Elimination of Everyday Objects

When it comes to tables, we have been here before, of course, with the famous case ofEddington and his ‘two tables’. In the introduction to his popular exposition, based on his Gifford lectures (1928), he compares the ‘commonplace’ table which has extension, iscoloured and ‘above all’ is substantial, with the ‘scientific’ table, which is mostly empty and is not substantial at all (ibid., pp. xi-xiii). It is the latter that is ‘really there’, whereas the former is an illusion (ibid., p. 323). Presented thus, this seems a standard example of the presentation of scientificeliminativism . This is certainly howStebbing views it in her dismissal ofEddington’s claims as ‘preposterous nonsense’ (1937, p. 54). Her core objection is that the object of scientific descriptions is not the ‘table’, as this term is used in common discourse, and thus there cannot be two tables, with one granted ontological priority over the other. Furthermore, the ‘scientific’ cannot duplicate, and consequently replace, the everyday, since the properties of the latter, such ascolour , cannot be duplicated via entities that do not possess such properties.

Now,Stebbing is certainly right in pointing out thatEddington’s language and lack of training in philosophy does not help his case. More importantly, his articulation of the relationship between ‘everyday’ objects and the entities we should take as fundamental is less than clear in the passages she considers. Nevertheless, a more charitable reading would have filtered out the rhetoric deployed in the service of a set of public lectures and perhaps pulled together arguments and claims from acrossEddington’s works, both scientific and popular, in order to produce a (more) rational reconstruction of his position. Two aspects of these works might then have become clear. The first is that like many who have sought a radical ontologicalreconceptualisation ,Eddington struggles to find a language that is not corrupted by the very ontology he is trying to replace. The cost of constructing such a language is evident in the difficulty one encounters in trying to understand his final work which attempted to construct a form of quantum gravity (1946). This ontology that he is trying to get away from is one of things and, in particular, substances. This brings us to the second aspect, which isEddington’s structuralism, something thatStebbing fails to grasp (see French 2003)[4] . The crucial feature of ‘everyday’ objects thatEddington wants to eliminate from our ontology is their substantiality and, as with otherstructuralists of the time, such as Cassirer, his structuralism can becharacterised in those terms. How one expressed that elimination was a central problem forEddington but it can be understood as an appropriatelycontextualised version of the issue we are facing here, namely how tocharacterise and represent the relationship between ‘everyday’ objects and the underlying structures that physics presents to us.

Stebbing’s attack has been taken up again more recently byThomasson (2007) who defends an ontology of ordinary objects againsteliminativist arguments. She explicitly addresses the impact of science on such an ontology, identifying two forms of this impact (ibid., Ch. 7): according to one, associated withEddington , science and the ‘everyday’ are in conflict; according to the other, associated withSellars , they are merely rivals. With regard to the first, there can be only conflict if the two sides are talking about the same thing.[5] However, here again,sortal considerations enter the picture asThomasson argues that reference to things is fixed via some categorical framework. Hence, she maintains that,

‘… scientific theories … do not usesortals such as ‘table’, and if science and common sense are usingsortals of different categories, the ‘things’ picked out by the two descriptions cannot be identical.’ (Thomasson 2007, p. 142)

One might try to present the conflict in terms of some neutral sense of ‘thing’ but ‘thing’ in that sense would not then be asortal term and could not be used to establish reference. Or one could appeal to a common notion of ‘physical object’ or ‘occupant of aspatio -temporal region’, but, she argues, the first finds no place within physicsitself , and the second is hardly common in everyday descriptions. Hence there is no conflict between science and ordinary discourse: both have their distinctontologies .

With regard to theSellarsian view of a rivalry between the ‘scientific image’ and the ‘manifest image’, in which the former has primacy over the latter,Thomasson again argues that any account of what there is presupposes a certainsortal framework. Such accounts can only offer a complete description in terms of that framework in the sense of covering all the things in those categories. However, the scientific and manifest images presuppose differentsortal frameworks and hence cannot be complete in any way that renders them rivals (ibid., p. 148). Consequently, acceptance of the scientific image does not require rejection of the ontology of the manifest.

