C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 1 [1–18] 10.8.2012 10:59AM Introduction Georg Gasser and Matthias Stefan the p ro j e c t One worthwhile task for philosophy is to give an overview of a whole domain of thought and to present the conceptual relationships that characterize it. The domain we have striven to portray in this introduction, on a quite general level with a broad brush, is the contemporary debate about personal identity over time. We proceed as follows: First, we specify the metaphysical question of personal identity tackled in this volume: namely, what makes a person P1 at t1 identical to a person P2 at t2? Second, we discuss views which analyze personal identity in terms of bodily and psychological relations. Problems associated with these theories have recently made a fourdimensional interpretation of such views quite popular. The following section presents this canny metaphysical alternative to traditional threedimensional views. Finally we discuss a rather neglected approach to personal identity over time, the so-called "simple view," according to which personal identity does not consist in anything other than itself; it is simple and unanalyzable. Eric Olson once suggested that the simple view is poorly understood, and therefore deserves more attention than it has received so far (Olson 2010, section 3). A specific aim of this volume was to take up this suggestion. In the first section, "Framing the question," the authors draw attention to the wider framework in which the question of personal identity is posed. They reveal some of the hitherto implicit background assumptions of the theories at hand, as well as the explanatory demands one should expect of the theories. The contributions of the second section, "Arguments for and against simplicity," provide original in-depth analyses of arguments put forward in favor of and against the claim that personal identity is analyzable. The last section, "Reconsidering simplicity," contains innovative and so far rather unnoticed arguments that might strengthen the case for the simple view. 1 C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 2 [1–18] 10.8.2012 10:59AM the que s t i on of p e r sona l i d ent i t y In our ordinary non-philosophical moments we take it for granted in almost everything we do that persons persist over time: when we make plans, we assume that we will carry them out in the future. When we punish someone for a crime, we assume that she is the same person as the one who committed it. When we regret a misdeed, we assume that we are identical with the agent who performed it. These examples indicate that the assumption that personal identity is continuous is of particular importance for practices central to our lives, pertaining to both the treatment of ourselves and of others. Furthermore, to know an entity's identity conditions is to know what kind of entity it is; a fortiori, this is true of human beings: if you want to figure out who you are essentially, you must ask which conditions guarantee your identity over time. Philosophers often refer to this problem as "the" question of personal identity. But this is misleading; the question of personal identity is not a single problem (see e.g. Rorty 1976). It is important to distinguish between various meanings of "personal identity." For our purposes we identify four: (i) Biographical (or narrative) identity: Who am I? This question asks how an individual understands and defines herself in light of her values, convictions, and aims. "Identity" in this context is a normative or evaluative concept which incorporates an individual's selfunderstanding and her broader life-plan. (ii) Personhood: What are the conditions for personhood? This question seeks conditions that make something a person as opposed to a nonperson. It calls for necessary and sufficient conditions for personhood, such as being an intelligent, conscious and feeling agent. (iii) Metaphysical nature: To which metaphysical category do human persons belong? Possible answers include the claims that human persons are temporary stages of human organisms, thinking substances (souls), collections of temporal parts, or bundles of mental and physical states. (iv) Diachronic (personal) identity: What makes it the case that a person X at t1 is identical with a person Y at t2? This question seeks the persistence conditions of persons: that is, what it takes for the same person to exist at different times. Note that the question about epistemic criteria for determining the persistence conditions for persons must be distinguished from (iv). The question of what it takes for a person to persist over time is different from the question of how to find out whether a person at one time is identical to a person at another time. Epistemic criteria for recognizing personal identity 2 georg gasser and matthias stefan C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 3 [1–18] 10.8.2012 10:59AM over time must not be confused with criteria for identity itself. Generally, of course, epistemic criteria – such as the continuity of psychological and physical features – are reliable signs for tracking personal identity over time. It is easy to imagine, however, that epistemic criteria for metaphysical identity come apart from identity itself. Consider the case of physical disfigurement after a serious accident: in such a case a person can no longer be recognized by her physical appearance, but this does not imply that there are two different persons, one before and one after the accident. This volume is about question (iv). An adequate answer to the question of the diachronic identity of human persons can be presented schematically in the following way: "If x and y are things of kind K, then x is identical with y if and only if x and y stand in the relation Rk to one another" (Lowe 2000, p. 272). If you ask yourself whether the woman at the