Dickson - Metaphysics and Science (Draft)

8/9/2019 Dickson - Metaphysics and Science (Draft)

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(Rough!) DRAFT: Not for quotation

Metaphysics and Science

Michael Dickson1

History and Philosophy of ScienceIndiana University2

1 The scope and limitations of this discussion

This paper is about the relationship between science and metaphysics. I am particularlyconcerned to comment on how metaphysics as currently conceived by its practitioners is, orought to be, closely connected to contemporary science and philosophy of science, thoughsuch a concern naturally leads me to propose my own account of metaphysics, an account thatis largely based (as many contemporary accounts are) on Aristotle. Such a discussion belongsto meta-philosophy, and as such, it suffers the limitations of any philosophical discussion withpretense of great generality.

First, generality precludes detailed consideration of a wide range of examples. The best Ican offer here is a consideration of some examples that may be judged ‘important’ at least inthe sense that they come from well-read mainstream journals and books, written by people

who seem to have considerable standing in the profession. And while my consideration of these examples will be somewhat brief, a brief consideration is sufficient to illustrate thegeneral points I want to make.

Second, general claims can be difficult to apply in specific cases. Consider this parallelcase: to claim that the foundations of mathematics should be based on set theory does nottell one how to produce those foundations. Similarly, I will claim that metaphysics ought tobe pursued in a certain way, in relation to science and philosophy of science. Doing so doesnot, however, provide more than a hint about how to proceed in specific cases (i.e., how topursue specific metaphysical projects).

Third, generality presupposes that there is something about its subject matter that canbe captured in very general terms. In the present case, I am assuming that there is an

‘essence’ of metaphysics, that is, some general account that applies to just about anythingthat one would care to call ‘metaphysics’. I am far from clear that this presupposition

1Author’s full address: 1011 East Third Street, 130 Goodbody Hall, HPS, Indiana University, Blooming-ton, IN 47401 USA

2Thanks to audiences at Indiana University, the University of Minnesota, the University of Chicago, andthe University of Connecticut for comments on related talks. Thanks also to Michael Friedman and JonJacobs for some helpful comments. Finally, thanks to Jeremy Butterfield for helpful conversations, andespecially for pointing out some references on rational continuum mechanics.


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is true, and even less clear that I am the right person to provide a general definition of contemporary metaphysics. Hence I shall take it as an important part of my discussionto provide an account of metaphysics that is based on the accounts of those who professthe discipline. My only defense here is that there is sufficient commonality amongst thoseaccounts to suggest a common activity. As we shall see, however, there is also considerablevariation, so that my discussion will have to be quite general indeed if it is to capture all,or most, of the varieties of contemporary metaphysics. As I suggested above, the specificexamples that I discuss will leave most of this variety unexplored.

Fourth, very general arguments invariably require presuppositions that are themselvesvery general in scope, and therefore not amenable to detailed defense with a limited amountof ink. For example, I shall have to make some assumptions about the long-standing debatein philosophy of science about the ‘underdetermination of theory by evidence’. While I willneed to take a position on this debate, I can do no more than indicate a line of argumenthere.

The paper has seven sections, including this introduction. In the next section I shalldiscuss Aristotle’s account of metaphysics, with the help of Irwin’s (1988) analysis. Insection three I shall consider the accounts of three contemporary metaphysicians, payingspecial attention to their apparent adherence to some methodological principles that seemin part to characterize contemporary metaphysics. In section four I shall propose a specificaccount of the relationship between metaphysics and science, which will of course include aparticular conception of metaphysics itself. In section five, I present an argument in favorof this account, based on the nature of evidence in metaphysics. In section six, I present arelated argument, based on a conception of the nature of intellectual inquiry and the point of doing metaphysics in the first place. Finally, in section seven, I illustrate the preceding

considerations with a brief look at a few examples.

2 The nature of metaphysics according to Aristotle

A study of various contemporary attempts to describe metaphysics turns up two noteworthyresults: (1) amongst contemporary metaphysicians (i.e., those contemporary philosopherswho claim to ‘do metaphysics’), there is a considerable variety of opinion about what theyactually do (though also a few notable points of agreement, as I shall discuss in the nextsection); and (2) at the same time, almost every account of the nature of metaphysics beginswith a discussion of Aristotle. (Apparently it is obligatory to mention that the title of Aristotle’s Metaphysics can be understood to mean ‘the book that comes after the physics’

and historically it probably should be understood in that way.) Indeed, whatever all, ormost, contemporary metaphysicians have in common seems to be largely contained in thiscommon heritage, so before turning to some contemporary accounts of metaphysics, I shallconsider Aristotle. Later, I shall adopt what I take to be the essence of Aristotle’s account.

Alas, even Aristotle presents us with multiple accounts of metaphysics. There are fourteenbooks in the Metaphysics , seven of which begin with an account of what exactly is being donein this treatise, and several of which differ, at least prima facie , in this account. This fact canbe explained in part by noting that the Metaphysics was almost certainly not intended by

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Aristotle to be a single treatise. Instead, the various books of the Metaphysics were almostcertainly put together by some later editor. Even so, it seems clear that from one book tothe next, Aristotle does take himself to be describing roughly the same activity. After all, heuses similar terminology in each case (e.g., ‘first philosophy’ and ‘the highest science’—I shallcontinue to use the term ‘metaphysics’). Indeed, following Irwin3, I read the Metaphysics inpart as a defense of the possibility of metaphysics in the face of severe difficulties.

The structure of Aristotle’s defense can be seen in a brief synopsis of the relevant partsof the Metaphysics , focusing on those passages where Aristotle gives something like a def-inition or account of metaphysics. At the beginning of book 1, Aristotle gives an accountof metaphysics as a kind of wisdom ( ), the ‘science [ ] about certain causes[ ] and principles [ ]’ (982a2-3). Those ‘certain’ causes and principles turn out tobe the ‘first’ and ‘most universal’ ones; God [ ] is found to be both the proper possessorof such knowledge and, in part at least, the object of such knowledge. In a related account,at the beginning of book 2, metaphysics is described as the ‘science of truth [ ]’ (993b21), and it turns out that such a science requires a knowledge of causes,which are themselves ‘most true [ ]’ (993b29) when they are the ‘principles of eternal things [ ]’ (993b27). Together, then, these accounts point to aconception of metaphysics as something like philosophical theology. Aristotle writes:

For the most divine science is the most honorable, and a science would be mostdivine in only two ways: if God above all would have it, or if it were a scienceof divine objects. This science alone [that is, the science that is being done here,in the Metaphysics ] happens to be divine in both ways; for God is thought by allto be one of the causes and a principle, and God alone or in the highest degreewould possess such a science.4

Later, Aristotle argues that there is an immovable, eternal, substance—presumably theGod mentioned here—which is the ultimate principle or cause of all other beings, so thatmetaphysics is, ultimately, concerned with this particular substance, at least in the sensethat it is paradigmatic of substance. So metaphysics is a science, the science of truth, orwisdom, which entails that it is a science of first principle of causes, which entails that it is,at least paradigmatically, a science of God.

Book 3 introduces several difficulties, both methodological and substantive, for the verypossibility of metaphysics so conceived. There are three sorts of difficulty: questions aboutwhat could be the subject-matter of metaphysics, questions about how metaphysical knowl-edge is possible, and specific questions about the nature of first principles. The first two

sorts of difficulty arise from Aristotle’s conception of scientific knowledge. The theory thatAristotle expounds at length in the Prior Analytics and Posterior Analytics is that each

3Irwin, T. Aristotle’s First Principles (Oxford University Press, 1988). See especially the whole of chapter8, which makes in detail the case that I am outlining here.

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(983a5-9)

This and subsequent translations of Aristotle are mine.

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specific science takes some principles as its starting-point, and demonstrates (in the logicalsense, by way of syllogisms of a certain kind) what must follow from them. The princi-ples themselves are indemonstrable within that science, though they might be demonstrablewithin some other science. (Indeed, exactly in this way later Aristotelians would build ahierarchy of the sciences, hints of which can be found in Aristotle himself.) By a principle’sbeing indemonstrable, Aristotle means that the specific science does not demonstrate thatits principles apply to anything. So, for example, in the Physics Aristotle quickly dismissesParmenides on the grounds that it is no part of physics to show that things change. Changeis a principle of the science of physics, and therefore it is not the physicist’s responsibilityto show that anything does in fact change.

