Irving Copi once defined the problem of identity through time bynoting that the following two statements both seem true but, on theassumption that there is change, appear to be inconsistent:

1. If a changing thing really changes, there can't literally be oneand the same thing before and after the change.
2. However, if there isn't literally one and the same thing beforeand after the change, then no thing has really undergone anychange.

Traditionally, this puzzle has been solved in various ways. Aristotle,for example, distinguished between “accidental” and“essential” changes. Accidental changes are ones thatdon't result in a change in an objects' identity after the change,such as when a house is painted, or one's hair turns gray, etc.Aristotle thought of these as changes in the accidental properties ofa thing. Essential changes, by contrast, are those which don'tpreserve the identity of the object when it changes, such as when ahouse burns to the ground and becomes ashes, or when someone dies.Armed with these distinctions, Aristotle would then say that, in thecase of accidental changes, (1) is false—a changing thing canreally change one of its “accidental properties” and yetliterally remain one and the same thing before and after thechange.

Of course, this solution to the puzzle depends on there being acoherent distinction between accidental and essential changes, andbetween accidental and essential properties. Some philosophers findthis distinction problematic and have developed other solutions thatdon't require this distinction. In what follows, we discuss thesesolutions to the puzzle, along with other puzzles that arise whenconsidering the identity of objects over time.

• 1. Introduction
• 2. Identity and Change
  • 2.1 Diachronic and Synchronic Identity
  • 2.2 Identity as an Equivalence Relation
  • 2.3 Leibniz's Law and the Possibility of Change—The Problem of Temporary Intrinsics
  • 2.4 Candidate Solutions
• 3. Necessary and Determinate Identities
• 4. Diachronic Identity Puzzles
  • 4.1 Constitution
  • 4.2 Relative Identity
  • 4.3 Identity: ‘Strict and Loose’
  • 4.4 Arbitrary Undetached Parts
  • 4.5 Four Dimensionalism
  • 4.6 Temporary Identity
  • 4.7 Further Puzzle Cases
• 5. Personal Identity
• Bibliography
• Academic Tools
• Other Internet Resources
• Related Entries

1. Introduction

As a number of philosophers have remarked, one of the many puzzlesabout identity, given its apparent simplicity, is why it proves sopuzzling. Indeed, one pervasive sentiment is that identity cannot poseany philosophical problems. Anything that looks like a problem aboutidentity must really be a problem about something else. David Lewisgives striking expression to this sentiment when he says:

More important, we should not suppose that we have here any problemaboutidentity. We never have. Identity is utterly simple andunproblematic. Everything is identical to itself; nothing is everidentical to anything except itself. There is never any problem aboutwhat makes something identical to itself; nothing can ever fail to be.(Lewis 1986, 192–193)

Despite that, problems about identity appear to play a central role ina large number of philosophical issues whose discussion dates back tothe ancient world. One of the most venerable concerns identity andchange. Things change, but remain the same. The same poker is at onetime hot, another time cold. How can something be both identical anddifferent from one time to another? At first sight this problemevaporates once we draw the time honored distinction between numericaland qualitative identity. To say thata andb arequalitatively identical is to say thata exactly resemblesb. To say thata andb are numericallyidentical is, at least, to saya andb are one thingand not two. Whethera andb can havealltheir qualities in common without being numerically identical iscontroversial. Nevertheless, it seems thata andbcan be numerically identical without being qualitatively identical byhaving different qualities at different times.

Some find problematic the very same thing having different propertiesat different times (see the problem of temporary intrinsics discussedbelow). Setting that general problem aside, there are special cases ofit that generate some of the most intractable issues about identity.One results from persisting things putatively having different partsat different times. Consider an object capable of changing its parts,such as a cup at a time when its handle is still attached. At thattime the cup appears to consist of the following two parts: a smallerone, its handle, together with a larger one consisting of the rest ofthe cup. Call the larger of these parts the truncated cup. The cup,otherwise unscathed, proceeds to lose its handle. At the earlier time,with its handle still intact, the cup is surely distinct from thetruncated cup. Later, after the removal of the cup's handle, the cupspatially coincides with the truncated cup. Each object is, at thelater time, composed from exactly the same atoms. As one philosopherhas put it about a different example, at the later time the cup andthe truncated cup are as alike as one pea in a pod (Denis Robinson, inconversation). Should we say that the cup and truncated cup areearlier distinct, but later identical? The problem is that saying soarguably conflicts with a fundamental principle governing identitycalled Leibniz's Law.

Identity looms large in Leibniz's philosophy. He is responsible forarticulating two principles that, he claims, are constitutive ofidentity. The first, more controversial, of these, called the identityof indiscernibles, says that qualitative indiscernibility impliesidentity. The second, often referred to as Leibniz's Law or theIndiscernibility of Identicals, says that identity implies qualitativeindiscernibility. According to Leibniz's Law, ifa isidentical withb, every quality ofa will be aquality ofb. (See the entry onidentity of indiscernibles.)

Here are two ways in which, it seems, saying that the cup is earlierdistinct from, but later identical with, the truncated cup conflictswith Leibniz's Law. Ostensibly one of the cup's later properties ishaving earlier had a handle. That is the property the truncated cupnever has. So, identifying the later cup and truncated cup appears toviolate Leibniz's Law. There is, at least, one property, havingformerly had a handle, that the cup and truncated cup never have incommon.

Here is a second way in which the claim that the cup and truncated cupare sometimes, but not always, identical appears to violate Leibniz'sLaw. Let us bestow a name on the cup. Call it ‘Cup’. Letus also call the truncated cup ‘Tcup’. We are envisagingthat Cup is sometimes, but not always, identical with Tcup. Leibniz'sLaw tells us that Cup and Tcup share all their properties at any timethey are identical. Some properties are commonly referred to as modalproperties. A modal property is the property of possibly ornecessarily having some further property. Modal properties includesuch properties as being possibly red, necessarily extended, possiblytaller than a giraffe, or necessarily cup shaped. Arguably one ofCup's modal properties is the property of being necessarily identicalwith Cup. Suppose Cup and Tcup are at some time identical. In thatcase, by Leibniz's Law, Tcup will, at some time, share with Cup themodal property of being necessarily identical with Cup. So, if Cup isever identical with Tcup, then Tcup has the modal property of beingnecessarily identical with Cup. But if Tcup is necessarily identicalwith Cup, there can be no time when Tcup is distinct from Cup.

Let us say that the identity ofa withb istemporary ifa is sometimes, but not always, identical withb. Later we shall look at other types of puzzle cases thatprovide some motivation for countenancing temporary identity. Despitethe existence of such cases the majority of philosophers arereluctant, principally because of the putative conflict with Leibniz'sLaw, to allow temporary identity. Instead, to deal with puzzles aboutidentity through time a wide range of alternatives have been proposed.These include: maintaining that Cup is later constituted by Tcup(where constitution does not imply identity); denying that Tcup isearlier a proper part of Cup; maintaining that Cup and Tcup are neveridentical, but only share a later temporal part in common; holdingthat the identity between the earlier Tcup and later Cup is notliteral, but only loose and popular.

By synchronic identity we mean an identity holding at a single time.By diachronic identity we mean an identity holding between somethingexisting at one time and something existing at another. One questionis whether synchronic and diachronic identity are different kinds ofidentity. Some philosophers are willing to countenance different kindsof identity. Others are reluctant to do so. One philosopher who iswilling to postulate a multiplicity of different kinds of identity isPeter Geach. Geach, among others, has addressed puzzles about bothsynchronic and diachronic identity by denying that there is a singleabsolute relation of identity rather than a host of relative identityrelations. On this view we cannot simply say thata isidentical withb. Instead there must be a concept of a kindof thing, a so called sortal concept, that serves to answer thequestion:a is the samewhat asb? This isso, according to the champions of relative identity, because thefollowing can happen:a andb both fall under thesortal conceptsF andG,a is the sameF asb, buta is not the sameG asb (Geach 1967, and see the entry onrelative identity).

Consider the case of Cup and Tcup. Is Cup at the later timet′ identical with Tcup? Is Tcup att′identical with Tcup att? A relative identity theorist woulddeny that these questions have answers. For such a theorist to have ananswerable question we would need to replace, for example, the firstwith: Att′ is Cup the samecup as Tcup?

How could insisting on the relativity of the answer to an identityquestion to a kind help with the diachronic identity puzzle posed byCup and Tcup? Here is one way that it could. Suppose that nothing is acup when it is a proper part of a cup. Then Tcup fails to qualify as acup at t when it is a proper part of Cup. In that case a relativeidentity theorist can say the following. At the later timet′ Cup is the same cup as Tcup. Since Tcup is not a cupat the earlier timet, neither Cup not Tcup att′ is the same cup as Tcup att. Moreover, forany kindK, Cup is not the sameK as Tcup att. Identifying Cup with Tcup as the same cup att′ places us under no constraint to identify Cup withone of its proper parts, Tcup, att.

Some of those who reject relative identity nevertheless accept thata cannot be identical withb, unless there is a morespecific answer to the question whethera is the samething asb. Many philosophers distinguish betweentwo kinds of concepts which are applicable to whatever can persistthrough time. One kind is illustrated by the concepts of gold (asopposed to a quantity or piece of gold), snow, or rain. In the case ofany such conceptF, there is no answer to the question: howmanyFs are there? In contrast, in the case of other conceptssuch as the concept of a horse, a tall person, an artwork, or a statuethere is an answer to the question: how manyFs are there?For example, though we may not know it, there is an answer to thequestion: how many statues are there? Concepts of this last kind areoften referred to as sortal concepts. Those who take the view that thequestion whethera is the same asb is illegitimate,unless it is construed as elliptical for the question whethera is the same thing of such and such a kind asbtypically also hold the following views. We should distinguish betweentwo types of sortal concepts: phase and substance sortals. A phasesortal such as child, utensil or prize is a concept that something cancease to fall under without ceasing to exist. If, in contrast,something falls under a substance sortal, it must always do so. Ifa at some timet is the same asb at thesame, or a different timet′, it must, say advocates ofthe view in question, be that, for some sortalS,aatt is the sameS asb att′. For example, if John's favorite artwork att is identical with Sally's most valuable possession att′, there must be a substance sortal, the concept of astatue as it may be, under which John's favorite artwork att, and Sally's most valuable possession att′both fall. Moreover, a substance sortal is said to go together with acriterion of identity where a criterion of identity associated withsubstance sortalS is, inter alia, a criterion for someearlierS being the sameS as some laterS.

