by Wesley Cooper
1 Schema and Theory
The Closest-Continuer schema is a theory of identity according to which identity through time is a function of appropriate weighted dimensions. A at time 1 and B at time 2 are the same just in case B is the closest continuer of A, according to a metric determined by continuity of the appropriate weighted dimensions. For example, the metric for a functional artifact such as a ship arguably is equally weighted between the dimension of physical make-up and the dimension of functional structure. So the Ship of Theseus creates a dilemma. Its physical parts are gradually removed at sea and deposited on shore, but they are replaced by new parts that maintain the same functional structure. If the old parts are reconstituted into the same functional structure, is the ship with the new parts the original Ship of Theseus, or does the ship with the old parts warrant that designation? Continuity of physical make-up favors the old-parts ship, whereas continuity of functional structure favors the new-parts ship. There is no closest continuer, given equal weighting, so neither is the original ship.
There might or might not be motivation to apply the concept of identity in the Ship of Theseus, but Nozick thinks there would be ample motivation to apply it if one were a person liable to branching of equally close continuers. This would not be tantamount to death, he proposes, because one would see them through Platonic glasses as the best realized instantiation of oneself. In the Closest Realized Instantiation mode of conceptualization that is applicable to branching, no other instantiated relation of continuity comes closer to the concept of personal identity than branching does. There is no closest continuer. So one should adopt the Closest Instantiated Relation view instead of the Closest Continuer view. The branches would be the trunk person, although the concept of identity would not strictly apply. The motivation, which gets a grip on human beings but not ships, is that by wearing Platonic glasses one does not sink into oblivion.
Nozick's Closest-Continuer schema should be understood as integrated with a theory of specifically personal identity, his theory of the reflexively self-aware self. The Closest-Continuer schema becomes a theory of personal identity through an account of the self as self-creating: through an act of reflexive self-awareness that «entifies» the self, and of self-defining through the self's management of its dimensions, as in weighting them and adding new dimensions. Nozick holds that identity through time is a process of constructive self-synthesis. The self-synthesis begins early in a human life with the development of the capacity for reflexive self-reference, the sort of reference to a given self that only that self can achieve. (Not «that one» or even «this one» but rather something like «this very one».) There is no preexisting I. Rather the I is synthesized or delineated around an early act of reflexive self-referring, an act without a doer in which a doer first comes to exist, a thought without a thinker in which a thinker comes to exist. This process is constructive in that dimensions may then be added. Additions or deletions of dimensions, changes of weightings, and changes in the metric are possible throughout life; there is no requirement that they be the same for any two lives. Each of us is a self-definer.
The Closest-Continuer schema is meant to apply to the identity of all continuants, whereas its application to persons requires recognition of their self-defining nature. Buddhist no-self doctrine has force against the soul-pellet view (Descartes' Thinking Substance, etc.) but not against a person as an ongoing unification of diverse dimensions, as theorized by the closest-continuer theory in Philosophical Explanations, for instance. It is reflexive self-consciousness that constitutes and organizes this unification. He tells a genealogical story about many «bits of consciousness», such as a memory of an earlier conscious event, among which is a bit which is «very special», because it is an awareness of many other bits of «experience and thought, plus an awareness of itself, a reflexive self-awareness». In this way the self begins. Somehow the step gets made from being aware of these bits of consciousness to having or possessing them. They come to belong to the self. The self is built upon reflexivity and appropriation.
Nozick realizes that the Closest-Continuer schema doesn't focus especially on personal identity but rather on a general framework for identity through time. To remedy this defect he offers a theory of the self as arising and defining itself through acts of reflexive self-awareness. This agency is a deep fact about the self, beyond the dimensions that the self selects and weighs. The Nozickean self -- he calls it, with some relish, a Fichtetious object -- does not reduce to these weighted dimensions, for it is the cause of their being its dimensions and being weighted so. Its being a deep fact does not mean that it shares anything more in common with Descartes's Res Cogitans. For instance, Nozick's self is mutable and indeed protean in its possibilities for self-definition; and its reflexive self-awareness, though essential to it, does not imply that it is non-physical. That selfhood for Nozick is a deep fact will become important later, where it will be argued that Parfit incorrectly assumes that Nozick shares Parfit's Reductionism and the attendant denial that personal identity is a deep fact.
