It is not easy to say what metaphysics is. Ancient and Medievalphilosophers might have said that metaphysics was, like chemistry orastrology, to be defined by its subject-matter: metaphysics was the“science” that studied “being as such” or“the first causes of things” or “things that do notchange”. It is no longer possible to define metaphysics thatway, for two reasons. First, a philosopher who denied the existence ofthose things that had once been seen as constituting thesubject-matter of metaphysics—first causes or unchangingthings—would now be considered to be making thereby ametaphysical assertion. Second, there are many philosophical problemsthat are now considered to be metaphysical problems (or at leastpartly metaphysical problems) that are in no way related to firstcauses or unchanging things—the problem of free will, forexample, or the problem of the mental and the physical.

The first three sections of this entry examine a broad selection ofproblems considered to be metaphysical and discuss ways in which thepurview of metaphysics has expanded over time. We shall see that thecentral problems of metaphysics were significantly more unified in theAncient and Medieval eras. Which raises a question—is there anycommon feature that unites the problems of contemporary metaphysics?The final two sections discuss some recent theories of the nature andmethodology of metaphysics. We will also consider arguments thatmetaphysics, however defined, is an impossible enterprise.

• 1. The Word ‘Metaphysics’ and the Concept of Metaphysics
• 2. The Problems of Metaphysics: the “Old” Metaphysics
  • 2.1 Being As Such, First Causes, Unchanging Things
  • 2.2 Categories of Being and Universals
  • 2.3 Substance
• 3. The Problems of Metaphysics: the “New” Metaphysics
  • 3.1 Modality
  • 3.2 Space and Time
  • 3.3 Persistence and Constitution
  • 3.4 Causation, Freedom and Determinism
  • 3.5 The Mental and Physical
  • 3.6 Social Metaphysics
• 4. The Methodology of Metaphysics
• 5. Is Metaphysics Possible?
• Bibliography
• Academic Tools
• Other Internet Resources
• Related Entries

1. The Word ‘Metaphysics’ and the Concept of Metaphysics

The word ‘metaphysics’ is notoriously hard to define.Twentieth-century coinages like ‘meta-language’ and‘metaphilosophy’ encourage the impression that metaphysicsis a study that somehow “goes beyond” physics, a studydevoted to matters that transcend the mundane concerns of Newton andEinstein and Heisenberg. This impression is mistaken. The word‘metaphysics’ is derived from a collective title of thefourteen books by Aristotle that we currently think of as making upAristotle’sMetaphysics. Aristotle himself did not knowthe word. (He had four names for the branch of philosophy that is thesubject-matter of Metaphysics: ‘first philosophy’,‘first science’, ‘wisdom’, and‘theology’.) At least one hundred years afterAristotle’s death, an editor of his works (in all probability,Andronicus of Rhodes) titled those fourteen books “Ta metata phusika”—“the after the physicals” or“the ones after the physical ones”—the“physical ones” being the books contained in what we nowcall Aristotle’sPhysics. The title was probably meantto warn students of Aristotle’s philosophy that they shouldattempt Metaphysics only after they had mastered “the physicalones”, the books about nature or the natural world—that isto say, about change, for change is the defining feature of thenatural world.

This is the probable meaning of the title becauseMetaphysicsis about things that do not change. In one place, Aristotle identifiesthe subject-matter of first philosophy as “being as such”,and, in another as “first causes”. It is a nice—andvexed—question what the connection between these two definitionsis. Perhaps this is the answer: The unchanging first causes havenothing but being in common with the mutable things they cause. Likeus and the objects of our experience—they are, and there theresemblance ceases. (For a detailed and informative recent guide toAristotle’sMetaphysics, see Politis 2004.)

Should we assume that ‘metaphysics’ is a name for that“science” which is the subject-matter of Aristotle’sMetaphysics? If we assume this, we should be committed tosomething in the neighborhood of the following theses:

• The subject-matter of metaphysics is “being assuch”
• The subject-matter of metaphysics is the first causes ofthings
• The subject-matter of metaphysics is that which does notchange

Any of these three theses might have been regarded as a defensiblestatement of the subject-matter of what was called‘metaphysics’ until the seventeenth century. But then,rather suddenly, many topics and problems that Aristotle and theMedievals would have classified as belonging to physics (the relationof mind and body, for example, or the freedom of the will, or personalidentity across time) began to be reassigned to metaphysics. One mightalmost say that in the seventeenth century metaphysics began to be acatch-all category, a repository of philosophical problems that couldnot be otherwise classified as epistemology, logic, ethics or otherbranches of philosophy. (It was at about that time that the word‘ontology’ was invented—to be a name for the scienceof being as such, an office that the word ‘metaphysics’could no longer fill.) The academic rationalists of thepost-Leibnizian school were aware that the word‘metaphysics’ had come to be used in a more inclusivesense than it had once been. Christian Wolff attempted to justify thismore inclusive sense of the word by this device: while thesubject-matter of metaphysics is being, being can be investigatedeither in general or in relation to objects in particular categories.He distinguished between ‘general metaphysics’ (orontology), the study of being as such, and the various branches of‘special metaphysics’, which study the being of objects ofvarious special sorts, such as souls and material bodies. (He does notassign first causes to general metaphysics, however: the study offirst causes belongs to natural theology, a branch of specialmetaphysics.) It is doubtful whether this maneuver is anything morethan a verbal ploy. In what sense, for example, is the practitioner ofrational psychology (the branch of special metaphysics devoted to thesoul) engaged in a study of being? Do souls have a different sort ofbeing from that of other objects?—so that in studying the soulone learns not only about its nature (that is, its properties:rationality, immateriality, immortality, its capacity or lack thereofto affect the body …), but also about its “mode ofbeing”, and hence learns something about being? It is certainlynot true that all, or even very many, rational psychologists saidanything,qua rational psychologists, that could plausibly beconstrued as a contribution to our understanding of being.

Perhaps the wider application of the word ‘metaphysics’was due to the fact that the word ‘physics’ was coming tobe a name for a new, quantitative science, the science that bears thatname today, and was becoming increasingly inapplicable to theinvestigation of many traditional philosophical problems aboutchanging things (and of some newly discovered problems about changingthings).

Whatever the reason for the change may have been, it would be flyingin the face of current usage (and indeed of the usage of the lastthree or four hundred years) to stipulate that the subject-matter ofmetaphysics was to be the subject-matter of Aristotle’sMetaphysics. It would, moreover, fly in the face of the factthat there are and have been paradigmatic metaphysicians who deny thatthere are first causes—this denial is certainly a metaphysicalthesis in the current sense—others who insist that everythingchanges (Heraclitus and any more recent philosopher who is both amaterialist and a nominalist), and others still (Parmenides and Zeno)who deny that there is a special class of objects that do not change.In trying to characterize metaphysics as a field, the best startingpoint is to consider the myriad topics traditionally assigned toit.

2. The Problems of Metaphysics: the “Old” Metaphysics

2.1 Being As Such, First Causes, Unchanging Things

If metaphysics now considers a wider range of problems than thosestudied in Aristotle’sMetaphysics, those originalproblems continue to belong to its subject-matter. For instance, thetopic of “being as such” (and “existence assuch”, if existence is something other than being) is one of thematters that belong to metaphysics on any conception of metaphysics.The following theses are all paradigmatically metaphysical:

• “Being is; not-being is not” [Parmenides];
• “Essence precedes existence” [Avicenna,paraphrased];
• “Existence in reality is greater than existence in theunderstanding alone” [St Anselm, paraphrased];
• “Existence is a perfection” [Descartes,paraphrased];
• “Being is a logical, not a real predicate” [Kant,paraphrased];
• “Being is the most barren and abstract of allcategories” [Hegel, paraphrased];
• “Affirmation of existence is in fact nothing but denial ofthe number zero” [Frege];
• “Universals do not exist but rather subsist or havebeing” [Russell, paraphrased];
• “To be is to be the value of a bound variable”[Quine].
• “An object’s degree of being is proportionate to thenaturalness of its mode of existence” [McDaniel].

It seems reasonable, moreover, to say that investigations intonon-being belong to the topic “being as such” and thusbelong to metaphysics. (This did not seem reasonable to Meinong, whowished to confine the subject-matter of metaphysics to “theactual” and who therefore did not regard his Theory of Objectsas a metaphysical theory. According to the conception of metaphysicsadopted in this article, however, his thesis [paraphrased]“Predication is independent of being” is paradigmaticallymetaphysical.)

The topics “the first causes of things” and“unchanging things”—have continued to interestmetaphysicians, though they are not now seen as having any importantconnection with the topic “being as such”. The first threeof Aquinas’s Five Ways are metaphysical arguments on anyconception of metaphysics. Additionally the thesis that there are nofirst causes and the thesis that there are no things that do notchange count as metaphysical theses, for in the current conception ofmetaphysics, the denial of a metaphysical thesis is a metaphysicalthesis. No post-Medieval philosopher would say anything like this:

I study the first causes of things, and am therefore a metaphysician.My colleague Dr McZed denies that there are any first causes and istherefore not a metaphysician; she is rather, an anti-metaphysician.In her view, metaphysics is a science with a non-existentsubject-matter, like astrology.

This feature of the contemporary conception of metaphysics is nicelyillustrated by a statement of Sartre’s:

I do not think myself any less a metaphysician in denying theexistence of God than Leibniz was in affirming it. (1949: 139)

An anti-metaphysician in the contemporary sense is not a philosopherwho denies that there are objects of the sorts that an earlierphilosopher might have said formed the subject-matter of metaphysics(first causes, things that do not change, universals, substances,…), but rather a philosopher who denies the legitimacy of thequestion whether there are objects of those sorts.

The three original topics—the nature of being; the first causesof things; things that do not change—remained topics ofinvestigation by metaphysicians after Aristotle. Another topic,discussed in the following subsection, occupies an intermediateposition between Aristotle and his successors.

2.2 Categories of Being and Universals

We human beings sort things into various classes. And we often supposethat the classes into which we sort things enjoy a kind of internalunity. In this respect they differ from sets in the strict sense ofthe word. (And no doubt in others. It would seem, for example, that wethink of the classes we sort things into—biological species,say—as comprising different members at different times.) Theclasses into which we sort things are in most cases“natural” classes, classes whose membership is in someimportant sense uniform—“kinds”. We shall notattempt an account or definition of ‘natural class’ here.Examples must suffice. There are certainly sets whose members do notmake up natural classes: a set that contains all dogs but one, and aset that contains all dogs and exactly one cat do not correspond tonatural classes in anyone’s view. And it is tempting to supposethat there is a sense of “natural” in which dogs make up anatural class, to suppose that in dividing the world into dogs andnon-dogs, we “cut nature at the joints”. It is, however, arespectable philosophical thesis that the idea of a natural classcannot survive philosophical scrutiny. If that respectable thesis istrue, the topic “the categories of being” is apseudo-topic. Let us simply assume that the respectable thesis isfalse and that things fall into various naturalclasses—hereinafter, simply classes.