mall is the girl you knew in high school, then you ask yourself whether you refer to the same human person twice or refer once to each of two different persons. Although the question of diachronic identity is related to questions (i) to (iii), keeping them separate will help avoid confusion. Still, especially question (iii) will play a role in answering question (iv) because the metaphysical nature of an entity determines its persistence conditions. the de b a t e a bout p e r sona l i d ent i t y One way to introduce the contemporary debate about personal identity is to distinguish two basic kinds of account of personal identity in the sense of question (iv): the complex and the simple view. The complex view analyzes personal identity in terms of simpler relations. The fact that a person persists over time is nothing more than some other facts which are generally spelled out in either biological or psychological terms, or both. That is, the complex view takes talk about "what personal identity consists in" literally. It aims to provide necessary and sufficient conditions for personal identity, thereby reducing it to the holding of basic biological or psychological relations. Whenever these relations obtain, personal identity obtains. The simple view of personal identity, by contrast, denies that a person's identity through time consists in anything but itself. Biological and psychological continuitymay be regarded as epistemic criteria for diachronic identity, but they are neither necessary nor sufficient conditions for personal identity. There are no non-circular, informative necessary and sufficient conditions for personal identity: personal identity consists in nothing other than itself. Introduction 3 C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 4 [1–18] 10.8.2012 10:59AM the b i o log i c a l a p p roach A natural idea is that a human person's identity over time consists in biological persistence conditions either of the entire organism or of particular parts of it − for instance the brain. The former approach has become known as animalism (Olson 1997b); the latter might be called the brainbased approach (see e.g. Nagel 1986, p. 40, sketches this view as the empirical hypothesis of the self's true nature). Animalism assumes that the biological functioning of the human organism − that is, the persistence of the unity and interaction of metabolic processes − is essential for human beings to persist. Accordingly, a person's identity is no different from the identity of other living things like horses or mosquitoes. Her persistence does not consist in the preservation of the same matter but rather in the preservation of the same organizational biological form, since the matter constituting the organism is continually replaced. For animalism, the identity of a functioning organism and the identity of the person constituted by this organism do not necessarily go hand in hand. Take, for instance, an irreversibly comatose patient. If we assume that the actual performing of higher brain functions is a necessary condition for an individual's mental state, and if these brain functions are absent in a comatose patient, then the patient is a living and functioning organism, but she is not a person, because this presupposes that she enjoys a mental life of some complexity. According to the biological approach, we are not essentially human persons, but rather human organisms or animals. We can lose the status of personhood while remaining us, because our human organism can continue to be alive. A well-known argument for animalism is the "thinking animal problem." It starts with the insight that human animals exist. Wherever a human person is, there seems to be a human animal too: wherever you sit, a human animal sits too; whenever you work, so does an animal; whenever you are thirsty, an animal is too. The animal is most intimately related to you, so that it is difficult to tell the difference between you and it. Olson writes: In fact the animal seems to be mentally exactly like you: every thought or experience of yours appears to be a thought or experience on the part of the animal. How could you and the animal have different thoughts? But if the animal thinks your thoughts, then surely it is you. You could hardly be something other than the thing that thinks your thoughts. (Olson 2007, p. 29) How might one respond to this argument? One response is to deny that there are animals. A second is to say that there is an animal where you are 4 georg gasser and matthias stefan C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 5 [1–18] 10.8.2012 10:59AM but that it is only you and not the animal that enjoys a mental life. Animals are living but non-thinking beings. Finally, one could respond that there is an animal where you are, which has the same thoughts as you, but that nevertheless you are not identical with it. You share a mental life with an animal but not a metaphysical nature, because you are a human person whereas the animal is not. The first option is implausible. There are no good reasons to reject the existence of animals. The second option dissolves into a kind of dualism: one might argue that animals qua biological organisms are unable to think but that their soul is the entity endowed with a mental life. A materialist alternative to this option could instead identify human brains as thinking beings in contrast to animals. Accordingly, a mental life can be attributed only to a specific part of the human animal – the brain – rather than to the animal as such. The third alternative results in what is called the "too many thinkers problem." If we assume that the human animal enjoys the same mental life as the human person but that they are nonetheless two distinct entities, then apparently the human animal and the human person coincide spatially. Even though ordinary parlance refers to just one entity, there are in fact