Alas, if metaphysics is, as Aristotle describes in book 1, the science of first principles,then it must be impossible, on Aristotle’s conception of ‘science’. Aristotle notes this pointmore or less explicitly in his list of problems for metaphysics in book 3. For example, havingclaimed that the first principles of things are substances (because substances exist first andforemost), Aristotle asks:

Is our investigation concerned only with substances or also with their attributes?I mean, for example, if solids and lines and planes are substances, is it the concernof the same science to know these and their attributes (which are proved by themathematical sciences) for each genus, or of another science? If of the same,then the science of substances, too, would be a demonstrative science; but itseems that there is no demonstration of whatness. But if of another science,what science will be the one to investigate the attributes of substances? It isextremely difficult to answer this question.5

Aristotle is describing the dilemma in which he finds himself. If metaphysics is concernedto demonstrate the attributes of substances, then either it is no different from the specialsciences (also concerned with the attributes of various substances, though not all at once),or it differs from them by not taking substance for granted. But “it seems that there isno demonstration of whatness”—i.e., one cannot show that ‘substance’ applies to anything.Speaking more generally (abstracting from Aristotle’s peculiar claim that the first principlesare substances), first principles are (by definition) not demonstrable. And yet metaphysicsmust be concerned to demonstrate the attributes of substance (or more generally, with theattributes of the first principles) if it is to be a science of substances (first principles), foraccording to Aristotle’s conception of science, a science of X demonstrates the attributes of X.

Hence, again, either the science of metaphysics is just like any other science, and merely demonstrates the attributes of certain principles taken for granted, or somehow it sidesteps

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(997a25-34)

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the apparent impossibility of demonstrating first principles themselves. The dilemma leavesthe very possibility of metaphysics as a science (as able to generate knowledge) in seriousdoubt. On the one hand, metaphysics cannot just be another science, for it is in a far worseposition than they: the other sciences can appeal to ‘higher’ sciences for a demonstrationof their principles, while the principles of metaphysics would be free-floating, apparentlycompletely lacking in justification. On the other hand, it is far from clear how those principlescould be justified.

Apparently in response to these challenges to the possibility of metaphysics as a science,book 4 re-describes metaphysics as “a science that investigates being as being and whatbelongs to it by itself [ ]”(1003a20-21), that is, what belongs ‘essentially’ to it:

There is a science that investigates being as being and what belongs essentiallyto it. This science is not the same as any of the so-called special sciences; for

none of those sciences examines universally being qua being, but, cutting off some part of it, each of them investigates the attributes of that part, as in thecase of the mathematical sciences. Now, since we are seeking the principles andthe highest causes, clearly these must belong to some nature in virtue of itself.If, then, also those who were seeking the elements of things were seeking theseprinciples, these elements too must be elements of being, not accidentally, butas being. Accordingly, it is of being as being that we, too, must find the firstcauses.6

As Aristotle goes on to say (and as I have already noted), by ‘being’ he means, primarily,‘substance’ (anything that is a ‘this’). Later, Aristotle spells out the conclusion of these

considerations very clearly:

And indeed our inquiry or perplexity concerning what being is, in early timesand now and always, is just this: What is a substance?. . . And so we, too, mustspeculate most of all, and first of all, and exclusively, so to say, concerning beingthat is spoken of in this sense. What is being?7

Aristotle is clear here that he has not abandoned his earlier conception of the project. Hereiterates that metaphysics seeks to examine the ‘principles and highest causes’. Rather than

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(1003a21-33)

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. . .

(1028b3-7)

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abandoning his project, Aristotle is clarifying it partially in answer the problems describedin book 3. In particular, he shows how metaphysics, while studying the very same substancesstudied by the special sciences, can nonetheless be a distinct enterprise, for it studies thempurely as substances, as beings. Indeed, as Irwin writes, metaphysics distinguishes itself fromthe special sciences precisely because it “studies those properties of the objects of specialsciences that the special sciences themselves must assume.”8

However, distinguishing metaphysics, as the science of substance, from the other sciencesdoes not answer the more fundamental challenge remaining from book 3, namely, to showthat there can be such a science in the first place. Indeed, as the dilemma raised above shows,the distinction raises that particular challenge all the more acutely. Aristotle is painfullyaware of the problem, and in the end recognizes that his conception of science simply makesno room for metaphysics as a science. And yet he insists that metaphysical knowledge is,in some serious sense, possible. In particular, metaphysics cannot be approached merelydialectically, for dialectic begins with an examination of common opinion, which might itself be so far from the truth as to make even an exemplary application of the method of dialecticinsufficient to lead to the truth.9 He writes:

All of these sciences [the special sciences] single out some existent thing or class,and concern themselves with that, not with being unconditionally or in so far as itis being. Nor do they give any argument about the essence; but some make it clearby perception, others take it as an assumption, and from this demonstrate withmore or less necessity the intrinsic attributes of the genus that concerns them.Hence it is clear from this survey of examples that there is no demonstration of substance or of essence, but some other way of making it clear.10

What is this ‘other way’? Aristotle shows us more than tells us, by his various arguments thatappear in the Metaphysics . Those arguments are indeed dialectical in the logical sense, butthey can be distinguished from run-of-the-mill dialectical arguments in one crucial respect:their starting point is the necessary presupposition required for the special sciences, namely,the existence of the principles of those sciences. In other words, for Aristotle, metaphysicsgets its epistemological punch not by being demonstrative (in Aristotle’s sense), but bytaking as its starting-point the principles required for the possibility of the special sciences,that is, the possibility of them as genuine producers of knowledge, which he does not doubt.(And Aristotle takes the primary such principle to be substance.)

The clearest example we have, from Aristotle, is his defense of the principle of non-contradiction. Aristotle explicitly recognizes that this principle is taken for granted in the

8Irwin, op. cit., p. 170.9Topics ; cf. 1061b6-10.10

(1025b8-16); cf. 1064a8-10, also GA 742b32-4.

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special sciences, and therefore that a defense of the principle is properly a part of metaphysicsas he conceives it. He also notices precisely the sort of problems already raised aboutarguments concerning such principles. Pretty clearly we aren’t going to mount an argumentwhose conclusion is the principle of non-contradiction without begging the question:

Some, indeed, demand to have the law proved, but they do so because they lackeducation; for it shows lack of education not to know of what we should requireproof, and of what we should not. For it is quite impossible that everythingshould have a proof; the process would go on to infinity. . . 11

So how can it be defended? A plausible answer is crucial, because on the one hand, meta-physics cannot be mere dialectic for Aristotle, and yet on the other hand it is not science inthe usual sense (of deriving conclusions from principles).

Aristotle’s answer is that the principle can be demonstrated “by refutation”.12 Aristotle

imagines an opponent who claims that for any property, P , one can always assert that asubect, S , both has and does not have P . But then, Aristotle asks, what can possiblyidentify the subject as one and the same subject that both has and does not have P ? Forthe subject must itself be identified by its having some characteristic property. That is, S isS precisely because it has some property or other making it S .13 Call this property P S . Butthen, according to our imagined opponent, we can say of S both that it has P S and that itdoes not have P S . But in the latter case, we could not possible be making the assertion thatS fails to have the property P S , because if it failed to have that property, it would not beS . In other words, our opponent has in fact failed to assert that S both has and does nothave P S .

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So Aristotle has not, here, proven the principle of non-contradiction. Rather, he has

shown that denying it—at least, denying it in the specific way that he here imagines hisopponent to do—is impossible, because doing so undermines an assumption required fordenying it in the first place (namely, that in the statements ‘S has P ’ and ‘S does not haveP ’, S refers to the same subject in both cases). This sort of argument is supposed to beparadigmatic of metaphysical reasoning. Metaphysics is supposed to examine, in this way,the principles that are taken for granted by the ‘special sciences’ (that is, for Aristotle, allknowledge-producing inquiries apart from metaphysics—given his theory of knowledge, it ispretty clear that for Aristotle, such inquiries are logic, mathematics, and the other sciencessuch as physics, biology, astronomy, and so on).