Nozick tackles the special features of the self, notably its reflexive self-awareness, beginning at the linguistic level in the use of indexicals like `I' as opposed to proper names or definite descriptions. His account of reflexive self-reference leads to the conclusion that sentences containing `I', `me', `my', or `mine' (I-statements) are derivable from non-I-statements, specifically in terms of the more general reflexive self-referring phrase `this very': `the producer of this very token.' Dismissing as inadequate Kripke-style rigidity or referring to the same thing in all possible worlds, he opts for a feature that a subject of reference has «that is bestowed in that very act of reference». One refers «from the inside» in reflexive self-reference. He proposes that the most adequate linguistic formulation is, `this very reflexive self-referrer'. Nozick's linguistic approach to reflexive self-awareness is neutral with regard to the contentious issue about whether it is a «subjective fact» as implied by the accounts of Thomas Nagel and John Searle, or whether it is an objective physical fact as implied by the various materialist theories. However, Nozick makes explicit his preference for functionalism in Invariances (Nozick, 2001), so the tentative neutrality of his linguistic approach is upgraded into the metaphysical neutrality of functionalism about the mind in his last book.
To be an I or self is to have the capacity for reflexive self-reference. Nozick hypothesizes (it doesn't follow from the linguistic points he's made about how the term `I' refers) that selves are essentially selves, «that anything which is a self could not have existed yet been otherwise.» He explores this hypothesis by asking how reflexive self-knowledge is possible, dispensing with the suggestion that this is a special mode of relating to ourselves as objects, or a dispositional account, or a brute-fact account, or an account in which the self places itself into its reflexive self-referrings. He stalks a better answer by proposing that entification, the classifying which produces entities, «takes place in one fell swoop, rather than in the stages of transverse followed by longitudinal». An informative entification brings together a diversity that it unifies, maximizing the sum of the degrees of organic unity over the entities it classifies. With these remarks about classification in hand, and with some trepidation, he speculates that «the I is delineated, is synthesized» around an act of reflexive self-referring. The entity I comes to exist in the act of synthesis. (He asks at this point, «Can the rabbit be pulled out of the rabbit? .... Can the self really be a Fichtetious object?») A current synthesis does not determine the precise character of a later synthesis, but it can affect what happens later as a (non-binding) precedent, and «thereby syntheses at different times can mesh into a larger continuing entity,» a currently synthesized self including past self-stages in accordance with the closest continuer and closest predecessor schema. The idea that reference is to an independently preexisting and bounded entity is an illusion. Nozick's Fichtetious theory explains why selves are essentially selves: they are synthesized by reflexive self-reference «and around it qua something having it». He acknowledges the counter-intuitiveness of speaking of acts without independently existing agents, but he juxtaposes this with our willingness to hold that Descartes can reach only «thinking is going on» and not «I think».
Nozick embeds the Closest-Continuer theory in a broader view of how philosophical concepts like personal identity can be structured.
1. Intrinsic Abstract Structural. A concept C's holding means that an abstract structural description «involving only monadic predicates» holds. Example: Personal identity is is an intrinsic feature of a person, the soul.
2. Relational. X falls under concept C just in case X stands in a certain relationship R to «another, sometimes earlier, thing of a specified sort». Example: Personal identity as analyzed in terms of spatio-temporal continuity, or psychological continuity. (Relational rather than monadic predicates are required by 2.)
3. Closest Relative. To the relational view is added the condition that nothing else is as closely related under R to that other thing. Example: The closest continuer theory of personal identity. (Quantification is required by 3.)
4. Global. Something satisfies C only if it stands closest in R to a specified y, and also is a part of any wider thing that stands closer in R to y than do other comparably wide things. Example: «Thus, one might hold that any acceptable theory not only must fit the evidence as well as any alternative theory of the same phenomena, but also must be part of any wider theory of more inclusive phenomena that fits the evidence more closely than any other theory alternative to it.» (Quantification over wider entities is required by 4.)
