Structure and Significance in Metaphysics

Andrew J. Graham 1
  • 1 Department of Philosophy, University of Missouri, Kansas City, USA
Andrew J. Graham

Abstract

This paper discusses recent attempts to defend metaphysics as a worthwhile form of inquiry. According to such views, metaphysics concerns the world’s fundamental structure. I question whether this view can establish that metaphysical disputes are relevant to the rest of our theoretical activities. I take this relevance to be a criterion for whether disputes are worthwhile (or, as I call them, “significant”). I argue that the structure approach is unsatisfactory because appropriately structural disputes need not be worthwhile disputes, and vice versa. So, the structure approach threatens to render metaphysics irrelevant to our broader theorizing, undermining many of its legitimate successes, like the role theorizing about metaphysical modality played in the development of modal logic. Thus these structure-based views provide a poor defense of metaphysics. I then offer an alternative conception of metaphysics as an attempt to understand our most ubiquitous theoretical notions.

Metaphysics has long been the target of criticism in philosophy. From Hume’s critiques down to the logical positivists, the very existence of metaphysics as a field of inquiry has been a point of controversy for many philosophers. In recent times, many philosophers have continued this tradition and metaphysics has attracted new and sophisticated criticisms. At the same time, however, it has also attracted a number of defenders. These defenders argue that metaphysics is a worthwhile form of inquiry and that metaphysical disputes – like those over the existence of composite objects, over the nature of possible worlds, and so on – are not a waste of time.

The most well-known attempts to defend metaphysics appeal to a family of notions that are meant to explain what metaphysics is about and why we should care about it. Such notions include structure, fundamentality, something’s being the case in Reality. Most of these notions also have uses in ordinary contexts, but in this case something more is meant. The rough idea is that metaphysical disputes are about what is fundamental, or the world’s structure, or what is true not simpliciter, but in Reality.

I share the view that metaphysics is a worthwhile form of inquiry, but I do not think this standard line of defense is a promising one. My concern is not the notions of structure or fundamentality themselves but the question of their usefulness in defending metaphysics. Ultimately I will argue that it is a mistake to base one’s defense of metaphysics on such notions. Before that, however, it will help to get clearer on the role they play in such defenses.

Significance and structure

The most detailed view along these lines is Theodore Sider’s account in terms of structure (see Sider 2001, 2009, and 2011). There are other views, but in what follows I will take Sider’s view as representative.1 For Sider, the world has a fundamental structure. The more structural some aspect of the world is, the more eligible it is to supply the meaning (or referent, in some cases though not all) of some expression in our language. The model here is David Lewis’ theory of intentionality and the notion of natural properties it involves (see Lewis 1983 and 1999).2

On Lewis’s theory, there is a primitive distinction between the more and the less natural properties, with the perfectly natural properties at one end of the spectrum.3 Since the distinction is primitive, no definition of naturalness is available, but some basic features are notable: natural properties are non-disjunctive and non-gerrymandered, the sharing of them makes for objective similarities, they determine the causal powers of their bearers and they feature in laws of nature. Green, for instance, is more natural than grue, and negative charge is more natural than both.

Naturalness also functions as a constraint on the interpretation of our language. Meaning, on this view, can be thought of as the result of interpretation that satisfies certain constraints. One constraint is supplied by some version of the principle of charity, which requires that most of our utterances come out true or at least reasonable. The principle can be thought of as requiring that the interpretation of our language respect our usage of language. The other constraint, on Lewis’s view, is eligibility: the more natural some property or object (where the naturalness of objects is a function of the naturalness of their properties), the more eligible it is to stand as the semantic value of some expression. Thus the world itself plays a role in fixing the interpretation of our language, with better interpretations assigning more natural objects and properties as referents. Meaning is the outcome of applying these two constraints which often pull in opposite directions. (The exact details of this metasemantic picture are not essential to Sider’s view. The essential points are just that there be joint-carving meanings and that there be some metasemantic mechanism that can secure those meanings as the semantic values of the terms we use in theorizing. See, for instance, Sider (2011, sec. 3.2)).

Sider adopts this picture but generalizes it beyond properties and objects so that it can be applied to all aspects of our language. Of particular importance is his extension of this idea to logical vocabulary; in particular, to quantifiers and logical connectives. On this view, some interpretations of the existential quantifier are better than others not simply because they better match our usage, but rather because they are more natural. They are metaphysically privileged; they mirror the world’s existential structure. Similarly with other non-referential expressions like the logical connectives “and” and “or.”

