Might it be held that the microparticles that occupy the volume in which common sense supposes a familiar object to be present really cause anything that the familiar object appears to cause? That is what causal exclusion arguments contend. In this chapter I focus on what most philosophers would consider the most eminently excludable case of putative causation by a familiar object, namely mental causation – the case in which it appears that a person's beliefs and desires bring about some behavioral outcome. I argue that mental causation appears to be genuine causation, and that no there is no cause at all, at the level of small entities within the person, that can be held to bring about the same outcome. The argument against causal exclusion readily generalizes to other cases of apparent causation by familiar objects, in ways that I shall indicate, both here and in chapter 6.

THREE THREATS TO MENTAL CAUSATION

Can we vindicate the common-sense conviction that a person's mental states, and in particular her beliefs and desires, are causally efficacious – that they shape that person's behavior? Three obstacles appear to stand in the way. The first is the idea that any true causing must instantiate some exceptionless law. For it seems clear that the closest we can come to laws that link beliefs and desires to behavioral outcomes are mere generalizations that must be hedged by ceteris paribus clauses.

Metaphysicians who are sceptical about familiar objects for the most part suppose that the world is really populated by the fundamental particles of completed microphysics, or by mereological simples – or by both, should the fundamental particles turn out to be mereological simples. They then must explain why the world at least appears to contain objects that are so much larger, objects such as dogs and trees and boulders. The metaphysicians considered in the previous chapter suppose that they can explain this appearance by holding that adverbially identified “arrangements” obtain among the microparticles, such as dogwise and treewise arrangement. But other proponents of an ontology of the small respond differently. They hold that there really are unitary large objects, in all of the volumes in which common sense supposes a familiar object to be present, and that this follows merely from the premise that each of those volumes is occupied by microparticles or simples. These philosophers are adherents of UMC (universal mereological composition). In this chapter I argue that UMC is both unmotivated and untenable; the only way to have unitary, relatively large, objects in all the volumes where common sense supposes familiar objects to be present is to have familiar objects themselves.

But even apart from its relation to the ontology of familiar objects, UMC is of considerable intellectual interest.

Judgements asserting one or another of two kinds of sameness are crucial, I shall argue, both for our practical mastery of the world and for our theoretical understanding of it. On the one hand, there are judgements saying that one object is the same in kind as other objects, or that some matter is the same in kind as matter found elsewhere. On the other hand, there are judgements saying that the object in front of us is numerically the same object, or that the matter is the very same matter, as we encountered earlier or will encounter later.

In making these judgements we call upon observation and understanding. In order to affirm sameness in kind, we must observe that various similarities obtain between one object and others, or between matter here and matter elsewhere. In order to affirm persistence across a single episode of observation, we must observe that an object (or some matter) has moved continuously, while retaining largely the same features, and in order to affirm persistence across separate episodes, we must observe that the object (or the matter) now before us presents features appropriately related to those observed in an object (or some matter) encountered at other times. But we must also understand which sorts of similarities indicate sameness in kind, which sorts of relations mark out persistences.

In general, contemporary metaphysics is deeply sceptical of the familiar objects in which common sense believes. It is far more ready to attribute reality to entities that are much smaller – to the particles and wave packets and strings which microphysics treats as real, or to the “mereological simples” for which philosophical reflection provides some support. Any such view must find some way of explaining why there appear to be familiar medium-sized objects in the world. Many metaphysicians suppose that we can do just that. We can explain why it appears that the microparticles of the world compose familiar objects, why it appears that these objects persist across careers in which they lose and gain component microparticles, and why it appears that these objects have and exercise causal powers. The main business of this book is to argue that leading examples of such reductive explanations fail. For time and again such explanations project downwards, onto the small entities of the preferred ontology, structures and relations and features that properly belong to familiar objects. Such projection is harmless so long as one allows that there also are, in addition to the small entities, the familiar objects that form the starting point of the projection. But if – as is generally the case – the aim is to expunge familiar objects from ontology, the invocation of such structures and relations and features is illegitimate.

In chapter 1 I argued that judgements of numerical persistence are imperatives, directing us to discover and draw inferences from causal patterns by which newly arriving accidental features will either lead to their own continued presence, or will give way to particular other accidental features, depending on the natural kind to which the persisting object (or portion of matter) belongs. Such causal patterns are clear enough that we can discover them, at least widely enough to have rendered it fruitful for us to heed the imperatives embodied in judgements of numerical persistence – widely enough, then, to have earned for those judgements a place in our conceptual/linguistic repertoire. Where such patterns obtain, they are grounded in the properties essential to the natural kind in question. Thus in treating judgements about an object's course of persistence as guiding us to such patterns, we are treating the events that may befall an object over its course of persistence as governed by the properties essential to the kind to which it belongs. In effect, then, we treat any course of persistence as delimited by some instance of kind-membership. We act as if any object (or sample of matter) can continue to exist only so long as it stays in its natural kind: we treat the conditions on kind-membership as being, at the same time, persistence conditions for the members of that kind.

This position on persistence conditions is philosophically controversial. Nothing said in chapter 1 establishes that it is true.

