Kerry McKenzie

In this article, I address concerns that the ontological priority claims definitive of ontic structural realism are as they stand unclear, and I do so by placing these claims on a more rigorous formal footing than they typically have been hitherto. I first of all argue that Kit Fine’s analysis of ontological dependence furnishes us with an ontological priority relation that is particularly apt for structuralism. With that in place, and with reference to two case studies prominent within the structuralist literature, I consider whether any of structuralism’s distinctive priority claims may be regarded as warranted. The discussion as a whole has largely negative implications for the radical structuralism of French and Ladyman (including their ‘eliminativist’ interpretation of it), largely positive implications for the moderate structuralism primarily advocated by Esfeld and Lam, and some broad lessons for contemporary fundamentalist metaphysics as a whole. 1 Introduction2 The Right Priority Relation for Structuralism: Supervenience or Dependence?3 Introducing Ontological Dependence4 Fine’s System5 The Priority of Structure 1: Entangled Quantum Particles6 The Priority of Structure 2: The Group-Theoretic Conception of Elementary Particles7 Concluding Remarks

he relationship between metaphysics and science has recently become the focus of increased attention. Ladyman and Ross, in particular, have accused even naturalistically inclined metaphysicians of pursuing little more than the philosophy of A-level chemistry and have suggested that analytic metaphysics should simply be discontinued. In contrast, we shall argue, first of all, that even metaphysics that is disengaged from modern science may offer a set of resources that can be appropriated by philosophers of physics in order to set physics within an interpretational framework. Secondly, however, we shall urge that insofar as metaphysics is intended to be more than just a toolbox it needs to accommodate the implications of physics if many of its core claims are to be sustained. We shall illustrate this last point with a discussion of the nature of laws and modality in the context of modern physics

This paper aims to open up discussion on the relationship between fundamentality and naturalism, and in particular on the question of whether fundamentality may be denied on naturalistic grounds. A historico-inductive argument for an anti-fundamentalist conclusion, prominent within contemporary metaphysical literature, is examined; finding it wanting, an alternative ‘internal’ strategy is proposed. By means of an example from the history of modern physics - namely S-matrix theory - it is demonstrated that this strategy can generate similar anti-fundamentalist conclusions on more defensible naturalistic grounds, and that fundamentality questions can be empirical questions. Some implications and limitations of the proposed approach are discussed.

Ontic structural realism is at its core the view that “structure is ontologically fundamental.” Informed from its inception by the scientific revolutions that punctuated the 20th century, its advocates often present the position as the perspective on ontology best befitting of modern physics. But the idea that structure is fundamental has proved difficult to articulate adequately, and what OSR's claimed naturalistic credentials consist in is hard to precisify as well. Nor is it clear that the position is actually supported by our most fundamental physical theories. What is clear, however, is that structuralists have revealed a seam of material at the core of modern physics that is replete with implications for metaphysics. This article will survey some positions subsumed under the rubric of OSR, considering both their warrant and the interconnections that exist between them. It will be argued that the fundamental kind properties pose a challenge to ontic structuralism, because it seems that these properties do not supervene upon the relevant structures. But it will also be argued that the development of structuralist metaphysics will require both an engagement with the details of modern physical theories and the deployment of tools more typically developed in a priori metaphysics. As such, it seems armchair metaphysicians have not just a stake in whether OSR's claims may ultimately be shown to stand up, but a crucial role to play in getting them to the point where they can be subjected to scrutiny in the first place.

In metaphysics, the fundamental is standardly equated with that which has no explana- tion – with that which is, in other words, ‘brute’. But this doctrine of brutalism is in tension with physicists’ ambitions to not only describe but also explain why the fundamental is as it is. The tension would ease were science taken to be incapable of furnishing the sort of explanations that brutalism is concerned with, given that these are understood to be dis- tinctively ‘metaphysical’ in character. But to assume this is to assume a sharp demarcation between physics and metaphysics that surely cannot be taken for granted. This paper sets out to examine the standing of brutalism from the perspective of contem- porary fundamental physics, together with theories of explanation drawn from philosophy of science and metaphysics. Focusing on what fundamental kinds the world instantiates and how physicists go about determining them, I argue that a partial explanation, in Hempel’s sense, may be given of this fundamental feature. Moreover, since this partial explanation issues, at least in part, from stipulations as to the essential nature of the kinds involved, I claim that it has as much right to be regarded as a metaphysical explanation as do grounding explanations. As such, my conclusion will be that the doctrine of brutalism can no longer be regarded as tenable: at least modulo certain plausible essentialist assumptions, it is no longer the case that no explanation can be given of the fundamental.

A priori metaphysics has come under repeated attack by naturalistic metaphysicians, who take their closer connection to the sciences to confer greater epistemic credentials on their theories. But it is hard to see how this can be so unless the problem of theory change that has for so long vexed philosophers of science can be addressed in the context of scientific metaphysics. This paper argues that canonical metaphysical claims, unlike their scientific counterparts, cannot meaningfully be regarded as ‘approximately true,’ and that this means that the epistemic progress that science arguably enjoys through episodes of theory change cannot be expected to transfer to its metaphysics. What the value of engaging in metaphysics of science before the emergence of a final theory becomes correspondingly unclear.