On this generalized picture, expressions can be more or less structural, depending on how well they capture the world’s structure or depending on whether they have more or less eligible interpretations. Those that are highly structural can be said to “carve at the joints,” in a metaphor that Sider borrows from Plato. How does one tell whether some expression is structural in this way? The primary indicator is its ideological indispensability. A good indication that some expression is structural is that no fully adequate theory of the world can be formulated without employing that expression. It is, for instance, along these lines that Sider argues that the existential quantifier carves at the joints (as in Sider 2009 and 2011, sec. 9.6). It’s not clear to what extent this provides an independent criterion, since whether we think a theory is fully adequate might itself depend on our views about structure, but it does provide some constraints on whether to regard some expression as structural.

These notions play into the defense of metaphysics in the following way. Disputes are substantive, or deep, to the extent that they are couched in terms that carve at the joints. That is, each dispute can be understood as targeting some particular sentences; if those sentences are structural – if they have a univocal interpretation that is clearly best in terms of eligibility – then the dispute is substantive. On the other end of the spectrum are nonsubstantive disputes whose sentences are open to a number of equally eligible (or equally joint carving) yet incompatible interpretations. These disputes fail to be substantive for they can be resolved in a number of equally good yet incompatible ways. Nonsubstantivity comes in various forms, displaying different shades of conventionality or subjectivity. For instance, in one kind of case the disputed sentences have a single best interpretation but that interpretation is fixed by the principle of charity, or our usage of language, rather than eligibility, or the naturalness of the interpretation. In these cases, the dispute is not truly substantive but there is nonetheless a fact of the matter about which view is correct.

On Sider’s view, many familiar metaphysical disputes are substantive (the expressions they target carve at the joints) and so should be taken seriously. In particular, ontological disputes – those concerning what exists – tend to be substantive, since the existential quantifier carves at the joints. Some aspects of Sider’s picture – in particular the idea that the quantifier might have multiple interpretations, with some more natural than others – can be obscure at first, so it will help to consider an example. For instance, presentists argue that only objects that exist in the present exist at all, while on the other side eternalists defend the idea that past and future objects exist in addition to presently existing objects (they do not, of course, exist now or in the present, but that does not mean they do not exist simpliciter). A common deflationary reaction to this dispute is that both sides are right on some plausible interpretation of their existential claims and so no genuine disagreement remains. When the presentist uses “exist” they should be interpreted as saying something synonymous with “exists now,” as we would ordinarily use that expression. In that case, their claim that only presently existing things exist is obviously true; even the eternalist would agree that only presently existing things exist now. Eternalists, on the other hand, should be interpreted so that “exist” means the same in their mouths as “exists now or did exist or will exist” does in ours. Again, even the presentist would agree that past, present and future things all exist now or did exist or will exist. Given these interpretations of their existential claims, no real disagreement remains, since both positions become obvious trivialities. Any real disagreement hinges on there being a tenseless, atemporal notion of existence, one where it is an open question whether things that exist in that sense all exist in the present or whether some of them exist at times in the past or future. So, there are at least three interpretations of the quantifier in the vicinity: exists now, exists in the past or present or future, and exists simpliciter (where the last notion is tenseless). Here is where Sider’s idea that some interpretations are more natural than others comes into play, for one can argue that the last is more natural than the first two, containing no implicit tenses and being less disjunctive. If so, then the dispute is best understood using that particular interpretation and our initial deflationary reaction is seen to be mistaken.4 Assuming this tenseless quantifier is sufficiently joint-carving, the dispute counts as substantive on Sider’s view.

Call disputes that are substantive or deep on Sider’s view “structural.”5 The question I will investigate is whether being structural suffices for a dispute’s being a worthwhile dispute. It certainly undermines various reasons for doubting that a dispute is worthwhile, reasons that hinge on the dispute’s being non-substantive. But is being structural enough to guarantee that a dispute matters?

To clarify, there are various different things that might count as a defense of metaphysics and various different aspects of metaphysics that one might defend. One kind of question is whether metaphysical disputes are genuine, or factual, or objective, but another is whether they matter or are a waste of time, from the perspective of inquiry. In other words, one might wonder whether metaphysical disputes are worth taking seriously, or paying attention to, or investing time and effort into resolving. These questions are not necessarily the same as those concerning whether metaphysical disputes are genuine, substantive or factual, for many genuine, factual questions are pointless from the perspective of inquiry. For instance, we might, out of sheer fancy, wonder how many blades of grass are on my property and even come to disagree about the correct answer, but generally nothing of interest will hang on the question.

Although Sider’s view was not developed with this question explicitly in mind, it is fair to interpret him as holding that metaphysical disputes (the structural ones, at least) do matter. Consider, for instance, what Sider says in defense of his notion of metaphysical structure:

The goal of inquiry is not merely to believe many true propositions and few false ones. It is to discern the structure of the world. An ideal inquirer must think of the world in terms of its distinguished structure; she must carve the world at its joints in her thinking and language. Employers of worse languages are worse inquirers.