Eddington’s position is also undermined, according toThomasson , not least because on astructuralist interpretation, there is a ‘… lack of conflict between the merely structural properties physics imputes to the world and the qualitative content involved in ordinary world descriptions.’(ibid., p. 139). Now, the distinction between structure and content is one that has arisen repeatedly in discussions over structural realism but it evaporates as far as theontic form is concerned, since all relevant content is taken to be cashed out in structural terms. Insofar as the ‘qualitative content’ thatThomasson refers to goes beyond this, it becomes part of the more general issue having to do with the relationship between the scientific and the ‘everyday’.

Here a number of concerns arise, not the least being thatThomasson’s account creates a vastly inflationary ontology. Let me be clear about this: it is not thatThomasson is claiming that ordinary objects are somehow derivative; rather, they count as metaphysically robust elements of our ontology, just as elementary particles are. As a result her metaphysics is entirely detached from the relevant physics, since the latter incorporates an assortment of physical relations that hold between, for example, protons, neutrons andelectons , atoms and molecules, molecules and polymers and so on. One option for the kind of naturalistic approach indicated previously is to explore the possibility of meshing the metaphysics with the physics by constructing metaphysical relations that effectively track the physical ones; another, as we shall see, is to radically reconfigure the relevant ontology so as to remove the necessity for positing certain such relations. Either way, we keep the metaphysics and physics in touch with each other, as it were, rather than cleaving them entirely apart asThomasson does.

A further major worry has to do with the central role played bysortal frameworks in her view[6] . First of all, it is also worth noting the difficulty involved in constructing such a framework in the quantum context, particularly if one adopts the view of quantum particles as non-individuals (French and Krause 2006b). Of course, this may be taken as further fuel forThomasson’s position, since if the relevant frameworks are so different, not just in terms of the kinds of things they cover, but in terms of their underlying metaphysics and even logic, then how can then be said to rival or compete with one another? However efforts are being made to relate the two kinds of framework and attempts to construct a form of ‘quantummereology ’ can be seen as contributing to the establishment of an appropriate relationship. If these efforts are successful then one might regard this as bringing the logic and metaphysics into line with the physics, insofar as the explanations of the latter can be taken to relate the frameworks concerned.

The issue then is whether the establishment of such a relationship effectively guts the ontology of the ‘manifest’ framework by reducing it to the scientific. Consider a general metaphysicalcharacterisation of such relationships in terms of ‘grounding’, say:a is said to be grounded inb in the sense thata holds in virtue ofb , without it being the case that onlyb exists. Thus the ‘fact’ of there being a table in front of me (orEddington ) is grounded in facts about the relevant aggregate of quantum particles in the sense that the former fact holds in virtue of the latter (seeNorth forthcoming, p. 26). Now, explanatory relations such as this crop up elsewhere, of course and offer a broader framework than, say, causal accounts, whilst nottrivialising the relationships as deductive accounts do. However, as we saw in our brief discussion of dependence above, one worry here is that if we take this relation seriously, metaphysically speaking, then the kind of dependence that ‘in virtue of’ signifies effectively evacuates all there is toa infavour of the relevant features ofb . If all there is toa is explained in terms of features ofb , then what is left that has any independent existence? Of course, one might point to standard examples, such as the explanation of the shadow cast by the flagpole in terms of its height, the angle of the sun and some elementary geometry and insist that this does not imply that the shadow does not exist. However – leaving aside issues as to the nature of shadows – this just pushes the issue back a step or two: once I have given the best and most complete explanation available, articulated in terms of quantum field theory perhaps, then what is there to a shadow, as an object in its own right, that is not cashed out in terms of features that are more fundamental?