Here is a line of reflection that has dominated much recent metaphysics. Science gives us good reason to suppose that the familiar objects that common sense believes in are, if real at all, composed wholly of tiny microparticles – either of the microparticles that current microphysics regards as fundamental, or of other microparticles, perhaps smaller or stranger, that a perfected future microphysics will recognize. Yet as philosophers we must entertain seriously the possibility that some of these familiar objects do not really exist. Where common sense supposes there to be a tree or a baseball or a dog, we must be willing to say, there may just be many, many microparticles. It still would be possible to explain why common sense supposes, and is rewarded for supposing, that in just these regions there is a tree or a baseball or a dog. The explanation would be that the microparticles in these regions are arranged towards one another in particular ways, ways that reward the common-sense belief in a single object of a particular kind. Thus where common sense supposes that there is a dog, there might really be just microparticles dogwise arranged. We need not pause long to consider what dogwise (or treewise or baseballwise) arrangement consists in or amounts to. For, since it is certain that the world rewards the common-sense belief in dogs (and trees and baseballs), it is certain that that arrangement, whatever exactly it is, obtains among the microparticles in various regions.

In the previous chapter I defended a realist position on kind-sameness and on numerical persistence. I held that nature's kinds typically fall into families; that properties of certain sorts are common to the members of each such kind and differentiate the kinds within each family; and I briefly sketched the ways we learn, empirically, which sorts of properties are, in this way, constitutive of kind-membership. I held also that retention of properties of these same sorts sets up persistence conditions for the members (and samples) of nature's kinds – meaning that persistence conditions, too, are things we learn from nature. Both these claims are contested by the view I called “conventionalism.” Conventionalists, as I said, hold that descriptive content written into the very meanings of our sortals and matter-names fixes which sorts of properties are determinative of kind-membership and of persistence.

But this basic conventionalist message can be articulated in either of two quite different ways, and thus far I have examined only one. The articulation I have so far examined says: since it is the very meanings of our sortals and matter-names that fix which sorts of properties determine kind-membership and mark out persistences, the truths as to which properties these are, in the case of each natural kind, are analytic, and they do not have truth conditions. They are true, but they are not true in virtue of anything.

HEGEL AND CONTEMPORARY SCEPTICISM ABOUT FAMILIAR OBJECTS

Contemporary metaphysicians are deeply sceptical of the familiar objects recognized by common sense and by many empirical sciences. What explains the scepticism? I shall begin this chapter by suggesting that contemporary metaphysics is dominated by the style of thought which Hegel – using the nineteenth-century vocabulary of faculties – called “the Understanding,” and that “the Understanding” is constitutionally antipathetic to familiar objects. But first a few words about the style of thought that finds familiar objects congenial – the style of thought which Hegel identified under the title “Reason.”

A prime characteristic of “Reason” is that it is willing to recognize what Hegel called “identity in difference.” “Identity in difference” is a form of sameness which articulates itself in difference. One example is the sort of persistence that seems to characterize familiar objects. Typically, a familiar object goes on being itself while passing through different phases or properties, that is, while differing from itself. Indeed in many cases – and especially if we count such properties as age among the relevant ones – a familiar object can go on being numerically the same object only by differing more and more from its earlier self. Another example is the relation of a familiar object to its parts. One and the same familiar object comprises different parts at different times; in the particular case of organisms, a familiar object can go on being itself only by expelling former parts and adding new ones.

Common sense and learned science alike suppose that the objects that they believe in – or the overwhelming majority of them, at least – persist across changes, exchanging one intrinsic property for another. A point familiar to those who have followed the recent literature on persistence, and amazing to those who have not, is that defending this commonplace supposition takes considerable philosophical effort. The first message of this chapter is that it takes even more effort than has yet been recognized – that a widely favored way of dealing with the philosophical problems that arise here, namely “stage theory” or “exdurantism,” as much betrays the convictions of common sense and learned science as it honors them. For exdurantism, unless supplemented, lands us in the “explosivism” scouted in chapter 1; and the only supplementations that will avert explosivism require that the temporal stages, in which exdurantism believes, be tied together in ways that exdurantism cannot explain – tied together by jointly occupying shadows cast by entities to which exdurantism cannot appeal.

The reason why exdurantism is widely favored is that it appears to combine two virtues, of which each rival view can claim only one. Perdurantism has the virtue of ruling, along with our commonplace supposition, that no contradiction is involved in one and the same object's possessing contrary properties – in the same poker's being now hot and later cold, or the same person's being now seated and later standing upright.

Contrariety is not defined, I contend, for either the structural properties that typically characterize massive pluralities of microparticles, or for the structural properties that characterize typical universal mereological composition (UMC) objects. That is, there is no fixed and stable phenomenon of “more and less different from” that relates any two such properties to a third. Suppose that c1, c2, and c3 are structural properties of either sort, and at least appear to be contraries of one another. Then I contend that c3's being farther removed than c2 from c1, along some dimension D1 of difference, does not in and of itself amount to c3's being more different than c2 from c1. On the contrary, depending on how c3 and c2 stand towards c1 on other dimensions of difference, c3's being farther away than c2 is from c1, along D1, may amount to c3's being less different from c1 than c2 is. The same is true of any dimension of difference along which c3's difference from c1 may be compared with c2's difference. No dimension trumps all the rest. There is no final, stable product of c2's and c3's relative differences from c1 along all the dimensions of difference.

My experience shows that this contention is initially hard to believe, or perhaps just hard to understand. Initially, it can seem obvious that c2 and c3 each lie at some determinate distance from c1 along D1; that they are each also separated from c1 by some determinate interval along dimension D2; and so on through all the dimensions with respect to which both c2 and c3 both have locations.