(Sider 2009, 401)

It’s clear that on this picture, structural disputes should matter to ideal inquirers. More generally, a defense of metaphysics which leaves it open to the charge that it is entirely irrelevant to any serious project of inquiry would be a rather disappointing defense.

The question, then, is whether Sider’s account of metaphysics gives us any reason to think that metaphysical disputes matter, regardless of whether they are substantive or deep. To answer this question, we will need to clarify the notion of a dispute’s mattering. Call disputes that do matter “significant” and those that do not “insignificant.” A rough but helpful criterion for distinguishing significant disputes from insignificant disputes is provided by the degree to which the disputes in question are integrated into our general theoretical projects. On this view, significant disputes are those that have consequences for other disputes or lines of research (by, for example, helping us answer other questions, resolve other disputes, or open new lines of inquiry); they are the product of previous inquiry or tensions in our theorizing; they open up new and fruitful theoretical space or lines of research, and so on. Significant disputes are those with appropriate connections to the rest of our theorizing while insignificant disputes are insular, with no clear implications for anything beyond themselves.6

Two virtues of this proposal are that it has very wide application and that it is largely independent of one’s metaphysical views (it does not, for instance, require one to adopt any new metaphysical primitives). On the first point, the proposal is meant to explain why any dispute whatsoever is worthwhile. It does not, in other words, apply only to metaphysical disputes. On the second point, this standard of significance should be intelligible to people with a very wide range of metaphysical and anti-metaphysical views. Demonstrating that a dispute is significant involves demonstrating its relevance for other disputes outside itself; defending the significance of metaphysics, then, requires one to establish connections between metaphysical questions and our other theoretical projects. This standard thus offers us a way of investigating whether metaphysics matters that requires no special treatment of metaphysics and should, in principle, be compelling even to those not initially supportive of metaphysics (and hence suspicious of primitive metaphysical notions like structure).

Although I have a great deal of sympathy for Sider’s view, I do not think that it can provide an effective defense of metaphysics as a worthwhile form of inquiry, given the criterion articulated above. On this understanding, the question becomes: is there any connection between a dispute’s being structural and its being significant, and vice versa? I will argue that there is no good reason to think there is any such connection.

If correct, this result raises a serious problem for any defense of metaphysics along the lines that Sider provides. Simply arguing that certain disputes concern the world’s structure, or concern what is metaphysically fundamental, is dialectically disappointing, unless there is some reason to think that such issues matter for our broader theoretical projects. Someone initially skeptical will find this little reason to care about such disputes. A more compelling defense would show that such disputes cannot simply be ignored because they are relevant to other questions that even someone working outside of metaphysics could be interested in. For that reason, a lack of connection between structure and significance would leave the defense in terms of structure in a weak dialectical position. The problem is not so much an internal tension within Sider’s framework. The complaint, rather, is that his view leaves us with an inaccurate and dialectically weak conception of metaphysics, one that strengthens rather than weakens many of the common negative reactions people have towards it.

The question, then, is whether the following two claims are true:

Necessity: If a dispute is significant, it is structural.

Sufficiency: If a dispute is structural, it is significant.

I will argue that both are false.

Necessity

Must all significant disputes be structural? I think not. This should not come as a big surprise to proponents of Sider’s view; indeed, as I will say in a moment, I think Sider concedes that Necessity is false and so the falsity of Necessity alone is not a fatal problem for Sider’s view. Yet I do think its falsity is important. Seeing how it is false helps us understand the difference between being structural and being significant. More importantly, its falsity figures into a larger problem with Sider’s view, a problem concerning the conception of metaphysics we are left with once all the ties between structural and significance are severed.

Why think Necessity is false? Consider an example. For several decades, disputes about the nature of modality have been at the forefront of metaphysics. They concern questions like: are possible worlds concrete or abstract? Are there merely possible things or are all possible things actual? What is the extent of metaphysical necessity and how does it differ from physical necessity and logical necessity?

The work on these and similar questions has been highly influential not just within metaphysics, but throughout philosophy and, more indirectly, outside philosophy as well. These disputes have had an impact on the philosophy of language (e.g. in arguments Kripke (1980) offers for his theory of names), philosophy of mind (e.g. in the many modal arguments offered for dualism, like those in David Chalmers (1996)), epistemology (e.g. in counterfactual theories of knowledge), and in the philosophy of science (e.g. in disputes over the nature of physical laws and causation).