11

. . . (1006a5-9)

12

(1006a12). What is being shown to beimpossible, here, is the denial of the principle of non-contradiction.

13Although Aristotle might think that this property is something like an ‘essential property’ in some strongsense, there is no clear need to make this assumption. For example, the property could just be ‘filling agiven spatial temporal region’.

14See Irwin, op. cit., pp. 179–183.

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3 The nature of metaphysics according to contemporary meta-physicians

While Aristotle may reasonably be thought to have first defined the discipline of metaphysics,that discipline has certainly not always lived up to his definition. Indeed, metaphysicscame to include the study of being from more specialized perspectives. Some rationalistphilosophers referred to two types, or branches, of metaphysics: ‘general metaphysics’, thescience of being qua being more or less as conceived by Aristotle; and ‘special metaphysics’,the science of being from some perspective. For example, Christian Wolff explicitly dividedmetaphysics into general (which he took to be the study of being qua being, or ontology)and special, the latter of which was subdivided into rational theology, rational psychology,and rational cosmology. Now Aristotle himself (as I understand him) would not have deniedthat metaphysics can address some of the topics that the rationalist philosopher places

under ‘special metaphysics’, so long as it does not make the mistake of doing so in a waythat encroaches on issues that properly come under the purview of the special sciences.While, on the one hand, it is no part of physics to prove that there are changeable things,it is likewise no part of metaphysics to draw conclusions that are properly derived fromconsiderations internal to physics. (The metaphysician might claim to argue for them fromother considerations, but in this case he or she is really doing armchair physics. The point isthat if the conclusions could follow from considerations entirely within physics, then they arenot, in Aristotle’s conception, a part of metaphysics.) So in general, an Aristotelian shouldbe quite skeptical of ‘special metaphysics’, at least as it was practiced by some rationalistphilosophers.

But many contemporary metaphysicians do not seem to share this skepticism. Indeed,

the Wolffian distinction between general and special metaphysics seems to have survived,with both aspects of the enterprise alive and well. As Simons puts it:15 “”Metaphysics isgenerally practised today as, on the one hand, general ontology or theory of objects and,on the other hand, an assortment of more or less traditional metaphysical disputes, on suchtopics as free will, God, universals, space and time and persons.” However, I do not wishto rely on the second-order observations. Instead, I turn, first, to an examination of somecontemporary views about metaphysics as given by those who practice the discipline. LaterI shall consider some examples.

I begin with Laurence and MacDonald’s introduction to the nature of metaphysics.

Metaphysics, as Aristotle characterized it, is concerned with the study of ‘beingqua being’. That is, it is concerned to study being as such. . . . Other disciplines,specifically the sciences, . . . are not interested in being in general, the kind of beingthat abstracts from the nature of this or that particular thing. But metaphysicsis interested in this. Metaphysics is interested in determining what is required,what conditions need to be met, for something—anything—to exist.16

15Peter Simons, p. 312 in Kim, Jaegwon, and Sosa, Ernest (eds.) A Companion to Metaphysics (BlackwellPublishers, Oxford, 1995).

16Contemporary Readings in the Foundations of Metaphysics , p. 1.

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Apparently this interest extends to, or implies, an interest in what types of thing thereare, for they write later that “one of the central questions in metaphysics is the questionof what types of things or entities there are” (ibid.). Apparently it also extends to at leastsome forms of what the rationalist philosophers called ‘special metaphysics’, for while specialmetaphysics does not make it into their official account of the nature of metaphysics, a brief look at the index of their book reveals substantial discussion of notions such as ‘physicalobjects’, ‘physical properties’, ‘numbers’, ‘time’, and more, not from the point of view of their being mere beings , but from the point of view of their being physical objects, physicalproperties, and so on.

The other essential ingredient in their account of metaphysics is a statement of somemethodological principles that further characterize the enterprise. Two of these principleswill be especially important for me, and are quite commonly adopted by contemporarymetaphysicians:17

The Principle of Parsimony: The issue of whether or not to accept prop-erties, for example, or numbers, or events, thus turns on the question of whatexplanatory roles entities of these sorts are needed to play. If they are not nec-essary, then we reject them. If they play a valuable explanatory role in our besttheories, then we accept them.The Principle of Commitment: A criterion of ontological commitment couldhelp us decide what to believe about what exists by telling us what featuresin our language or thought, or theory embodied in language and thought, haveontological significance, or have implications for what exists.

On the one hand, these principles seem to be compatible with the Aristotelian conception

of metaphysics as I outlined it above. In more explicitly Aristotelian terms, the Principle of Commitment is the principle that the possibility of the special sciences requires the existenceof the principles of the special sciences. (Mathematics does not study whether numbers exist,but the possibility of mathematical knowledge relies on the existence of numbers. And soon.) Similarly, according to (an explicitly Aristotelian version of) the Principle of Parsimony,if it can be shown that a given special science can dispense with a certain principle, then weno longer have any reason to accept such a principle. (So one might, for example, argue thatin fact mathematics can get along just fine without the supposition that numbers exist.)

On the other hand, one could well ask, in the first place, whether the principles are tobe interpreted in quite this way. Evidence from the practice of metaphysicians (for example,evidence from other parts of the book in question) seems to suggest not. In particular, it

seems that they have a much wider conception of what sorts of explanations and ‘features...’the metaphysician ought to take seriously. But I shall return to this issue later.Our next example is from Van Inwagen. His account is more or less linguistic, an attempt

to say which statements count as ‘metaphysical’. He writes:

Perhaps, in the end, all we can say is this: some ‘categories’ or ‘concepts’ aresufficiently ‘general’ that a statement will count as a ‘metaphysical statement’ if—

17The principles are from ibid., p. 5 and are written here as they are there. Many contemporary meta-physicians explicitly or implicitly adopt these or very similar principles. We shall see an example later.

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given that it is made in a context in which no restrictions of intended reference arein force, and given that the person who makes it is making a serious effort to saywhat is strictly and literally true—it employs only these categories. Among thesecategories are many that we have already used in our examples: ‘physical thing’,‘spatial object’, ‘cause’, ‘event’, ‘past’, ‘property’. . . . [T]here will be borderlinecases of ‘sufficiently general’ categories: ‘impenetrable’, ‘pain’, ‘straight’ and‘surface’ are possible examples of borderline cases.18

This characterization apparently leaves wide open the door to the house of metaphysics. Isuspect that a little clever thought could produce a great many statements that meet vanInwagen’s characterization but that seem to come rather under the purview of science, orthe philosophy of the special sciences. In particular, many statements from physics and theinterpretation of contemporary physics seem to satisfy van Inwagen’s criterion. Consider:‘No physical thing is impenetrable’ (arguably a statement from some field theories), or ‘no

event can be the cause of another event in its past’ (arguably a statement from the theory of relativity), or ‘every physical thing is composed of parts with no spatial extension’ (arguablya statement from Bohm’s theory or from relativistic quantum field theory19).

What about the qualifier that there be no restrictions of intended reference? Let usconsider just one example and see how this qualifier might apply. I suggested that thestatement ‘no event can be the cause of another event in its past’ might meet van Inwagen’scriterion. One might retort that this statement comes with an implicit restriction, and shouldbe parsed as: ‘if the theory of relativity is true of a world, then in that world, no event...’.But no: this restriction is not part of the meaning of the original statement. Instead, theappeal to special relativity is part of the justification. The claim is intended to be perfectlyand absolutely general: ‘in the class of all things that are events, there is not a single one

that is the cause of another in its past’. One can argue for this claim on the basis of specialrelativity, and of course the evidence for the truth of that theory is at least in part empirical,but the claim itself does not rely on these points.

Again, however, one might retort that empirical considerations simply cannot be a partof metaphysics, because the very nature of the enterprise is somehow incompatible with thepossibility that empirical considerations could either justify or defeat a metaphysical claim.But some (if not all) of the categories mentioned by van Inwagen have plainly empiricalimport. Can one be said to be ‘making a serious effort to say what is strictly and literallytrue’ while ignoring this fact? Again, I turn to such questions in greater detail later. (Of course, I do not suppose that van Inwagen would endorse or reject any of the arguments here.He is in any case clearly uneasy about pronouncing a definition of metaphysics. I shall, on

the other hand, press van Inwagen on such questions later, not while considering his generaldiscussion of the nature of metaphysics, but while considering a specific example of his ownmetaphysical practice.)