Ontic structural realism is a thesis of fundamentality metaphysics: the thesis that structure, not objects, has fundamental status. Claimed as the metaphysic most befitting of modern physics, OSR first emerged as an entreaty to eliminate objects from the metaphysics of fundamental physics. Such elimination was urged by Steven French and James Ladyman on the grounds that only it could resolve the ‘underdetermination of metaphysics by physics’ that they claimed reduced any putative objectual commitment to a merely ‘ersatz’ form of realism. Few, however, have joined French and Ladyman either in acknowledging that such underdetermination exists or in attributing to it such drastic consequences. However, an alternative view that physics does sanction objects, albeit merely as ontologically secondary entities, represents a different and seemingly less extreme route to the same conclusion regarding the fundamentality of structure. But since what it means to be ‘ontologically prior’ is itself a vexed philosophical question, a stance must be taken as to how we are to understand priority before its prospects may be evaluated. In an earlier paper, I outlined how Fine’s notion of ontological dependence might be utilized to defend the priority-based approach to structuralism. Since then, however, I have become convinced that that ontological dependence is not a relation of priority after all. As a result, the arguments outlined in that paper stand in need of reassessment. In this work, I consider the prospects for priority-based structuralism when expressed in the idiom of determination. My conclusion will be that it has yet to be vindicated by our best physical theories, owing to the failure of symmetry structures to determine the world’s inventory of fundamental kinds. Nevertheless, the same symmetry considerations point towards there being renewed prospects for eliminativism—an eliminativism, moreover, of more naturalistic appeal than that hitherto associated with OSR. 1Introduction 2Structuralist Strategies 3Defining Ontological Priority: Dependence or Determination? 4Structuralism in the Idiom of Determination 4.1Determining plurality 4.2Determining kind properties 5A Reinvigorated Eliminativism

The view that the fundamental kind properties are intrinsic properties enjoys reflexive endorsement by most metaphysicians of science. But ontic structural realists deny that there are any fundamental intrinsic properties at all. Given that structuralists distrust intuition as a guide to truth, and given that we currently lack a fundamental physical theory that we could consult instead to order settle the issue, it might seem as if there is simply nowhere for this debate to go at present. However, I will argue that there exists an as-yet untapped resource for arguing for ontic structuralism – namely, the way that fundamentality is conceptualized in our most fundamental physical frameworks. By arguing that physical objects must be subject to the ‘Goldilock's principle’ if they are to count as fundamental at all, I argue that we can no longer view the majority of properties defining them as intrinsic. As such, ontic structural realism can be regarded as the most promising metaphysics for fundamental physics, and that this is so even though we do not yet claim to know precisely what that fundamental physics is.

In a recent work, ‘Thinking Outside the Toolbox’, we mounted a qualified defence of analytic metaphysics in the face of ardent criticism. While sympathizing with other philosophers of science in decrying the lack of engagement of metaphysicians with real science when addressing central metaphysical problems, we also wanted to acknowledge the role that analytic metaphysics has played in providing useful tools for naturalistic metaphysicians. This double-edged stance compels us to identify what feature it is that marks out as problematic some, but not all, analytic metaphysics, and this we thought we could do by appeal to something we call here the compatibility principle. It now strikes us, however, that the approach we took in that earlier work is fundamentally unstable. After giving a streamlined presentation of our earlier argument, we will identify where we take the instability to lie. From there we shall make a more nuanced proposal for how naturalistic metaphysicians should regard the work of their analytic counterparts.

The Special Composition Question asks under what conditions a plurality of objects form another, composite object. We propose a condition grounded in our scientific knowledge of physical reality, the essence of which is that objects form a composite object when and only when they are in a bound state – whence our Bound State Proposal. We provide a variety of reasons in favour of a mereological theory that accommodates our Proposal. We consider but reject another proposal, which is quantum-physical in nature: the Entanglement Proposal. We close by responding to Teller’s ‘Suit Objection’.

This paper reflects on the prospects of an effective metaphysics. By analogy with effective physics, an `effective metaphysics' describes non-fundamental ontology in its own terms and independently of those that describe the fundamental level. And an effective metaphysics will be said to have prospects if (i) there are metaphysical truths about non-fundamental ontology out there to be discovered, and (ii) these facts can be known prior to the emergence of a fundamental theory. This question is of whether effective metaphysics has prospects is an important one. For one thing, if it does then many of the criticisms of analytic metaphysicians by naturalistic metaphysics might be tempered, since those criticisms are largely based on the classical presumptions underlying their worldview. But more significantly, if effective metaphysics does not have prospects then the value of engaging in metaphysics prior to a fundamental theory is far from clear. In this paper, I will argue that we should in fact be deeply sceptical about the prospects of effective metaphysics: sceptical about our ability to access metaphysical truths about non-fundamental ontology prior to the emergence of a final theory, and perhaps also about the very idea that there are any such truths out there to be discovered.

A suite of questions concerning fundamentality lies at the heart of contemporary metaphysics. The relation of grounding, thought to connect the more to the less fundamental, sits at the heart of those debates in turn. Since most contemporary metaphysicians embrace the doctrine of physicalism and thus hold that reality is fundamentally physical, a natural question is how physics can inform the current debates over fundamentality and grounding. This Element introduces the reader to the concept of grounding and some of the key issues that animate contemporary debates around it, such as the question of whether grounding is 'unified' or 'plural' and whether there exists a fundamental level of reality. It moves on to show how resources from physics can help point the way towards their answers - thus furthering the case for a naturalistic approach to even the most fundamental of questions in metaphysics.

In recent years there has been an ‘explosion’ of work in metaphysics aimed at articulating ‘levels of reality’ – a structural aspect of the world both suggested and investigated by the sciences. And in that context, the relation of grounding has emerged as the preferred relation with which to connect the levels. This paper argues that we cannot take grounding to be the relation that connects levels, insofar as those levels are described by effective quantum field theories. This is a problem for the grounding theorist, because effective field theory is taken to provide an explanation of why there seem to be levels in physics at all.