Outside philosophy the importance of these disputes derives from their influence on the development of modal logic. Much of the groundbreaking work in modal logic throughout the last century was entangled with these metaphysical issues. Difficult questions about how to interpret modal operators, especially when iterated, gained new clarity when viewed in terms of possible worlds, an idea derived from the metaphysical views of Leibniz. Disagreements, including those between Quine (1976) and Kripke (1980), over the coherence of Aristotelian essentialism fed into disagreements over the coherence of modal logic. Questions about the ideas of transworld identity and de re modality led to the development of various formal frameworks for handling them, including the counterpart semantics developed by Lewis (1968 and 1986). Similar connections appear in work on other modal notions, like counterfactuals and causation.

It’s clear that much of the formal work on modal logics and the semantics of modal terms was motivated and influenced by metaphysical concerns. Modal logic, however, has a life outside metaphysics as well. It has important applications outside of philosophy altogether, in computer science and mathematics.7 Although computer scientists are not typically concerned with metaphysical questions about the nature and extent of necessity, the ontological status of possible worlds, and the coherence of de re modality, they employ formal tools whose development was closely tied to those metaphysical questions. Their work is not metaphysical, but metaphysics has had some impact on their work.

These disputes over modal metaphysics are among the least controversial examples of significant metaphysical disputes. Nonetheless, they are not necessarily structural. Sider, in particular, argues that they are not: “At bottom, the world is an amodal place. Necessity and possibility do not carve at the joints… The book of the world says how things are, not how they must or might be” (2011, 266). Of course, he still admits that there are modal truths, but they are not properly the concern of metaphysics. The only interesting metaphysical question concerning modality is how to get rid of it: how to reduce it or to account for it in terms of what is fundamental. He goes on to offer a Humean view on which modality is largely a matter of convention.

Why think modality does not carve at the joints? The motivation is to minimize the required stock of primitive notions we should employ in our theories. Metaphysicians should seek to characterize the world as it is fundamentally using the most economical ideology possible and modal notions do not make the cut. Admitting them would needlessly bloat our fundamental language, where a fundamental language includes all and only those expressions that carve at the joints. One might think this begs the question, for one must already think modality is not part of the world’s structure in order to think that modal notions aren’t needed to describe that structure. The point, however, might simply be that we should try to get by with as little as possible and modality is a better candidate for reduction than existence or various properties mentioned in physics. The important observation is that on the austere conception of structure that Sider prefers, modality is nowhere to be found. Thus disputes over whether something is necessary are not structural.

Nonetheless, Sider grants that notions like necessity are “conceptually deep” in his terms, even though they are not structural (Sider 2011, 70, sec. 12.12). In other words, they are deeply embedded in our conceptual scheme and play a role in many central aspects of our thinking. In this way they are similar to other target notions in metaphysics, like causation and personal identity.8 All of these are cases where the relevant disputes target some notion that is commonly employed not just in metaphysics but throughout our lives and they have an impact on many issues beyond themselves.9 Yet they also concern some notion which should not, on Sider’s view, be included in the austere characterization of the world’s structure.

So Sider should agree that the disputes about modality I mentioned at the outset are significant, in my sense, but not deep or structural. We differ in what conclusions we draw from this. For Sider, I take it, this result means that modality should not be a primary concern of metaphysicians. He grants that there might be good reason to continue with some disputes about modality (as he says, they might “reveal important aspects of our conceptual scheme” (2011, 70)), but it is clear that for the dedicated metaphysician, the real action lies elsewhere. Some questions remain for such a metaphysician (for instance, what is the best way to reduce modality or to understand modal notions in terms of others that do carve at the joints?), but it is a mistake to think that modality is a central metaphysical notion.

I think this reaction is a grave mistake. Discovering that a metaphysical dispute bears on other questions and is entangled with issues from other disciplines provides a powerful reason to take it seriously as an important theoretical issue, one that could convince someone who is not antecedently friendly to metaphysics. For this reason, my reaction is the opposite of Sider’s: modality is a prime example of a metaphysical notion the study of which produced important results not just for metaphysics, but for our inquiries in general. It is, therefore, one which deserves the least suspicion and a central place in metaphysical investigations.

This example illustrates how a dispute’s significance does not require that it be structural. The reason is that the disputes with the widest relevance are not necessarily those that concern the most structural notions, which is no real surprise given how much of human inquiry concerns phenomena that go beyond what is purely fundamental. Sider, I think, would grant this, but that does not mean it is entirely unproblematic for his view. An initial concern is that using Sider’s view as a guide to which disputes to take seriously might result in a misallocation of intellectual resources, since it would recommend that we ignore or at least downplay disputes that are highly significant (as in the case of modality). A plausible response to this worry is that Sider’s view offers a recommendation for what metaphysicians should work on, and if these issues are truly important, they can be taken up by those outside of metaphysics (after all, why does it matter if we think of them as part of metaphysics or not?). But here a greater worry begins to emerge, for we have taken the first step towards severing any link between structure and significance, leaving us with a view of metaphysics as cut off from the rest of our inquiry, rendered irrelevant and uninteresting to everyone but metaphysicians themselves. We might then question whether metaphysics – of whatever sort we’re left with – is really worth defending.