Finally, I consider Loux’s account of metaphysics. He too begins with Aristotle, and

18van Inwagen, ‘The Nature of Metaphysics’, pp. 13-14.19It might sound odd that I mention field theory in this context, but in fact many physicists have ar-

gued that relativistic quantum field theory (unlike its non-relativistic counterpart) cannot sustain a fieldinterpretation but must instead be understood to describe particles, possibly point-like particles.

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indeed he takes the view that metaphysics most properly conceived is just the science of being qua being, without extension to ‘special metaphysics’. Especially important, for Loux,is the identification of categories. He writes:

In this book, we will follow the Aristotelian characterization of metaphysics asa discipline concerned with being qua being. That characterization gives rise tothe attempt to identify the most general kinds or categories under which thingsfall and to delineate the relations that hold among those categories.20

Loux goes on to endorse something like the conjunction of the Principle of Parsimony andthe Principle of Commitment in the course of discussing an imagined dispute about whatcould make the sentence ‘George performed five somersaults’ true. One philosopher saysthat the truth of the statement rests on the real existence of certain somersaults (namely,the ones that George did), while another says that there is no special class of entities as

‘somersaults’, in much the same way that behavioral psychologists denied a special categoryof ‘intentions’. Loux writes:

They are disagreeing about whether the relevant facts of ordinary usage and thetruth of the relevant prephilosophical claims require us to recognize somersaultsin our ‘official’ philosophical story about the world and its workings; they aredisagreeing about whether things like somersaults should enter into our ‘official’philosophical inventory of things that are.21

Later, speaking more generally, Loux writes:

Are there properties? Are there relations? Are there events? . . . In each case,

there is a body of prephilosophical facts that function as data for the dispute.One party to the dispute insists that to explain the relevant prephilosophicalfacts, we must answer the existential question affirmatively.

The other party, of course, argues that an alternative explanation can be found.Again, one wonders exactly which ‘prephilosophical facts’ must be explained, and perhaps

more importantly, how one determines whether a given potential explanandum is indeed a‘fact’ in the first place. The actual practice of metaphysics, on Loux’s account, appears todepend crucially on this issue. I shall return to it later.

4 Metaphysics and science

Given these accounts of metaphysics (and they are quite typical of what one finds amongstcontemporary metaphysicians), what can we say about the relationship between metaphysicsand science? Let us note, first, that, unlike Aristotle, contemporary accounts of the nature of metaphysics mention the special sciences only to distinguish metaphysics from them. Recallthat Aristotle, in the end, grounded the epistemic value of metaphysics on the fact that it

20Loux, M. Metaphysics , p. 2.21Loux, op. cit., p. 15.

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takes as its own starting-point the presuppositions required for the special sciences. I knowof no contemporary metaphysician who follows Aristotle on this point.22

On the other hand, as I noted earlier, it does not follow that according to the con-temporary accounts, the special sciences do not play an important role in the practice of metaphysics, and indeed one does find occasional reference to the special sciences in the prac-tice of metaphysics, though one also finds explicit denial of their relevance to metaphysicalissues.

The central claim of this paper is that by abandoning this aspect of Aristotelian metaphysics—that is, by dropping the idea that the ‘prephilosophical facts’ requiring explanation are theprinciples of the special sciences—contemporary metaphysics runs a serious risk of beingunrespectable, epistemically. In other words, in a way that I shall discuss, metaphysics (asdescribed by many contemporary metaphysicians) must look to science and the interpretationof science. My discussion will largely focus on physics (my own area of expertise), but thepoint extends to other sciences. (I will give one example from biology.) For a while longer,I will also maintain the sharp Aristotelian distinction between issues concerning being quabeing and other issues apparently allowed into metaphysics by at least some contemporaryaccounts, for example, van Inwagen’s. In the end, I shall propose that we may blur thisdistinction somewhat without harm to the project of metaphysics.

To illustrate the relationship between science and metaphysics that I have in mind, Ishall begin with Loux’s account. He says that metaphysics is ultimately concerned with thetypes of thing that there are. One might be tempted to say, in response, that of coursescience is also concerned with what types of thing that there are. Are there atoms? Arethere forces? Does luminiferous ether exist? These sorts of question have been and stillare, raised by physics. However, maintaining for the moment the Loux’s strict definition of

metaphysics, we should point out that prima facie at least, physics appears to be concernedwith what types of physical things there are, while metaphysics, under Loux’s conception,is concerned with what types of thing there are, period. Presumably physical things wouldbe just one (though according to some philosophers, the only) example. To put the pointin Aristotelian terms, physics presupposes its principle—physical things—and then perhapsgoes on to study what types of physical thing that there are. So the quick and dirty argumentfor the relevance of physics to metaphysics does not work.

But that argument also misses something important about the nature of physics. It isnot, in fact, concerned merely with what physical things there are. Rather, it is concerned togive an account of those things, and doing so involves, even if only implicitly, some referenceto what types of things that there are, in general. Are there events? Well, can we make any

sense of the theories of special and general relativity without them? (Probably not.) Arethe possible worlds? Well, can we make sense of quantum theory without them? (Probably.)And if we can, are we thereby committed to the existence of some other basic category of things, perhaps mathematical objects of some sort, or chances? Physicists and philosophersof physics grapple with exactly these sorts of question. In other words, they grapple withquestions that are, by metaphysicians’ own lights, metaphysical. The subject-matter of metaphysics is, in part, the subject-matter of physics and the philosophy of physics.

22Of course I may well just be ignorant of them.

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I hope it is clear that I am not claiming that there is nothing for metaphysics to do. I amclaiming, rather, that metaphysical questions are properly addressed to, and in the contextof, that is, while respecting, or taking into account, what is required for or presupposed byscientific explanations. Thus far, I have only pointed out that science can indirectly playthe role of addressing metaphysical questions by means of an analysis of what is requiredfor scientific understanding (or at least by means of taking such requirements as evidence ).I have not yet argued that science should be taken to play that role, much less that theevidence thus provided has a special authority in metaphysical investigations.

I turn now to that argument, which has two parts. The first concerns the methodologyof metaphysics, and the second concerns the point of metaphysics.

5 The methodology of metaphysics

My claim that science provides a kind of evidence for metaphysics that has special authoritytherein is based, in part, on the methodological principles that we have already seen. ThePrinciple of Parsimony confirms the crucial evidentiary role that explanatory power has inmetaphysical arguments, and the Principle of Commitment asserts that what needs explain-ing is, in Laurence and MacDonald’s words, “features in our language or thought”, or moregenerally, in Loux’s words, “prephilosophical facts”.

Why adopt such principles? The issue here is what will count as evidence in metaphysics.While all disciplines raise this issue—for example, there are serious questions in science aboutthe nature of experimental evidence and about what sorts of experiment do provide goodevidence, and so on—metaphysics raises it in a particularly pressing form. It does so inpart because in comparison with other disciplines (and I am not thinking only of science

here) metaphysics shows precious little agreement amongst its practitioners. Another causefor concern about the nature of evidence in metaphysics arises from the pronouncements of some metaphysicians themselves. Consider this notable (and admittedly radical, but by nomeans unique) account from Schlesinger:

[I]t seems we cannot coherently imagine any fact, no matter how strange anddifferent from anything so far observed, that might be discovered in the futureand that would affect the credibility of any metaphysical hypothesis.23

Indeed, Schlesinger considers a situation where in fact some empirical evidence is successfullybrought to bear on a purported metaphysical question, and he says:

I do not believe that this would disprove my thesis; it would show rather thanwhat was thought to be a metaphysical problem turned out to be a scientificproblem.24

23Schlesinger, George N. Metaphysics: Methods and Problems (Barnes and Noble Books, New Jersey,1983), p. 31.

24ibid., p. 22.

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One is left tempted by Bradley’s quip that ”metaphysics is the finding of bad reasons forwhat we believe upon instinct”.25

Of course, we need not follow Schlesinger’s conception of evidence in metaphysics, andmany metaphysicians do not. My point is that while many disciplines have agreed (thoughchanging) standards of evidence, metaphysics shows considerable variation amongst its prac-titioners on this issue. This fact alone makes the question of what the standards ought tobe in metaphysics somewhat more pressing than it is in other disciplines.