Finally, there are a group of issues that fall under the heading ofthe dispensability of identity. According to one tradition that goesback, at least, to Wittgenstein'sTractatus, we cantheoretically dispense with identity talk without loss of information.Some, but by no means all, who take this view, do so because they holdthat the predicate ‘is identical with’ corresponds to nogenuine property. Issues about the dispensability of identity engagewith issues about identity across time in the following way. Thissection opened with a quote from David Lewis claiming that there isnever any philosophical problem about identity. The case of Cup andTcup raises what is ostensibly a problem about identity across time.That problem only arises, it seems, because the later Cup isputatively identical with the earlier Tcup. If the problem is not, inpart, about that putative identity holding, what is it about?

According to a four dimensionalist like David Lewis a table isextended through the time of its life, and constituted from temporalparts which are themselves short lived tables. As such a fourdimensionalist like Lewis would not hesitate to give the followinganswer to the above question. The problem is, in part, a problem aboutwhether a cup-like object that exists only att′ issuitably related to a cup-like object, itself a proper part of alarger cup-like object, that exists only att so that bothcup-like objects are temporal stages or parts of a four-dimensionallyextended cup.

If we are not prepared to endorse four dimensionalism, it remains tobe seen how the putative problem about Cup and Tcup's identity throughtime can be reformulated so that it is no longer a problem aboutidentity through time.

2. Identity and Change

2.1 Diachronic and Synchronic Identity

It is customary to distinguish identity at a time from identity acrosstime. An example of an identity holding at a single time is: the tablein the next room is (now) identical with my favorite table. An exampleof an identity holding across different times is: The table in thenext room is identical with the one you purchased last year.Diachronic identities pose some of the most intractable problems aboutidentity. Before looking at those problems, and some of the mostfrequently proposed solutions to them, let us ask whether there isanything that distinguishes identity from other relations.

The most commonly agreed on distinguishing feature of identity is thatit conforms to the Indiscernibility of Identicals, what was earliercalled Leibniz's Law. Taking ‘∀F’ to be aquantifier ranging over properties, here is one way to formulateLeibniz's Law:

LL: ∀x∀y[x=y →∀F(Fx →Fy)]

LL, understood to range over identity properties, if any, such asbeing identical with a, says that ifx is identical withy, then any property ofx is a property ofy.

2.2 Identity as an Equivalence Relation

A relationR is reflexive if each thing stands inRto itself. It is symmetrical ifa's standing inR tob implies thatb stands inR toa.It is transitive ifa's standing inR tobandb's likewise standing inR toctogether imply thata stands inR toc.Identity is trivially reflexive. Each thing trivially stands in therelation of identity to itself. That identity is also symmetrical andtransitive follows from Leibniz's Law. Suppose identity fails to besymmetrical, and for somea andb,a isidentical withb, butb is not identical witha. In that case,a has a property, being identicalwithb, whichb fails to have. Suppose identity isnot transitive, and, for somea,b andc,a is identical withb andb is identicalwithc, buta is not identical withc. Inthat caseb has a property, being identical withc,thata lacks.

2.3 Leibniz's Law and the Possibility of Change: The Problem of Temporary Intrinsics

Identity through time generates a number of problems posed by puzzlecases such as the case of Cup and Tcup. Later we will review a numberof solutions to those problems offered in the literature. One problemabout identity through time is not raised by consideration of puzzlecases. It arises simply because persisting things can change theirintrinsic properties. For that reason it has been labeled by DavidLewis the problem of temporary intrinsics (Lewis 1986,202–205).

A decent test for distinguishing between extrinsic and intrinsicproperties is this. A propertyF is an extrinsic property ofan objecto ifo havingF implies thatsomething distinct from, and not a proper part of,o exists.For example, being married to Sally is an extrinsic property of John'ssince John can only have that property if something, Sally, distinctfrom, and not a proper part, of him exists. A propertyF isan intrinsic property ofo if and only ifo havingF is compatible with nothing apart fromo and itsproper parts existing, and also compatible with something apart fromo existing. For example, the property of being round is anintrinsic property because a surfaceS having that propertyis compatible with nothing other thanS and its proper partsexisting. Here is one reason why this is only a rough way of drawingthe distinction between intrinsic and extrinsic properties. It looksas though the property of existing in complete isolation, which Lewiscalls loneliness, is extrinsic. Nevertheless being, in this sense,lonely is not only compatible with, but requires that nothing elseexists. (For more discussion, see the entry onintrinsic vs. extrinsic properties.)

Suppose some object, a metal plate we will call Plate, changes frombeing round att₁ to being square att₂. How can that be? After all, though somethingcan have a round part and a square part, nothing can be round andsquare. No problem, you might say. Nothing can be round and square ata single time, place and world. But something can be round at one timeand square at another.

According to Lewis the original problem of temporary intrinsicsremains, unless we can show how something can have incompatibleproperties at different times. To show how that can be so we need togive at least a partial answer to the following question. What is itfor something to have a property at a time?

2.4 Candidate Solutions

Lewis considers three answers to this question. According to the firstfor some objectO to beF att is for therelation of beingF to tenselessly, or timelessly, holdbetweenO and timet. For example, for Plate to beround att₁ is for the two-place relation of beinground at to hold between Plate andt₁. Somethingcan stand in the relation of being round at to the earlier timet₁ without standing in that relation to the latertimet₂. So there is no reason to think thatstanding in the relation of being round at tot₁is incompatible with standing in the relation of being square at tot₂. By transmuting the ostensibly one placerelational properties of being round and being square into the twoplace relational properties of being round at and being square at wecan show how something can be round at one time and square atanother.

Lewis' principle objection to this first solution is that ittransforms intrinsic into extrinsic properties. He takes it as evidentthat properties such as being round and being red are intrinsic. Whyso? Call the view that putatively one place intrinsic properties aretwo place relational properties the relational view. Why does Lewis soadamantly reject that view? One difficulty with answering thisquestion is a difficulty about locating the source of Lewis' disquietwith the relational view.

Is it that Lewis rejects the relational view because it treatsputatively intrinsic properties as extrinsic, or because it discernsan extra place in a putatively monadic property? That it is the latteris suggested by the following. The problem of temporary intrinsicsappears to arise because nothing can have the intrinsic properties ofbeing round and being square, unless it has those properties atdifferent times. The same goes for pairs of extrinsic properties. Theproperty of being the same height as the Eiffel Tower is extrinsic asis the property of being different in height from the Eiffel Tower.Something can change from being the same height as the Eiffel Tower tobeing different in height from that structure even though nothing cansimultaneously have the properties of being the same height as, andbeing different in height from, the Eiffel Tower. Suppose we say thatsomething can be the same height as the Eiffel Tower at some timet₁ without being the same height as the Eiffeltower at some distinct timet₂. In that case weappear to be confronted with the same problem as the one thatoriginally raised the problem of temporary intrinsics. We areconfronted with the task of explaining what it is for something tohave, in this case, the property of being the same height as theEiffel Tower at timet₁. If we respond, it is forthe three place relation of being the same height as at to holdbetween some object, the Eiffel Tower, and timet₁we are, treating an ostensibly two place relation as a three place oneeven though we are not treating an intrinsic property asextrinsic.

Lewis considers an alternative explanation of what it is for an objectto have a property at a time. What might be called the‘according to’ explanation. We are used to somethinghaving a property according to one story, but failing to have thatproperty according to another. If we think of a time as a set ofpropositions describing what holds at that time, we can say thataccording to one such set plate is round, but according to another itis square.

Lewis gives the according to explanation short shrift. We may think itcannot be so readily dismissed if it is combined with a view aboutexistence and time that has received considerable discussion in recentyears. The view is called Presentism. On the Presentist view the onlythings that exist without qualification are things that presentlyexist. Supposet₁, a time when Plate is round, isthe present. In that case if Plate is ever square it will be, or wassquare. What is it for Plate to be round? Given that plate ispresently round what makes it the case that Plate is round is not justthat Plate is round according to some set of propositions about thepresent. Instead what makes it the case that Plate is presently roundis that plate exists and is round. So, what makes it the case thatPlate, say, will be square? Not, the Presentist will say, this: Platetenselessly or timelessly exists, and will be square. So what makes itthe case that Plate will be square? Perhaps this. What makes it truethat Plate will be square is that Plate is square according to somerelevant future tensed presently existing propositions.

Here is one reason why we might think that Presentism does not, in theend, help with the problem of temporary intrinsics. Suppose that, att₁, we send a circular object forward in time tot₂. Att₂ the shape of thecircular object changes so that it becomes elliptical. Retaining itselliptical shape the object is sent back tot₁. Evenif Presentism is true att₁ we have an object withincompatible intrinsic properties.

Of course, to embrace this combination of an according to explanationwith Presentism is to embrace just one of a number of optionsavailable to the Presentist for giving the truthmakers of future andpast tense propositions.

Whether or not a Presentist wishes to take over in this way the‘according to’ explanation, Presentism provides a solutionto the problem of temporary intrinsics. Presentists can deny that itfollows from something at one time being round that will at anothertime be square that there exists something both round and square.

Lewis, we saw, denies that a sentence such as ‘Plate is squareatt₁’ states something true just in casePlate stands in the square at relation tot₁. Inhis original exposition of the problem of temporary intrinsics, Lewisdoes not consider a variety of other ways of understanding sentencesattributing ostensibly intrinsic properties to objects at times. Hereis one. Many take it that a relation of instantiation holds between aproperty and its instances. Suppose instantiation is not a two place,but, at least, a three place relation holding between an object,property and time. If so, Plate is round att₁ ifand only if Plate stands in the instantiation relation to the(non-relational) property of roundness andt₁.Moreover Plate standing in the instantiation relation to roundness andt₁ is clearly consistent with Plate failing tostand in the instantiation relation to roundness and the differenttimet₂.