The problem, however, would be mitigated if being structural were sufficient for being significant. Although metaphysicians would, in that case, miss out on some significant disputes, metaphysics as a whole could not be accused of being insular and irrelevant.

Sufficiency

Must structural disputes be significant? Again, I think the answer is no. Consider the following example. After claiming that the sentential connectives of propositional logic carve at the joints, Sider asks: “But which ones? Just [conjunction] and [negation]? Just [disjunction] and [negation]? Or perhaps the only joint-carving connective is the Sheffer stroke?” (Sider 2011, sec. 10.2). Now imagine a dispute over which connectives to use in formalizing one’s theory, with one side arguing that the theory should only include disjunction and negation while the other argues it should only include conjunction and negation. Such a dispute ought to count as structural. Its key vocabulary carves at the joints and the theory may end up a better reflection of the world’s structure depending on how the dispute plays out. We can also grant that there really is a fact of the matter about which connectives we ought to use.10 Even granting all this, it’s hard to see how it is significant, precisely because the connectives are interdefinable in a quite straightforward way. Choosing one set of connectives over the other is unlikely to have any ramifications for issues beyond the dispute itself.

We can find similar counterexamples to Sufficiency by picking up on the idea that disputes couched in terms of logical vocabulary tend to be structural on Sider’s view. Consider, for instance, a dispute over whether to always use the existential quantifier as opposed to the universal quantifier. Or, a somewhat different case, consider a dispute over how many things there are; as Sider mentions (2009, 390) claims about how many things there are (such as “there are at least n things”) can be stated using purely logical vocabulary and so the disputes in question are structural. Yet it’s hard to see what, if anything, would hang on them.11

These examples, however, are a bit artificial, since these aren’t the kind of disputes people are interested in when raising questions about the status of metaphysics. (Although that itself might be a problem for Sider: if the best that can be said for metaphysical disputes is that they are analogous to disputes like these, then one might wonder if any real progress has been made towards showing that metaphysics is a worthwhile form of inquiry.) In fact, this strategy of argument – offering specific counterexamples to claims like Sufficiency – is in some ways unsatisfactory. For Sider could grant the falsity of Sufficiency in the strict form I’ve presented, favoring instead a generic reading of the claim. The important point for Sider is that structural disputes tend to be significant and, when this is so, it is precisely because they are structural. So he might well grant that the move from structure to significance is not without exceptions while insisting that being structural tends to make disputes significant.

So, let’s investigate whether a dispute’s being structural gives us a reason to think that it is significant and let’s consider a more realistic example in the process. There are some metaphysical disputes that should count as structural but where it is doubtful that we should regard them as significant for that reason alone. One example is the dispute over composition: imagine a disagreement over whether there are any composite objects (e.g. tables as opposed to particles-arranged-tablewise) at all. Sider notes that

some of the metaphysically deepest disputes – certain ontological disputes, for example… – are conceptually shallow in that they have few implications outside rarified metaphysics. This, I suspect, contributes to the common distrust of those disputes.

(Sider 2011, 74)

Assuming that the dispute over the existence of composite objects is one of the ontological disputes that Sider has in mind here, then, in my terms, the composition dispute is not significant, even though it is structural. I do not, however, want to assume that this dispute is insignificant. Demonstrating that would require careful consideration of the dispute itself which goes beyond my concerns here. Instead, let’s leave that question aside for the time being and focus on what follows from its being structural. The important question is whether granting that assumption is enough to establish that it is also significant. It is that connection that I want to question.

What can we infer from the assumption that the composition dispute is structural? The characteristic feature of such disputes is that the expressions they target carve at the joints. In the case of composition, the relevant bits of language include the idioms of quantification (especially the existential quantifier and the identity symbol) and mereology (including expressions like “is a part of”). What can we infer from the assumption that such terms carve at the joints? We can conclude that they, in some sense, capture the world’s metaphysical structure and that no fully adequate theory of the world could fail to include them. But that is not enough to show that any dispute which targets those terms is significant. For what we need is some reason to think that the dispute itself has connections to issues beyond itself, and the fact that the terms employed are joint carving and indispensable supplies no such reason. This is illustrated by our initial counterexamples: the fact that terms are joint carving doesn’t prevent one from formulating insignificant disputes by using them. We can take theoretically indispensable terms and then have pointless disputes involving them. If that were not the case, then any dispute over what exists, phrased in joint-carving terms, would be significant, no matter how foolish (as in questions like “Does conjunction exist?” or “Is there conjunction?” which are hard to make sense of).