It is difficult to know how to proceed, here. Indeed, we saw above that Aristotle himself had a very hard time with this question. Reading extensive accounts about the nature of evidence in metaphysics leaves one with the impression that any answer to the question willbeg questions against those who have a different conception of the enterprise. However, weare not at a total loss for guidance. In the remainder of this section, I will take as my guidethe following two claims, each more or less stolen from Aristotle:

Absence of first principles: Unlike other disciplines, metaphysics does nothave first principles that it can take for granted and upon which metaphysicalarguments can be based.

Need for objective evidence: Arguments in metaphysics must proceed fromsomething other than personal intuition.

A few brief comments about these principles are in order.Unlike Aristotle (perhaps), I have no grand theory in mind of what a ‘first principle’ is.

The point I am making in the first claim is rather mundane: metaphysics cannot take theexistence of any type of being for granted. Physics can take the existence of a physical world

for granted, without worrying about radical idealism. And subdisciplines within physicsoften take other things for granted. Psychology can take the existence of other minds forgranted, without worrying about the problem (if it is a problem) of other minds. Metaphysics,because it is the study of the conditions that anything must satisfy if it is to exist, can takethe existence of no thing for granted. What is more, it cannot take anything for granted asprinciple from which, logically, metaphysical conclusions can be derived . As we saw fromAristotle, even the principle of non-contradiction is up for grabs, and subject to metaphysicalanalysis.

For now, I have a similarly unremarkable claim in mind in asserting the need for objectiveevidence. The point of this claim is just to rule out personal intuition as insufficient toestablish a metaphysical claim. I have in mind some metaphysicians who seem to appeal

to personal intuition. For example, after offering a definitions of various temporal concepts,Slote writes, ”It should be noted, however, that the correctness of our definitions depends onthe logical impossibility of certain kinds of time travel into the past” and then, after makinga few brief remarks about relativity, dismisses this problem, saying that ”I am not sure thatsuch time travel is impossible, but I think the whole idea of it is very suspicious and hard tomake sense of”.26 My point here is not to question Slote’s attitude towards time travel, but

25Bradley, F.H. Appearance and Reality (Oxford University Press, 1893)., p. x.26Slote, Michael A. Metaphysics and Essence (Basil Blackwell, Oxford, 1975), pp. 38-39.

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rather to question the relevance of his own opinion of the matter, thus expressed. My claimis that something other than an individual’s intuition, or ability to ‘make sense of’ a claim,is needed as evidence in metaphysics. There is no evident connection between anybody’spersonal intuition about a claim, or anybody’s ability to ‘make sense of’ a claim, and thetruth of that claim.

Returning to the methodological principles of Parsimony and Commitment, I believethat the point of introducing them must be, on the one hand, to acknowledge the absenceof first principles in metaphysics, and on the other hand, to provide a kind of objectiveevidence for metaphysics, that evidence being the ‘features in our language or thought’ orthe ‘prephilosophical facts’ that we seek to explain in as parsimonious a manner as possible.

But why do these things need explaining, and why does explaining them (parsimoniously)lend credence to a metaphysical claim or system? There are apparently several presupposi-tions at work here that one might want to question, for example, whether the more parsimo-nious explanation is more likely true, and so forth—questions familiar from the philosophyof science. But there is a question that logically precedes this and related questions, namely,why we should take ‘features in our language or thought’ as any kind of evidence in the firstplace.

The answer must be based on some sort of principle of optimism about the humanintellect. The idea, I suppose, is that human beings somehow ‘naturally’ get things basicallyright about the world. Human beings are not radically mistaken about the nature of reality.If we say or think that there are somersaults, then there must, in some sense or other, besomersaults. If we say or think that there are numbers, or whatever, then there must, insome sense or other, be numbers. If the existence of somersaults, or numbers, or whatever,can be explained, or best explained, only by the assumption that they form a basic category,

then in fact they must be a basic category.What might justify this principle of optimism? Apart from the idea that human beingssomehow generate reality—so that, in effect, human intuitions about reality are somethingakin to self-fulfilling prophecies—I can think of two basic forms of an answer to this question,a ‘theological’ form, and a ‘naturalistic’ form. The theological answer is that God createdhuman beings to be capable of grasping the world (for whatever reason). Some contemporaryphilosophers believe this answer on the basis of some particular understanding of God. Thenaturalistic answer is that, by some force of nature, human beings are so constituted thatthey will, as a matter of fact, basically gets things right. Some contemporary philosophersbelieve this answer on the basis of some particular understanding of the theory of evolution.

There is an obvious objection to the principle of optimism, however. As a matter of

fact, we humans have often been dead wrong about the nature of reality. Many humanbeings have supposed (and some still do suppose) that the earth is a disk, or that it is atthe center of the universe. Many humans beings have supposed (and many still do suppose)that heavier bodies fall significantly faster than lighter bodies, or that simultaneity is anabsolute relation. We were wrong about those things. Indeed, and more to the point, abrief perusal of journals in experimental human cognition reveals a plethora of cases wherewhat we believe ‘instinctively’ about the world is simply wrong. And I am not speaking,here, of sophisticated scientific beliefs such as the belief in phlogiston or the belief in thePtolemaic model of the solar system (though of course we were wrong about them too). I

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am speaking about our more or less everyday beliefs about the world, beliefs that manypeople continue to presume to be obviously true. In fact, it remains quite easy to astoundsmart undergraduates with simple experiments involving Galilean relativity, or the MontyHall problem.

Aristotle was aware of these problems, and precisely because of them, he ruled out di-alectic as a way to produce knowledge. Dialectic begins with ‘common beliefs’, carefullyexamining them and evaluating them against one another. But such an examination canproduce, at best, a coherent set of beliefs that may well remain false. In other words, if thePrinciple of Commitment really is just about ‘human language and thought’, then it doesnot, after all, seem to be able to provide a sound basis for metaphysical investigation, becauseupon reflection, it does not seem that we really should commit ourselves to the deliverancesof ‘human thought and language’, at least not of the everyday, allegedly ‘intuitive’ sort.

To what should we commit ourselves? Loux’s phrase ‘prephilosophical facts’ provides aclue how to proceed. Loux himself might have had in mind mundane ‘facts’ such as thepurported existence of somersaults, but the bare notion of a ‘prephilosophical fact’ leavesopen other possibilities. The issue that we face is this: mere opinion, or intuition, or instinct,or commonly held belief, appears to be insufficient to ground metaphysical arguments. Butthe deliverances of science will not do either, for they are inevitably based on assumptionsthat metaphysics as the science of being qua being ought not take for granted. To put thepoint differently, metaphysics cannot provide the explanation of the deliverances of science,for science itself provides that sort of explanation. However, there is something left formetaphysics to explain, namely, the possibility of science in the first place. In other words, Iam proposing, along more or less Aristotelian lines, that metaphysics as the science of beingqua being has a reasonable claim to produce knowledge if it takes as its task the parsimonious

explanation of the commitments or presuppositions of science, rather than the commitmentsof quotidian human language and thought.Why? What is special about science and more specifically its presuppositions or com-

mitments? The brief answer is that the commitments of science—whatever they are (and itmight be part of the task of metaphysics to identify them)—give rise to the most reliableand best-tested claims that we know about. (Of course, they are not infallible.)

As I shall discuss later, this proposal for metaphysics does in fact leave intact a numberof traditional metaphysical questions, but it re-orients metaphysics towards science in away that is often lacking in contemporary metaphysics, which still often seems to takepersonal intuition or ‘the way things seem to us’ as its starting-point. Indeed, even somemetaphysicians who appear to be cognizant of the role that science might play in metaphysics

do not, in my view, quite properly appreciate it. I shall conclude this section with an exampleto illustrate the point. This example will also help to illustrate my general proposal.Zimmerman wrote, in the 1990s, a series of papers27 discussing the issue whether extended

physical objects are composed of simple, indivisible parts. One is immediately tempted topeg this work as exactly the sort of work that should be undertaken only in relation to the

27I have in mind specifically the following: “Could Extended Objects Be Made Out of Simple Parts?”,Philosophy and Phenomenological Research 56 (1996):1–29; “Indivisible Parts and Extended Objects: SomePhilosophical Episodes from Topology’s Prehistory”, The Monist 79 (1996):148–180.