two. This proposal thus fails to solve the problem of coincidence. If there is a human animal thinking your thoughts as well as you as a human person thinking your thoughts, then why should you assume that you are the human person and not the thinking human animal? There is a serious epistemological problem because you are not in a position to tell which of the two entities you are. In addition, someone might wonder why a thinking human animal should count as an animal and not as a person. What keeps the human animal from being a human person? If this argument for animalism is sound, there is strong reason to think that we are, at least during certain episodes of our existence, essentially animals capable of thought, unless human persons are identical either to mental substances or to brains. This conclusion pertains to the metaphysical nature of human beings, but is closely related to the question of conditions for personal identity: if we are biological organisms, then our identity conditions are those of biological organisms − that is, our identity consists in the continuity of a living body over time. An alternative to animalism is the brain-based approach. It claims that there are certain biological conditions for personal identity which, however, fall short of the entire organism. It starts from the assumption that one part of the body − the brain (or certain parts thereof ) − is of particular importance because it produces the mental life characteristic of being a Introduction 5 C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 6 [1–18] 10.8.2012 10:59AM person. Damage to the brain can result in personality changes and amnesia, and in severe cases can utterly obliterate the capacity for higher cognitive functions, whereas damage to the limbs, stomach or other organs has no such dramatic effects. Admittedly, we might undergo a personality change as a consequence, but these events would not affect the brain's capacity for maintaining a mental life. You can even imagine that your brain could be removed from your body and preserved in a functional state by a complex machine. Assuming that your brain works as well after as before its disembodiment, you might still be considered the same person under these artificial conditions. A thought experiment by Sydney Shoemaker (1963) underpins this line of thought. Imagine that the brain of one person, Brown, is removed and transplanted into the body of another person, Robinson. The resulting person, Brownson, has the body of Robinson but the brain of Brown and thus Brown's whole psychological makeup. Most of us would be inclined to say that the newly created person Brownson is identical with the former person Brown. Derek Parfit formulates this intuition as follows: "Receiving a new skull and a new body is just the limiting case of receiving a new heart, new lungs, new arms, and so on" (Parfit 1984, p. 253). These considerations favor the view that the functioning brain (or a certain part thereof) needs to persist for the human person to persist, but that the entire organism is not required to do so because only a functioning (and appropriately stimulated) brain, and no other organs, is needed for producing an individual's mental life. Note that the brain-based approach places so much emphasis on the brain because the latter sustains one's mental life. Herein lies a major difference between the brain-based view and animalism: for animalism, the fact that a human organism can enjoy a mental life is of no importance in deciding identity over time. For the brainbased approach, by contrast, the brain is essential for guaranteeing one's identity over time because it guarantees the continuity of one's mental life. the p s y cholog i c a l a p p roach As the thought experiment of the brain transplantation between Robinson and Brown shows, some intuitions motivate a link between personal identity and psychological continuity rather than between personal identity and the identity of the brain. Such intuitions are encouraged by another thought experiment involving what Shoemaker (e.g. 1984, p. 108) called a "brain state transfer device": this device reads the states of a person P1's brain, writes them into the brain of person P2, and then destroys P1's brain, 6 georg gasser and matthias stefan C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 7 [1–18] 10.8.2012 10:59AM turning P1's organism irreversibly into a human vegetable. What becomes of P1? Is she identical to the human vegetable or did she just acquire a new organism thanks to the brain state transfer device? Pace the brain-based approach, P1 ceases to exist once her brain is destroyed. The line of thought pursued in the thought experiment, however, provokes the question whether we should say that personal identity consists in the continuing functioning of the human brain at all. We could imagine that no brain is needed anymore and that anything would do the job as long as it sustains one's psychological life. If psychological states and their continuity are the mark of personal identity rather than the continuity of the brain (or some other biological fact), then P1 continues to exist by acquiring P2's body. This approach to analyzing personal identity amounts to the claim that a human person's persistence consists in a particular constellation of psychological relations over time. It is known as the psychological approach. An advocate of some version of the psychological approach must specify what kind of psychological relations are necessary and sufficient for human persons to persist. Philosophers generally try to spell out psychological continuity in terms of causal connections between earlier and later psychological states, such as remembering earlier experiences, forming and carrying out intentions, and holding beliefs over time. Sydney Shoemaker characterizes this approach this way: Reverting to the "person-stage" terminology, two