Alternative ways of taking ‘a is red att’ include treating ‘att’ as anadverbial modifier, or as a sentential operator. According to thefirst ‘att’, better written as ‘att-ly’, is an adverbial modifier specifying the way inwhich something has a property. So ‘Plate is round att₁’ is true just in case Plate has roundnessat-t₁-ly. Plate, on this view, can be round att₁, but square att₂ becausePlate can have roundness att₁-ly without havingroundness at-t₂-ly (See Johnston 1987, Haslanger1989).

According to the temporal operator view ‘att₁’ and ‘att₂’ should be understood as the temporaloperators: ‘att₁ it is true that…’ and ‘att₂ it is true that…’. Just as ‘it is possible that Plate isround’ is consistent with ‘it is possible that Plate issquare’ so ‘att₁ it is true thatPlate is round’ is consistent with ‘att₂ it is true that Plate is square’.

Solutions to the problem of temporary intrinsics abound. Here isanother that treats being true and being false as three placerelations between propositions, facts and times. Consider thepropositions:

(i) Plate is round,

And:

(ii) Plate is square.

We should distinguish between a property of a proposition, and aproperty that is a constituent of a proposition. Being a propositionis a property of (i), but is not a constituent of (i). In contrast,being round is a constituent of (i), but is not a property of (i).Propositions have no shape. Can we hold that (i) and (ii) are bothtrue compatibly with taking roundness and squareness to be intrinsicproperties?

It is plausible to suppose that that the truth value of a propositionsuch as (i) or (ii) depends on the existence of something distinctfrom that proposition. Since that is so, let us, as some adherents ofa correspondence theory of truth would do, allow that if (i), say, istrue, it has a relational property of being true. For example beingtrue may be a relation that holds between (i) and the fact that Plateis round.

How many places are there in what we may call the truth relation? Itis often though to be a two place relation. Suppose that is wrong, andtruth is a three place relation holding between a proposition, factand time. In that case, the three place relation of truth can holdbetween (i), the fact that Plate is round, andt₁,without holding between (i), the same fact andt₂.

Of course whether this is a solution to the problem of temporaryintrinsics depends on what that problem is. It is a solution if theproblem is to explain time indexing without turning intrinsic intoextrinsic properties. After all, no correspondance theorist wouldallow truth is an intrinsic property. It is not a solution if theproblem is to explain time indexing without adding extra places to, itmay be, relational properties.

Alternatively, we can follow Haslanger in Haslanger 1989 and Lowe inLowe 1987 and treat the relevant propositions as tensed. A change inan intrinsic property corresponds, on this view, to a change in thetense of a proposition atrributing that property.

Lewis (2002) objects to this last solution on the grounds that atensed proposition should itself be identified with a relationalproperty. But, such identification leaves it unexplained how somethingcan change its non-relational intrinsic properties. Ben Caplan inCaplan 2005 has replied to Lewis that Lewis's objection depends on aview about propositions that is not compulsory.

Lewis favors a different solution to the problem of temporaryintrinsics (Lewis 1986). Whether or not there is a problem with thesame object being round and square, there is no problem with the sameobject having a round part and a square part. To solve the problem oftemporary intrinsics, Lewis invokes the view that, in addition totheir spatial parts, objects have temporal parts or stages. Thisallows him to hold that Plate is round att₁ andsquare att₂ because Plate has a round part att₁ and a square part att₂.Plate's roundt₁ part exists only att₁, and Plate's squaret₂ partexists only att₂. Hence there is no problem posedby either temporal part changing its shape. Plate itself is an objectconsisting of a suitably interrelated sequence of such temporal parts.For thet₁ temporal part of Plate to be round isjust for it to be round. For the longer lived Plate to be round att₁ is for Plate to be appropriately related to around temporal part att₁.

As we have seen in invoking temporal parts or stages Lewis endorsesone species of what has come to be called Four Dimensionalism. Theexpression ‘Four Dimensionalism’ has been applied to anumber of different positions that it is well to distinguish heresince not all of them are relevant to identity across time.‘Four Dimensionalism’ has sometimes been used for thethesis, particularly associated with Relativity Theory, that time isspace like. On another use of ‘Four Dimensionalism’ apersisting thing is identical with its history. On this view an objectis a sequence of events. Sometimes ‘Four Dimensionalism’is used to label the view that, contra Presentism, things past presentand future are equally real.

Lewis' version of Four Dimensionalism should be distinguished from allof the above. It is the view that, just as an object such as Plate isextended in space with spatial parts, so it is extended in time withtemporal parts.

The problem of temporary intrinsics focuses on the possibility ofpersisting things changing their properties, or, at least, changingtheir intrinsic properties. Many of the problems about identitythrough time are posed by puzzle cases that involve change of parts.Four dimensionalism is one, widely accepted, solution to thosepuzzles. It is not overstretching it to suggest that each of thepuzzle cases we will shortly consider appears to be a case oftemporary identity. That is, each one appears to be a case of thefollowing. For somex andy, at some timetx is identical withy, and at some timet′x is distinct fromy.

In the first section we briefly looked at one argument, the so-calledmodal argument for the necessity of identities, for denying that therecould be temporary identities. Some philosophers have responded tosome of the diachronic identity puzzles by maintaining that therecould be indeterminate identities. An argument with a similarstructure to the modal argument has been deployed to rule outindeterminate identities. Give their implications for identity acrosstime the modal argument and the argument against indeterminateidentities are set out in more detail in the next section.

3. Necessary and Determinate Identities

Here are two examples of identity statements:

(i) The table in the next room is (now) identical with my favoritetable.

(ii) The table in the next room is identical with the one youpurchased last year.

(i) and (ii) are contingent. Even if the table in the next room is myfavorite table, it might not have been. Even if the table in the nextroom is the one you purchased last year, it might not have been. Oneof the most important discussions of identity is to be found in SaulKripke's paper ‘Identity and Necessity’ and his bookNaming and Necessity (in Munitz 1971, Kripke 1980). Onelesson to be learned from Kripke's discussion is that it isillegitimate to infer from identity statements such as (i) and (ii)having their truth value contingently that the relation of identitycan hold contingently.

Why is this inference illegitimate? Compare (i) with:

(iii) The table in the next room is the same size as my favoritetable.

Being the same size as is an equivalence relation that holdscontingently. What does it take for that relation to hold contingentlybetween the table in the next room and my favorite table? Thinking interms of possible worlds the table in the next room is contingentlythe same size as my favorite table just in case the following is so.The table in the next room is the same size as my favorite table, but,in some possible worldW, something identical to (or acounterpart of) the actual table in the next room is not the same sizeas what is actually my favorite table.

Without having recourse to possible worlds, what this comes to is thatthe table in the next room is contingently the same size as myfavorite table only if, in addition to (iii), the following istrue:

(iv) (∃x)(∃y)[(x = the table in the next room)& (y = my favorite table) & (possibly,x isnot the same size asy)].

Likewise the table in the next room is contingently identical with myfavorite table only if, in some worldW, what is actually myfavorite table is not identical with what is actually the table in thenext room. That condition need not be satisfied for (i) to becontingently true. All it takes for (i) to be contingently true isthat, for example, (i) is true, but in some worldW somethingqualifies as my favorite table without also qualifying as the table inthe next room. For that to be so nothing need be identical, orcounterpart related, across worlds.

Kripke and Ruth Barcan Marcus offer an argument to show that there areno contingent identities. Here is one version of that argument oftenreferred to as the Modal Argument for the Necessity of Identities:

Suppose:

(1)a=b.

But each thing is necessarily identical with itself. Hence;

(2) □ (a=a)

Taking ‘[λx Φ]’ to mean: being anx such that Φ (where Φ is some logical formula inwhich ‘x’ is a free variable), we supposedlyhave:

(3) [λx □(x=a)]a

Since, by Leibniz's Law, if (1) thena andb shareall properties in common. Hence (1) and (3) yield:

(4) [λx □(x=a)]b

which in turn yields:

(5) □(a=b).

Though widely accepted this type of argument can be contested.Leibniz's Law, again understood as ranging over identity properties,is used to derive step (4)—b has the property of beingnecessarily identical witha—from step (3),ahas the property of being necessarily identical witha. Wemight deny that there are any such modal properties. Doing so blocksthe argument if the application of LL is restricted to properties.Alternatively we might allow that there are such properties as beingnecessarily identical witha, but deny that (3) follows from(2). On one view all that follows from (2) is thata has theproperty of being necessarily identical with itself expressed by thepredicate‘[λx x=x]’. We needto distinguish the property of being necessarily identical withitself, which every existent has, from the property of beingnecessarily identical witha—which onlya has(Lowe 1982). Finally, we might reject (2) on the following grounds.There is a well entrenched convention that repeated tokens of the sametype of name, constant or variable are assigned the same value. Fromthe existence of this convention it follows that ‘a =a’ expresses a truth. It does not follow that‘a =a’ expresses something necessarilytrue.

Here is one way of making clear why it does not follow. According towhat we may call the identity convention two tokens of the same namestandardly refer to the same thing. So in, for example, the sentence‘Napoleon admires Napoleon’ we are, unless otherwiseindicated, to take the second occurrence of ‘Napoleon’ tohave a referent identical with the referent of the first. In the caseof ‘Napoleon admires Napoleon’ the relation Napoleon issaid to stand in to himself is different from the relation governingthe repeated use of a proper name. In the one case it is the relationof admiration. In the other it is identity. But, suppose they were thesame relation. Suppose, the repeated use of a proper name weregoverned, not by the identity convention, but by what we may call theadmiration convention. According to the admiration convention asubsequent occurrence of a proper name in a sentence should be takento refer to something only if it is admired by the referent of thefirst occurrence. In the light of this, admittedly bizarre, conventionwhat should we say about the truth value of ‘Napoleon admiresNapoleon’. Well if the second occurrence of‘Napoleon’ refers, it will refer to someone admired by thereferent of the first occurrence. So, if the admiration convention isadhered to, ‘Napoleon admires Napoleon’ will, if itexpresses any proposition, will express a true one. Despite that,‘Napoleon admires Napoleon’ expresses a contingent truth.Likewise, ‘a=a’ expresses a true propositionif it expresses any proposition at all, since the relation governingthe repeated use of ‘a’ is the same as the one thata is said to stand in to a. But, as with ‘Napoleon admiresNapoleon’ given the admiration convention, there is no reason tosuppose that the truth expressed by ‘a=a’ isa necessary one. A like observation applies to ‘a isidentical with itself’.