Some of the classes into which we sort things are more comprehensivethan others: all dogs are animals, but not all animals are dogs; allanimals are living organisms, but not all living organisms are animals…. Now the very expression “sort things intoclasses” suggests that there is a most comprehensive class: theclass of things, the class of things that can be sorted into classes.But is this so?—and if it is so, are there classes that are“just less comprehensive” than this universal class? Ifthere are, can we identify them?—and are there a vast (perhapseven an infinite) number of them, or some largish, messy number likeforty-nine, or some small, neat number like seven or four? Let us callany such less comprehensive classes the ‘categories ofbeing’ or the ‘ontological categories’. (The formerterm, if not the latter, presupposes a particular position on onequestion about the nature of being: that everything is, that theuniversal class is the class of beings, the class of things that are.It thus presupposes that Meinong was wrong to say that “thereare things of which it is true that there are no suchthings”.)

The topic “the categories of being” is intermediatebetween the topic “the nature of being” and the topicsthat fall under the post-Medieval conception of metaphysics for areason that can be illustrated by considering the problem ofuniversals. Universals, if they indeed exist, are, in the firstinstance, properties or qualities or attributes (i.e.,“ductility” or “whiteness”) that aresupposedly universally “present in” the members of classesof things and relations (i.e., “being to the north of”)that are supposedly universally present in the members of classes ofsequences of things. “In the first instance”: it may bethat things other than qualities and relations are universals,although qualities and relations are the items most commonly putforward as examples of universals. It may be that the novelWarand Peace is a universal, a thing that is in some mode present ineach of the many tangible copies of the novel. It may be that the word“horse” is a universal, a thing that is present in each ofthe many audible utterances of the word. And it may be that naturalclasses or kinds are themselves universals—it may be that thereis such a thing as “the horse” or the speciesEquuscaballus, distinct from its defining attribute “being ahorse” or “equinity”, and in some sense“present in” each horse. (Perhaps some difference betweenthe attribute “being a horse” and the attribute“being either a horse or a kitten” explains why the formeris the defining attribute of a kind and the latter is not. Perhaps theformer attribute exists and the latter does not; perhaps the formerhas the second-order attribute “naturalness” and thelatter does not; perhaps the former is more easily apprehended by theintellect than the latter.)

The thesis that universals exist—or at any rate“subsist” or “have being”—is variouslycalled ‘realism’ or ‘Platonic realism’ or‘platonism’. All three terms are objectionable. Aristotlebelieved in the reality of universals, but it would be at best anoxymoron to call him a platonist or a Platonic realist. And‘realism’ tout court has served as a name for a variety ofphilosophical theses. The thesis that universals do not exist—donot so much as subsist; have no being of any sort—is generallycalled ‘nominalism’. This term, too is objectionable. Atone time, those who denied the existence of universals were fond ofsaying things like:

There is no such thing as “being a horse”: there is onlythe name [nomen, gen.nominis] “horse”,a mereflatus vocis [puff of sound].

Present-day nominalists, however, are aware, if earlier nominalistswere not, that if the phrase ‘the name“horse” ’ designated an object, the object itdesignated would itself be a universal or something very like one. Itwould not be a mere puff of sound but would rather be what was commonto the many puffs of sound that were its tokens.

The old debate between the nominalists and the realists continues tothe present day. Most realists suppose that universals constitute oneof the categories of being. This supposition could certainly bedisputed without absurdity. Perhaps there is a natural class of thingsto which all universals belong but which contains other things as well(and is not the class of all things). Perhaps, for example, numbersand propositions are not universals, and perhaps numbers andpropositions and universals are all members of a class of“abstract objects”, a class that some things do not belongto. Or perhaps there is such a thing as “the whiteness of theTaj Mahal” and perhaps this object and the universal“whiteness”—but not the Taj Mahal itself—bothbelong to the class of “properties”. Let us call such aclass—a proper subclass of an ontological category, a naturalclass that is neither the class of all things nor one of theontological categories—an ‘ontologicalsub-category’. It may indeed be that universals make up asub-category of being and are members of the category of being“abstract object”. But few if any philosophers wouldsuppose that universals were members of forty-ninesub-categories—much less of a vast number or an infinity ofsub-categories. Most philosophers who believe in the reality ofuniversals would want to say that universals, if they do notconstitute an ontological category, at least constitute one of the“higher” sub-categories. If dogs form a natural class,this class is—by the terms of our definition—anontological sub-category. And this class will no doubt be a subclassof many sub-categories: the genuscanis, the class (in thebiological sense)mammalia, …, and so through a chainof sub-categories that eventually reaches some very generalsub-category like “substance” or “materialobject”. Thus, although dogs may compose an ontologicalsub-category, this sub-category—unlike the category“universal”—is one of the “lower” ones.These reflections suggest that the topic “the categories ofbeing” should be understood to comprehend both the categories ofbeingsensu stricto and their immediate sub-categories.

Does the topic “the categories of being” belong tometaphysics in the “old” sense? A case can be made forsaying that it does, based on the fact that Plato’s theory offorms (universals, attributes) is a recurrent theme inAristotle’sMetaphysics. InMetaphysics, twoof Plato’s central theses about the forms come in for vigorouscriticism: (i) that things that would, if they existed, be“inactive” (the forms) could be the primary beings, the“most real” things, and (ii) that the attributes of thingsexist “separately” from the things whose attributes theyare. We shall be concerned only with (ii). In the terminology of theSchools, that criticism can be put this way: Plato wrongly believedthat universals existedante res (prior to objects); thecorrect view is that universals existin rebus (in objects).It is because this aspect of the problem of universals—whetheruniversals existante res orin rebus—isdiscussed at length inMetaphysics, that a strong case can bemade for saying that the problem of universals falls under the oldconception of metaphysics. (And the question whether universals, giventhat they exist at all, existante res orin rebusis as controversial in the twenty-first century as it was in thethirteenth century and the fourth century B.C.E.) If we do decide thatthe problem of universals belongs to metaphysics on the oldconception, then, since we have liberalized the old conception byapplying to it the contemporary rule that the denial of a metaphysicalposition is to be regarded as a metaphysical position, we shall haveto say that the question whether universals exist at all is ametaphysical question under the old conception—and thatnominalism is therefore a metaphysical thesis.

There is, however, also a case to be made against classifying the problemof universals as a problem of metaphysics in the (liberalized) oldsense. For there is more to the problem of universals than thequestion whether universals exist and the question whether, if they doexist, their existence isante res orin rebus. Forexample, the problem of universals also includes questions about therelation between universals (if such there be) and the things that arenot universals, the things usually called particulars. Aristotle didnot consider these questions in theMetaphysics. One mighttherefore plausibly contend that only one part of the problem ofuniversals (the part that pertains to the existence and nature ofuniversals) belongs to metaphysics in the old sense. At one time, aphilosopher might have said,

The universal “doghood” is a thing that does not change.Therefore, questions about its nature belong to metaphysics, thescience of things that do not change. But dogs are things that change.Therefore, questions concerning the relation of dogs to doghood do notbelong to metaphysics.

But no contemporary philosopher would divide the topics thatway—not even if he or she believed that doghood existed and wasa thing that did not change. A contemporary philosopher—if thatphilosopher concedes that there is any problem that can properly becalled “the problem of universals”—will see theproblem of universals as a problem properly so called, as a problemhaving the kind of internal unity that leads philosophers to speak ofa philosophical problem. And the same point applies to thetopic “the categories of being”: every philosopher who iswilling to say that “What are the categories of being?” isa meaningful question will assign every aspect of that question tometaphysics

Let us consider some aspects of the problem of universals that concernchanging things. (That is, that concern particulars—for even ifthere are particulars that do not change, most of the particulars thatfigure in discussions of the problem of universals as examples arethings that change.) Consider two white particulars—the TajMahal, say, and the Washington Monument. And suppose that both theseparticulars are white in virtue of (i.e., their being white consistsin) their bearing some one, identifiable relation to the universal“whiteness”. Suppose further that we are able to singleout this relation by some sort of act of intellectual attention orabstraction, and that (having done so) we have given it the name“falling under”. All white things and only white thingsfall under whiteness, and falling under whiteness is what it is to bewhite. (We pass over many questions that would have to be addressed ifwe were discussing the problem of universals for its own sake. Forexample, both blueness and redness are spectral color-properties, andwhiteness is not. Does this fact imply that “being a spectralcolor-property” is, as one might say, a second-order universal?If so, does blueness “fall under” this universal in thesame sense as the sense in which a copy ofPhilosophicalStudies falls under blueness?)

Now what can we say about this relation, this “fallingunder”? What is it about the two objects whiteness and the TajMahal that is responsible for the fact that the latter falls under theformer? Is the Taj perhaps a “bundle” ofuniversaliaante res, and does it fall under whiteness in virtue of the factthat whiteness is one of the universals that is a constituent of thebundle that it is? Or might it be that a particular like the Taj,although it indeed has universals as constituents, is something morethan its universal constituents? Might it be that the Taj has aconstituent that is not a universal, a “substrate”, aparticular that is in some sense property-less and that holds theuniversal constituents of the Taj together—that“bundles” them? (If we take that position, then we maywant to say, with Armstrong (1989: 94–96), that the Taj is a‘thick particular’ and its substrate a ‘thinparticular’: a thick particular being a thin particular takentogether with the properties it bundles.) Or might the Taj haveconstituents that are neither universals nor substrates? Might we havebeen too hasty when we defined ‘particulars’ as thingsthat are not universals? Could there perhaps be two kinds ofnon-universals, concrete non-universals or concrete individuals (thosewould be the particulars, thick or thin), and abstract non-universalsor abstract individuals (‘accidents’ or‘tropes’ or ‘property instances’), things thatare properties or qualities (and relations as well), things like“the (individual) whiteness of the Taj Mahal”? Is the Tajperhaps a bundle not of universals but of accidents? Or is it composedof a substrate and a bundle of accidents? And we cannot neglect thepossibility that Aristotle was right and that universals exist onlyin rebus. If that is so, we must ask what the relation isbetween the matter that composes a particular and the universals thatinhere in it—that inhere simultaneously in “this”matter and in “that” matter.