person-stages will be directly connected, psychologically, if the later of them contains a psychological state (a memory impression, personality trait, etc.) which stands in the appropriate relation of causal dependence to a state contained in the earlier one; and two stages belong to the same person if and only if . . . they are connected by a series of stages such that each member of the series is directly connected, psychologically, to the immediately preceding member. (Shoemaker 1984, p. 90) On this view, whether a person at t1 is the same as a person at t2 depends on what constitutes an "appropriate" relation of causal dependence between psychological states – however "appropriateness" is specified in detail. We have been led by a series of considerations from animalism, via the brain-based approach, to the psychological approach to personal identity. Whichever version of the complex view one prefers, either way the biological and psychological approaches agree that a person's identity over time is definable in terms of something other than itself. They differ merely in spelling out what that something is. Introduction 7 C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 8 [1–18] 10.8.2012 10:59AM two prob l em s for comp l e x a p p roache s The general claim of any complex approach is that a person's identity over time can be analyzed into necessary and sufficient components other than identity over time itself. This claim comes with problems of its own. This section briefly examines two of these problems, the problem of graduality and the problem of fission. First, the problem of graduality (Noonan 1989, pp. 128–48). If personal identity consists in simpler items such as bodily and/or psychological relations, then we can imagine situations in which these relations admit of degree (Lewis 1976). This leads to the question of what is the threshold that demarcates personal identity from non-identity. Imagine that in a series of operations the parts of P1's body are discarded and replaced with parts of P2's body, until all parts of P1's original body have been replaced with parts of P2's body.With each operation some of P1's psychological states are also lost and are replaced by psychological states of P2. By the end, P1's entire body and consequently all of her psychological states are exchanged with P2's body and her psychological states so that P1 is identical to P2 in terms of her body and psychology. It is very likely that, after only a few operations, P1 still exists with just minor changes in her bodily and psychological states. At the end of this series of operations, however, one might have the intuition that P1 does not exist anymore but was replaced with P2. The crucial question is: is there a way to indicate the sort of relations needed between two person-stages of P1 so that changes in these relations do not result in her dropping out of existence by being replaced with P2? Is there a precise threshold demarcating P1's persistence in time? As can easily be imagined, it is unclear how to specify the exact threshold demarcating P1's existence. It may well always be possible to present examples of deviant continuity relations which leave it undetermined whether or not two person-stages are continuous. It is very likely that complex views go hand in hand with bodily or psychological continuity relations that admit of degree, and it is hard, if not impossible, to specify what degree must obtain to guarantee personal identity. Thus the sort of continuity relations that personal identity consists in is elusive. One could argue that this might only be an epistemic problem for finite minds such as ours, because human bodies and human psychology are extremely complex phenomena. An omniscient being, by contrast, might be able to specify the appropriate sort of bodily and psychological continuity needed for a human person to persist. But who can tell? There are no 8 georg gasser and matthias stefan C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 9 [1–18] 10.8.2012 10:59AM points of reference that a clear demarcation exists. This suggestion is merely speculative and we will not pursue it here any further. Apart from the insight that complex views might provide us with a less specific account of personal identity than we would wish for, there is a more serious objection to these views. Opponents of the complex view point to an intuition to the effect that it does not make sense to think that personal identity can be gradual. They say: whatever tomorrow brings, there is the strong intuition that either P1 will exist or will not; of all the people existing, either she will be one of them or none will be identical with P1. Either of these two states of affairs will obtain and, so the claim goes, the viewmust be rejected which admits of degrees between these two states. If personal identity is determinate, it cannot be the case that there is just P1 at t1 and just P2 at t2 while being indeterminate whether P1 is identical to P2. Maybe no one can tell whether P1 is identical to P2, but nevertheless the statement about P1's identity is either true or false. One way to challenge this line of argument is by appeal to well-known puzzle cases such as Parfit's club (1984, p. 213). Imagine that, for some years, a club exists, then that the regular meetings cease, and a few years later that the members of the same club start to meet again with the same rules and the same name. Someone could ask: have the members set up a new club similar to the old one? Or do they continue the same club which exists intermittently? It seems reasonable to argue that these questions can be answered conventionally. Points can be made in favor of the thesis that the old and the new club are identical, and other points can be made in favor of the alternative thesis that they are not identical. Depending on the conditions of identity one