Philosophers have appealed to contingent identities to solve identitypuzzles. They have also appealed to vague or indeterminate identitiesto solve such puzzles. Consider a club that over an extended timechanges its rules, membership and location. Is the original clubidentical with the club having a new location, rules and membership?Call the original club the Identity Club, and the club with new rules,membership and location the Constitution Club. Is the followingtrue?:

C: The Identity Club = The Constitution Club.

Some would say that that the identity stated by C is vague orindeterminate. What does it mean to say that an identity is vague orindeterminate? At least this. C is not determinately true, ordeterminately false. If C does lack a determinate truth value, is thatenough to ensure that the identity of the clubs referred to by C isindeterminate?

In the case of the identity sentence:

(i) The table in the next room is (now) identical with my favoritetable.

we saw the need to distinguish between (i) having its truth valuecontingently, and (i) stating an identity that holds onlycontingently. We likewise need to distinguish C having anindeterminate truth value from C stating an identity that holds onlyindeterminately. C may lack a determinate truth value because one, orboth, of the referring expressions ‘The Identity Club’ and‘The Constitution Club’ lacks a determinate referent.Nevertheless for any determinate choice of referents for thoseexpressions C has a determinate truth value.

Can it happen that the referring expressions ‘a’and ‘b’ refer precisely in the identity sentence‘a=b’ without that sentence beingdeterminately true or false? Here is one version of an argument, dueto Gareth Evans and Nathan Salmon, that is supposed to show that itcannot (Evans 1978, Salmon 1981). Let ‘Ip’ mean:it is indeterminate whetherp, that isp is neitherdeterminately true nor determinately false, and let‘Dp’ mean: it is determinate thatp. Wehave:

(1′)I(a=b).

But:

(2′)D (a=a).

(2’) yields:

(3′)[λx D(x=a)]a

Suppose:

(4′)a=b

Applying Leibniz's Law to (3′) and (4′) gives:

(5′)[λx D(a=x)]b

from which it follows that:

(6′)D(a=b),

which contradicts (1′). Hence (1′) implies:

(7′) ¬(a=b)

If (7′) is true then it is not true thata is identicalwithb. So if (7′) is true,a is determinatelydistinct fromb. (1′) cannot be true.

Of course, defenders of indeterminate identity do not let this passunquestioned. One assumption of the argument is that (7′)implies thata is determinately distinct frombrather than just thata is not determinately identical withb.

Arguments against contingent and indeterminate identities appeal toLeibniz's Law. Seen as a principle about the transmission ofproperties across identity Leibniz's Law has rarely been challenged.Still, it has been challenged. One interesting challenge is brought byBenjamin Schnieder in Schnieder 2006. Similarly, Evans' argument hasbeen challenged from a number of directions. A recent challenger isElizabeth Barnes who in Barnes 2009 invokes counterpart theory todefuse it.

4. Diachronic Identity Puzzles

In the introduction we encountered one type of puzzle about identityacross time: the case of Cup and Tcup. The puzzle arose because weenvisaged Cup losing one of its parts, and coming to have the samematerial constitution (being, for example, composed of exactly thesame atoms as), and spatial boundaries as Tcup. Call this the cupcase. Let us say thata andb are coincident at atimet just in case the following holds. Something is aproper part ofa att if and only if it is a properpart ofb at that same time. Cup and Tcup are coincident atthe later time since something at that later time is, for example, andatomic part ofa if and only if it is an atomic part ofb.

There are cases that pose similar diachronic identity puzzles that donot involve change of parts. One of the best known involves a lump ofclay which, at an earlier time, is coincident with a statue, but, at alater, say as a result of deformation, is just a shapeless lump ofclay. Other much discussed cases of putatively distinct things at onetime being coincident at another involve fission or fusion. One of themost famous examples of a fission case is provided by the ship ofTheseus. Over a long period all of the planks composing a certain shipare replaced one by one. Eventually a ship indiscernible from theoriginal, but composed of entirely different planks, results. Callthat later ship Replacement. As each plank is removed from theoriginal ship it is used to construct a ship that is constituted fromall and only the planks belonging to the original ship. Call the shipcomposed of the same planks as the ones initially composing theoriginal ship Reassembly.

Identity is, very plausibly, an equivalence relation (seeSection 2.2). One consequence of it being an equivalence relation is that it issubject to transitivity: the principle that ifaRb andbRc, thenaRc. Saying that, in the case of Theseus'ship, Replacement and Reassembly are both identical with the originalship putatively conflicts with the transitivity of identity sinceReplacement seems to be later clearly distinct from Reassembly.

What is the best account of these cases? Here are some of the majorones on offer:

4.1 Constitution

Constitution accounts pivot on the distinction between constitutionand identity. Defenders of such accounts hold that constitution,unlike identity, is not an equivalence relation (Baker 2002).Constitution is said to be, at least, non-symmetrical. According to aconstitution account, we say the following about the three types ofpuzzle cases described above. Cup is never identical with Tcup. LaterCup is constituted by Tcup [alternatively: Cup and Tcup neverconstitute each other, but later are constituted from the very sameatoms]. Likewise the lump of clay is never identical with the statue,but earlier only constitutes the statue. Finally, the reassembly shipis never identical, but only constituted from exactly the same planksas, the original.

Kit Fine has deployed a number of novel Leibniz's Law arguments infavour of a constitution accounts. Such arguments are replied to byBrian Frances in Frances 2006.

The constitution view has come in for its share of criticisms. Somethink it engages in metaphysical multiple vision, seeing amultiplicity of things at a given place and time where there isplausibly only one. Others argue that constitutionisidentity (see Noonan 1993).

A number of objections have been raised against constitution views.One is an objection from causal overdetermination. Another is anobjection from grounding. Consider a statue allegedly constituted froma statue shaped piece of clay. Someone throws the statue against apane of glass, which breaks. What caused the glass to break? Surely,the statue impacting it. But the glass was also impacted by the statueshaped piece of clay with sufficient force to break it. So, ifconstitution is not identity, the glass breaking has two causes. Somewould say that is one cause too many.

The objection from grounding is not so much an objection to theconstitution view, but an objection designed to undermine a principlereason for adopting it. A principle reason for adopting theconstitution view is that it seems to allow, for example, the statueand the piece of clay to have different properties. In particular, itseems to allow them to have different modal properties such as beingsquashable. Since constitution, unlike identity, does not conform tothe indiscernibility of identicals, the clay can be squashable even ifthe statue is not.

The problem is that the clay and the statue are made up of exactly thesame atoms organized in the same way. Since that is so it is hard tosee how the clay can be squashable without the statue being so aswell.

A further problem for constitution views is the so called too manyminds objection (see Olsen 1997 and Shoemaker 1999). Advocates ofconstitutionalism typically hold that a person is constituted by aliving organism. If so, the person and the living organismconstituting that person share the same thoughts. Whenever youencounter a person you encounter a distinct living organism havingoccupying the same region and having the same thoughts. Not a goodresult.

4.2 Relative Identity

Advocates of relative identity deny that there is a single identityrelation (see Geach 1967, Griffin 1977). On their view it is improperto ask whether, say, the statue is the same thing as the later lump ofclay. Instead we should ask whether it is the same statue, or the samelump of clay. For an advocate of relative identity denying that theearlier statue is the same statue as the later lump of clay isconsistent with allowing that the earlier statue is the same lump ofclay as the later lump of clay. It is natural for the relativeidentity theorist to insist on relativising the transitivity ofidentity to the same sortal concept in the following way. What therelativised transitivity principle says is that:a is thesameF asb, andb is the sameFasc implies only thata is the sameF asc (see Griffin 1977).

One objection to relative identity is that it conflicts with Leibniz'sLaw. Here is one way in which such conflict may be thought to arise.Consider the property version of Leibniz's Law:

LL: ∀x∀y[x=y →∀F(Fx →Fy)]

The relation of identity mentioned in the antecedent of LL isunrelativised to a sortal. To make it acceptable to the relativeidentity theorist, let us amend LL to:

LLR:∀x∀y[∀F(x isthe sameF asy) →∀G(Gx →Gy)]

Suppose we replace ‘is the sameF asy’in LLR with ‘is the same lump of clay’,‘x’ with ‘the earlier statue’,‘y’ with ‘the later clay lump’, andinstantiate the quantifier ∀G with ‘is the samestatue as the earlier statue’. We then obtain:

R: the earlier statue is the same lump of clay as the later clay lump→ (the earlier statue is the same statue as the earlier statue→ the earlier statue is the same statue as the later clay lump ).

The trouble is that R is false. The earlier statue is the same lump ofclay as the clay lump, and the earlier statue is the same statue isthe same statue as the earlier statue, but the earlier statue is not,contrary to LLR, the same statue as the later clay lump.

4.3 Identity: ‘Strict’ and ‘Loose’

Following Bishop Butler [seeSection 5], Roderick Chisholm distinguishes between a strict and a loose sense ofidentity (see Chisholm 1969a). To see what this distinction comes to,and how it might help with the puzzle cases, consider the case of Cupand Tcup. For Chisholm things have their parts essentially in thefollowing sense. It is impossible fora to be identical withb in the strict and philosophical sense, unlessaandb have all their parts in common. Earlier Cup has a part,a handle, that later Cup, not to say earlier and later Tcup, lacks.Hence, on Chisholm's view, earlier Cup is not strictly identical withlater Cup.

Earlier Cup is nontheless identical with later Cup in a loose andpopular sense. What then, according to Chisholm, is it for earlier Cupand later Cup to be identical in a loose and popular sense? Tosimplify let us suppose, unrealistically, that the only change ofparts that Cup in, Chisholm would say, a loose and popular senseundergoes is loss of a handle. Call Hcup the object that consists ofCup's handle together with Tcup. Chisholm would say this. Cup isearlier wholly constituted by Hcup, that is Tcup plus handle, andlater wholly constituted by Tcup alone. Moreover Tcup is related toHcup in such a way that, as Chisholm puts it, Tcup att₂ is theens successivum of Hcup at anearlier timet₁. For Chisholm what makesTcup att₂ anens successivum of Hcup att₁ seems to be this. Tcup is a proper part of Hcupatt₁. There is a sequenceS of cups suchthat each member ofS that is not identical with Hcup is, atsome time, a proper part of some member ofS. For each timebetween and includingt₁ andt₂ Cup is wholly constituted by some member ofS.

Cup is wholly constituted by Tcup att₂. Since thelater Cup is wholly constituted by something, Tcup, that is anenssuccessivum of something, Hcup, that wholly constitutes Cup wemay say that earlier cup is loosely identical with later Cup.

4.4 Arbitrary Undetached Parts

One solution to the problem posed by the cup case is to reject whatPeter van Inwagen calls the Doctrine of Arbitrary Undetached Parts(see van Inwagen 1981). In setting the problem up we assumed thatearlier Cup consists of the following parts: a handle together withTcup. That assumption is justified if the following is. Tcup existedas a part of Cup when Cup still had its handle. Van Inwagen wouldreject that assumption. According to him it is illegitimate to assumethat any old way of notionally dividing up an object yields anexisting undetached part.

Instead of denying that Tcup exists att₁ when itis ostensibly a proper part of Cup, we might instead deny that Tcup att₁ is identical with what looks very much likeTcup att₂. In this way we can preservetransitivity without having to identify the earlier cup with one ofits proper parts.

One way to allow that Tcup earlier exists without conceding its lateridentity with Cup is, following Michael Burke, to maintain that Tcupgoes out of existence when Cup loses its handle (see Burke 1994).

4.5 Four Dimensionalism

Here is what a classical four dimensionalist would say about the caseof the cup. Suppose the interval fromt₁ tot₂ is the time during which Cup has a handleattached to it, andt₂ tot₃the interval during which Cup is without a handle, and, so, putativelyidentical with Tcup. As before Hcup is the fusion of Tcup and Cup'shandle. According to the four dimensionalist, Cup, Tcup and Hcup areall extended in time as well as space. Tcup has a temporal part thatextends fromt₁ tot₂ togetherwith a temporal part that extends fromt₂ tot₃. Tcup'st₁ tot₂ andt₂ tot₃ temporal parts are distinct from each other aswell as being distinct from the temporally longer Tcup. Hcup, that isTcup plus handle, is a four dimensional object that extends fromt₁ tot₂. Cup itself consistsof the following two, among indefinitely many other, temporal parts:Hcup and thet₂ tot₃ part ofTcup.

What we should say according to the classical four dimensionalist isthis. Thet₁ tot₂ temporalpart of Tcup is a proper temporal and spatial part of Hcup. Hcup andthet₂ tot₃ temporal parts ofTcup are proper temporal parts of Cup. Cup is not identical with anyof Hcup, Tcup fromt₁ tot₂,Tcup fromt₂ tot₃, or Tcupfromt₁ tot₃. In particularthere is no question of Cup being literally identical with Tcup fromt₂ tot₃, when they areindiscernible, though, following David Lewis, we may say that Cup andTcup are identical at any time betweent₂ andt₃ in the sense that they share temporal partsduring those times (see Lewis 1986).

Many four-dimensionalists subscribe to a principle that a number ofwriters call unrestricted mereological composition. According to thatprinciple any set of, in this case four-dimensional, objectsconstitute a further four dimensional object. Armed with theunrestricted mereological composition principle a four-dimensionalistcan say that what there is, in the case of Theseus' ship, is a Ybranching object dividable in an indefinite number of ways into fourdimensional proper parts an indefinite number of which are ships. Forexample the ship consisting of the stem together with the replacementbranch has as two of its proper parts a ship consisting of just thestem, and one consisting of just the replacement branch.

Apart from the argument that it provides the best solution todiachronic identity puzzles four dimensionalism has been defended on anumber of other grounds. One we have reviewed already; the argumentthat four dimensionalism gives the best solution to the problem oftemporary intrinsics. Another, also offered by David Lewis, invokesthe principle that facts in general supervene on facts about theinstantiations of intrinsic properties and external relations. Callfacts about the instantiation of intrinsic properties and externalrelations basic facts, and letR be the spatio-temporalregion occupied by Plate throughout its career. According to Lewisthere is a worldW in which a sequence of shorter Plate-likeobjects occupyR, and all of the basic facts that obtain inour world obtain inW. Lewis' supervenience principle tellsus that all facts supervene on basic facts. The same basic factsobtain in both our world andW. So whatever is true of theoccupant ofR inW is true of the occupant ofR in our world. The occupant ofR inW is asequence of, appropriately interrelated Plate-like objects. Hence theoccupant ofR in our world, that is Plate, is likewise asequence of interrelated Plate-like objects.

Recently Sider (2002) developed an argument for Four Dimensionalismfrom considerations about vagueness. He argues that FourDimensionalism is true if it cannot be vague how many things thereare, and also that it cannot be vague how many things there are.

It should be noted that Sider and Katherine Hawley defend analternative version of Four Dimensionalism which identifies objectswith what, on the first version, would qualify as their stages (Hawley2001, Sider 2002). In order to make this identification Sider invokessomething close to Lewis’ counterpart relation. Will the table I amcurrently looking at persist through the next ten minutes? Accordingto the classical four-dimensionalist, otherwise known as theperdurantist, the table will persist through that period provided ithas a present and a ten minutes from now table stage that are bothstages of the table without either one being identical with the table.In contrast the stage theorist identifies the table with the presentstage of the table. How can that be since the present table stage onlyexists now, and the table is supposed to be around ten minutes fromnow? It can be, says the stage theorist, because, though the tenminute from now table stage is not now identical with the table, itwill be identical with the table. Moreover it will be identical withthe table since it stands in the appropriate counterpart relation tothe present table stage.

Stage theory enjoys the following advantage over classicalfour-dimensionalism. Consider the case of a person fissioning into twolater people. A classical four-dimensionalist like Lewis will say thatbefore the fission there are two separate people that cannot be toldapart. The stage theorist has no need to say that. Instead the stagetheorist can say there is a single present person who will beidentical with each of a pair of later individuals in virtue ofstanding in the relevant counterpart relations to each one.

It should also be noted that four dimensionalism differs fromChisholm's invocation of loose and popular identity in, at least, thefollowing way. The persistence of an object for any length of timewill, on a four dimensionalist view, require the existence of shorterlived objects setting aside the possibility of extended simples. Thepersistence for any length of time, on Chisholm's view, of a threedimensional object does not require the existence of shorter livedthree dimensional objects. It does not do so because the objectpersisting for a lengthy period may undergo no change of parts.

4.6 Temporary Identity

In the case of, for example, the truncated cup we saw that one optionis to claim that Cup is earlier distinct from Tcup [cup minus itshandle], but later identical with Tcup. According to this option theidentity of Cup with Tcup is only temporary. We also saw that manyrefuse to countenance temporary identity because it allegedlyconflicts with Leibniz's Law [LL]. After all, later Cup, but not Tcup,apparently later has the property of having had a handle.

Despite this putative conflict with LL, some philosophers are preparedto defend temporary identity as the best solution to the puzzles aboutdiachronic identity. George Myro does so by restricting the scope ofLL to exclude such properties as having had a handle (Myro 1985).Gallois (1998) does so by arguing that if the identity of Cup and Tcupis temporary, we cannot infer from Tcup having had a handle earlierthat earlier Tcup has a handle.

4.7 Further Puzzle Cases

We have focused attention on one type of case that raises a puzzleabout diachronic identity. Such a case involves something ostensiblybecoming, or ceasing to be identical with something that is ostensiblyone of its earlier or later proper parts. It would be wrong to givethe impression that such a “Deon-Theon” case named afterthe individuals involved in the example is the only, or even main,type of case posing a problem about diachronic identity. In additionthere are what are often referred to as fission and fusion cases. Afission case has the following features. We have putatively distinctthingsb andc existing at some later timet₂. Each ofb andc is relatedtoa, which exists at an earlier timet₁,in such a way that each one is ostensibly identical witha.

Fission cases come in two varieties: symmetrical and asymmetrical.Examples of symmetrical fission cases include amoebic and hemisphericdivision [for the latter see Personal Identity below]. In asymmetrical case there is some relation that each ofb andc stand in toa, where standing in that relation iswhat makes each one putatively identical witha. In anasymmetric case,b is putatively identical with a because itstands in a certain relation toa, butc isputatively identical witha because it stands in a differentrelation toa. The best known example of a symmetricalfission case is the Ship of Theseus described at the beginning of thissection.

Let us see how the proposals for dealing with the cup case apply tofission cases. Constitution only delivers a candidate solution in asymmetric fission case. As we noted above, a constitution theorist cansay the following about Theseus' Ship. The ship resulting from thereplacement of the original planks is identical with, but notconstituted from the original planks. The ship reconstituted from theoriginal planks is not identical with the one originally constitutedfrom those planks.

Some relative identity theorists have this to say about Theseus' Ship.In that case conflict with the transitivity of identity is avoided bymaintaining the following. The replacement ship is the same ship asthe original, and the original is the same collection of planks as thereassembly ship. Conflict with transitivity is avoided because we neednot allow that the reassembly ship is the same ship as theoriginal.

Distinguishing between a strict and loose sense of‘identical’ yields the following solution in the case ofTheseus' Ship. Let Original be the original ship, Replacement be theship that results from replacing Original's original planks, andReassembly the one that results from their reassembly. In that case,deploying the distinction between a strict and loose sense ofidentity, we can say this. Reassembly is strictly identical withOriginal, but Replacement is only loosely identical with Original. Aconflict with transitivity of identity is avoided for the followingreason. It follows by transitivity from Replacement being identicalwith Original, and Original being identical with Reassembly, thatReplacement is identical with Reassembly only if a single relation ofidentity is involved.

Here is what a four dimensionalist such as Lewis will say aboutTheseus' ship. In that case there are two initially indiscernibleships. The first is a four dimensionally extended ship located wherethe original ship is initially located that ends up coinciding onlywith the reassembly ship. The second, also initially located where theoriginal ship is initially ends up coinciding with the replacementship. We thus have a Y-branching four dimensionally extended objectwith one ship constituted by the stem together with one branch, andthe other constituted by the stem together with the remainingbranch.