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deliverances of science. But Zimmerman is aware of this objection to his project, and clarifieshis position thus:

The question . . . is intended to be a peculilarly metaphysics one; it is not, “Arethere any extended bodies, and if there are do any happen to be composed of simples?”, but rather, “If there were such things as extended physical bodies,could they be composed entirely of simples?”28

He further clarifies his notion of an ‘extended body’ thus:

If something is . . . an extended body, then (1) it fills a precise three-dimensionalregion of space . . . , and (2) it is in some manner impenetrable with respect toother classes of space-occupiers.29

Zimmerman acknowledges that contemporary quantum theory probably entails that there

are no extended objects, in his sense. He does not seem to appreciate that no scientifictheory has ever explicitly countenanced his particular notion of extended objects, and herelies the basis of my main point.

Here, I suspect that Zimmerman would object. In the article that I am discussing,he cites Locke, and in other places, Descartes and Newton, as holding this view of bodies.However, as Zimmerman’s notion of a three-dimensionally extended body unfolds, it becomesclear not only that they did not hold such a view, but also that they could not have doneso. Zimmerman’s argument relies heavily on his notion of ‘filling a region of space’. Itturns out that what he means is ‘filling a region of a topological space that is topologicallyclosed’. Then, cleverly applying what are essentially simple facts from topology, he makeshis argument. I suppose it is obvious to any historian, and to most of the rest of us, that

Newton could have had no such account of ‘filling a space’ in mind.And he didn’t need it. Although Newton sometimes couched his theory in language

that appears to involve a commitment to extended impenetrable bodies—in a loose sense,certainly not in Zimmerman’s sense—the thery itself, in Newton’s hands at least, had noneed of any precise account of such things. (One can apply Newton’s theory to the motionsof the planets, the tides, the motion of falling bodies, and so on, without a half of a thoughtabout impenetrability or extension. Indeed, with a few simple assumptions, one can evenapply the theory to collisions.) So what does Zimmerman’s argument show, assuming thatthe argument is valid? It shows, in that case, only that some people may have harbored aconcept that, if made precise in a certain way, leads to a contradiction. (Can it be madeprecise in some other way? Yes, and I shall return to that point later.)

Now, although he mentions Newtonian science, Zimmerman does not, I think, really takehimself to be addressing the presuppositions of scientists. Indeed, as I have suggested, qua scientists, they did not need to be making any particularly precise presuppositions about thenature of extended bodies (at least not in the 17th and 18th centuries). It was scientificallypermissible for them to maintain a näıve, everyday, instictive, view that tables and chairsare solid through and through, and so on. It is this näıve, everyday, view that I think

28“Could Extended Objects Be Made Out of Simple Parts?”, op. cit., p. 2.29Ibid.

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Zimmerman takes himself to be addressing, and it is in addressing this view that I thinkhe has gone astray. Why should it be subject to metaphysical analysis? While the analysisitself may be admirable, insofar as it adopts a rigor that modern topology can provide, itis not clear what the value of the analysis is. It is not really an analysis of our everydaynotions—surely they do not contain the topological content that Zimmerman gives them—but neither is it an analysis of the requirements of (at least early Newtonian) science, forthat science did not require such notions. Zimmerman has, let us grant, shown that the bestexplanation of the existence of ‘extended objects’ is that they are made of ‘atomless gunk’,but once we learn what he means by ‘extended objects’, it is far from clear why we shouldbelieve that they exist in the first place.

It is crucial to bear in mind that my point is not that modern science might cast doubt onthe existence of such things. Zimmerman is aware of this objection, but thinks that even theassertion of the possibility of the existence of such objects is enough to get the metaphysicalwheels turning in a useful direction. I have my doubts about that claim, but nevermind.The crucial point is that Zimmerman’s conclusions are significant only if the precise meaningthat he attaches to the phrase ‘extended object’ makes sense in some scientific context. (Itcould not possibly be the content of our everyday beliefs about extended objects—very fewof us have anything like correct intuitions about the sorts of topological notions employedin Zimmerman’s analysis.)

There is a scientific context in which the notion of an extended body composed of impen-etrable point-like parts is important, namely, rational continuum mechanics. It is here thatZimmerman’s analysis potentially has some bite: he seems to have shown that one way of making sense of this concept, that is, one way of understanding the very possibility of rationalcontinuum mechanics, that is, one way to understand its foundational presupposition, does

not pan out. Of course, it does not follow that the concept is inherently self-contradictory.It is more likely—given the successes of rational continuum mechanics—that we have simplynot yet seen how to make sense of its presuppositions.

Well, that conclusion would be correct in this case if others had not already provideda foundational understanding of the presuppositions of the theory. However, as Zimmer-man seems not to have noticed, others have asked the question: How is rational continuummechanics possible? In particular, what understanding of extended bodies does it require?Authors such as Truesdell and Noll and Virga have addressed this question in detail, provid-ing a topologically respectable account of extended bodies that makes sense in the contextof rational continuum mechanics, and shows how, as a science of extended bodies, it is pos-sible.30 Of course, their account is incompatible with Zimmerman’s, but what does this fact

show? What recourse can Zimmerman take? He could argue that his account better accordswith our ‘intuitions’ about what extended bodies are like. But what weight could such anargument have (especially given that our ‘intuitions’ are clearly not explicitly topological)in the face of the empirical success of a science that can be understood in terms of an al-

30See Truesdell, C.A., III. A First Course in Rational Continuum Mechanics, Part I , 2nd edition (Boston:Academic Press, 1991); Noll, W. and Virga, E. G. “Fit regions and functions of bounded variation” Archive

for Rational Mechanics and Analysis 102 (1988):1–21. I am grateful to Jeremy Butterfield for pointing outthese references to me.

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ternative, incompatible, account? In light of this situation, Zimmerman is in fact very farfrom discussing the implications of the even the possible existence of ‘extended bodies’. Heis discussing the implications of the possible exemplification of a topological concept madeup by him, one that we now have good reason to believe does not correspond to a reasonabledefinition of an extended physical body. It is far from clear what the significance of such adiscussion is.

My own discussion, now, has encroached on a slightly new issue, namely, the point of metaphysics. I turn, now, to a consideration of this issue.

6 The point of metaphysics

My proposal that metaphysics should take as its starting point those concepts that arefoundational to science more or less exhausts what I have to say about how, in my view,

metaphysics ought to proceed. However, it is useful to approach the same conclusion froma slightly different direction, by asking: What is the point of metaphysics?

No doubt some would claim that it is inherently valuable. Indeed, Aristotle seems tosay as much on occasion in the Metaphysics , and in Book 10 of the Nicomachean Ethics he apparently argues that engaging in something like metaphysics (‘ ’) is at leastpart of the most blessed life, the aim of human existence. Such views raise very weightyissues, and I am not qualified to say much about them. Suffice it to say that if engaging inmetaphysics plays a role in the most blessed life, then it does, after all, have a point. I willpause only to notice that under this conception, what would have a point is not the product of metaphysical thinking, but rather the practice of metaphysics. (For example, Aristotleargues that contemplation, an activity, is the aim of human existence.)

Let us not consider metaphysics as human activity, but rather metaphysics as the productof that activity. Does it have a point? Is it good for something? It is hard to know howto answer this question. We have already seen that, for Aristotle at least, metaphysicsexamines, clarifies, and justifies, the principles, or foundations, of the other sciences. Itprovides, in modern terminology, the foundations for the special sciences such as physics,mathematics, and biology, and my proposal more or less follows Aristotle in this conception.Indeed, we can easily see what he means in at least the practical sense by looking at his ownpractice of physics and biology. In both cases, he makes considerable and substantive use of what are, apparently, the concepts that are clarified and justified by metaphysics—this likehis own account of substances, his own account of the nature of causality, and so on.

Moreover, I suggested in the previous section that an inquiry into the nature of meta-

physics leads naturally to the Aristotelian conception (as I understand it), because meta-physics, necessarily lacking its own principles, can do no better than to take the commitmentsof successful scientific theory as its starting point (though determining those commitmentsmight also be a part of the enterprise). In this section, I shall arrive at a similar conclusionby way of a conditional principle:

If metaphysics (considered as a product, not as an activity) has a point, thenit must be possible to make correct metaphysical claims, and there must existintersubjectively available evidence that bears on the truth of those claims.