At best, the fact that the terms used in some disagreement are joint carving shows that a different but related dispute might be significant. Consider the question of whether the dispute over composition is structural. A disagreement over that question might well be significant, for it bears on issues concerning the correct ideology to employ in formulating our theories. There are connections, in other words, between it and our theorizing in general. But that does not show that the composition dispute itself is significant, even if it is structural. In other words, a dispute over whether the composition dispute is structural could well be significant even if the composition dispute is insignificant (even if we assume that it is in fact structural).

The general problem here is that a dispute’s being structural is only enough to establish a connection between the vocabulary employed in that dispute and our theorizing in general. It does not establish any connection between the disputed positions and our theorizing in general. Even if the vocabulary carves at the joints, it could still make no difference which particular view expressed in that vocabulary ends up being true. Both views will employ the same terms, so even if it is a significant question whether to employ those terms, the question of which of those views is true need not be significant.

I am not arguing that structural disputes tend to be insignificant. I remain neutral, at this point, about whether the dispute over composition is significant or not. Rather, I’m arguing that a dispute’s being structural is not, by itself, enough to show that it is significant. I think there are clear examples that demonstrate this and we can explain why it would be so in terms of Sider’s overall view.

These observations provide compelling reason for rejecting Sufficiency in both its strict and its more generic forms. The strict reading is open to counterexamples that can be constructed using the observation that nothing prevents us from formulating pointless disputes using joint-carving language. The more generic reading, according to which being structural tends to explain why certain disputes are significant, is called into doubt because it is not at all clear how such explanations would proceed. As we’ve seen, assuming that a dispute is in fact structural doesn’t seem to provide any reason, on its own, to think that it is significant. Even if we assume that the dispute over composition is both structural and significant, its being structural would not explain why it is significant nor even provide much guidance to whether it is or not. Thus even if it were true that, in general, structural disputes are significant, it needn’t be that they are significant because they are structural. On its own, being structural is not sufficient for being significant, cannot explain why a dispute is significant, and is not a reliable indication that a dispute is significant (except, perhaps, purely by accident).

If the claim that certain metaphysical disputes are structural is meant to provide a reason for those suspicious of metaphysics to take it more seriously, then our conclusion presents a serious problem for the view. For simply arguing that a dispute is structural is not enough to show that it matters for anything beyond itself. Given the falsity of Necessity and Sufficiency, Sider’s view feeds directly into the suspicion that metaphysical disputes are irrelevant to the rest of philosophy and science and can be safely ignored. They might well be deep or substantive or fundamental but few find that a compelling reason, on its own, to take them seriously. We are left with a picture of metaphysics on which it is an insular and irrelevant form of inquiry and the appeal to structure does little, dialectically, to reassure those who doubt its significance. A defense of metaphysics which leads to such a conception of the discipline is, I think, both inaccurate and undesirable.

An alternative picture

I have argued that the picture of metaphysics as the study of the world’s fundamental structure is an unfortunate one. It does, however, possess the advantage of giving us some grasp of what metaphysics is and where it belongs in our inquiry more generally. If we reject that picture, is there another that could take its place?

Sider defends the idea that the key notions that metaphysics investigates all carve at the joints; in other words, they have a great deal of depth. I think a better picture of metaphysics is available if we focus on breadth instead of depth: the distinctive feature of metaphysics is that it targets notions used throughout the rest of our inquiry with exceedingly high frequency, so that their application is near ubiquitous (in Sider’s terms, the target notions of metaphysics have an exceedingly high degree of conceptual depth, though I prefer not to put it that way). Consider, for instance, the primary targets of metaphysical investigation: existence, necessity, properties, number, parthood, identity, personhood, time, causation, and so on. They find employment in almost every theoretical activity. Not so for the objects of most other disciplines; bosons, for instance, play little role in economics, while emerging markets don’t often figure in physics. That’s not to say that these other disciplines take existence or properties, for instance, as objects of study, but they rely on notions of existence or properties in the course of performing their investigations. The characteristic feature of metaphysics is that it reverses this trend. It takes as its objects those notions that find application throughout the rest of our inquiry.

This feature is not, of course, unique to metaphysics, nor is it universally true of all metaphysics. It does not give us a perfect way of demarcating metaphysics from other areas of investigation. Yet I don’t think this should trouble us, for I don’t think metaphysics is clearly demarcated from other areas of investigation and it is precisely those areas which also share the feature I’m describing with metaphysics that share the fuzziest boundaries with it. I have in mind other areas of philosophy like epistemology and logic, both of which also target notions with widespread application but which also shade into metaphysics in many cases. This characterization is a bit fuzzy, but it sheds light on what metaphysics is and where it belongs in our inquiry.