Talk of ‘facts’ here may actually obscure the issue: granted that the fact expressed in the claim ‘there is a table in front of me’ is a ‘real’, albeit non-fundamental fact (North op. cit.), this does not imply that the table itself should be taken as an element of our ontology. Consider the property thatStebbing focuses on in her critique ofEddington , namely solidity. As already noted, this holds in virtue of the relevant physics as expressed in the Exclusion Principle and, more fundamentally, theantisymmetrisation of the relevant aggregate wave function. In this case one might then insist that the latter feature of quantum mechanics entirely explicates the solidity of everyday objects and in doing so eliminates the predicate from the scope of our fundamental ontology. Of course, as we shall see, one may still utter truths about tables, how solid they are and so on and these truths may be regarded as further facts beyond those that are fundamental, but one can still have all this and deny that the entities exist. I shall return to this point shortly.

There is also an obvious concern here thatThomasson appears to have introduced a form ofsortal relativism into this context. Note that the role ofsortals in her account is different from the role they play in Hawley’s approach: in the latter case, it is the composition relations that are tied to differentsortal frameworks; inThomasson’s case, it is the existence of objects. The latter has obvious problematic implications for realism. This is something that Schaffer takes up in his critical review (2009): the invocation of appropriatesortal concepts is crucial for various aspects ofThomasson’s account but in particular, existence claims appear to besortal relative (ibid., p. 149). This would not only have radical implications for the semantics of existential quantification (ibid.), but would also take her account outside of the broadly realist stance that is being adopted here. However, as Schaffer notes (ibid.),Thomasson attempts to evade this conclusion and retain the standard account of simple quantification while maintaining her radical conclusions about everyday ontology, by arguing that what her account of reference determination viasortal frameworks does is specify thedomain of quantification. Thus, existence claims are only evaluable once an appropriate domain is specified, where that involves specifying or presupposing the relevant sorts of entities involved (Thomasson , op. cit. pp. 464-465).

In response, Schaffer points out (op. cit., p. 150) that althoughsortals can act as perfectly good domainspecifiers , so can properties, for example, and so we don’t need to dally withsortal relativism. But thenThomasson’s defence ofan ontology of ordinary objects would fall apart. Furthermore, Schaffer argues that we can straightforwardly specify the total domain of ‘everything’ and do so in a way that does not involve a non-category-specific sense of ‘thing’ (ibid., pp. 150-151). Again, with the prop ofsortal specificity taken away,Thomasson’s account collapses. And for our purposes here, the latter response allows us to talk of the universal domain, as it were, while the former allows us to talk of putative things belonging to different domains, and the relationships between them, without presupposing asortal framework that, in effect, existentially neuters these relationships. Obviously ‘domain’ here is better understood as ‘level’, so we can now talk of the relationship between the level of ordinary objects, such as tables, and that of elementary particles, without having to accept that the specification of such levels necessarily involvessortals in terms of which distinctontologies must be acknowledged, asThomasson demands. In particular, we can articulate a reductive relationship in terms of which such ordinary objects are eliminated.

Eliminativism about ordinary objects may seem a radical position to adopt[7] but it is one that meshes with our understanding of contemporary physics, according to which there is only a limited number of certain fundamental kinds of elementary particles and four fundamental forces – everything else is effectively composed out of these. I aim to take this picture seriously, in the sense of indicating, in at least a preliminary way, how an appropriate metaphysics might be constructed on this basis[8] .

Now one reason this seems such a radical line to take is that we have considerable everyday experience of tables: we use them in various ways, set chairs around them,bump into them and so on. Thus we face a dilemma: according toeliminativism , tables don’t exist and yet the statement ‘Tables exist’ appears to be true! Indeed, the fact expressed by such a statement might well be taken to be ‘Moorean ’ in the sense that we have better knowledge of it than the premises of any argument that seeks to deny it. In that sense, it trumps any attempt ateliminativism . However, this is a dangerous line to take as it would not simply underminescepticism as in Moore’s ‘here is a hand’ case, but would preclude the possibility of the kind of reductive analysis that physics appears to push us toward.

Let me now briefly sketch different metaphysicalmanoeuvres we candeply to help resolve the above dilemma: