The world, according to Ted Sider, has a basic structure. An optimal description of the world must capture this structure. It must also consist of truths. But these are two distinct requirements. We can produce more and more truths about the world and still not come any closer to capturing its structure. To do the latter we need to produce not just truths, but truths of the right sort. Now it has long been acknowledged that a mere assemblage of truths does not count for much. They might be uninteresting and insignificant truths; for that matter, they might be interesting and significant truths, but assembled in an uninteresting and insignificant way – without any attempt at systematisation or explanation, without any attempt to establish connections. The idea of basic structure gives a further fillip to this familiar fact. It signals another respect in which, if we are to give the best possible account of the world, we need to do more than tell the truth. The concepts we use to couch the truth – the properties to which we advert, the sorts of thing we recognise as instantiating these properties, even the connectives we use to conjoin claims about such things – need to reflect the world’s basic structure. They need to ‘carve at the joints’. There is a privileged way to write the book of the world.

In the course of defending this vision, Sider works through an impressive list of philosophical problems and shows in each case how the idea of basic structure can help us address them. I shall give just two examples. First, consider the fact that some questions seem intuitively insubstantial. For instance: Is Snowdon high enough to be a mountain? Even if this question has a correct answer, it still seems insubstantial. We feel that nothing of importance separates us from a community whose understanding of what counts as a mountain is sufficiently different from ours that they would answer their analogous question differently. By contrast, the question of whether Snowdon is high enough to prevent the planet Venus from being seen from a given location at a given time does seem substantial. It is surprisingly difficult, however, to articulate what the distinction consists in. Sider is able to give an account of it. On his view, a question is insubstantial if one of the expressions used to formulate the question (‘mountain’ in this case) has a range of equally good available meanings, on some of which the question is to be answered one way and on some of which the question is to be answered the opposite way, where what makes two or more meanings equally good is the fact that none of them does better than the others in carving at the joints. The difference between mountains and mere hills is not part of the basic structure of the world, it is just a matter of how we happen to carve things up.

The second example concerns the philosophy of time. Participants in debates about the fundamental nature of time use various metaphors to illustrate their different conceptions. Thus we hear talk of a four-dimensional ‘block universe’. Sometimes this is supplemented with talk of a ‘moving spotlight’ that illuminates different parts of the block at different times. Sometimes the block is allowed to ‘grow’ over time. Then there is talk of the ‘flow’ of time. Other examples abound. But vivid though these metaphors are, it is irresistible, after a while, to wonder whether they represent genuine differences of view. There are two concerns. The less serious concern is that there is nothing genuinely separating the views to which these metaphors give expression. The more serious concern is that these metaphors do not give expression to genuine views in the first place. Sider is able to arrest such scepticism. He argues that there are indeed genuine views involved, and that there are genuine differences between them. Participants in these debates can be represented as differing about the basic structure of the world. Suppose that the expression ‘there are’ can be understood in such a way that it carves well at the joints. In these terms, some of the participants in the debates about time – those who are liable to express their view by saying that the past is as real as the present – can be represented as believing that there are, say, dinosaurs. Others – those who are liable to express their view by saying that nothing is true unless it is true now – can be represented as believing that there are no such things.

Now, I began by talking about what we need to do if we are to give an optimal description of the world. But who are ‘we’? This familiar philosophical question is always lurking. In this case, it alerts us to some heady and important issues concerning whether various aspects of our attempt to write the book of the world – for instance, the criteria for the success of our attempt – may turn out to reflect certain peculiarities of ours. Is there something about the exercise that is fundamentally anthropocentric, for example? Or fundamentally ethnocentric? Or fundamentally androcentric? Perhaps what counts as an optimal description of the world for us rational primates is profoundly different from what counts for those rational beings, if such there be, with a quite alien biological constitution. Perhaps what counts for us modern Westerners is profoundly different from what counts for those in other times and places. Perhaps what counts for us Anglophones is profoundly different from what counts for those whose natural language is not English.

These issues are of crucial significance to Sider. He is adamant that his enterprise exhibits no sensitivity to who ‘we’ are. Indeed that is part of the point of his insisting that a description of the world is to be judged by how well it captures the world’s structure: the world’s structure, for Sider, is independent of us – whoever ‘we’ are. Before addressing these issues, however, I want to consider a much more modest interpretation of the question: ‘Who are “we”?’ That question need not be heard as an allusion to hidden biases or other elements of perspective in our attempt to write the book of the world. It can be heard as a question about disciplinary boundaries. Whose business is it to capture the world’s structure? Is it the business of physicists? Or is it the business of metaphysicians? Is it perhaps both? Or neither? When ‘we’ reflect on what ‘we’ need to do in order to give the best possible account of the world, are we simultaneously adopting a stance both in the arena of physics and in the arena of metaphysics? Or are we simultaneously adopting a stance both in the arena of metaphysics and in the arena of meta-metaphysics – where meta-metaphysics, on Sider’s helpful characterisation, is ‘inquiry into the status of metaphysics’. Or are we doing something quite different from either of these?

Consider the three following claims:

(1) e = mc2

(2) Among the concepts that carve perfectly at the joints are those of physics

(3) Metaphysics is concerned with the structure of reality

On a broadly Siderian view, (1) is the sort of claim that physicists make; (2) is the sort of claim that metaphysicians make; and (3) is the sort of claim that meta-metaphysicians make. That (1) is the sort of claim physicists make is hardly open to dispute. That (2) is the sort of claim metaphysicians make is implied by Sider’s actually making it in the course of sketching what he takes to be a plausible metaphysical worldview in the final chapter of the book. That (3) is the sort of claim meta-metaphysicians make is implied by (2)’s being the sort of claim that metaphysicians make. In these terms, when ‘we’ reflect on what ‘we’ need to do in order to give the best possible account of the world, what we are doing, at least in part, is reflecting qua metaphysicians on what we are up to qua physicists; and when ‘we’ register this fact, we are registering qua meta-metaphysicians something about the relationship between metaphysics and physics.

To be sure, none of these boundaries is sharp. It would be out of the question for anyone seriously engaged in any of these endeavours not thereby to be engaged, to a significant extent, in one or more of the others. In particular, metaphysicians, on this conception, will not want to confine their efforts to explaining the special role that physicists play in writing the book of the world; they will want to muscle in and help to write it. (Sider is always clear that, whatever role physicists have to play in writing the book of the world, it is not their sole prerogative. There is also work to be done by metaphysicians – as indeed there is work to be done by logicians and pure mathematicians.) Moreover, these roles themselves are not sharply separated. There are, Sider writes, ‘laws of metaphysics concerning the behaviour of the physical predicates. These are given to us by physics. (Perhaps these should not be called laws of metaphysics, since they are also laws of physics.)’ Be that as it may, we have here an indication of how and why, on Sider’s conception, metaphysics centrally involves deliberation on the nature of physics.

This is significant. It already marks one way, indeed a central way, in which metaphysicians are not themselves engaged in writing the book of the world. For even if the concepts of physics carve perfectly at the joints, the concept of physics, with which (on Sider’s conception) metaphysicians have to reckon, assuredly does not. True, there is a section in Sider’s book in which he argues that the concept of basic structure itself carves perfectly at the joints, which, in somewhat looser terms, means that structure is itself structural. But even if that argument is successful, there is no analogous argument to show that physics is itself physical, in any relevant sense of ‘physical’. Physics is a science. It is the study of something, the pursuit of something. It has an essential connection with aims, interests and values. These are not, on Sider’s view, part of the basic structure of the world.

The idea that one of the central concerns of metaphysicians places them outside the project of writing the book of the world can be approached from a slightly different direction. Suppose we ask: ‘What is structure?’ On Sider’s conception, that is a metaphysical question. As a metaphysician, he tries to answer it. But he does not try to answer it by offering a definition. For he does not think that structure has a definition: he takes it to be a primitive notion. Instead, he tries to say enough about structure, for instance about its connection with other notions, about its workings, and about what would be a canonical way of representing it, to elucidate what he has in mind. Central to what he wants to say about it is something that he repeatedly does say about it and something that initiated my discussion here, namely that an optimal description of the world must capture the world’s structure. Here are some variations on the same theme:

We think of scientific discovery as satisfying the aims of inquiry particularly well; why? Answer: it is because scientific discoveries are phrased in particularly joint-carving terms. It is better to think and speak in joint-carving terms. Regard as joint-carving the ideology that is indispensable to your best theory.

These remarks further indicate how metaphysics, in Sider’s view, deals with aims, interests and values, and thus with that which is not itself part of the basic structure of the world. In fact they indicate something more. They indicate how metaphysics, trafficking as it does in the notions of what is ‘particularly good’, ‘better’, or ‘best’, not only deals with aims, interests and values, but betrays its own.

Is this a problem? Not at all; but it does mean that, when we return to the original posing of the question, ‘Who are “we”?’, on its headier and more ambitious interpretation, it seems to demand and deserve an answer. If these metaphysical deliberations of ours – about what is required of us if we are to give an optimal description of the world – are as steeped in evaluation as this (something that the very use of the word ‘optimal’ ought already to have suggested), then it seems to be legitimate and important to ask, whose evaluation is at stake and what difference it might have made if others had been doing the evaluating. As physicists we are interested in the behaviour of rocks and stars. As metaphysicians we are interested in the merits of being interested in the behaviour of rocks and stars. Is it not possible that the concerns and values that inform the second of these interests are every bit as subjective and parochial as the concerns and values that inform an interest in the behaviour of rock stars?

For Sider, it would be an anathema to suggest that metaphysics exhibits any such subjectivity. The metaphysician’s concern with the structure of reality, in Sider’s view, has no more to do with the idiosyncrasies of one particular group than the physicist’s does. The difference between the physicist and the metaphysician is rather a difference in the levels at which they operate. And the superiority of thinking and speaking in joint-carving terms, which it is the metaphysician’s business to proclaim, is as objective, if not as metaphysically basic, as the joints themselves.

It would be a yet greater anathema, for Sider, to combine the suggestion that metaphysics exhibits such subjectivity with the suggestion that the subjectivity it exhibits infects the very notion of structure. When he declines to define structure in favour of making various elucidatory claims about it, he does so precisely because he does not want the other notions to which he relates it to be understood as playing definiens to its definiendum. He does not even want them to be understood as enjoying some kind of explanatory priority over it. The reason why it is optimal to think in a way that reflects structure, in Sider’s view, is because that is what structure itself demands, not because structure is to be understood as that which is reflected by a way of thinking that can be independently recognised as optimal. To reverse the order of priority here, to think that the optimality concerned is subjective – on the grounds, say, that the very idea of objective optimality is incoherent – and to conclude that there is something correspondingly subjective about structure itself is to get things just about as badly wrong, in Sider’s book, as it is possible for any right-minded person to get them.

There is a huge amount in Sider’s acute and brilliant discussion of these issues that I admire. There is much indeed with which I agree. Even so, I have a fundamentally different conception of metaphysics from his. And to the extent that I have any sympathy at all for his notion of structure, then I am in fact strongly inclined to get things – as Sider would see it – that badly wrong, and in just the way I have described. Admittedly, this is just autobiography. What is required at this point is argument. But the very fact that what is required at this point is argument is part of my reason for seeing things so differently from Sider. For it seems to me that what is required isn’t just argument, but metaphysical argument, indeed metaphysical argument from a point of evaluative engagement with the issues, including the issue of the status of just such evaluation. It is striking and significant that all Sider himself offers at this point is autobiography. Lots of it. Here is a sample:

Speaking just for myself, [subjectivism about structure] is incredible. A certain ‘knee-jerk realism’ is an unargued presupposition of this book. Knee-jerk realism is a vague picture rather than a precise thesis. According to the picture … the world is ‘out there’, and our job is to wrap our minds around it. This picture is perhaps my deepest philosophical conviction. I’ve never questioned it. Knee-jerk realism requires recognising that there is something better about [thinking in physical terms than thinking in terms of some non-joint-carving rival to physics] … Knee-jerk realism further requires that the betterness be objective. If structure is subjective, so is this betterness. This would be a disaster … If there is no sense in which the physical truths are objectively better than the [non-joint-carving] truths … then the postmodern forces of darkness have won.