The series of questions that was set out in the preceding paragraphwas introduced by observing that the problem of universals includesboth questions about the existence and nature of universals andquestions about how universals are related to the particulars thatfall under them. Many of the theories that were alluded to in thatseries of questions could be described as theories of the“ontological structure” of non-universals. We can contrastontological structure with mereological structure. A philosophicalquestion concerns the mereological structure of an object if it is aquestion about the relation between that object and those of itsconstituents that belong to the same ontological category as theobject. For example, the philosopher who asks whether the Taj Mahalhas a certain block of marble among its constituents essentially oronly accidentally is asking a question about the mereologicalstructure of the Taj, since the block and the building belong to thesame ontological category. But the philosopher who asks whether theTaj has “whiteness” as a constituent and the philosopherwho supposes that the Taj does have this property-constituent andasks, “What is the nature of this relation ‘constituentof’ that ‘whiteness’ bears to the Taj?” areasking questions about its ontological structure.

Many philosophers have supposed that particulars fall under universalsby somehow incorporating them into their ontological structure. Andother philosophers have supposed that the ontological structure of aparticular incorporates individual properties or accidents—andthat an accident is an accident of a certain particular just in virtueof being a constituent of that particular.

Advocates of the existence ofante res universals, andparticularly those who deny that these universals are constituents ofparticulars, tend to suppose that universals abound—that thereis not only such a universal as whiteness but such a universal as“being both white and round and either shiny or not made ofsilver”. Advocates of other theories of universals are almostalways less liberal in the range of universals whose existence theywill allow. The advocate ofin rebus universals is unlikelyto grant the existence of “being both white and round and eithershiny or not made of silver”, even in the case in which there isan object that is both white and round and either shiny or not made ofsilver (such as a non-shiny white plastic ball).

The two topics “the categories of being” and “theontological structure of objects” are intimately related to eachother and to the problem of universals. It is not possible to proposea solution to the problem of universals that does not haveimplications for the topic “the categories of being”.(Even nominalism implies that at least one popular candidate for theoffice “ontological category” is non-existent or empty.)It is certainly possible to maintain that there are ontologicalcategories that are not directly related to the problem of universals(“proposition”, “state of affairs”,“event”, “merepossibile”), but anyphilosopher who maintains this will nevertheless maintain that ifthere are universals they make up at least one of the higherontological sub-categories. And it seems that it is possible to speakof ontological structure only if one supposes that there are objectsof different ontological categories. So whatever metaphysicscomprehends, it must comprehend every aspect of the problem ofuniversals and every aspect of the topics “the categories ofbeing” and “the ontological structure of objects”.For a recent investigation of the problems that have been discussed inthis section, see Lowe (2006).

We turn now to a topic that strictly speaking belongs to “thecategories of being”, but which is important enough to betreated separately.

2.3 Substance

Some things (if they exist at all) are present only “in”other things: a smile, a haircut (product, not process), a hole…. Such things may be opposed to things that exist “intheir own right”. Metaphysicians call the things that exist intheir own right ‘substances’. Aristotle called them‘protai ousiai’ or “primary beings”.They make up the most important of his ontological categories. Severalfeatures defineprotai ousiai: they are subjects ofpredication that cannot themselves be predicated of things (they arenot universals); things exist “in” them, but they do notexist “in” things (they are not accidents likeSocrates’ wisdom or his ironic smile); they have determinateidentities (essences). This last feature could be put this way incontemporary terms: if theprote ousiax exists at acertain time and theprote ousiay exists at someother time, it makes sense to ask whetherx andyare the same, are numerically identical (and the question must have adeterminate answer); and the question whether a givenproteousia would exist in some set of counterfactual circumstancesmust likewise have an answer (at least if the circumstances aresufficiently determinate—if, for example, they constitute apossible world. More on this in the next section). It is difficult tosuppose that smiles or holes have this sort of determinate identity.To ask whether the smile Socrates smiled today is the smile he smiledyesterday (or is the smile he would have smiled if Crito had asked oneof his charmingly naïve questions) can only be a question aboutdescriptive identity.

Aristotle uses ‘(prote)ousia’ not onlyas a count-noun but as a mass term. (He generally writes‘ousia’ without qualification when he believesthat the context will make it clear that he means ‘proteousia’.) For example, he not only asks questions like“Is Socrates a (prote)ousia?” and“What is a (prote)ousia”?, butquestions like “What is the (prote)ousia ofSocrates?” and “What is (prote)ousia?” (Which question he is asking sometimes has tobe inferred from the context, since there is no indefinite article inGreek.) In the count-noun sense of the term, Aristotle identifies atleast some (protai)ousiai withtahupokeimena or “underlying things”. Socrates, forexample, is ahupokeimenon in that he “liesunder” thein rebus universals under which he falls andthe accidents that inhere in him. ‘Tohupokeimenon’ has an approximate Latin equivalent in‘substantia’, “that which standsunder”. (Apparently, “to stand under” and “tolie under” are equally good metaphorical descriptions of therelations a thing bears to its qualities and accidents.) Owing both tothe close association of (protai)ousiai andhupokeimena in Aristotle’s philosophy and to theabsence of a suitable Latin equivalent of ‘ousia’‘substantia’ became the customary Latintranslation of the count-noun ‘(prote)ousia’.

The question whether there in fact are substances continues to be oneof the central questions of metaphysics. Several closely relatedquestions are: How, precisely, should the concept of substance beunderstood?; Which of the items (if any of them) among those weencounter in everyday life are substances?; If there are substances atall, how many of them are there?—is there only one as Spinozacontended, or are there many as most of the rationalists supposed?;What kinds of substances are there?—are there immaterialsubstances, eternal substances, necessarily existent substances?

It must be emphasized that there is no universally accepted andprecise definition of ‘substance’. Depending on how oneunderstood the word (or the concept) one might say either that Humedenied that there were any substances or that he held that the onlysubstances (or the only substances of which we have any knowledge)were impressions and ideas. It would seem, however, that mostphilosophers who are willing to use the word ‘substance’at all would deny that any of the following (if they exist) aresubstances:

• Universals and other abstract objects. (It should be noted thatAristotle criticized Plato for supposing that theprotaiousiai wereante res universals.)
• Events, processes, or changes. (But some metaphysicians contendthat substance/event is a false dichotomy.)
• Stuffs, such as flesh or iron or butter. (Unfortunately forbeginning students of metaphysics, the usual meaning of‘substance’ outside philosophy is stuff. Aristotlecriticized “the natural philosophers” for supposing thattheprote ousia could be a stuff—water or air or fireor matter.)

The nature of being, the problem of universals, and the nature ofsubstance have been recognized as topics that belong to“metaphysics” by almost everyone who has used the word. Wenow turn to topics that belong to metaphysics only in thepost-Medieval sense.

3. The Problems of Metaphysics: the “New” Metaphysics

3.1 Modality

Philosophers have long recognized that there is an importantdistinction within the class of true propositions: the distinctionbetween those propositions that might have been false and those thatcould not have been false (those that must be true). Compare, forexample, the proposition that Paris is the capital of France and theproposition that there is a prime between every number greater than 1and its double. Both are true, but the former could have been falseand the latter could not have been false. Likewise, there is adistinction to be made within the class of false propositions: betweenthose that could have been true and those that could not have beentrue (those that had to be false).

Some Medieval philosophers supposed that the fact that truepropositions are of the two sorts “necessarily true” and“contingently true” (and the corresponding fact aboutfalse propositions) showed that there were two “modes” inwhich a proposition could be true (or false): the mode of contingencyand the mode of necessity—hence the term ‘modality’.Present-day philosophers retain the Medieval term‘modality’ but now it means no more than “pertainingto possibility and necessity”. The types of modality of interestto metaphysicians fall into two camps: modalityde re andmodalityde dicto.

Modalityde dicto is the modality of propositions(‘dictum’ means proposition, or close enough). Ifmodality were coextensive with modalityde dicto, it would beat least a defensible position that the topic of modality belongs tologic rather than to metaphysics. (Indeed, the study of modal logicsgoes back to Aristotle’sPrior Analytics.)

But many philosophers also think there is a second kind of modality,modalityde re—the modality of things. (The modality ofsubstances, certainly, and perhaps of things in other ontologicalcategories.) The status of modalityde re is undeniably ametaphysical topic, and we assign it to the “new”metaphysics because, although one can ask modal questions about thingsthat do not change—God, for example, or universals—a largeproportion of the work that has been done in this area concerns themodal features of changing things.

There are two types of modalityde re. The first concerns theexistence of things—of human beings, for example. If Sally, anordinary human being, says, “I might not have existed”,almost everyone will take her to have stated an obvious truth. And ifwhat she has said is indeed true, then she exists contingently. Thatis to say, she is a contingent being: a being who might not haveexisted. A necessary being, in contrast, is a being of which it isfalse that it might not have existed. Whether any objects arenecessary beings is an important question of modal metaphysics. Somephilosophers have gone so far to maintain that all objects arenecessary beings, since necessary existence is a truth of logic inwhat seems to them to be the best quantified modal logic. (See Barcan1946 for the first modern connection between necessary existence andquantified modal logic. Barcan did not draw any metaphysicalconclusions from her logical results, but later authors, especiallyWilliamson 2013 have.)

The second kind of modalityde re concerns the properties ofthings. Like the existence of things, the possession of properties bythings is subject to modal qualification. If Sally, who speaksEnglish, says, “I might have spoken only French”, almosteveryone will take that statement to be no less obviously true thanher statement that she might not have existed. And if what she hassaid is indeed true, then “speaking English” is a propertythat she has only contingently or (the more usual word) onlyaccidentally. Additionally there may be properties which some objectshave essentially. A thing has a property essentially if it could notexist without having that property. Examples of essential propertiestend to be controversial, largely because the most plausible examplesof a certain object’s possessing a property essentially are onlyas plausible as the thesis that that object possesses those propertiesat all. For example, if Sally is a physical object, as physicalistssuppose, then it is very plausible for them to suppose further thatshe is essentially a physical object—but it is controversialwhether they are right to suppose that she is a physical object. And,of course, the same thing can be said,mutatis mutandis,concerning dualists and the property of being a non-physical object.It would seem, however, that Sally is either essentially a physicalobject or essentially a non-physical object. And many find itplausible to suppose that (whether she is physical or non-physical)she has the property “not being a poached egg”essentially.