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I am suggesting that unless this principle is true, metaphysics as product does not have apoint, by which I mean that we have no good reasons to accept its conclusions, or to considerit a worthwhile intellectual pursuit. For suppose that the principle failed. Failure in virtue of the impossibility of making true metaphysical claims clearly renders it pointless in the sense

just described. Indeed, many arguments—for example, those made by some positivists—against metaphysics are really arguments that it is impossible to make true statements inmetaphysics (because, for example, those statements may be meaningless). Here, I shall setsuch arguments aside, and therefore focus on the condition that there be intersubjectivelyavailable evidence that bears on the truth of those claims. So suppose that this condition fails.Then, at the very least, the products of metaphysics will not be admissible assumptions inany intellectual activity that requires the availability of intersubjectively available evidence.Of course, such activities exist—poetry, for example (and bad metaphysics can inspire goodpoetry, though perhaps not the best poetry).

But I contend that if (the products of) metaphysics are not subject to evaluation byintersubjectively available evidence, then those products cannot be a part of any projectof intellectual inquiry, which I take to include giving reasons for claims, which reasons weought to acknowledge as reasons for any rational person to believe the claims. My positionon this point is surely controversial, and the statement of the position is itself fraught withphilosophically problematic concepts; I cannot provide a justification of the position, exceptby allusion: my view is that intellectual projects are essentially (in the strong sense of thatterm) intersubjective. Human inquiry is, in other words, necessarily a group project. Anyattempt to justify this assumption would take us back to those weighty issues about humannature that I avoided earlier, so here I shall have to take it as an unjustified assumption of my argument.

What, then, could count as intersubjectively available evidence for metaphysical claims?And what relation would this evidence bear to the products of metaphysics? Apparentlythere are two possible answers to the second question. First, there may be some pieces of evidence that can server as the premises of some argument whose conclusion is a metaphysicalclaim. Second, there may be some pieces of evidence that are the consequences of someargument whose premises are the products of metaphysics. The former relation is somethinglike deductive, while the latter is, roughly speaking, hypopthetico-deductive. I inserted thequalifiers ‘something like’ and ‘roughly speaking’ on purpose: I do not mean to supposethat the relationship between evidence and that for which it is evidence must be logicallydeductive, but only that some form of argument can either get us from the evidence to theevidenced, or from the evidenced to the evidence.

What sorts of evidence could bear one of those relations to the products of metaphysics?Historically, four sorts have been adduced: theological, logical, mathematical, and empirical.Let us consider each.Theological

Many metaphysical arguments have been based on claims about ‘how God must havedone things’. In other words, those arguments take the form: ‘God created the cosmos, andbeing such-and-such type of being, God could have to have done so in the following way...’. Iam dubious that ‘God’s being such-and-such type of being’ is an intersubjectively availablepiece of evidence. The point is not that a God who is prior to, or the source of, all being

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could not, in effect, serve as the principle of metaphysics itself, from which metaphysics couldderive something about the nature of being. The point, rather, is that it seems we do nothave the sort of epistemic access to such a principle to render appeal to it (i.e., God, or thenature of God) intersubjectively available.Logical

On the other hand, sometimes arguments based on an appeal to God, or how God musthave done things, are more of a trope for arguments that are essentially logical. Manymetaphysical arguments, particularly within certain branches of rationalism, take the form:‘It is logically necessary that...’. But it is unclear how such arguments could ever succeed inmetaphysics, for as we saw in Aristotle’s defense of the principle of non-contradiction, logicalprinciples themselves are up for grabs in metaphysics. Indeed, prior to those principlesthemselves, we must confront the issue of the nature of logical principles. I believe thatcontemporary quantum theory raises this issue in a particularly pressing way, but I leavethat point aside for now. Moreover, from logical principles alone, one presumably cannotderive anything but further purely logical claims—the failure of rationalist philosophy shouldteach us at least that lesson.

But having committed ourselves—for whatever reasons—to some logical principles, onemight hope that metaphysics could seek a foundation for those principles. Indeed, we sawAristotle make just such an attempt. However, we must be careful about what ought andought not be expected, here. Clearly one is not going to derive , in a non-circular way,logical principles from some more primitive principles. (Aristotle makes no such claim, forexample.) Instead, one is presumably going to ‘justify’ the principles in some ultimately non-logical fashion. Various such justifications have been proposed. For example, Dummett31

has claimed that realism requires the law of distributivity in logic. My view, expressed

elsewhere,

32

is that the only sorts of justification for the claim that one or another logi-cal principle is ‘true’ are empirical or mathematical. That is, only by showing that oneor another logical principle makes better sense of the deliverances of empirical science ormathematics can we provide anything like a compelling account of the truth of some set of logical principles. I do not have time, here, to pursue that point, however.Mathematical

Here I think that we are in much the same situation. From purely mathematical claims,one can surely only derive other mathematical claims. (Some have seemingly failed to noticethis point, and tried to understand, for example, the value of the fine structure constant inquantum theory in purely mathematical terms.) On the other hand, as I claimed just above,mathematics can provide some sort of evidence for metaphysics. Above I claimed that it

could do so by serving as evidence in an argument of the form: “in order to make senseof the deliverances of mathematics, one must adopt such-and-such logical principles”. Thusmathematics can provide evidence for metaphysical accounts of the foundations of logic. Butit can also provide a more direct kind of evidence. After all, surely part of metaphysics isto examine the nature of mathematical objects, for example. While one certainly cannot

31Dummett, M. (1976). ‘Is Logic Empirical?’ In Lewis, H., editor, Contemporary British Philosophy ,pages 45–68. Allen and Unwin, London.

32“Quantum Logic is Alive ∧ (It is True ∨ It is False)”, Philosophy of Science 68 (Supp):274–287.

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derive claims about the nature of mathematical objects, in logical or mathematical fashion,mathematics can serve (and, in the better examples of the metaphysics of mathematicalobjects, has served) as evidence for such claims. For example, some philosophers haveargued against a finitist conception of mathematical objects on the grounds that finitismcannot make sense of certain crucial parts of mathematical practice.Empirical

The same relation holds, or ought to hold, I argue, between metaphysics and the fourthsort of evidence traditionally adduced for metaphysical claims, empirical evidence. Manymetaphysical arguments have taken the form: “In order to make sense of what we know,or think we know, about physical reality, we must accept as true such-and-such claim of metaphysics.” And at this point in my argument, I take it as given that the sort of knowledge,or purported knowledge, that is most worthy of this sort of examination is the knoweldgeprovided by science. We return, therefore, to the position that I adopted at the end of theprevious section, namely, that empirical science is the datum that must be respected bymetaphysics, in the roughly hypothetico-deductive sense that I mentioned above.

My argument, in summary, is the following. If metaphysics as product has a point, thenit must be subject to some form of intersubjectively available evidence. Personal intuitionis (by definition) not intersubjectively available. Theological evidence is not either. Logicalevidence is. One cannot derive metaphysical claims from logical principles, but one can,perhaps, taking a logical principle as given, investigate how best to understand the truth of the principle. Doing so is a kind of metaphysics. Mathematical evidence is intersubjectivelyavailable. Again, from mathematics one cannot derive metaphysical claims, but one caninvestigate how best to understand the truth of some piece of mathematics. Empiricalevidence is intersubjectively available, and serves as evidence for metaphysics in the way I

have already described.Those who are unfamiliar with the philosophy of the special sciences may have one of two forms of skepticism about my claim that metaphysics ought to be about the foundationsof the concepts to which science is committed.

First, they may suppose that science just isn’t the right sort of thing to play the roleof guide metaphysics in this way. Science is about the empirical, the a posteriori, and ingeneral about begins qua physical beings, while metaphysics is about the a priori, and ingeneral about beings qua beings. Doesn’t my view stumble over this point?