Four Dimensionalism, like the thesis that identities can be temporary,applies to both symmetric and asymmetric cases of fission.

A temporary identity theorist will hold that Replacement andReassembly are identical att₁, but distinct shipsatt₂.

In the previous section we reviewed an argument designed to rule outindeterminate identities. If that argument can be met, it is open tous to say the following about Theseus' Ship. Each of Replacement andReassembly is indeterminately identical with Original.

The puzzle cases are puzzle cases because they bring into putativeconflict intuitions all of which we want to subscribe to. Consider astatue and the collection of atoms that constitute it. We wish to saythat the statue is identical with the collection of atoms. We alsowish to say that the statue, but not the collection, can survive theloss of one atom belonging to that collection. Leibniz's Law appearsto force us to renounce one of these intuitions. Thomas Sattig arguesfor a compatibilist view according to which we can hold on to bothintuitions without giving up, or modifying, Leibniz's Law. We can doso by relativising identities to different perspectives. From theordinary object perspective the statue is distinct from the atoms thatconstitute it. From the material object perspective the statue isidentical with the atoms that constitute it.

5. Personal Identity

Personal identity is perhaps the most extensively discussed specialcase of identity. What is it for a person existing at one time to beidentical to a person existing at another? This question was firstclearly posed by John Locke in his celebrated discussion of personalidentity in theEssay (Locke 1975). Locke distinguishesbetween being the same man and being the same person. To be the sameman is to be the same member of the species human being. For Lockewhat is crucial is that having the same consciousness is notsufficient for being the same man, but is sufficient for being thesame person.

Famously Locke calls the concept of a person a forensic concept. ForLocke much of the importance attaching to being the same person isthat moral responsibility for past deeds goes with being the sameperson, rather than being the same man or even the same immaterialsubstance, as a past person. In his view it is enough to be morallyresponsible for some deed that one is the same person as itsperformer. It is not required that one be the same man or the sameimmaterial substance as the one who performed the act in question.

What then, according to Locke, is it to have the same consciousness assome past person? He is customarily interpreted as holding that personA is the same person as earlier personB just incaseA is able to remember enough of what happened toB. This is sometimes referred to as the memory criterion ofpersonal identity. The memory criterion was criticized by Butler andReid principally because it was said to be circular, and, as acriterion of personal identity, incompatible with the transitivity ofidentity. (See Section 2.2, and Joseph Butler ‘Of PersonalIdentity’ and Thomas Reid ‘Of Mr. Locke's Account of OurPersonal Identity’ in Perry 1975.)

The argument for the circularity of the memory criterion went likethis. Suppose we think of the memory criterion as giving what would belater called an analysis ofA being the same person asB. If so, we are invited to analyzeA being the sameperson asb in terms ofA remembering enough of whathappened toB. But any plausible analysis ofAremembering what happened toB will mention, in theanalysans,A being the same person asB.

Sydney Shoemaker has responded to the circularity charge bydistinguishing remembering from what he calls Q-remembering (Shoemaker1975).A Q-remembers something that happened tobjust in case there is an appropriate causal link between the eventQ-remembered andA's memory impression of that event. Unlikeremembering, Q-remembering a past experience does not imply theidentity of the one having the Q-memory with the one who had theexperience. We can avoid the charge of circularity by restating thememory criterion in the following way.A is the same personas some earlier individualB if and only ifAQ-remembers enough of what happened toB.

The charge that the memory criterion conflicts with the transitivityof identity was illustrated by the famous case of the schoolboy, theyoung lieutenant and the elderly general (Reid 1975). The elderlygeneral can Q-remember enough of what happened to the young lieutenantto qualify, by the memory criterion, as being the same person as theyoung lieutenant. The young lieutenant in turn Q-remembers enough ofwhat happened to the young schoolboy. But the elderly general canremember almost nothing of what happened to the young schoolboy. Sincethe memory criterion has it thatA Q-remembering enough ofwhat happened toB is a necessary condition forAbeing the same person as an earlier personB, it followsthat, according to the memory criterion, the elderly general is notthe same person as the young schoolboy. Hence, the memory criterionimplies, contrary to the transitivity of identity, that, although theelderly general is the same person as the young lieutenant, and theyoung lieutenant is the same person as the schoolboy, the elderlygeneral is not the same person as the young schoolboy.

The memory criterion came to be modified in two further ways. Thefirst modification provides a way of reconciling the memory criterionwith the transitivity of identity in the light of cases such as theelderly general. Instead of saying thatA is the same personas some earlierB if and only ifA can Q-rememberenough of what happened toB, we say the following.A is the same person asB if and only if there is aQ-memory chain linkingA withB. For there to be aQ-memory link betweenA andB, eitherAremembers enough of what happened toB, orAremembers enough of what happened to someone who remembers enough ofwhat happened toB, orA remembers enough of whathappened to someone who remembers enough of what happened to someonewho remembers enough of what happened toB, and so on. In thecase of the elderly general, the elderly general does remember enoughof what happened to, someone, the young lieutenant, who remembersenough of what happened to the young schoolboy to count, by themodified criterion, as the same person as the young schoolboy.

The second modification extends the memory criterion to includeforward looking psychological connections, such as that betweenpresent intention and future action, as determinants of personalidentity.

With these modifications incorporated the memory criterion has come tobe known as the psychological continuity criterion of personalidentity. The psychological continuity criterion is an improvement onthe original memory criterion. Nevertheless one of the problemsconfronting the original memory criterion, its putative conflict withthe transitivity of identity, can be brought against its successor ina different form. We saw that making certain identifications in afission case such as the ship of Theseus [see Section 4: DiachronicIdentity Puzzles] threatens the transitivity of identity. One muchdiscussed type of fission case, hemispheric division, is taken by manyto show that the psychological continuity criterion is, after all,incompatible with the transitivity of identity (Nagel 1975).

Suppose, as may one day be medically feasible, an individualA's still functioning upper brain is transplanted fromA's body to the debrained, but living, body formerlybelonging toB. Upon being transplanted A's upper brain isconnected to what remains ofB's central nervous system sothat a person, call herA-B, results.A-B believes herself to beA, canQ-remember what happened toA, hasA's psychologicaldispositions, and so on. Should we say thatA-B isthe same person asA, the same person asB, or analtogether new person? Psychological continuity theorists will havelittle hesitation in answering thatA-B is the sameperson asA.

A person can function fairly normally with much of their braindestroyed. SupposeA loses an entire brain hemisphere. Giventhe plasticity of the brain, and aided by our hypothetical futuremedical technology, it may be thatA could survive such aloss. If so, it would be unreasonable to deny thatA couldsurvive the transplantation of only one brain hemisphere given thatshe could survive the transplantation of he entire intact upperbrain.

The putative conflict with transitivity arises when we consider a casein which both of the separated hemispheres ofA's originalbrain are transplanted to separate bodies resulting in what certainlylook to be distinct individuals. Suppose, one ofA's brainhemispheres is transferred toB's body, resulting in a personPB, and the other to C's body resulting in a personPC. It flouts transitivity to say thatPC isidentical withA, and thatA is identical withPB, but deny, at it seems we should, thatPC isidentical withPB.

There are a number of ways that defenders of a psychologicalcontinuity criterion have attempted to evade this result. One, adoptedby David Lewis, goes like this (Lewis 1976). We say that earlier, whenA is around with an intact brain, there are two indiscernibleindividuals,PB andPC, sharing a single body.Another, advocated by Robert Nozick, concedes that if both hemispheresare successfully transplanted, neither of the later individuals withjust one brain hemisphere is identical with the earlier one with anintact brain, but insist that if only one hemisphere is transplanted,the resulting individual is identical with the former possessor of twohemispheres. On this view whether, for example,PB isidentical with the earlier person withA's body depends onwhether there is an equally good later candidate, such asPC,for being the earlierA-body person (Nozick 1981).

In one of the most influential discussions of personal identity DerekParfit defends a view close to Nozick's by distinguishing betweensurvival and identity (in Perry 1975). In Nozick's view whatpsychological continuity guarantees is not identity, but survival. Inthe case where both ofA's hemispheres are transplanted toyieldPB andPC,A survives asPB,and survives asPC, though she is identical with neitherPB norPC.

Parfit, Nozick and Lewis all take psychological continuity to beintegral to personal identity in the following sense. In cases wherethere is no branching psychological continuity is sufficient to ensurethe identity of a later with an earlier person. A number ofphilosophers would reject this claim insisting that bodily persistenceis required for personal identity. Some, for example Eric Olson, wouldargue that psychological continuity is irrelevant to the identity ofthose things, human beings, who are the only things we know to bepersons. Instead, on this view, what is crucial to personal identityfor humans is continuing to be the same animal (Olson 1997).

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A. Identity and Change

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B. Necessary and Determinate Identities

B.1 Necessary Identities

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• Pendlbury, M., 1975, “Necessary identity,”Philosophical Papers, 4: 12–20.
• Salmon, N., 1981,Reference and Essence, Princeton:Princeton University Press.
• Schnieder, B., 2006, “By Leibniz's Law: Remarks on aFallacy,”Philosophical Quarterly, 56(222):39–54.
• Wiggins, D., 1986, “On Singling Out An ObjectDeterminately,” in P. Pettit, and J. McDowell (eds.),Subject, Thought and Context, Oxford: Oxford UniversityPress.
• Williamson, T., 1996. “The Necessity and Determinacy ofDistinctness,” in S. Lovibond and S. Williams (eds.)Essaysfor David Wiggins: Identity, Truth and Value, Oxford: OxfordUniversity Press.
• Wilson, M., 1983. “Why Contingent Identity isNecessary,”Philosophical Studies, 43:301–328.
• Wreen, M., 1998, “Proper names and the Necessity of IdentityStatements,”Synthese, 114(2): 319–335.