accepts, one can legitimately hold either thesis, for there are no right or wrong answers. It seems obvious that once it is settled which conditions of identity are accepted, it does not make sense to continue to argue about the correct answers for this case. But can we proceed in this way when it comes to human persons? Defenders of the thesis that personal identity is determinate claim it is not absurd to ask whether a correct answer can be given. On the contrary, it would be absurd if a human person, facing this question for herself, thought it sensible to consult a general meeting or a law court. It does not make sense, the argument goes, to assume that (under certain circumstances) a general meeting or a law court could simply decide whether or not a person at one time is identical to a person at another. In contrast to the case of the club, there is a pertinent intuition that whatever decision is made, the possibility remains open that it would be the wrong one. Any decision is made under risk, that is, because things could differ from the way the court Introduction 9 C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 10 [1–18] 10.8.2012 10:59AM decides. This intuition is particularly strong when one considers the matter from a first-person perspective. David H. Lund, for instance, writes: I am unable to imagine being involved in circumstances under which I am neither fully admitted nor fully excluded. The experiences occurring under these circumstances would have to be something for me if I am to be involved in them at all, but the suggestion that they would be something for me even though it is indeterminate as to whether I am having them seems simply unintelligible when one takes the first-person perspective and reflects upon what it is to have experience. (Lund 2005, p. 229) Second, the problem of fission (Noonan 1989, pp. 149–68). The complex view does not rule out the possibility that the necessary and sufficient relations for personal identity over time are not one-to-one but one-tomany (Shoemaker 1963; Williams 1970). Imagine the scenario of a person P1 splitting up at t1 into two subsequent distinct persons at t2, P2 and P3. They stand to the original person symmetrically in the identity-defining relation. Both P2 and P3 are fully continuous with P1 in terms of the latter's psychological and biological characteristics. Neither from the outside nor the inside can it be determined which of the two successors is identical to P1. Although the same identity-defining relations obtain between P1 and P2 as well as between P1 and P3, P1 cannot be identical with both successors at the same time because P2 and P3 are numerically different persons. The proponent of the complex view must have a story to tell about such scenarios. One option is for her to reject the presupposition which is often called the "only x and y principle." This principle says that two persons, P1 at t1 and P2 at t2, are identical iff (a) they stand in the appropriate internal relationship and (b) there is no other competing person, P3 at t2, who stands in the same relationship with P1 as P2 at t2 (see e.g. Nozick 1981, pp. 29–47). In other words, whether P1 and P2 are identical depends on whether a process of fission occurs. If fission occurs, identity does not obtain; if fission does not occur, identity obtains. However, this line of argument seems to imply that questions of personal identity do not depend only on facts internal to the relation between a person existing at different times. Instead, whether or not P1 exists after t1 depends on the seemingly secondary issue of whether or not another person similar to P1 will exist at t2. The adoption of the "only x and y principle" has been criticized as counterintuitive: what else could a person's and her successor's being identical depend on other than facts about themselves? In addition, the "only x and y principle" appears ad hoc, its only ostensible 10 georg gasser and matthias stefan C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 11 [1–18] 10.8.2012 10:59AM purpose being to exclude fission cases from the discussion about personal identity. A related solution to this puzzle could propose that what matters to P1's survival is not personal identity but simply that someone stands in the appropriate continuity relations. If more than one person does so, then this is no cause for concern but a sign that one's continuing existence should not be understood in terms of a personal identity rather than an (appropriate) continuity relation. It is not identity that matters, but continuity. As long as at least one person exists in the future who will be related to P1 in the way in which P1 is related to her past selves, P1 continues to exist. Fission represents no particular difficulty to this approach because, unlike the normal one-toone case, in such a scenario the person continues to exist "twice over" and she has no reason not to value the existence of her successors as much as her own existence before fission took place. Since it is not identity that matters in survival, no violation of transitivity of the identity relation takes place in such fission scenarios (Parfit 1984, pp. 245–80). The bottom line of the discussion so far is that no complex account of personal identity is wholly satisfactory. One way to deal with this result is to assume that our intuitive beliefs concerning personal identity are somehow confused or even inconsistent. Another possibility is to assume that the thought experiments lead us astray because they do not represent real possibilities in our world (Wilkes 1988, pp. 8–18). A third possibility is to propose an alternative metaphysical framework which can account for these puzzle cases. So far we have considered only a three-dimensional metaphysical framework. It seems, however, that four-dimensionalism fares better with the problems discussed than its three-dimensionalist