This account also helps explain a number of common reactions people have to metaphysics in general, without necessarily vindicating them. For instance, it helps explain the traditional, though currently unpopular, view that metaphysics is first philosophy. A natural (though likely misguided) thought is that if metaphysics studies things presupposed by every other area of inquiry, without presupposing much from those other areas itself, then our theoretical projects ought to begin with metaphysics. Our picture of metaphysics can explain why this thought sometimes strikes people as plausible, but we need not agree with it for reasons I will discuss in a moment.

It also helps explain various negative reactions to metaphysics, like the thought that metaphysics is transcendental (in some objectionable sense), or that it lacks content, or is focused on external questions rather than internal ones, as in Rudolf Carnap (1956). The complaint is that metaphysics takes the conceptual apparatus we employ throughout the rest of our inquiry and tries to turn it into an object of study on its own. It treats the tools of inquiry as objects of study. This naturally gives rise to the thought that something has gone wrong in metaphysics: that it lacks content or rests on some kind of conceptual use/mention confusion. The plausibility of this thought can be explained by this picture, for it is true that the objects of metaphysics are generally the notions relied on throughout the rest of inquiry and which can thus come to seem like a kind of presupposed conceptual background rather than a potential object of study.

The mistake in both these reactions is in assuming some link between the idea that the targets of metaphysics are very widely employed and the issue of whether metaphysical questions (or the disputes over their correct answers) are significant. The first assumes that they must be highly significant, if they target these ubiquitous notions, while the second assumes the opposite. I think the truth lies somewhere in the middle, for the mere fact that the key terms of metaphysics are widely employed cannot, by itself, settle the question of whether metaphysical disputes are significant. This helps explain a third, less partisan reaction to metaphysics, which is that even if metaphysical disputes turn out to be worthwhile, metaphysics, at the outset, stands more in need of defense than most other areas of inquiry. There is, in other words, a stronger presumption of guilt when it comes to metaphysics compared to most other disciplines. That feeling stems from the implicit recognition that the constraints on metaphysical questions are very thin and by themselves do not suffice to show that the questions matter much for anything else. The terms “number” and “existence” have extremely widespread application, but that alone does not show that disputes over the question “Do numbers exist?” are fruitful. At this level of abstraction, it is totally unclear whether anything hangs on it.

The reasoning here is much the same as that towards the end of Section “Sufficiency”. There I argued that the mere fact that some term carves at the joints does not show that disputes formulated using it are significant, since it is possible to express silly positions in joint-carving terms. The nature of the vocabulary alone is not enough to give the positions that employ it, and the disagreements between them, any purchase. The same is true, however, in the case of widely used vocabulary as well. The fact that some terms are widely employed doesn’t show that every question we might ask about them leads to fruitful theorizing and it doesn’t show the opposite either, that questions we might ask about them are somehow defective or pointless. It shows that we must, in each case, consider carefully whether anything is really at stake. In some cases, once we fill in the story we will find that there are rival conceptions of these commonly used notions which would lead to widespread differences throughout the rest of our inquiry. In those cases, we have a significant metaphysical disagreement.

Acknowledgements

Many thanks to Susanna Rinard, Stephen Yablo, Agustin Rayo, Robert Stalnaker, Matti Eklund, Mahrad Almotahari and Stephen Maitzen.

References

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  • Johnston, M. 1992. “Reasons and Reductionism.” The Philosophical Review 101(3):589618.

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  • Lewis, D. 1968. “Counterpart Theory and Quantified Modal Logic.” Journal of Philosophy 65:11326.

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  • Sider, T. 2001. Four-Dimensionalism. New York: Oxford University Press.

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  • Sider, T. 2011. Writing the Book of the World. New York: Oxford University Press.

1

Two views in the vicinity of Sider’s are those defended by Kit Fine (2009) and Jonathan Schaffer (2009). Their views differ from Sider’s in various respects, so it will be simpler to focus on Sider’s view alone, although I think similar criticisms can be extended to their positions as well.

2

The theory of natural properties that Lewis and Sider accept has broad motivations and wide-ranging applications, as is clear from the discussion in Lewis (1983). I am focusing on its uses in their theories of intentionality, but that shouldn’t be thought of as the whole story. Similarly, the idea of structure needn’t be assimilated to the natural property model, though it does provide a convenient framework for making sense of the idea.

3

It’s possible to have a similar view where naturalness does not come in degrees. On that view, something is either natural or not. This more absolute conception of naturalness may be more amenable to Sider’s views, since it better captures the idea of the world’s fundamental structure. It’s also hard to make sense of degrees of naturalness when extending the notion of naturalness to cover logical vocabulary, as below.

4

Compare Sider (2011, sec. 11.3).

5

There may be another natural interpretation of what it is for a dispute to be structural: it is for a dispute to be about structure or to concern what is structural. That is not what I have in mind in what follows.