B.2 Determinate Identities

• Barnes, E., 2009, “Indeterminacy,Identity and Counterparts:Evans Reconsidered,”Synthese, 168(1):81–96.
• Broome, J., 1984, “Indefiniteness in Identity,”Analysis, 44(1): 6–12.
• Burgess, J., 1990, “Vague Objects and IndefiniteIdentity,”Philosophical Studies, 59:263–87.
• –––, 1989, “Vague Identity: EvansMisrepresented,”Analysis, 49: 112–19.
• –––, 1990, “Vague Objects and IndefiniteIdentity,”Philosophical Studies, 59:263–87.
• Cook, M., 1986, “Indeterminacy of Identity,”Analysis, 46: 179–86.
• Copeland, J., 1997, “Vague Identity and Fuzzy Logic,”Journal of Philosophy, 94: 514–34.
• Evans, G., 1978, “Can There Be Vague Objects?,”Analysis, 38: 208.
• French, S., and Krause, D., 1995, “Vague Identity andQuantum Indeterminacy,”Analysis, 55: 20–6.
• Garrett, B., 1988, “Vagueness and Identity,”Analysis, 48(3): 130–44.
• –––, 1991, “Vague Identity and VagueObjects,”Noûs, 25: 341–51.
• Hirsh, E., 1999, “The Vagueness of Identity,”Philosophical Topics, 26: 139–58.
• Johnsen, B., 1989, “Is Vague Identity Incoherent?,”Analysis, 49: 103–12.
• Keefe, R., and Smith, P. (eds.), 1996,Vagueness: AReader, Cambridge, MA: MIT Press.
• Lewis, D.K., 1988, “Vague identity: EvansMisunderstood,”Analysis, 48: 128–30.
• Lowe, E.J., 1982, “Vague Identity and QuantumIndeterminacy,”Analysis, 54: 110–114.
• Miller, K., 2006, “Vagueness, Persistence and IndeterminateIdentity,”Erkenntnis, 64(2): 223–230.
• Noonan, H., 1985, “Indefinite Identity: A Reply toBroome,”Analysis, 44(3): 117–21.
• –––, 1990, “Vague Identity YetAgain,”Analysis, 50: 157–62.
• –––, 1991, “Indeterminate Identity,Contingent Identity and Abelardian Predicates,”Philosophical Quarterly, 41: 183–93.
• –––, 1995, “E.J. Lowe on Vague Identityand Quantum Indeterminacy,”Analysis, 55:14–19.
• Over, D.E., 1989, “Vague Objects and Identity,”Analysis, 49: 97–9.
• Parfit, D., 1993, “The Indeterminacy of Identity: A Reply toBrueckner,”Philosophical Studies, 70:23–33.
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• –––, and Woodruff, P., 1995, “WorldlyIndeterminacy of Identity,”Proceedings of the AristotelianSociety, 95: 171–91.
• Pinillos, N.A., 2003, “Counting and IndeterminateIdentity,”Mind, 112(445): 35–50.
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• Thomason, R., 1982, “Identity and Vagueness,”Philosophical Studies, 43: 329–32.
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• Wiggins, D., 1986, “On Singling Out an ObjectDeterminately,” in P. Pettit and J. McDowell (eds.),Subject, Thought and Context, Oxford: Oxford UniversityPress.
• Williamson, T., 1990,Identity and Discrimination,Oxford: Oxford University Press.

C. Diachronic Identity Puzzles

• Armstrong, D.M. 1980, “Identity Through Time,” Petervan Inwagen (ed.),Time and Cause:Essays Presented to RichardTaylor, Dordrecht: D. Reidel, 67–78.
• Baker, L.R., 1997, “Why Constitution is not Identity,”Journal of Philosophy, 94(12): 599–621.
• –––, 2000,Persons and Bodies,Cambridge: Cambridge University Press.
• –––, 2013, “Three-Dimensionalism Rescued:A Brief Reply to Michael Della Rocca,”Journal ofPhilosophy, 110(3): 166–170.
• Balashov, Y., 2000, “Enduring and Perduring Objects inMinkowski Space-Time,”Philosophical Studies, 99:129–166.
• Baxter, D., 1988a, “Many-One Identity,”Philosophical Papers, 17: 193–216.
• –––, 1988b, “Identity in the Loose andpopular Sense,”Mind, 97: 575–82.
• –––, 2001, “Loose Identity and BecomingSomething Else,”Noûs, 35(4): 592–601.
• Broad, C.D., 1923,Scientific Thought, New York: HarcourtPress.
• Frances, B., 2006, “The New Leibniz's Law Arguments forPluralism,”Mind, 115(460): 1007–1021.
• Burke, M., 1980, “Cohabitation, Stuff and IntermittentExistence,”Mind, 89: 391–405.
• –––, 1994, “Deon and Theon: AnEssentialist Solution to an Ancient Puzzle,”Journal ofPhilosophy, 91: 129–39.
• –––, 1994, “Copper Statues and pieces ofCopper,”Analysis, 52: 12–17.
• –––, 1994, “Preserving the Principle ofOne Object to a Place,”Philosophy and PhenomenologicalResearch, 54: 591–624.
• Butterfield, J., 1984, “Spatial and Temporal Parts,”Philosophical Quarterly, 35: 32–44.
• Carroll, J.W., and Wentz, L., 2003, “A Puzzle aboutPersistence,”Canadian Journal of Philosophy, 33(3):323–342.
• Carter W., 1982, “On Contingent Identity and TemporalWorms,”Philosophical Studies, 41: 213–30.
• –––, 1983, “Artifacts of Theseus Fact andFission,”Australasian journal of Philosophy, 61(3):248–65.
• –––, 1983, “In Defence of UndetachedParts,”Pacific Philosophical Quarterly, 64:126–143.
• –––, and Heller, M., 1989, “MetaphysicalBoundaries: A Question of Independence,”AustralasianJournal of Philosophy, 67: 263–276.
• Cartwright, R., 1975, “Scattered Objects,” in KeithLehrer (ed.)Analysis and Metaphysics, Dordrecht: D. Reidel,153–171.
• Chisholm, R., 1969a, “The Loose and Popular and the Strictand philosophical Senses of Identity,” in Care, N and Grimm, H,Perception and Identity, Cleveland: Case Western ReserveUniversity Press, 82–106.
• –––, 1969b, “Reply to Shoemaker,” inN. Care and H. Grimm (eds.),Perception and Identity,Cleveland: Case Western University Press.
• –––, 1971, “Problems of Identity,”Identity and Individuation, in Milton K. Munitz (ed.), NewYork: New York University Press, 3–30.
• –––, 1973, “Parts As Essential to theirWholes,”Review of Metaphysics, 26: 581–603.
• –––, 1976,Person and Object: A MetaphysicalStudy, La Salle: Open Court.
• –––, 1979, “Objects and Persons: Revisionsand Replies,”Grazier Philosophishe Studien, 7/8:317–388.
• Cleve, J.V., 1986, “Mereological Essentialism, MereologicalConjunctivism, and Identity Through Time,”Midwest Studiesin Philosophy, 11: 141–56.
• Cortens, A. and O'Leary Hawthorne, J., 1995, “TowardsOntological Nihilism,”Philosophical Studies, 91:205–219.
• Dau, P., 1986, “Part Time Objets,”Midwest Studiesin Philosophy, 11: 459–74.
• Doepke, F., 1982, “Spatially Coinciding Objects,”Ratio, 24(1): 45–60.
• –––, 1987, “Contingent Identity and RigidDesignation,”Mind, 95: 250–5.
• Donnelly, M., 2011, “Endurantist and Perdurantist Accountsof Persistence,”Philosophical Studies, 154(1):27–51.
• Elder, C., 1998, “Essential Properties and CoincidingObjects,”Philosophy and Phenomenological Research, 58:317–331.
• Fine, K., 1994, “Compounds and Aggregates,”Noûs, 28: 137–158.
• –––, 1999, “Things and Their Parts,”Midwest Studies in Philosophy, 23: 61–74.
• –––, 2003, “The Non-identity of a MaterialThing and Its Matter,”Mind, 112: 195–234.
• Gabbay, D., and Moravcsik, J.M., 1973, “Sameness andIndividuation,”Journal of Philosophy, 70:513–526.
• Gallois, A., 1998,Occasions of Identity: The metaphysics ofPersistence, Change, and Sameness, New York: Oxford UniversityPress.
• –––, 1986, “Rigid Designation and theContingency of Identity,”Mind, 95: 57–76.
• –––, 1990, “Occasional Identity,”Philosophical Studies, 58: 203–24.
• –––, Gibbard, A., 1975, “ContingentIdentity,”Journal of Philosophical Logic, 4:187–221.
• Griffin, N., 1977,Relative Identity, Oxford: OxfordUniversity Press.
• Hansson W, T., 2008, “Can I Be an Instantaneous Stage andYet Persist Through Time?,”Metaphysica, 9(2):235–239.
• Haslanger, S., 1994, “Humean Supervenience and EnduringThings,”Australasian Journal of Philosophy 72:339–359.
• –––, 2003, “Persistence ThroughTime,” in Loux M.J. and Zimmerman D. (eds.),the OxfordHandbook of Metaphysics, Oxford: Oxford University Press,315–354.
• Haslanger, S., and Kurtz, R.M. (eds.), 2006,Persistence:Contemporary Readings, Cambridge: Cambridge UniversityPress.
• Hawley, K., 1999, “Persistence and Non-SupervenientRelations,”Mind 108: 53–67.
• –––, 2001,How Things Persist, Oxford:Oxford University Press.
• Hawthorne, J., Scala, M. and Wasserman R., 2003,“Recombination, Humean Supervenience and Causal Constraints: AnArgument for Temporal Parts?,” inOxford Studies inMetaphysics, 1: 301–318.
• Heller, M., 1984, “Temporal parts of Four DimensionalObjects,”Philosophical Studies, 46:323–334.
• –––, 1990,The Ontology of PhysicalObjects, Cambridge: Cambridge University Press.
• –––, 1992, “Things Change,”Philosophy and Phenomenological Research, 52:695–704.
• –––, 1993, “Varieties of FourDimensionalism,”Australasian Journal of Philosophy,71: 47–59.
• Hirsh, E., 1976, “Physical Identity,”Philosophical Review, 85: 357–389.
• –––, 1982.The Concept of Identity,Oxford: Oxford University Press.
• Hudson, H., 1999, “Temporal Parts and MoralPersonhood,”Philosophical Studies, 93:299–316.
• Hughes, C., 1986, “Is a Thing Just the Sum of itsParts?,”Proceedings of the Aristotelian Society, 86:213–23.
• Johnston, M., 1989, “Fission and the Facts,” inPhilosophical Perspectives 3 (Philosophy of mind and ActionTheory), Atascadero: Ridgeview Press.
• –––, 1992, “Constitution is notIdentity,”Mind, 101: 89–105.
• Jubien, M., 1993,Ontology, Modality and the Fallacy ofReference, Cambridge: Cambridge University Press.
• Kazmi, A., 1990, “Parthood and Persistence,”Canadian Journal of Philosophy (Supplementary Volume), 16:227–250.
• Levy, S., 1997, “Coincidence and Principles ofComposition,”Analysis, 57: 1–10.
• Lewis, D., 1971, “Counterparts of Persons and TheirBodies,”Journal of Philosophy, 68: 203–211.
• –––, 1986,On the Plurality of Worlds,Oxford: Oxford University Press.
• –––, 1986,Philosophical Papers (Volume2), Oxford: Oxford University Press.
• –––, 1993, “Many, but Almost One,”in J.Bacon (ed),Ontology, Causality and Mind: Essays in Honour ofD.M. Armstrong, Cambridge: Cambridge University Press.
• Lombard, L., 1994, “The Doctrine of Temporal Parts and the‘No-Change’ Objection,”Philosophy andPhenomenological Research, 54: 365–372.
• –––, 1999, “On the Alleged Incompatibilityof Presentism and Temporal Parts,”Philosophia, 27:253–260.
• Lowe, E.J., 1983, “On the Identity of Artifacts,”Journal of Philosophy, 80: 220–232.
• –––, 1983, “Instantiation, Identity andConstitution,”Philosophical Studies, 44:45–59.
• –––, and Noonan, H., 1988, “Substance,identity and Time,”Proceedings of the AristotelianSociety (Supplementary Volume), 62: 61–100.
• –––, 1989,Kinds of Being, Oxford:Blackwell.
• –––, 1995, “Coinciding Objects: In Defenseof the ‘Standard Account’,”Analysis, 55:171–178.
• Markosian, N., 1998, “Brutal Composition,”Philosophical Studies, 79: 95–105.
• Merricks, T., 1998, “There Are No Criteria of Identity OverTime,”Noûs, 323: 106–12.
• –––, 1999, “Composition as Identity,Mereological Essentialism and Counterpart Theory,”Australasian Journal of Philosophy, 77: 192–195.
• Miller, K., 2005, “A New Definition of Endurance,”Theoria, 71(4): 309–332.
• Miller, K. and Braddon-Mitchell, D., 2007, “There is no‘Simpliciter Simpliciter’”,PhilosophicalStudies, 136(2): 249–278.
• Moyer, M., 2006, “Statues and Lumps a StrangeCoincidence,”Synthese, 148(2): 401–423.
• –––, 2001,Objects and Persons, Oxford:Oxford University Press.
• Myro, G., 1986, “Identity and Time,” in R. Grandy andR. Warner (eds.),Philosophical Grounds of Rationality: IntentionsCategories and Ends, Oxford: Clarendon Press, 383–409.
• –––, 1986, “Time and Essence,” inMidwest Studies in Philosophy, 11: 331–41.
• Needham, P., 2010, “Transient Things and PermanentStuff,”Australasian Journal of Philosophy, 88(1):147–166.
• Noonan, H., 1976, “The Four Dimensional World,”Analysis, 37: 32–39.
• –––, 1980,Objects and Identity, TheHague: Martinus Nijhoff.
• –––, 1985, “A Note on TemporalParts,”Analysis, 45: 151–152.
• –––, 1987, “Reply to Grham Spinkes onTemporal Parts,”Analysis, 47: 187–189.
• –––, 1988, “Substance, Identity andTime,”Proceedings of the Aristotelian Society(Supplementary Volume), 62: 79–100.
• –––, 1993, “Constitution isIdentity,”Mind 102: 133–146.
• –––, 2001, “The Case forPerdurance,” inReality and Humean Supervenience: Essays onthe Philosophy of David Lewis, Gerhard Preyer (ed.), Lanham:Rowman and Littlefield, 123–139.
• Oaklander, N., 1992, “Temporal Passage and TemporalParts,”Noûs, 26: 79–84.
• Oderberg, D.S., 1993,The Metaphysics of identity OverTime, London: Macmillan.
• Parsons J., 2000, “Must a Four-Dimensionalist believe intemporal Parts?,”The Monist, 83: 399–814.
• Perry, J., 1970, “The Same F,”PhilosophicalReview, 79: 181–200.
• Rea, M., 1995, “The Problem of Material Constitution,”Philosophical Review, 104: 525–552.
• –––, (ed.) 1997,Material Constitution,Cornell: Cornell University Press.
• –––, 1998, “Temporal PartsUnmotivated,”Philosophical Review, 107:225–260.
• –––, 2003, “Four-dimensionalism,” inM. Loux and D. Zimmerman (eds.),Oxford Handbook ofMetaphysics, Oxford: Oxford University Press, 246–280.
• Robinson, D., 1982, “Re-identifying Matter,”Philosophical Review, 91: 317–342.
• –––, 1985, “Can Amoebae Divide WithoutMultiplying?,”Australasian Journal of Philosophy, 63:299–319.
• –––, 1989, “Matter, Motion and HumeanSupervenience,”Australasian Journal of Philosophy, 67:394–409.
• Sanford, D.H., 2005, “Distinctness and Non-Identity,”Analysis, 65(4): 269-274.
• –––, 2011, “Can a Sum Change ItsParts?”Analysis, 71(2): 235–239.
• Sattig, T., 2008, “Identity in 4D,”PhilosophicalStudies, 104(2): 179–195.
• –––, 2010, “Compatibilism AboutCoincidence,”Philosophical Review, 119:273–313.
• Shoemaker, S., 2015, “Persistence and Properties,”Journal of the American Philosophical Association, 1(3):433–448.
• Sidelle, A., 1998, “A Sweater Unraveled: Following OneThread of Thought For Avoiding Coincident Entities,”Noûs 32: 423–44.
• Sider T., 2003,Four Dimensionalism, Oxford: OxfordUniversity Press.
• Wahlberg, T. H, 2008, “Can I Be an Instantaneous Stage andYet Persist Through Time?”Metaphysica, 9(2):235–239.
• Wiggins, D., 2001,Sameness and Substance Renewed,Cambridge: Cambridge University Press.
• Wilson, R.A., 2009, “The Transitivity of MaterialConstitution,”Noûs, 43(2): 363–377.
• Wright, S., 2010, “The Leibniz's Law Problem (for StageTheory),”Metaphysica, 11(2): 137–151.