The most able and influential enemy of modality (bothdedicto andde re) was W. V. Quine, who vigorouslydefended both the following theses. First, that modalitydedicto can be understood only in terms of the concept ofanalyticity (a problematical concept in his view). Secondly, thatmodalityde re cannot be understood in terms of analyticityand therefore cannot be understood at all. Quine argued for thislatter claim by proposing what he took to be decisive counterexamplesto theories that take essentiality to be meaningful. If modalityde re makes any sense, Quine contended (1960: 199–200),cyclists must be regarded as essentially bipedal—for“Cyclists are bipedal” would be regarded as an analyticsentence by those who believe in analyticity. But mathematicians areonly accidentally bipedal (“Mathematicians are bipedal” isnot analytic by anyone’s lights). What then, Quine proceeded toask, of someone who is both a mathematician and a cyclist?—thatperson seems both essentially and only accidentally bi-pedal. Sincethis is incoherent, Quine thought that modalityde re isincoherent.

Most philosophers are now convinced, however, that Quine’s“mathematical cyclist” argument has been adequatelyanswered by Saul Kripke (1972), Alvin Plantinga (1974) and variousother defenders of modalityde re. Kripke andPlantinga’s defenses of modality are paradigmaticallymetaphysical (except insofar as they directly address Quine’slinguistic argument). Both make extensive use of the concept of apossible world in defending the intelligibility of modality (bothde re andde dicto). Leibniz was the firstphilosopher to use ‘possible world’ as a philosophicalterm of art, but Kripke’s and Plantinga’s use of thephrase is different from his. For Leibniz, a possible world was apossible creation: God’s act of creation consists in hischoosing one possible world among many to be the one world that hecreates—the “actual” world. For Kripke andPlantinga, however, a possible world is a possible “whole ofreality”. For Leibniz, God and his actions “standoutside” all possible worlds. For Kripke and Plantinga, nobeing, not even God, could stand outside the whole system of possibleworlds. A Kripke-Plantinga (KP) world is an abstract object of somesort. Let us suppose that a KP world is a possible state of affairs(this is Plantinga’s idea; Kripke says nothing so definite).Consider any given state of affairs; let us say,Paris being thecapital of France. This state of affairs obtains, since Parisis the capital of France. By contrast, the state of affairsTours being the capital of France does not obtain. The latterstate of affairs does, however, exist, for there is such a state ofaffairs. (Obtaining thus stands to states of affairs as truth standsto propositions: although the proposition that Tours is the capital ofFrance is not true, there nevertheless is such a proposition.) Thestate of affairsx is said to include the state of affairsy if it is impossible forx to obtain andynot to obtain. If it is impossible for bothx andyto obtain, then each precludes the other. A possible world is simply apossible state of affairs that, for every state of affairsx,either includes or precludesx; the actual world is the onesuch state of affairs that obtains.

Using the KP theory we can answer Quine’s challenge as follows.In every possible world, every cyclist in that world is bipedal inthat world. (Assuming with Quine that necessarily cyclists arebipedal. Apparently he had not foreseen adaptive bicycles.)Nevertheless for any particular cyclist, there is some possible worldwhere he (the same person) is not bipedal. Once we draw thisdistinction, we can see that Quine’s argument is invalid. Moregenerally, on the KP theory, theses aboutde re essentialproperties need not be analytic; they are meaningful because theyexpress claims about an object’s properties in various possibleworlds.

We can also use the notion of possible worlds to define many othermodal concepts. For example, a necessarily true proposition is aproposition that would be true no matter what possible world wasactual. Socrates is a contingent being if there is some possible worldsuch that he would not exist if that world were actual, and he has theproperty “being human” essentially if every possible worldthat includes his existence also includes his being human. Kripke andPlantinga have greatly increased the clarity of modal discourse (andparticularly of modal discoursede re), but at the expense ofintroducing a modal ontology, an ontology of possible worlds.

Theirs is not the only modal ontology on offer. The main alternativeto the KP theory has been the ‘modal realism’ championedby David Lewis (1986). Lewis’s modal ontology appeals to objectscalled possible worlds, but these “worlds” are concreteobjects. What we call the actual world is one of these concreteobjects, the spatiotemporally connected universe we inhabit. What wecall “non-actual” worlds are other concrete universes thatare spatiotemporally isolated from ours (and from each other). Thereis, Lewis contends, a vast array of non-actual worlds, an array thatcontains at least those worlds that are generated by an ingeniousprinciple of recombination, a principle that can be stated without theuse of modal language (1986: 87). For Lewis, moreover,“actual” is an indexical term: when I speak of the actualworld, I refer to the world of which I am an inhabitant—and sofor any speaker who is “in” (who is a part of) anyworld.

In the matter of modalityde dicto, Lewis’s theoryproceeds in a manner that is at least parallel to the KP theory: therecould be flying pigs if there are flying pigs in some possible world(if some world has flying pigs as parts). But the case is otherwisewith modalityde re. Since every ordinary object is in onlyone of the concrete worlds, Lewis must either say that each suchobject has all its properties essentially or else adopt a treatment ofmodalityde re that is not parallel to the KP treatment. Hechooses the latter alternative. Although Socrates is in only theactual world, Lewis holds, he has ‘counterparts’ in someother worlds, objects that play the role in those worlds that he playsin this world. If all Socrates’ counterparts are human, then wemay say that he is essentially human. If one of HubertHumphrey’s counterparts won (the counterpart of) the 1968presidential election, it is correct to say of Humphrey that he couldhave won that election.

In addition to the obvious stark ontological contrast between the twotheories, they differ in two important ways in their implications forthe philosophy of modality. First, if Lewis is right, then modalconcepts can be defined in terms of paradigmatically non-modalconcepts, since ‘world’ and all of Lewis’s othertechnical terms can be defined using only ‘is spatiotemporallyrelated to’, ‘is a part of’ and the vocabulary ofset theory. For Kripke and Plantinga, however, modal concepts aresui generis, indefinable or having only definitions thatappeal to other modal concepts. Secondly, Lewis’s theory impliesa kind of anti-realism concerning modalityde re. This isbecause there is no one relation that is the counterpartrelation—there are rather various ways or respects in which onecould say that objects in two worlds “play the same role”in their respective worlds. Socrates, therefore, may well havenon-human counterparts under one counterpart relation and no non-humancounterparts under another. And the choice of a counterpart relationis a pragmatic or interest-relative choice. But on the KP theory, itis an entirely objective question whether Socrates fails to be humanin some world in which he exists: the answer must be Yes or No and isindependent of human choices and interests.

Whatever one may think of these theories when one considers them intheir own right (as theories of modality, as theories with variousperhaps objectionable ontological commitments), one must concede thatthey are paradigmatically metaphysical theories. They bear witness tothe resurgence of metaphysics in analytical philosophy in the lastthird of the twentieth century.

3.2 Space and Time

Long before the theory of relativity represented space and time asaspects of or abstractions from a single entity, spacetime,philosophers saw space and time as intimately related. (A glancethrough any dictionary of quotations suggests that the philosophicalpairing of space and time reflects a natural, pre-philosophicaltendency: “Had we but world enough, and time …”;“Dwellers all in time and space”.) Kant, for example,treated space and time in hisTranscendental Aesthetic asthings that should be explained by a single, unified theory. And histheory of space and time, revolutionary though it may have been inother respects, was in this respect typical of philosophical accountsof space and time. Whatever the source of the conviction that spaceand time are two members of a “species” (and the only twomembers of that species), they certainly raise similar philosophicalquestions. It can be asked whether space extends infinitely in everydirection, and it can be asked whether time extends infinitely ineither of the two temporal “directions”. Just as one canask whether, if space is finite, it has an “end” (whetherit is bounded or unbounded), one may ask of time whether, if it isfinite, it had a beginning or will have an end or whether it mighthave neither, but rather be “circular” (be finite butunbounded). As one can ask whether there could be two extended objectsthat were not spatially related to each other, one can ask whetherthere could be two events that were not temporally related to eachother. One can ask whether space is (a) a real thing—asubstance—a thing that exists independently of its inhabitants,or (b) a mere system of relations among those inhabitants. One can askthe same question about time, and also about modality. (See Wallace(2019) for an elucidation of temporal/ modal analogies.)

But there are also questions about time that have no spatialanalogues—or at least no obvious and uncontroversial analogues.There are, for example, questions about the grounds of variousasymmetries between the past and the future—why is our knowledgeof the past better than our knowledge of the future?; why do we regardan unpleasant event that is about to happen differently from the waywe regard an unpleasant event that has recently happened?; why doescausation seem to have a privileged temporal direction? There do notseem to be objective asymmetries like this in space.

There is also the question of temporal passage—the questionwhether the apparent “movement” of time (or the apparentmovement of ourselves and the objects of our experience through or intime) is a real feature of the world or some sort of illusion. In oneway of thinking about time, there is a privileged temporal directionmarking the difference between the past, present, and future.A-theorists hold that time is fundamentally structured in terms of apast/present/future distinction. Times change from past to present tofuture, giving rise to passage. (The name ‘A-theorist’descends from J.M.E. McTaggart’s (1908) name for the sequencepast/present/future which he called the ‘A-series’.)Within the A-theory, we might further ask whether the past and futurehave the “same sort of reality” as the present. PresentistA-theorists, like Prior 1998, deny that the past or future have anyconcrete reality. Presentists typically think of the past and futureas, at best, akin to abstract possible worlds—they are the waythe world was or will be, just as possible worlds are ways the actualworld could be. Other A-theorists, like Sullivan (2012), hold that thepresent is metaphysically privileged but deny that there is anyontological difference between the past, present, and future. Moregenerally, A-theorists often incorporate strategies from modalmetaphysics into their theories about the relation of the past and thefuture to the present.

According to B-theories of time, the only fundamental distinction weshould draw is that some events and times are earlier or laterrelative to others. (These relations are called‘B-relations’, a term also derived from McTaggart).According to the B-theorists, there is no objective passage of time,or at least not in the sense of time passing from future to presentand from present to past. B-theorists typically maintain that all pastand future times are real in the same sense in which the present timeis real—the present is in no sense metaphysicallyprivileged.

It is also true, and less often remarked on, that space raisesphilosophical questions that have no temporal analogues—or atleast no obvious and uncontroversial analogues. Why, for example, doesspace have three dimensions and not four or seven? On the face of it,time is essentially one-dimensional and space is not essentiallythree-dimensional. It also seems that the metaphysical problems aboutspace that have no temporal analogues depend on the fact that space,unlike time, has more than one dimension. For example, consider theproblem of incongruent counterparts: those who think space is a meresystem of relations struggled to explain our intuition that we coulddistinguish a world containing only a left hand from a worldcontaining only a right hand. So it seems there is an intuitiveorientation to objects in space itself. It is less clear whether theproblems about time that have no spatial analogues are connected withthe one-dimensionality of time.