5. Closest Instantiated Relation R'. This adds to 1-4 that there is no other instantiated relation R' which comes closer to the concept C than R does. Example: In cases where there is no closest continuer R but rather a tie R' such that the concept of personal identity does not strictly apply, one should (in the Platonic mode; see above) adopt the Closest Instantiated Relation view 5 instead of the Closest Continuer view 3. (Quantification over relations is required by 5.)
The integrated Closest-Continuer theory does not imply that hypothetical cases of cloning or branching, familiar in the literature of personal identity, are tantamount to death when the branches are equally close to the originating or «trunk» person. This is because one can view one's continuation through «Platonic glasses» as the best instantiated realization of one's identity, even if the concept of identity does not strictly apply, in order to keep oneself from sliding into oblivion. This same motivation is at work in the Closest-Continuer theory to bind reflexive self-awareness at different times into a continuant person. In this latter case the concept of personal identity does «strictly apply» according to the Closest-Relative mode of conceptualization, in contrast to cases of Parfitian branching. But in both kinds of case Platonic glasses are at work. In normal human life Platonic glasses justify knitting the momentary or episodic self-aware selves into a continuing person, and in the branching cases the original person's caring about the branches just as he cares about himself, in such a way as to see himself as continued in the branches, is a rational response to an extraordinary circumstance.
The integration of the Closest-Continuer theory with Nozick's theory of selfhood is overlooked when Parfit, for instance, classifies Nozick as a Reductionist and presents both Nozick and himself as Closest-Continuer theorists for normal human lives. He views the two of them as ranged against the traditional theorists about personal identity who regarded personal identity as a «deep fact». Parfit doesn't think so. All that matters in personal identity is present in the survival that occurs in hypothetical cases of branching or cloning, in which the concept of identity does not apply, since the branches are definitely different people and therefore cannot, by the transitivity of identity, be one and the same with the person from whom they branched. If a=b and a=c then b=c, by transitivity. But branch 1 (b) and branch 2 (c) are not the same person, so the original person (a) can't be identical to either.
For Parfit these hypothetical cases reveal the triviality of personal identity. Everything that matters about a person's experience can be fully described without referring to the person at all. He is critical of Nozick's attempt to salvage the concept of personal identity in these hard cases by seeing the forked continuers through «Platonic glasses,» as close-enough real-world instantiations of the original person to be (all of them) that person, despite the fact that the concept of personal identity does not strictly apply. Parfit deems this salvaging to be a conflation of theoretical and practical rationality. It may be practically rational for the original person to believe this in order to escape oblivion, since otherwise forking would mean death, but it is not theoretically rational. The truth is, on his view, that the original person no longer exists after forking or branching (and yet everything that matters is there).
Parfit misleads when he classifies himself as a Closest-Continuer theorist like Nozick, except for the hypothetical cases that reveal the triviality of personal identity. Nozick is not a Reductionist in Parfit's sense alluded to above; he does not hold that a person's experience can be fully described without reference to the person at all. This is evident when the Closest-Continuer schema is integrated, as it should be, with the theory of the reflexively self-aware self. The self guides the application of the schema to himself, so to speak, assigning weighted dimensions to himself. Selves are different from other continuants in this respect. A ship for instance is assigned the weighted dimensions appropriate to it by us, those who created and apply the concept ship. Although a self operates with a concept of a person that has been externally created and has rules of application that forbid a self to self-define as, say, a number, the imposed framework leaves much leeway for partial self-definition in the assignment of dimensions and weights.