alternative. four -d im en s i ona l i sm Theorists of personal identity generally hold that a human person exists at different times. How she persists, however, is a matter ofmetaphysical dispute. Three-dimensionalism claims that a human person, like any other material object, is wholly present at each time that she exists and has no temporal parts. Four-dimensionalism, instead, holds that human persons not only have spatial parts, but successive temporal parts as well. They are temporally extended composites filling up regions of space-time. Ted Sider writes: My spatial parts extend through time like I do. We call them spatial parts because they are smaller than I, spatially speaking; they are "cut out of" me along a spatial dimension. Reverse time and space in this description and we obtain a description Introduction 11 C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 12 [1–18] 10.8.2012 10:59AM of my temporal parts, which extend through space like I do but are smaller than I, temporally speaking; they are what you get by slicing me along a temporal dimension. (Sider 2001, p. 2) According to this approach, persons have temporal parts located at different times, in a way that is analogous to having spatial parts located at different places. A person who exists throughout the decade between 1990 and 2000 does so by having connected temporal parts at every time between 1990 and 2000. She extends along not three but four dimensions, being "spread out" over a region of space-time. Persons, like material objects, are conceived as four-dimensional space-time worms whose single parts are united by relations which – depending on the account one favors – can be specified in various ways. John Perry (2008, pp. 7–12), for instance, underlines that the unity relation is of crucial importance for understanding personal identity because it determines which parts belong to the same entity. The identity relation, instead, indicates whether one or two (or more) distinct entities are present. Thus, it has to be kept distinct from identity over time even though both relations are themselves closely related (see e.g. Perry 2008, pp. 7–12). Perry clarifies the distinction between these two relations with the following example: If we want to learn about a baseball game we need to know when events in the game are parts of one single baseball game. If we just knew about the parts of the game, but not about when they belong to one single game rather than to two different ones, we would not possess the concept of a baseball game. Thus, we are looking for the unity relation between the single events of the one baseball game. Unity is a relation between the events of one game specifying which events belong to the same game. When different events or parts stand in the unity relation, they are events or parts of one single entity. Identity, by contrast, specifies whether game A is numerically the same as game B. The unity relation can be understood in various ways. You could have psychological continuity, bodily continuity or whatever unifies spatiotemporal parts into one single person. Depending on one's preferred account of personal identity, variants of bodily theories of personal identity are as correct as variants of psychological ones. Different accounts of personal identity over time simply define persons differently: whereas one theory employs bodily connections between temporal parts to pick out "bodily" persons, the other theory employs psychological connections to pick out "psychological" persons. Facts about personal identity over time are up to us to determine, since it is up to us to decide which kind of "person" to refer to. Those who employ different unity relations may not 12 georg gasser and matthias stefan C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 13 [1–18] 10.8.2012 10:59AM disagree about the correct approach to personal identity at all. Rather, they may refer to different kinds of persons − persons being composed of personstages related to one another by bodily continuity and persons being composed of person-stages related to one another by psychological continuity. With this ontological framework, four-dimensionalism gets a grip on the problems of fission and graduality (see e.g. Perry 1972). As noted, fission violates the transitivity of identity. Not so the unity relation, which is not transitive. If x and y are parts ofA and y and z are parts of B, then this does not imply that x must be a part of B and z be a part of A. Different objects can share some but not all of their parts. The same holds for temporal parts of persons: if two persons share temporal parts P1 and P2 at t1 and t2, then this does not imply that they share their temporal parts P3 and P4 at t3 as well: imagine there is one person composed of the temporal parts P1, P2 and P3, and another composed of P1, P2 and P4, but there is no person composed of P2, P3 and P4. So there is one single person with the temporal parts P1, P2 and P3, and another with the temporal parts P1, P2 and P4. These two persons are numerically distinct: they share temporal parts P1 and P2, and they therefore cannot be distinguished during the times t1 and t2. Fission does not pose a particular problem to a four-dimensionalist account, because there is not one single person dividing into two but two persons parting ways after they have coincided for some time. Four-dimensionalism suggests a solution to the problem of graduality, too (Noonan 1989, pp. 140–8). Graduality is understood as the result of semantic underdetermination and not a result of metaphysical puzzles. Once it is agreed that all there is are spatio-temporal parts, then there is no open ontological question. We only have to specify our concept of the human person: that is, we have to specify the unity relation we pick out with this concept, and then we can state precisely which spatio-temporal parts belong