Finally, one can raise questions about whether space and time are realat all—and, if they are real, to what extent (so to speak) theyare real. Might it be that space and time are not constituents ofreality as God perceives reality but nevertheless “well-foundedphenomena” (as Leibniz held)? Was Kant right when he deniedspatial and temporal features to “things as they are inthemselves”?—and right to contend that space and time are“forms of our intuition”? Or was McTaggart’sposition the right one: that space and time are wholly unreal?

If these problems about space and time belong to metaphysics only inthe post-Medieval sense, they are nevertheless closely related toquestions about first causes and universals. First causes aregenerally thought by those who believe in them to be eternal andnon-local. God, for example—both the impersonal God of Aristotleand the personal God of Medieval Christian, Jewish, and Muslimphilosophy—is generally said to be eternal, and the personal Godis said to be omnipresent. To say that God is eternal is to say eitherthat he is everlasting or that he is somehow outside time. And thisraises the metaphysical question of whether it is possible for thereto be a being—not a universal or an abstract object of someother sort, but an active substance—that is everlasting ornon-temporal. An omnipresent being is a being that does not occupy anyregion of space (not even the whole of it, as the luminiferous etherof nineteenth-century physics would if it existed), and whose causalinfluence is nevertheless equally present in every region of space(unlike universals, to which the concept of causality does not apply).The doctrine of divine omnipresence raises the metaphysical questionwhether it is possible for there to be a being with this feature.Ante res universals are said by some of their proponents(precisely those who deny that universals are constituents ofparticulars) to have no relations to space and time but“vicarious” ones: theante res universal“whiteness” may be said to be present where each whiteparticular is, but only in a way analogous to the way in which thenumber two is present where each pair of spatial things is. But it isdoubtful whether this is a position that is possible for ametaphysician who says that a white thing is a bundle composed ofwhiteness and various other universals. Those who believe in theexistence ofin rebus universals are fond of saying, or havebeen in recent years, that these universals (‘immanentuniversals’ is a currently popular name for them) are“multiply located”—“wholly present” ateach place at which the things that fall under them are present. Andby this they certainly do not mean that whiteness is present in manydifferent regions of space only vicariously, only as a number might besaid to be present wherever there are things in that number, only invirtue of bearing the non-spatial relation “being had by”to a multitude of particulars each of which is present in a singleregion of space. All theories of universals, therefore, raisequestions about how things in various ontological categories arerelated to space. And all these questions have temporal analogues.

3.3 Persistence and Constitution

Related to questions about the nature of space and time are questionsabout the nature of objects that take up space or persist throughtime, and these questions form yet another central theme inpost-medieval metaphysics. Are some or all objects composed of properparts? Must an object have proper parts in order to “fillup” a region of space—or are there extended simples? Canmore than one object be located in exactly the same region? Do objectspersist through change by having temporal parts?

Much work on persistence and constitution has focused on efforts toaddress a closely knit family of puzzles—the puzzles ofcoincidence. One such puzzle is the “problem of the statue andthe lump”. Consider a gold statue. Many metaphysicians contendthat there is at least one material object that is spatiallyco-extensive with the statue, a lump of gold. This is easily shown,they say, by an appeal to Leibniz’s Law (the principle of thenon-identity of discernibles). There is a statue here and there is alump of gold here, and—if the causal story of the statue’scoming to be is of the usual sort—the lump of gold existedbefore the statue. And even if God has created the statue (andperforce the lump)ex nihilo and will at some pointannihilate the statue (and thereby annihilate the lump), they furtherargue, the statue and the lump, although they exist at exactly thesame times, have different modal properties: the lump has the property“can survive radical deformation” and the statue does not.Or so these metaphysicians conclude. But it has seemed to othermetaphysicians that this conclusion is absurd, for it is absurd tosuppose (these others say) that there could be spatially coincidentphysical objects that share all their momentary non-modal properties.Hence, the problem: What, if anything, is the flaw in the argument forthe non-identity of the statue and the lump?

A second puzzle in this family is the “problem of Tib andTibbles”. Tibbles is a cat. Call his tail “Tail”.Call all of him but his tail “Tib”. Suppose Tail is cutoff—or, better, annihilated. Tibbles still exists, for a cat cansurvive the loss of its tail. And it would seem that Tib will existafter the “loss” of Tail, because Tib lost no part. Butwhat will be the relation between Tib and Tibbles? Can it be identity?No, that is ruled out by the non-identity of discernibles, for Tibbleswill have become smaller and Tib will remain the same size. But then,once again, we seem to have a case of spatially coincident materialobjects that share their momentary non-modal properties.

Both these constitution problems turn on questions about theidentities of spatially coincident objects—and, indeed, ofobjects that share all their (proper) parts. (A third famous problemof material constitution—the problem of the Ship ofTheseus—raises questions of a different sort.) Somemetaphysicians contend that the relation between the lump and thestatue, on the one hand, and the relation between Tib and Tibbles, onthe other, cannot be fully understood in terms of the concepts ofparthood and (non-) identity, but require a further concept, anon-mereological concept, the concept of “constitution”:the pre-existent lump at a certain point in time comes to constitutethe statue (or a certain quantity of gold or certain gold atoms thatfirst constituted only the lump come to constitute them both);pre-existent Tib at a certain point in time comes to constituteTibbles (or certain cat-flesh or certain molecules …). (Baker2000 is a defense of this thesis.) Others contend that all therelations between the objects that figure in both problems can befully analyzed in terms of parthood and identity. For a more thoroughoverview of the solutions to these puzzles and different theories ofconstitution in play, see Rea (ed.) 1997 and Thomson 1998.

3.4 Causation, Freedom and Determinism

Questions about causation form yet a fourth important category ofissues in the “new” metaphysics. Of course, discussion ofcauses go back to Ancient Philosophy, featuring prominently inAristotle’sMetaphysics andPhysics. ButAristotle understood ‘cause’ in a much broader sense thanwe do today. In Aristotle’s sense, a ‘cause’ or‘aiton’ is an explanatory condition of anobject—an answer to a “why” question about theobject. Aristotle classifies four such explanatory conditions—anobject’s form, matter, efficient cause, and teleology. Anobject’s efficient cause is the cause which explains change ormotion in an object. With the rise of modern physics in theseventeenth century, interest in efficient causal relations becameacute, and it remains so today. And when contemporary philosophersdiscuss problems of causation, they typically mean this sense.

One major issue in the metaphysics of causation concerns specifyingthe relata of causal relations. Consider a mundane claim: an icebergcaused theTitanic to sink. Does the causal relation holdbetween two events: the event of the ship hitting the iceberg and theevent of the ship sinking? Or does it hold between two sets of statesof affairs? Or does it hold between two substances, the iceberg andthe ship? Must causal relations be triadic or otherwise poly-adic? Forexample, one might think that we are always required to qualify acausal claim: the iceberg, rather than the captain’s negligence,was causally responsible for the ship’s foundering. And canabsences feature in causal relations? For example, does it make senseto claim that a lack of lifeboats was the cause of a third-classpassenger’s death? Bernstein (2014) and Sartorio (2004) arguethat absences can be causes. Beebee (2004) suggests that absences arecausal explanations, but not causes.

Another question taken up by contemporary literature is whethercausation comes in degrees. For example: if two people lift a heavyplank and one person bears more of the weight, has one personcontributed more than the other to the lifting of the plank? Bernstein(2017) suggests that causation comes in degrees, but that mostmetaphysical theories of causation cannot account for this idea.Demirtas (2022) and Kaiserman (2018) agree, while Sartorio (2020)argues that the appearance that causation comes in degrees isillusory, and can be explained away.

We might further ask whether causal relations are objective andirreducible features of reality. Hume famously doubted this,theorizing that our observations of causation were nothing more thanobservations of constant conjunction. For example, perhaps we thinkicebergs cause ships to sink only because we always observeship-sinking events occurring after iceberg-hitting events and notbecause there is a real causal relation that holds between icebergsand foundering ships.

Contemporary metaphysicians have been attracted to other kinds ofreductive treatments of causation. Some—like Stalnaker andLewis—have argued that causal relations should be understood interms of counterfactual dependencies (Stalnaker 1968 and Lewis 1973).For example, an iceberg’s striking the ship caused its sinkingat timet if and only if in the nearest possible worlds wherethe iceberg did not strike the ship at timet, the ship didnot sink. Others have argued that causal relations should beunderstood in terms of instantiations of laws of nature. (Davidson(1967) and Armstrong (1997) each defend this view albeit in differentways.) All of these theories expand on an idea from Hume’sTreatise in attempting to reduce causation to different ormore fundamental categories. (For a more complete survey of recenttheories of causation, see Paul and Hall 2013.)

Debates about causation and laws of nature further give rise to arelated set of pressing philosophical questions—questions offreedom. In the seventeenth century, celestial mechanics gavephilosophers a certain picture of a way the world might be: it mightbe a world whose future states were entirely determined by the pastand the laws of nature (of which Newton’s laws of motion and lawof universal gravitation served as paradigms). In the nineteenthcentury the thesis that the world was indeed this way came to becalled ‘determinism’. The problem of free will can bestated as a dilemma. If determinism is true, there is only onephysically possible future. But then how can anyone ever have actedotherwise? For, as Carl Ginet has said (1990: 103), our freedom canonly be the freedom to add to the actual past; and if determinismholds, then there is only one way that the given—theactual—past can be “added to”. But if determinismdoes not hold, if there are alternative physically possible futures,then which one comes to pass must be a mere matter of chance. And ifit is a mere matter of chance whether I lie or tell the truth, how canit be “up to me” whether I lie or tell the truth? Unlessthere is something wrong with one of these two arguments, the argumentfor the incompatibility of free will and determinism or the argumentfor the incompatibility of free will and the falsity of determinism,free will is impossible. The problem of free will may be identifiedwith the problem of discovering whether free will ispossible—and, if free will is possible, the problem of giving anaccount of free will that displays an error in one of (or both) thesearguments.

Van Inwagen (1998) defends the position that, although the modernproblem of free will has its origin in philosophical reflections onthe consequences of supposing the physical universe to be governed bydeterministic laws, the problem cannot be evaded by embracing ametaphysic (like dualism or idealism) that supposes that agents areimmaterial or non-physical. This leads into our next and final sampleof topics from the “new” metaphysics.