I don’t think that it does, because I don’t think that science is restricted in quite that way.It is true, of course, the empirical investigation characterizes the methods of science. Arm-chair physics does not have a very noble history, except in those cases where one has already

brought to the armchair a concern with known empirical phenomena. However, metaphysicalpropositions—and more generally, propositions that are not strictly derived from empiricalinvestigation alone—make a crucial appearance in science, indeed in two ways. First, suchpropositions often contribute to essential background assumptions. Philosophers and histo-rians of science are, in fact, largely engaged it he project of spelling out the metaphysicalpresuppositions of science. Second, and more important for us, metaphysical propositionsoften appear in our attempts to understand, to give an account of, the results of empiricalinquiry. Such attempts re, while not perhaps a part of empirical science proper, a crucialcomponent of the scientific enterprise, for the often guide further theorizing in an essential

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way. A nice example is afforded by contemporary efforts to formulate a consistent theory of quantum gravity. These efforts are largely, and often explicitly, guided by the interpretive,and frequently metaphysical, questions surrounding quantum theory, not to mention anothertraditional metaphysical issue, the nature of time.

Note also that be connecting metaphysics to science in this way, we do not therebylose altogether the distinctive character of metaphysical claims. Relying on Reichenbach’sdistinction between the constitutive and apodeictic senses of the a priori, we can maintain aconstitutive, and in this sense, a priori, status for metaphysics.

Recall that I am considering two objections to this conception of metaphysics. The secondobjection admits all I have said thus far, but calls into question my implicit assumption thatscience could adjudicate amongst metaphysical principles. In other words, it might be thatscience requires foundational principles, and it might be that the proper role of metaphysicsis to provide and examine them, but pretty much any principles will do. Metaphysics would,in this case, float free of science, though if my argument is correct, it is not clear that itwould then have a point.

I have some sympathy for this objection. After all, there is a bewildering variety of attempts to provide a metaphysical foundation for quantum theory, for example. From theoutside, at least, it is easy to suppose that the persistence of this variety—its apparent resis-tance to being trimmed down—points to the conclusion that pretty much any metaphysicswill do for science.

More or less the same issue comes up within the philosophy of science itself, in the form of a debate about the ‘underdetermination of theory by evidence’, which I think should reallybe labeled the ‘underdetermination of interpretation by evidence’. There are basically tworoutes to the conclusion that the evidence, namely, the results of empirical investigation, do

not uniquely imply any given interpretation, though the question is acutely complication bythe fact that, as I have pointed out, those results often already involve certain interpretationalpresuppositions. The first route is logical, the claim being that any system of propositions isopen to so-called ‘non-standard models’, so that, as a point of logic, multiple interpretationsof the empirical facts will always be available. The second route is based on the actualvariety of interpretations that seems to exist at any given moment in the history of science,and proceeds by asking the rhetorical question “What reason do we have for thinking thatthis variety will ever be reduced to a single alternative?”

I certainly do not want to get side-tracked into a long discussion of this debate; for thepurposes of this discussion, I think it is enough to assert my own view of the matter. 33 Thelogical route falters precisely because it is purely logical. The logical point being conceded,

we can still suppose that some criteria beyond that of mere logical consistency with theempirical facts will rule out some interpretations. Indeed, philosophy of physics, along withthe philosophy of other special sciences, does operate under this assumption. A proposedinterpretation must be fruitful for further investigation. it must contribute to understanding.And so on. Of course, spelling out these and other criteria in detail is itself a difficult task,

33Some additional discussion is in my “The Light at the End of the Tunneling: Observation and Under-determination”, Philosophy of Science 66 (Supp):47-58).

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but one that I shall leave aside here.34

The second route to underdetermination I find considerably more convincing, but alsoinsufficient to establish the claim that underdetermination rules out the possibility thatscience can adjudicate amongst metaphysical propositions (in the sense already described,that is, by its fundamental requirements conflicting with those propositions); for the actualvariety of interpretations in science—or at least, the actual variety of interpretations that arelive options—can rule out some metaphysical propositions. Moreover, this variety can changeover time in a way that rules out further interpretations—philosophy of the special sciencesis, after all, largely concerned with developing such interpretations to the point where theycan be either plausibly accepted or rued out. It may turn out, for example, that one canunderstand general relativity only under the assumption that space-time is itself some sortof substance—exactly this question is actively debated by philosophers of physics, and wecan see, in the history of the debate during the twentieth century, something like progress.We understand the issues now better than we did 50 years ago (largely thanks, of course, towork done 50 years ago). Moreover, that progress is closely connected with developments inscience, for example, the realization of the existence of Gödelian space-times, the so-called‘hole’ argument, and so on. In these cases, science has served as a datum for metaphysics,in the literal sense of ‘datum’—it may well turn out that any metaphysics that fails to makespace-time out as a substance is just wrong, and is wrong because such a metaphysics cannotmake sense of science.

What about those areas of metaphysics that do not, apparently, have any implicationsfor science? What about metaphysical debates about, for example, what it means to be a‘part’, or what it is to be identical with something, or any of a number of highly abstractquestions apparently irrelevant to science? I am open to the conclusion that these debates in

fact have no point, though I think that this conclusion can be reached too hastily. Quantumtheory—just to take the example most familiar to me—may well require such accounts. Forexample, there have been recent discussions about what version, if any, of the Principle of the Identity of Indiscernibles is required for a proper understanding of certain quantum-mechanical phenomena.

7 An illustration

I have already considered, in passing, some specific cases where science can provide evidenceconcerning metaphysical questions. To conclude, I shall consider an example in slightly moredetail, though only slightly more detail. I merely wish to indicate, by example, the claims

that I have been making.My example comes from Peter van Inwagen’s book Material Beings , which is, unsurpris-

ingly, an attempt to say what counts as a material object. More precisely, van Inwagen isconcerned to answer the following question, which he calls the ‘Special Composition Ques-tion’:

34In “The Light at the End of the Tunneling” (op. cit.), I argue that expressibility in a certain kind of mathematical formalism plays a crucial role, at least in physics.

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Suppose one had certain (nonoverlapping) objects, the xs, at one’s disposal: whatwould one have to do—what could one do—to get the xs to compose something?(p. 31)

By way of explanation, he continues:

For example: Suppose that one has a lot of wooden blocks that one may do withas one wills; what must one do to get the blocks to add up to something? (p.31)

After considering, and rejecting, a number of answers to this question, most of them involvingthe idea that the wooden blocks must be bonded together in some appropriate way, vanInwagen proposes the following answer to his question, which I have translated from logic-ese back into English:

The xs compose some y if and only if the activity of the xs constitutes a life (of there is only one of the xs). (p. 82, paraphrased)

As van Inwagen recognizes, it is now incumbent upon him to say what it means for theactivity of the xs to constitute a life, which he takes to involve two tasks: saying what itis for the activity of the xs to constitute any event at all, and then saying what it is for anevent to be a life. He says little about the former, but he does have something to say aboutthe latter.

I am not concerned with what he says, but rather with what he does not say. Indeed,my main concern is to point out that biology and the philosophy of biology are, apparently,relevant to his project. In particular, if van Inwagen’s definition of what it is to be a life

cannot make sense of biological practice, if it cannot make sense of our best attempts tostudy the subject of the definition (living beings), if it cannot be part of a foundation forbiology, then, I say, his definition should be judged wrong. If I am incorrect in making thisclaim—if it is open for van Inwagen to say ‘no matter how my account fairs with respectto the foundations of biology, it is the correct account of what constitutes a life’—thenapparently there is no intersubjectively available evidence external to metaphysics itself (orindeed van Inwagen’s and his readers’ intuition) that can bear on the correctness of theaccount, and in that case, I am willing to say that it does not have a point (for reasonsalready discussed). And in fact van Inwagen does not consider how his account fairs withrespect to the foundations of biology.

Now, van Inwagen does say that it is “the business of biology” (p. 83) to provide a full

account of life, and yet he goes on to claim that he does have “something useful” (p. 84) tosay on the matter. In my view, there are two problems with van Inwagen’s strategy. First,while it is certainly true, in a sense, that it is the business of biology to provide the fullaccount of life, at the same time, it is not the business of biology to provide a foundationalunderstanding of this concept or of the theories of life that form part of biology. Those

jobs (while sometimes performed by the same people) are better conceived as a part of thephilosophy of biology, or that part of it that is concerned with the metaphysical foundationsof biology. Second, and more to the point of our present concerns, van Inwagen makes no

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Dickson - Metaphysics and Science (Draft)

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