Also Parfit's use of the distinction between theoretical and practical rationality is invidious, given the theory of rational belief that Nozick developed in The Nature of Rationality after publication of the Closest-Continuer theory in Philosophical Explanations, in order to address problems like this. It introduces a practical element, symbolic utility, in its decision-value account of rational belief. The decision-value of believing that the branched persons are oneself may be sufficiently high to be rational, given the symbolic utility of that belief. This is what wearing Platonic glasses in such hard cases would amount to. On this reading, Platonic glasses are also worn in normal cases, in order to forge a continuing personal entity between temporally spread-out personal acts. One rationally believes oneself to continue between acts of reflexive self-awareness because decision-value validates this belief. That is, the belief is justified by the weight of the belief's symbolic utility to the reflexively self-aware self.
What Parfit dismissively calls the «deep fact» about personal identity is the existence of an irreducible subject of experience, a fact about the `I' that has experience, a reference to a person that cannot be eliminated in a full description of that experience. This is what Parfit's Reductionism denies. Historically the Deep Self has been understood to be transcendent to experience, as in Kant, or imminent to experience, as in Descartes. It has been observed however that Descartes' Self -- the I of his cogito, «I think therefore I am» -- is not a valid inference. From «I think» he is only entitled to infer «Thinking is going on.» On this reading Descartes' Self is transcendent from experience, just as Kant's transcendental unity of apperception.
However, it is arguable that an interestingly stronger inference can be drawn from «I think», namely, « This thinking is going on.» After all, the cogito can be performed by two or more people at the same time, but it is meant to pick out only one thought. Moreover the demonstrative is meant to pick out not the thought of the second or third person who performs the cogito, but this very thought. So the interesting replacement for the cogito becomes: «This very thought is going on.» Let this thought be termed an act of reflexive self-awareness. The thought is aware of itself in the intimate way implied by this very thought. Now suppose that this act somehow bootstraps itself into a subject of thought and other experiences. It entifies itself, as Nozick says. This subject is imminent to experience in acts of reflexive self-awareness. It is a reflexively self-aware self. This very self, WC, is writing this very sentence, which began with the word tokens «This very self».
Let this Nozickean self as developed so far be termed the Real Self. The Real Self may be picked out by a physical description, such as a description of the state of the nervous system that subserves the Real Self and its experiences. But reference to the self is not eliminable in favor of such a description, any more than a sculpture of a man riding on a horse is replaceable by a molecular description of the marble from which it is sculpted. The Closest-Continuer theory, when it applies to a person, is a theory about the identity conditions of a Real Self. It follows that Nozick is not a Parfitian Reductionist about personal identity. The Real Self is a «deep self», though not of Descartes' or Kant's varieties. There is rather a kinship with William James's seminal theorizing about the self in The Principles of Psychology.
It follows furthermore that Parfit cannot adhere to the Closest-Continuer theory for normal cases of personal identity, at least in the sense that Nozick intends. For Nozick intends the Closest-Continuer theory, when it is applied to persons, to be a theory of the identity conditions of the Real Self. More particularly, the Real Self is self-defining. The self-definition begins with the self-as-act entifying itself as a continuant and continues with its ascribing to itself dimensions, such as having a human body, to which it assigns weight. Personal identity cannot be reduced to such-and-such weighted dimensions, not only because the dimensions and their weights are liable to change as the process of self-definition continues, but also because a listing of the weighted dimensions would omit the crucial fact that they are precisely self-ascribed and self-weighted.
Parfit notes that Nozick's pattern of concern in cases of branching might be defended by reference to the Platonic mode of caring about something, in which «we see the world in its aspect of realizing what is beyond it, we see and can respond to its glimmerings of something finer which shine through.» As Nozick admits, viewing clones in this way involves «an unrealistic overestimate of actuality, a seeing of it through Platonic glasses», as opposed to the alternative of making «a more realistic assessment of things, seeing things as they are in themselves.» Nozick objects to this alternative that it «makes one a prisoner or a victim of the actual world, limited by the ways in which it falls short, by how it happens to be ...». (Nozick 1981, 67)
Parfit rejects this defense. He grants that, given the distinction between theoretical and practical rationality, Nozick's pattern of concern is defensible, but «theoretically irrational».