D. Personal Identity

• Ballie, J., 1990, “Recent Work on Personal Identity,”Philosophical Books, 34: 193–206.
• –––, 1993,Problems in PersonalIdentity, New York: Paragon House Publisher.
• Bermudez, J., 1998,The Paradox of Self-Consciousness,Cambridge: MIT.
• Brennan, A., 1988, “Best Candidate Theories ofIdentity,”Inquiry, 29: 423–38.
• –––, 1988,Conditions of Identity,Oxford: Oxford University Press.
• Brueckner, A., 1993, “Parfit on What Matters inSurvival,”Philosophical Studies, 70: 1–22.
• –––, 2009, “Endurantism and thePsychological Approach to Personal Identity,”Theoria,75(1): 28–33.
• Buford, C., 2009, “Memory, Quasi-Memory, and Pseudo-QuasiMemory,”Australasian Journal of Philosophy, 87(3):465–478.
• Butler J., 1736, “Of Personal Identity,” inTheAnalogy of Religion, New York: Cosimo, 2005.
• Campbell, J., 2011, “Personal Identity,”TheOxford Handbook of the Self, Oxford: Oxford UniversityPress.
• Cartwright, H.M., 1993, “On Two Arguments for theIndeterminacy of Personal Identity,”Synthese, 95:241–273.
• Chandler, H., 1969, “Shoemaker's Arguments AgainstLocke,”Philosophical Quarterly, 19: 17–37.
• Chihara, C., 1994, “The Many Persons Problem,”Philosophical Studies, 76: 45–9.
• Chisholm, R., 1976,Person and Object, La Salle: OpenCourt.
• Coburn, R., 1960, “Bodily Continuity and PersonalIdentity,”Analysis, 20: 117–120.
• Cole, D., 1991, “Artificial Intelligence and personalIdentity,”Synthese, 88: 399–417.
• Doepke, F., 1996,The Kinds of Things: A Theory of PersonalIdentity Based on Transcendental Argument, Chicago: Open CourtPublishing.
• Ehring, D., 1987, “Personal Identity and Time Travel,”Philosophical Studies, 52: 427–33.
• –––, 1990, “Nonbranching andNontransitivity,”Analysis, 50: 268–71.
• –––, 1995, “Personal Identity and theR-Relation: Reconciliation Through Cohabitation?,”Australasian Journal of Philosophy, 73: 337–346.
• ––&Ndash;, 2013, “Why Parfit Did Not Go FarEnough,”Philosophical Studies, 165(1):133–149.
• Eklund, M., 2004, “Personal Identity, Concerns, andIndeterminacy,”Monist, 87(4): 489–511.
• Elliott, R., 1991, “Personal Identity and the CausalContinuity Requirement,”Philosophical Quarterly, 41:55–75.
• Fuller, G., 1992, “Functionalism and personalIdentity,”Personalist Forum, 8: 133–143.
• Garrett, B., 1990, “Personal Identity andExtrinsicness,”Philosophical Studies, 59:177–94.
• –––, 1998,Personal Identity andSelf-Consciousness, London: Routledge.
• Gendler, T.Z., 2002, “Personal Identity and ThoughtExperiments,”Philosophical Quarterly, 52:34–54.
• Grice, H.P., 1941, “Personal Identity,”Mind,50: 330–350.
• Hamilton, A., 1995, “A New Look at Personal Identity,”Philosophical Quarterly, 45: 332–349.
• Hirsch, E., 1991, “Divided Minds,”PhilosophicalReview 100: 3–30.
• Johnston, M., 1987, “Human Beings,”Journal ofPhilosophy, 84(2): 59–83.
• –––, 1989, “Relativism and theSelf,” inRelativism, Interpretation and Confrontation,M. Krausz (ed.), Notre Dame: University of Notre Dame Press.
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