3.5 The Mental and Physical

If it is natural both to pair and to oppose time and space, it is alsonatural to pair and to oppose the mental and the physical. The modernidentity theory holds that all mental events or states are a specialsort of physical event or state. The theory is parsimonious (among itsother virtues) but we nevertheless exhibit a natural tendency todistinguish the mental and the physical. Perhaps the reason for thisis epistemological: whether our thoughts and sensations are physicalor not, the kind of awareness we have of them is of a radicallydifferent sort from the kind of awareness we have of the flight of abird or of a flowing stream, and it seems to be natural to infer thatthe objects of the one sort of awareness are radically different fromthe objects of the other. That the inference is logically invalid is(as is so often the case) no barrier to its being made. Whatever thereason may be, philosophers have generally (but not universally)supposed that the world of concrete particulars can be divided intotwo very different realms, the mental and the material. (As thetwentieth century passed and physical theory rendered“matter” an increasingly problematical concept, it becameincreasingly common to say “the mental and the physical”.)If one takes this view of things, one faces philosophical problemsthat modern philosophy has assigned to metaphysics.

Prominent among these is the problem of accounting for mentalcausation. If thoughts and sensations belong to an immaterial ornon-physical portion of reality—if, for example, they arechanges in immaterial or non-physical substances—how can theyhave effects in the physical world? How, for example, can a decisionor act of will cause a movement of a human body? How, for that matter,can changes in the physical world have effects in the non-physicalpart of reality? If one’s feeling pain is a non-physical event,how can a physical injury to one’s body cause one to feel pain?Both questions have troubled “two realm”philosophers—or ‘dualists’, to give them their moreusual name. But the former has troubled them more, since modernphysics is founded on principles that assert the conservation ofvarious physical quantities. (See Bennett (2021) for discussion of thecomparative explanatory demands of physicalism and dualism.) If anon-physical event causes a change in the physicalworld—dualists are repeatedly asked—does that not implythat physical quantities like energy or momentum fail to be conservedin any physically closed causal system in which that change occurs?And does that not imply that every voluntary movement of a human bodyinvolves a violation of the laws of physics—that is to say, amiracle?

A wide range of metaphysical theories have been generated by theattempts of dualists to answer these questions. Some have been lessthan successful for reasons that are not of much intrinsicphilosophical interest. C. D. Broad, for example, proposed (1925:103–113) that the mind affects the body by momentarily changingthe electrical resistance of certain synapses in the brain, (thusdiverting various current pulses, which literally follow the path ofleast resistance into paths other than those they would have taken).And this, he supposed, would not imply a violation of the principle ofthe conservation of energy. But it seems impossible to suppose that anagent could change the electrical resistance of a physical systemwithout expending energy in the process, for to do this wouldnecessitate changing the physical structure of the system, and thatimplies changing the positions of bits of matter on which forces areacting (think of turning the knob on a rheostat or variable resistor:one must expend energy to do this). If this example has anyphilosophical interest it is this: it illustrates the fact that it isimpossible to imagine a way for a non-physical thing to affect thebehavior of a (classical) physical system without violating aconservation principle.

The various dualistic theories of the mind treat the interactionproblem in different ways. The theory called ‘dualisticinteractionism’ does not, of itself, have anything to say aboutthe problem—although its various proponents (Broad, for example)have proposed solutions to it. ‘Occasionalism’ simplyconcedes that the “local” counterfactual dependence of thebehavior of a physical system on a non-physical event requires amiracle. The theory of pre-established harmony, which substitutes“global” for local counterfactual dependence of voluntaryphysical movements on the mental states of agents, avoids problemswith conservation principles—but secures this advantage at agreat price. (Like occasionalism, it presupposes theism, and, unlikeoccasionalism, it entails either that free will does not exist or thatfree will is compatible with determinism.)‘Epiphenomenalism’ simply denies that the mental canaffect the physical, and contents itself with an explanation of whythe mental appears to affect the physical.

In addition to these dualistic theories, there are monistic theories,theories that dissolve the interaction problem by denying theexistence of either the physical or the non-physical: idealism andphysicalism. (Present-day philosophers for the most part prefer theterm ‘physicalism’ to the older term‘materialism’ for reasons noted above.) Most current workin the philosophy of mind presupposes physicalism, and it is generallyagreed that a physicalistic theory that does not simply deny thereality of the mental (that is not an “eliminativist”theory), raises metaphysical questions. Such a theory must, of course,find a place for the mental in a wholly physical world, and such aplace exists only if mental events and states are certain specialphysical events and states. There are at least three importantmetaphysical questions raised by these theories. First, granted thatall particular mental events or states are identical with particularphysical events or states, can it also be that some or all mentaluniversals (‘event-types’ and ‘state-types’are the usual terms) are identical with physical universals? Secondly,does physicalism imply that mental events and states cannot really becauses (does physicalism imply a kind of epiphenomenalism)? Thirdly,can a physical thing have non-physical properties—might it bethat mental properties like “thinking of Vienna” or“perceiving redly” are non-physical properties of physicalorganisms? This last question, of course, raises a more basicmetaphysical question, ‘What is a non-physical property?’And all forms of the identity theory raise fundamental metaphysicalquestions, ontological questions, questions like, ‘What is anevent?’ and ‘What is a state?’.

3.6 Social Metaphysics

Recent years have seen an outpouring of interest insocialmetaphysics, which takes the nature of the social world as itssubject of study. Many contemporary social metaphysicians investigatethe ontological natures of socially constructed groups, entities, andinstitutions. Key questions include: what, exactly, are corporations,restaurants, and sports teams? What is the nature of money? What arethe natures of social categories, likewoman,Black,lesbian, anddisabled? What is the relationshipbetween individuals and macro-level social objects? What does it meanto say that something is “socially constructed,” and whatis the difference between the social and the natural in the firstplace?

Ritchie (2013, 2015, 2020a and 2020b) draws a distinction between“Type 1” social groups like corporations and institutions,which are organized and structured, and “Type 2” socialgroups, like Blacks and women, which are less structured social kinds.Epstein (2019) argues against these sorts of course-grainedclassifications, preferring to classify them according to theirinter-level metaphysical relationships. Ruben (1985) denies thatsocial groups and other macro-level social entities can be reduced toindividuals. Korman (2020) takes up the question of the nature ofestablishments like restaurants in further detail, suggesting thatthey are neither material objects nor constituted by the buildingsthat they occupy. Uzquiano (2004) questions the persistence conditionsof social groups like the Supreme Court, and ultimately argues thatthey are similar to the persistence conditions for artifacts. Drawingon this idea, Richardson (2022) holds that social groups are concretematerial particulars, since two different social groups can haveexactly the same members.

Other metaphysicians examine the ontological status of money, andespecially the status of virtual currency like bitcoin. Passinsky(2020) distinguishes between descriptive and normative approaches toexploring the topic, and argues in favor of the latter. In contrast,Warmke (2021) takes a descriptive approach, suggesting that bitcoin isa fictional substance in a collectively co-authored story.

There has also been a recent surge of interest in the metaphysics ofrace and gender. Haslanger (2000) famously holds that (roughly)x is a woman if one is oppressed on the basis of herwomanhood. Haslanger’s approach is ameliorative, taking intoaccount what sorts of concepts of gender and race might be most usefulin theorizing. Friendly to this approach, Ásta (2018) proposesa conferralist account of social categories, according to which socialcategories are externally conferred on individuals in specificcontexts. Others have taken on the topic of the natures of morespecific sorts of social categories: Bernstein (2020) suggests thatintersectional social categories likeBlack woman are to beviewed as explanatorily unified and prior to the individualconstituents likeBlack andwoman. Jorba andRodó de Zárate (2019) propose a framework of propertiesand emergent experience to account for intersectionality.

Dembroff (2016) takes up the puzzle of sexual orientation, arguing for“Bidimensional Dispositionalism.” According to that view,a person’s sexual orientation is grounded in a person’sdispositions to engage in sexual behaviors under the ordinaryconditions for these dispositions. A person’s dispositionsinclude sexes and genders of persons that one is disposed to sexuallyengage with under those conditions. Andler (2021) draws a distinctionbetween sexual orientation and sexual identity, arguing that thelatter is a more suitable and more explanatorily powerful category forcapturing the relevant phenomenon.

There is even a burgeoning meta-metaphysics of the social world,examining whether the central questions of social metaphysics aresubstantive. Barnes (2017) and Mikkola (2017) challenge Sider’s(2012) conception of a substantive question in metaphysics, on thegrounds that it does not accommodate substantive questions in themetaphysics of gender. Richardson (forthcoming) disagrees. And whilesocial metaphysics is often taken to contrast with so-called“fundamental” metaphysics (as in McKitrick (2018)),several philosophers have recently pointed out that elements of thesocial world might be fundamental, including Mason and Ritchie (2020)and Bernstein (2021). Social metaphysics can be viewed as acounterexample to the thesis that metaphysics is the study offundamental reality, as suggested in Bennett (2017). Passinsky (2021)holds that Finean metaphysics is a good framework for feministmetaphysics. Others such as Hacking (1999) and Díaz-León(2015) investigate what it is for something to be sociallyconstructed. See also the Social Ontology entry by Epstein (2021) fora comprehensive overview of social ontology.

4. The Methodology of Metaphysics

As is obvious from the discussion inSection 3, the scope of metaphysics has expanded beyond the tidy boundariesAristotle drew. So how should we answer our original question? Iscontemporary metaphysics just a compendium of philosophical problemsthat cannot be assigned to epistemology or logic or ethics oraesthetics or to any of the parts of philosophy that have relativelyclear definitions? Or is there a common theme that unites work onthese disparate problems and distinguishes contemporary metaphysicsfrom other areas of inquiry?