to the same (kind of) person. The upshot of this discussion is that four-dimensionalism's liberal ontology of objects provides a powerful metaphysical framework for solving the problems that plague complex approaches within a three-dimensionalist framework. Of course, not everybody sees this liberal ontology as a virtue. Some philosophers consider its cost to be prohibitive. There is no space to dwell on this discussion here. It suffices to note that, by construing any filled region of space-time as an object, for some philosophers fourdimensionalism countenances far too many objects which are not robust enough to make sense of our ordinary understanding of an object's persistence (see e.g. Baker 2007d, pp. 199–217). Introduction 13 C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 14 [1–18] 10.8.2012 10:59AM the s imp l e v i ew Some philosophers reject all the accounts of personal identity presented so far. They consider them fatally flawed and as a consequence take themselves to be justified in assuming that there are no informative non-circular conditions for personal identity. According to them, personal identity is something so fundamentally basic that it cannot be accounted for in more basic terms such as biological and psychological relations or temporal parts. E. J. Lowe, for instance, puts this account as follows: "The persistence of at least some sorts of things must . . . be primitive or ungrounded, in that it can consist neither in relationships between non-persisting things nor in the persistence of other sorts of things" (Lowe 1988, pp. 77–8). As a simple relation, personal identity does not have other relations as proper parts, and what has no proper parts cannot obtain partly, as this would presuppose that only some parts exist and others do not. Accordingly, personal identity either obtains or does not obtain, and as such it does not admit of degree. Taking personal identity to be ontologically basic does not imply any form of skepticism about the reality of persons and their identity over time. It seeks merely to distinguish between epistemic criteria and conditions for identity over time. Biological and psychological relations are epistemic criteria for justifying the assumption of personal identity, but they are not truth conditions for its obtaining. Even if one knew everything about a person's psychological and bodily relations, the question of personal identity would remain open. According to the simple view, it is metaphysically possible for there to be two worlds which are identical in their physical and psychological details, except for the distribution of personal identity. Of course, under ordinary circumstances psychological and bodily relations can doubtlessly be considered to be reliable signs for the obtaining of personal identity. Nevertheless this does not justify conflating them with conditions for the obtaining of identity over time because in the light of the simple view there is exactly one such a truth condition, which is the obtaining of personal identity itself. The claim that personal identity is simple implies that it cannot be analyzed because it is not possible to appeal to other entities of a suitable kind for formulating in a non-circular way what personal identity consists in. This does not imply that the simple view is entirely uninformative. The discovery − if it is a discovery − that personal identity is not analyzable is a kind of progress in understanding it. In addition, it should be clear by now why the simple view is mainly a negative thesis in light of which the most 14 georg gasser and matthias stefan C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 15 [1–18] 10.8.2012 10:59AM one can realistically hope to show is that its rivals come with prohibitive costs of their own. Arguments for the simple view may be grouped into arguments from intuition, epistemic arguments and ontological arguments. Arguments from intuition appeal to the intuitive force of the simple view by considering the various counterintuitive problems, such as fission and graduality, that burden the complex view (Chisholm 1976, pp. 110–12; Swinburne 1984, pp. 13–19). The simple view provides a clear answer to the problem of fission: since personal identity is a simple fact, either it obtains or it does not. In the fission scenario the simple view offers three possibilities: P1 is identical with P2 and not with P3, P1 is identical with P3 and not with P2, or P1 ceases to exist and is identical with neither P2 nor P3. Still, however, there is a fact of the matter about which possibility is realized, and therefore there is no need for the simple view to draw on conventionalism to decide whether identity obtains. The same is true in the case of graduality: there must be a definite borderline that demarcates identity from non-identity, because identity, being a simple fact, cannot obtain partly. One peculiar implication of the simple view is that we may well be ignorant about how identity is actually distributed. It may be that we simply cannot tell for certain whether P1 is identical with P2, with P3, or with neither. Though this might be unfortunate, it is an epistemological and not an ontological problem. Human beings are not omniscient, and facts about personal identity in fission and gradual cases might be among the things we do not know. The second type of argument for the simple view appeals to the idea that knowing everything about bodily and psychological properties and their relations would still leave open the question of personal identity, because this question must be answered from a first-person perspective. This type of argument starts from the claim that personal identity is conceivable in the absence of psychological and bodily relations, and moves on to its metaphysical possibility (e.g. Madell 1981, pp. 78–106). Accordingly, there are two conceivable possibilities: first, I might