6

Throughout this paper, I am using “significant” and “insignificant” as technical terms, signifying the properties of disputes that make them worthwhile and not worthwhile respectively (which are, in my view, the property of being connected to the rest of our inquiry in the right way and the property of being insular). “Significant” can also carry connotations of being meaningful or genuine, but that is not my intention; the intended reading is that significant disputes matter.

7

For instance, in computer science, modal logics have been used to help understand distributed systems (a simple model might treat each computer as a possible world and relations of accessibility as network connections between them, allowing theorists to model how information is shared in the system), alongside other, more general applications in modeling computer operations, the evolution of databases over time, error-handling, and so on. In mathematics more generally, modal logic has been useful in clarifying the concept of provability (as in George Boolos (1993)).

8

Sider also discusses these examples (2011, 73). See also Mark Johnston (1992), where Johnston argues that even if personal identity cannot be reduced to, and doesn’t supervene on, the fundamental physical properties and relations of the sort Derek Parfit (1984) takes to be the only plausible candidates, it doesn’t follow that we shouldn’t care about personal identity or that it isn’t the relation that really matters to us.

9

I do not mean to suggest that the mere fact that some dispute targets a conceptually deep notion is enough to guarantee its significance (see Sections “Sufficiency” and “An alternative picture” for why I think it is not enough). Some disputes about necessity, for instance, might well be insignificant. In the cases I’ve been discussing, however, we have good reason to think that the disputes do have important connections.

10

It can be difficult to make sense of this suggestion, but we could imagine that there is some primitive fact about what the correct selection of connectives is, or we might tell a story which privileges one group over the other (perhaps in creating reality, God created conjunction and negation, leaving disjunction to emerge from those as an after-thought).

11

Of course it’s not inconceivable that how many things there are might matter for some question in mathematics, say, or physics or metaphysics, but on the face of it, without filling in the story, it’s hard to see what that question would be. Nonetheless, some philosophers have held that it does matter, especially finitists in the philosophy of mathematics (of which F. P. Ramsey and the later Wittgenstein may have been examples). The important point for me is that, as I will argue in a moment, the mere fact that how many things there are can be stated in structural terms isn’t enough to show that anything hangs on the issue.

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  • Boolos, G. 1993. The Logic of Provability. New York: Cambridge University Press..

  • Carnap, R. 1956. “Empiricism, Semantics and Ontology,” reprinted as supplement to Meaning and Necessity: A Study in Semantics and Modal Logic, Chicago: University of Chicago Press.

    • Google Scholar
    • Export Citation
  • Chalmers, D. 1996. The Conscious Mind. New York: Oxford University Press..

  • Fine, K. 2009. “The Question of Ontology.” In Metametaphysics: New Essays on the Foundations of Ontology, edited by D. Chalmers, D. Manley, and R. Wasserman, 157–177. New York: Oxford University Press.

    • Google Scholar
    • Export Citation
  • Johnston, M. 1992. “Reasons and Reductionism.” The Philosophical Review 101(3):589618.

  • Kripke, S. 1980. Naming and Necessity. Cambridge: Harvard University Press.

  • Lewis, D. 1968. “Counterpart Theory and Quantified Modal Logic.” Journal of Philosophy 65:11326.

  • Lewis, D. 1983. “New Work for a Theory of Universals.” Australasian Journal of Philosophy 61:34377.

  • Lewis, D. 1986. On the Plurality of Worlds. Malden: Blackwell.

  • Lewis, D. 1999. “Putnam’s Paradox.” In Papers in Metaphysics and Epistemology, 5677. New York: Cambridge University Press.

    • Crossref
    • Google Scholar
    • Export Citation
  • Parfit, D. 1984. Reasons and Persons. New York: Oxford University Press.

  • Quine, W. V. O. 1976. “Three Grades of Modal Involvement.” In The Ways of Paradox and Other Essays, 158176. Cambridge: Harvard University Press.

    • Google Scholar
    • Export Citation
  • Schaffer, J. 2009. “On What Grounds What.” In Metametaphysics: New Essays on the Foundations of Ontology, edited by D. Chalmers, D. Manley, and R. Wasserman, 347383. New York: Oxford University Press.

    • Google Scholar
    • Export Citation
  • Sider, T. 2001. Four-Dimensionalism. New York: Oxford University Press.

  • Sider, T. 2009. “Ontological Realism.” In Metametaphysics: New Essays on the Foundations of Ontology, edited by D. Chalmers, D. Manley, and R. Wasserman, 384423. New York: Oxford University Press.

    • Google Scholar
    • Export Citation
  • Sider, T. 2011. Writing the Book of the World. New York: Oxford University Press.

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