These issues concerning the nature of metaphysics are furtherconnected with issues about the epistemic status of variousmetaphysical theories. Aristotle and most of the Medievals took it forgranted that, at least in its most fundamental aspects, the ordinaryperson’s picture of the world is “correct as far as itgoes”. But many post-Medieval metaphysicians have refused totake this for granted. Some of them, in fact, have been willing todefend the thesis that the world is very different from, perhapsradically different from, the way people thought it was before theybegan to reason philosophically. For example, in response to thepuzzles of coincidence considered inSection 3.3, some metaphysicians have maintained that there are no objects withproper parts. This entails that composite objects—tables,chairs, cats, and so on—do not exist, a somewhat startling view.And as we saw inSection 3.1, other metaphysicians have been happy to postulate the reality ofconcrete merely possible worlds if this posit makes for a simpler andmore explanatorily powerful theory of modality. Perhaps thiscontemporary openness to “revisionary” metaphysics issimply a recovery of or a reversion to a pre-Aristotelian conceptionof a “permissible metaphysical conclusion”, a conceptionthat is illustrated by Zeno’s arguments against the reality ofmotion and Plato’s Allegory of the Cave. But no matter how weclassify it, the surprising nature of many contemporary metaphysicalclaims puts additional pressure on practioners to explain just whatthey are up to. They raise questions of the methodology ofmetaphysics.

One attractive strategy for answering these questions emphasizes thecontinuity of metaphysics with science. On this conception,metaphysics is primarily or exclusively concerned with developinggeneralizations from our best-confirmed scientific theories. Forexample, in the mid-twentieth century, Quine (1948) proposed that thatthe “old/intermediate” metaphysical debate over the statusof abstract objects should be settled in this way. He observed that ifour best scientific theories are recast in the “canonicalnotation of (first-order) quantification” (in sufficient depththat all the inferences that users of these theories will want to makeare valid in first-order logic), then many of these theories, if notall of them, will have as a logical consequence the existentialgeneralization on a predicate \(F\) such that \(F\) is satisfied onlyby abstract objects. It would seem, therefore, that our bestscientific theories “carry ontological commitment” toobjects whose existence is denied by nominalism. (These objects maynot be universals in the classical sense. They may, for example, besets.) Take for example the simple theory, ‘There arehomogeneous objects, and the mass of a homogeneous object in grams isthe product of its density in grams per cubic centimeter and itsvolume in cubic centimeters’. A typical recasting of this theoryin the canonical notation of quantification is:

\(\exists Hx\) & \(\forall x(Hx \rightarrow Mx = Dx \times Vx)\)

(‘\(Hx\)’: ‘\(x\) is homogeneous’;‘\(Mx\)’: ‘the mass of \(x\) in grams’;‘\(Dx\)’: ‘the density of \(x\) in grams per cubiccentimeter’; ‘\(Vx\)’: ‘the volume of \(x\) incubic centimeters’.) A first-order logical consequence of this“theory” is

\(\exists x\exists y\exists z(x = y \times z)\)

That is: there exists at least one thing that is a product (at leastone thing that, for some \(x\) and some \(y\) is the product of \(x\)and \(y\)). And a product must be a number, for the operation“product of” applies only to numbers. Our little theory,at least if it is recast in the way shown above, is therefore, in avery obvious sense, “committed” to the existence ofnumbers. It would seem, therefore, that a nominalist cannotconsistently affirm that theory. (In this example, the role played by‘the predicateF’ in the abstract statement ofQuine’s “observation” is played by the predicate‘…=…×…’.)

Quine’s work on nominalism inspired a much broader program forapproaching ontological questions. According to“neo-Quineans”, questions about the existence of abstractobjects, mental events, objects with proper parts, temporal parts, andeven other concrete possible worlds are united to the extent that theyare questions about the ontological machinery required to account forthe truth of our best-confirmed theories. Still, many questions of thenew and old metaphysics are not questions of ontology. For example,many participants in the debate over causation are not particularlyworried about whether causes and effects exist. Rather, they want toknow “in virtue of what” something is a cause or effect.Few involved in the debate over the mental and physical are interestedin the question whether there are mental properties (in some sense orother). Rather, they are interested in whether mental properties are“basic” orsui generis—or whether they aregrounded, partially or fully, in physical properties.

Is there a unified methodology for metaphysics more broadlyunderstood? Some think the task of the metaphysician is to identifyand argue for explanatory relations of various kinds. According toFine (2001), metaphysicians are in the business of providing theoriesof which facts or propositions ground other facts or propositions, andwhich facts or propositions hold “in reality”. Forexample, a philosopher might hold that tables and other compositeobjects exist, but think that facts about tables are completelygrounded in facts about the arrangements of point particles or factsabout the state of a wave function. This metaphysician would hold thatthere are no facts about tables “in reality”; rather,there are facts about arrangements of particles. Schaffer 2010proposes a similar view, but holds that metaphysical groundingrelations hold not between facts but between entities. According toSchaffer, the fundamental entity/entities should be understood as theentity/entities that grounds/ground all others. On Schaffer’sconception we can meaningfully ask whether a table is grounded in itsparts or vice versa. We can even theorize (as Schaffer does) that theworld as a whole is the ultimate ground for everything.

Another noteworthy approach (Sider 2012) holds that the task of themetaphysician is to “explain the world” in terms of itsfundamental structure. For Sider, what unites (good) metaphysics as adiscipline is that its theories are all framed in terms that pick outthe fundamental structure of the world. For example, according toSider we may understand ‘causal nihilism’ as the view thatcausal relations do not feature in the fundamental structure of theworld, and so the best language for describing the world will eschewcausal predicates.

It should be emphasized that these ways of delimiting metaphysics donot presuppose that all of the topics we’ve considered asexamples of metaphysics are substantive or important to the subject.Consider the debate about modality. Quine (1953) and Sider (2012) bothargue from their respective theories about the nature of metaphysicsthat aspects of the debate over the correct metaphysical theory ofmodality are misguided. Others are skeptical of the debates aboutcomposition or persistence through time. So theories about the natureof metaphysics might give us new resources for criticizing particularfirst-order debates that have historically been consideredmetaphysical, and it is common practice for metaphysicians to regardsome debates as substantive while adopting a deflationist attitudeabout others.

5. Is Metaphysics Possible?

It may also be that there is no internal unity to metaphysics. Morestrongly, perhaps there is no such thing as metaphysics—or atleast nothing that deserves to be called a science or a study or adiscipline. Perhaps, as some philosophers have proposed, nometaphysical statement or theory is either true or false. Or perhaps,as others have proposed, metaphysical theories have truth-values, butit is impossible to find out what they are. At least since the time ofHume, there have been philosophers who have proposed that metaphysicsis “impossible”—either because its questions aremeaningless or because they are impossible to answer. The remainder ofthis entry will be a discussion of some recent arguments for theimpossibility of metaphysics.

Let us suppose that we are confident that we are able to identifyevery statement as either “a metaphysical statement” or“not a metaphysical statement”. (We need not suppose thatthis ability is grounded in some non-trivial definition or account ofmetaphysics.) Let us call the thesis that all metaphysical statementsare meaningless “the strong form” of the thesis thatmetaphysics is impossible. (At one time, an enemy of metaphysics mighthave been content to say that all metaphysical statements were false.But this is obviously not a possible thesis if the denial of ametaphysical statement must itself be a metaphysical statement.) Andlet us call the following statement the “weak form” of thethesis that metaphysics is impossible: metaphysical statements aremeaningful, but human beings can never discover whether anymetaphysical statement is true or false (or probable or improbable orwarranted or unwarranted).

Let us briefly examine an example of the strong form of the thesisthat metaphysics is impossible. The logical positivists maintainedthat the meaning of a (non-analytic) statement consisted entirely inthe predictions it made about possible experience. They maintained,further, that metaphysical statements (which were obviously not putforward as analytic truths) made no predictions about experience.Therefore, they concluded, metaphysical statements aremeaningless—or, better, the “statements” we classifyas metaphysical are not really statements at all: they are things thatlook like statements but aren’t, rather as mannequins are thingsthat look like human beings but aren’t.

But (many philosophers asked) how does the logical positivist’scentral thesis

The meaning of a statement consists entirely in the predictions itmakes about possible experience

fare by its own standards? Does this thesis make any predictions aboutpossible experiences? Could some observation show that it was true?Could some experiment show that it was false? It would seem not. Itwould seem that everything in the world would look the same—likethis—whether this thesis was true or false. (Will the positivistreply that the offset sentence is analytic? This reply is problematicin that it implies that the multitude of native speakers of Englishwho reject the logical positivists’ account of meaning somehowcannot see that that sentence is true in virtue of the meaning of theword “meaning”—which is no technical term but a wordof ordinary English.) And, therefore, if the statement is true it ismeaningless; or, what is the same thing, if it is meaningful, it isfalse. Logical positivism would therefore seem to say of itself thatit is false or meaningless; it would be seem to be, to use a currentlyfashionable phrase, “self-referentially incoherent”.

Current advocates of ‘metaphysical anti-realism’ alsoadvocate a strong form of the thesis that metaphysics is impossible.Insofar as it is possible to find a coherent line of argument in thewritings of any anti-realist, it is hard to see why they, like thelogical positivists, are not open to a charge of self-referentialincoherency. Indeed, there is much to be said for the conclusion thatall forms of the strong thesis fall prey to self-referentialincoherency. Put very abstractly, the case against proponents of thestrong thesis may be put like this. Dr. McZed, a “stronganti-metaphysician”, contends that any piece of text that doesnot pass some test she specifies is meaningless (if she is typical ofstrong anti-metaphysicians, she will say that any text that fails thetest represents an attempt to use language in a way in which languagecannot be used). And she contends further that any piece of text thatcan plausibly be identified as “metaphysical” must failthis test. But it invariably turns out that various sentences that areessential components of McZed’s case against metaphysicsthemselves fail to pass her test. A test-case for this very schematicand abstract refutation of all refutations of metaphysics is the verysophisticated and subtle critique of metaphysics (it purports to applyonly to the kind of metaphysics exemplified by the seventeenth-centuryrationalists and current analytical metaphysics) presented in vanFraassen 2002. It is a defensible position that van Fraassen’scase against metaphysics depends essentially on certain theses that,although they are not themselves metaphysical theses, are neverthelessopen to many of the criticisms he brings against metaphysicaltheses.

The weak form of the thesis that metaphysics is impossible is this:there is something about the human mind (perhaps even the minds of allrational agents or all finite rational agents) that unfits it forreaching metaphysical conclusions in any reliable way. This idea is atleast as old as Kant, but a version of it that is much more modestthan Kant’s (and much easier to understand) has been carefullypresented in McGinn 1993. McGinn’s argument for the conclusionthat the human mind is (as a matter of evolutionary contingency, andnot simply because it is “a mind”) incapable of asatisfactory treatment of a large range of philosophical questions (arange that includes all metaphysical questions), however, depends onspeculative factual theses about human cognitive capacities that arein principle subject to empirical refutation and which are at presentwithout significant empirical support. For a different defense of theweak thesis, see Thomasson 2009.