have had a totally different life: for example, living in a different century with a different body and a different psychological makeup. I might, for instance, have lived in seventeenth-century France, been born of different parents and had different memories, intentions, desires and so forth. Nevertheless, so the argument goes, from my first-person perspective it is still conceivable that it is me that lives that life. A similar argument points to changes of body and psychology (see e.g. Swinburne 1984, pp. 22–3). I can conceive of myself as having your body and psychology and of you as having mine. I could also imagine that I might not have existed, but that instead someone else exists Introduction 15 C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 16 [1–18] 10.8.2012 10:59AM with the same life and body that I actually have. If these scenarios really are metaphysical possibilities, then the obtaining of psychological or of bodily relations is neither necessary nor sufficient for personal identity: there is a possible world in which I exist without the bodily and psychological properties that I actually have, and another in which the bodily and psychological properties I actually have belong to another person. It should be noted that this is an argument against the claim that synchronic personal identity is analyzable. However, synchronic and diachronic identity are not different in kind. Rather, they are instances of the same relation as it obtains either at one time or at different times. Accordingly, if synchronic personal identity cannot be analyzed, then we have every reason to assume that diachronic personal identity cannot be analyzed either. There is another epistemic argument closely related to this one. It argues that whether one has a conceptual grasp of personal identity over time has nothing to do with whether one has knowledge of psychological and bodily relations. In other words, we understand clearly what it means for a person at t1 to be identical with a person at t2 without knowing any bodily and psychological criteria for personal identity (see e.g. Nida-Rümelin 2010). This becomes clear on consideration of epistemically underdetermined cases such as fission scenarios: if there is perfect symmetry between P1 and P2 as well as between P1 and P3, then there are no bodily or psychological criteria available to decide which of the two successors at t2, P2 or P3, is identical with P1 at t1. Nevertheless, one can clearly conceive of the difference between the case in which P2 is identical with P1 and the case in which P3 is identical with P1. In the former case P2 would have P1's first-person perspective, whereas in the latter case P3 would have it. There is, according to this argument, a conceptual difference between bodily and psychological relations and identity. As a human person, each one of us is able to take the perspective of P1 and from this viewpoint she knows, independently of considerations about the bodily and psychological relations obtaining between P1 and P2 and P1 and P3, what must be the case for herself as P1 to be identical to P3 in contrast to P2 (or vice versa). What is claimed is that one has a clear conceptual grasp of personal identity independently of one's knowledge of psychological and bodily relations. Nida-Rümelin corroborates her conceptual reflections by arguing that one cannot reasonably give up this understanding of personal identity, since it is deeply rooted in our capacity for first-person thought. She argues that there is good reason to interpret the findings of this conceptual analysis in a straightforwardly realist sense – as long as there are no strong reasons against 16 georg gasser and matthias stefan C:/ITOOLS/WMS/CUP-NEW/3283193/WORKINGFOLDER/GAST/9781107014442INT.3D 17 [1–18] 10.8.2012 10:59AM it. There is a difference between bodily and psychological criteria for personal identity and personal identity itself. Although these epistemic arguments resemble each other, they are distinct: the first claims that it is metaphysically possible for a person to have a totally different psychological and bodily composition and still be herself (and the other way around). The second argument says that, even in epistemically underdetermined cases, we have a clear conception of what must be the case for there to be a definite identity relation. A third type of argument for the simple view is ontological (Lowe 1988; Lowe 1994). It aims to show that persons are simple individual substances, and that as such they do not have proper parts. Entities without proper parts cannot have non-circular identity conditions, for then the latter would have to refer to the identity conditions of those entities constituting the entity in question. This would imply, however, that the entity has parts and as such would not be simple. Without delving into the details of the argument for the simplicity of persons (e.g. Lowe 2000, pp. 15–21; Barnett 2010, pp. 161–74), it suffices to note for present purposes that, once one accepts that persons have no parts, it seems plausible to assume that their identity conditions cannot be spelled out in terms different from personal identity itself. conc lu s i on The section on the simple view completes our presentation of the contemporary discussion about personal identity over time, a relation for which manifold approaches try to account. It is mostly taken for granted that personal identity consists in simpler relations of whatever kind, and that the major task is to specify in detail when personal identity obtains and when it does not. Against the background of this discussion, this volume tackles the more fundamental question first − whether personal identity is analyzable into simpler relations at all. Thus Personal Identity: Complex or Simple? contributes to a better understanding of what it means for human persons to be identical over time. Introduction