I find some of this autobiography as incredible as he finds subjectivism about structure. Has he really never questioned his philosophical conviction? His very claim never to have done so suggests otherwise. (If I could be persuaded of the truth of that claim, then my incredulity would give way to despair for the current state of philosophy.) But that is not the point. The point is that Sider’s autobiographical observations divert our attention away from a more subject-centred conception of what metaphysics can and should do.

Metaphysics can and should help us to make sense of ourselves. This can certainly include reflection on physics. Our capacity to engage in physics is one of our most distinctive features, serving as a kind of fulcrum between us and the rest of the world. But if the reflection exercised on physics in the course of our metaphysical deliberations is to be of value, then it needs to be of a very different sort from the reflection exercised in physics. This is not least because it needs to have a significant element of self-consciousness, making the identity of the ‘we’ who are engaged in reflecting an unavoidable focus of that reflection. We need to see metaphysics as an enterprise that is completely different from any of the natural sciences, an enterprise that, unlike them, not only betrays ‘our’ point of view but allows for exploration and refinement and creative development of that point of view.

To be sure, there is fuel for Sider’s fire in these suggestions. For he could agree that the enterprise I am describing is a worthwhile one, which differs from what he himself is disposed to regard as metaphysics, but then dismiss the question of which of the two is really metaphysics as insubstantial, like the question of whether Snowdon is a mountain, whose answer is sensitive to how some key expression is to be interpreted, there being a range of available meanings for the expression that do equally well (or, more to the point, equally badly) in carving at the joints. But I am not especially concerned to deny that the question is insubstantial. For, as Sider observes, ‘many expressions that fail to carve at the joints are embedded in our conceptual lives in important ways.’ He goes on to cite an example about which he says that, in learning how best to answer the question involved in the example, ‘we are primarily learning something about ourselves,’ then adds, ‘but we’re learning something important about ourselves.’ Quite. And this seems to me to be just the sort of thing that we should say in connection with what metaphysics is. Reflecting on how best to answer this question means reflecting on something important about ourselves. In particular, it means reflecting on something important about that extraordinary part of our heritage that includes the inventiveness, the visionariness and the insight into what it is to be human of Spinoza, Kant, Nietzsche and their like.

Sider is guilty, as I see it, of a sort of scientism. He doesn’t just want metaphysics to privilege physics. He wants it to ape it. He wants metaphysicians to play their own part in writing the book of the world. (This is one reason it is important for him that structure should itself be structural; for the concept of structure is the one joint-carving concept whose exercise is a speciality of metaphysicians.) He knows full well that metaphysics cannot be entirely like physics. Its very privileging of physics, which is an arrogation that we do not find within physics itself, precludes assimilation of the two. But the more like physics metaphysics is, Sider thinks, the better. And this is because physics is supremely good at capturing the world’s structure.

My own view is that metaphysics is not in the business of capturing the world’s structure. (This is not to deny that it has a concern with structure. Aesthetics has a concern with kitsch, but it is not in the business of capturing kitsch.) To do metaphysics justice, and to extend this part of our heritage in the most creative and the most effective way, we need to see metaphysics in the way in which Bernard Williams famously urged us to see philosophy as a whole: as a humanistic discipline. This is very different from the way in which Sider sees it. Nevertheless, there is much to applaud in this fascinating book. Even if it is not for metaphysicians to write the book of the world, there is no gainsaying their right to write books about writing the book of the world. Sider has done that very well indeed.