Bibliography

• Andler, Matthew, 2021, “The Sexual Orientation/IdentityDistinction”,Hypatia, 36(2):259–275.
• Armstrong, David, 1989,Universals: An OpinionatedIntroduction, Boulder, CO: Westview.
• –––, 1997,A World of States ofAffairs, Cambridge: Cambridge University Press.
• Ásta, 2018,Categories We Live By: The Construction ofSex, Gender, Race, and Other Social Categories, New York, USA:Oxford University Press.
• Baker, Lynne Rudder, 2000,Persons and Bodies: A ConstitutionView, Cambridge: Cambridge University Press.
• Barcan [Barcan Marcus], Ruth, 1946, “A Functional Calculusof First Order Based on Strict Implication”,Journal ofSymbolic Logic, 11: 1–16.
• Barnes, Elizabeth, 2016,The Minority Body: A Theory ofDisability. Oxford, United Kingdom: Oxford University Press.
• Barnes, Elizabeth, 2017, “Realism and socialstructure”,Philosophical Studies, 174(10):2417–2433.
• Beebee, Helen, 2004, “Causing and Nothingness”, inCausation and Counterfactuals, John Collins, Ned Hall andLaurie Paul (eds.), Cambridge: MIT Press, pp. 291–308.
• Bennett, Karen, 2021, “Why I am Not a Dualist” inOxford Studies in Philosophy of Mind, 1: 208–231.
• –––, 2017,Making Things Up,New York:Oxford University Press.
• Bernstein, Sara, 2014, “Omissions as Possibilities”,Philosophical Studies, 167(1): 1–23.
• –––, 2017, “Causal proportions and moralresponsibility” inOxford Studies in Agency andResponsibility, Volume 4, David Shoemaker (ed.), Oxford: OxfordUniversity Press, pp. 165–182.
• –––, 2020, “The Metaphysics ofIntersectionality”,Philosophical Studies, 177(2):321–335.
• –––, 2021, “Could a Middle Level be theMost Fundamental?”,Philosophical Studies, 178(4):1065–1078.
• Broad, C. D., 1925,The Mind and its Place in Nature,London: Lund Humphries.
• Davidson, Donald, 1967, “Causal Relations”,Journal of Philosophy, 64: 691–703.
• Dembroff, Robin A, 2016, “What Is SexualOrientation?”,Philosophers’ Imprint 16.
• Demirtas, Huzeyfe, 2022, “Causation Comes inDegrees”,Synthese, 200(1): 1–17.
• Díaz-León, Esa, 2015, “What Is SocialConstruction?”,European Journal of Philosophy, 23(4):1137–1152.
• Epstein, Brian, 2019, “What are Social Groups? TheirMetaphysics and How to Classify Them”,Synthese, 196(12): 4899–4932.
• –––, “Social Ontology”,TheStanford Encyclopedia of Philosophy(Winter 2021 Edition), EdwardN. Zalta (ed.), URL =<https://plato.stanford.edu/archives/win2021/entries/social-ontology/>
• Fine, Kit, 2001, “The Question of Realism”,Philosopher’s Imprint, 1: 1–30.
• Ginet, Carl, 1990,On Action, Cambridge: CambridgeUniversity Press.
• Hacking, Ian, 1999,The Social Construction of What?,Cambridge: Harvard University Press.
• Jorba, Marta & Rodó de Zárate, Maria, 2019,“Beyond Mutual Constitution: The Properties Framework forIntersectionality Studies”,Signs: Journal of Women inCulture and Society, 45(1): 175–200.
• Kaiserman, Alex, 2018, “‘More of a Cause’:Recent Work on Degrees of Causation and Responsibility”,Philosophy Compass, 13(7): e12498.
• Korman, Daniel Z, 2020, “The Metaphysics ofEstablishments”,Australasian Journal of Philosophy, 98(3): 434–448.
• Kripke, Saul, 1972,Naming and Necessity, Cambridge, MA:Harvard University Press.
• Laurence, Stephen and Cynthia Macdonald (eds.), 1998,Contemporary Readings in the Foundations of Metaphysics,Oxford: Blackwell.
• Lewis, David, 1973, “Causation”,Journal ofPhilosophy, 70: 556–67.
• –––, 1986,On the Plurality of Worlds,Oxford: Blackwell.
• Lowe, E. J., 2006,The Four-Category Ontology: A MetaphysicalFoundation for Natural Science, Oxford: The Clarendon Press.
• Mason, R. & Ritchie, K., 2020, “Social Ontology”,inRoutledge Handbook of Metametaphysics, R. Bliss and J.Miller (eds.), Routledge, pp. 312–324.
• McKitrick, J, 2018, “Feminist Metaphysics: Can ThisMarriage Be Saved?”,The Bloomsbury Companion to AcademicFeminism, Pieranna Garavaso (ed.), London: Bloomsbury Academic,pp. 58–79.
• McDaniel, Kris, 2013, “Degrees of Being”,Philosophers’ Imprint, 13.
• McGinn, Colin, 1993,Problems in Philosophy: The Limits ofInquiry, Oxford: Blackwell.
• McTaggart, J.M. E., 1908, “The Unreality of Time”,Mind, 17: 457–474.
• Mikkola, Mari, 2017, “On the Apparent Antagonism betweenFeminist and Mainstream Metaphysics”,PhilosophicalStudies, 174(10): 2435–2448.
• Passinsky, Asya, 2020, “Should Bitcoin Be Classified asMoney?”,Journal of Social Ontology, 6(2):281–292.
• –––, “Finean Feminist Metaphysics”,Inquiry: An Interdisciplinary Journal of Philosophy, 64(9):937–954.
• Paul, L.A. and Ned Hall, 2013,Causation: A User’sGuide, Oxford: Oxford University Press.
• Plantinga, Alvin, 1974,The Nature of Necessity, Oxford:The Clarendon Press.
• Politis, Vasilis, 2004,Aristotle and the Metaphysics,London and New York: Routledge.
• Prior, A.N., 1998, “The Notion of the Present”, inMetaphysics: The Big Questions, Peter van Inwagen and DeanZimmerman (eds.), Oxford: Blackwell Press, pp. 80–82.
• Quine, W. V. O., 1948, “On What There Is”, in Quine1961: 1–19.
• –––, 1953, “Reference andModality”, in Quine 1961: 139–159.
• –––, 1960,Word and Object, Cambridge,MA: MIT Press.
• –––, 1961,From a Logical Point ofView, Cambridge, MA: MIT Press.
• Rea, Michael (ed.), 1997,Material Constitution: AReader, Lanham, MD: Rowman & Littlefield.
• Richardson, Kevin, forthcoming, “The Metaphysics of Genderis (Relatively) Substantial”,Philosophy andPhenomenological Research.
• –––, 2022, “Social Groups Are ConcreteMaterial Particulars”,Canadian Journal of Philosophy52(4): 468–483.
• Ritchie, Katherine, 2020b, “Social Structures and theOntology of Social Groups”,Philosophy and PhenomenologicalResearch 100(2): 402–424.
• –––, 2015, “The Metaphysics of SocialGroups”,Philosophy Compass 10(5): 310–321.
• –––, 2013, “What are groups?”Philosophical Studies, 166(2): 257–272.
• Ruben, David-Hillel, 1985,The Metaphysics of the SocialWorld, London: Routledge & Kegan Paul.
• Sartorio, Carolina, 2004, “How to be Responsible forSomething Without Causing it”,PhilosophicalPerspectives, 18(1): 315–336.
• –––, 2020, “More of a Cause?”,Journal of Applied Philosophy, 37(3): 346–363.
• Sartre, Jean-Paul, 1949,Situations III, Paris:Gallimard.
• Schaffer, Jonathan, 2004, “Causes Need Not Be PhysicallyConnected to Their Effects: The Case for Negative Causation”, inContemporary Debates in Philosophy of Science, C. Hitchcock(ed.), Malden MA: Blackwell, pp. 197–216.
• ––– 2010, “Monism: The Priority of theWhole”,Philosophical Review, 119: 31–76.
• Sider, Theodore, 2012,Writing the Book of the World,Oxford: Oxford University Press.
• Stalnaker, Robert, 1968, “A Theory of Conditionals”,inStudies in Logical Theory, Nicholas Rescher (ed.), Oxford:Blackwell, pp. 98–112.
• Sullivan, Meghan, 2012, “The Minimal A-Theory”,Philosophical Studies, 158: 149–174.
• Thomasson, Amie, 2009, “Answerable and UnanswerableQuestions”, inMetametaphysics: New Essays on theFoundations of Ontology, David J. Chalmers, David Manley, andRyan Wasserman (eds.), Oxford: Oxford University Press, pp.444–471.
• Uzquiano, Gabriel, 2004, “The Supreme Court and the SupremeCourt Justices: A Metaphysical Puzzle”,Noûs, 38(1): 135–153.
• Thomson, Judith Jarvis, 1998, “The Statue and Clay”,Noûs, 32: 149–173
• Van Fraassen, Bas C., 2002,The Empirical Stance, NewHaven, CT: Yale University Press.
• Van Inwagen, Peter, 1998, “The Mystery of MetaphysicalFreedom”, in Peter van Inwagen and Dean W. Zimmerman (eds.),Metaphysics: The Big Questions, Malden, MA: Blackwell, pp.365–374.
• Wallace, Meg, 2019, “The Lump Sum: A Theory of ModalParts”,Philosophical Papers, 48(3):403–435.
• Warmke, Craig, 2021, “What is Bitcoin?”,Inquiry:An Interdisciplinary Journal of Philosophy.
• Williamson, Timothy, 2013,Modal Logic as Metaphysics,Oxford: Oxford University Press.
• Zimmerman, Dean W. (ed.), 2006,Oxford Studies inMetaphysics (Volume 2), Oxford: The Clarendon Press.

Academic Tools

	How to cite this entry.
	Preview the PDF version of this entry at theFriends of the SEP Society.
	Look up topics and thinkers related to this entry at the Internet Philosophy Ontology Project (InPhO).
	Enhanced bibliography for this entryatPhilPapers, with links to its database.

Other Internet Resources

• The Determinism and Freedom Philosophy Website, edited by Ted Honderich.

[Please contact the author with other suggestions.]

Related Entries

abstract objects |Aristotle |Aristotle, General Topics: metaphysics |categories |dualism |existence |free will |incompatibilism: arguments for | logical positivism |material constitution |mereology |nominalism: in metaphysics |ontological commitment |physicalism |Platonism: in metaphysics |properties |social ontology |substance |time