Parfit's distinction between theoretical and practical rationality is inadequate to articulate what is rational about believing that one's branching continuants are, each of them, oneself. Nozick's decision-value account of belief in The Nature of Rationality, which includes symbolic utility as well as credibility value in a decision-value formula for rational belief, justifies this belief about the branches, viewing them through Platonic glasses. The credibility value of projecting oneself into the branches is sufficiently high, given the great similarity that each branch has to oneself in terms of their weighted dimensions, including processes of self-definition that are continuous with the original person's.
Nozick supports the side-constraint view against classical utilitarianism and the idea that only felt experience matters, by introducing the famous Experience Machine thought experiment. It induces whatever illusory experience one might wish, but it prevents the subject from doing anything or making contact with anything. There is only pre-programmed neural stimulation sufficient for the illusion. Nozick pumps the intuition that each of us has a reason to avoid plugging into the Experience Machine forever. This not to say that «plugging in» might not be the best all-things-considered choice for some who are terminally ill and in great pain, or an amusing pastime for an afternoon. The point of the thought experiment is to articulate a weighty reason not to plug in permanently, a reason that should not be there if all that matters were felt experience. Nozick's Experience Machine is importantly different from David Deutsch's more attractive conception of a virtual-reality generator, which leaves intact «internal experience» such as belief, desire, and choice, altering only «external experience» such as input to the various sensory modalities. (Deutsch 1997) Nozick's Experience Machine programs both internal and external experiences, so that free will and even simple self-directed thought and action are out of the question.
One's agency ceases with the act of plugging in to the experience machine, and nothing like that agency and the consequent experience goes on from there. Not only is the content of experience determined by the programmer of the machine, but also the process of self-definition is usurped. Having chosen to plug in to the «politician» experience machine, the virtual politician's choices afterwards are simply those that were designed by the programmer. The erstwhile self-definer is slumped in a chair, a blob serving as a vehicle for simulated experiences. Clearly, wearing Platonic glasses is quite dissimilar to plugging in to the Experience Machine.
The Platonic-glasses diagnosis is that one ought to care about each of the equally close clones as one cares for one's single future self in the real (non-branching) world, because the clones would represent the closest real-world instantiation of the concept of personal identity, close enough to be oneself despite the violation of the logic of personal identity. This care might express itself in arranging that one's clones share equally in one's wealth, for example. The imperatival `ought' here should probably give way to the permissive `may': one is entitled to think of one's branches as continuations of oneself, other things being equal, to the extent that they enhance the meaning of one's life, prevent one's sinking into oblivion, enable one to transcend the limits of the current self, etc. The decision value of believing in this continuation may be high enough to make it rational, because of the symbolic utility of the enhanced meaning. This permits as consistent with self-interest the choice, when confronted with the prospect of branching, to donate one's wealth to a favorite charity. One weighs one's uniqueness so heavily that one's care can't extend to the branches.
The Real Self is episodic, because episodes of reflexive self-awareness are episodic, broken up by sleep and indeed, under the probing of skepticism, broken up by the passage of time from one «now» to another. Entifying these episodes into a continuing person is a step that is justified by viewing the episodes through Platonic glasses. Just as there is symbolic utility in believing that one is continued by branches, rather than one's sinking into oblivion when branching occurs, so too the reflexively self-aware self at time t prefers to see itself as continuous with earlier and later reflexively self-aware selves. Believing in the real self as an entified continuant has symbolic utility for the self-at-a-time, enough to make it rational, by the lights of a decision-value account, to believe in the Real Self. We do this as a matter of course, and the DV account theorizes it. Pathological cases are imaginable in which prudence fails to extend beyond a day. This is not because a soul-pellet disappears at the end of the day, but because the subject's utility profile today is not linked to a subject tomorrow, as it is in the normal case by the symbolic utility of seeing oneself today as continuant with a subject tomorrow, and conversely. This «conversely» clause may not be applicable in born-again psychologies, in which there is strong motivation to see oneself as discontinuous with a previous self.
Nozick's view has affinities in many respects with William James's discussion of the self a century previous, in The Principles of Psychology.
Less reliant on metaphor, Nozick's account of entification, including the decision value refinement of it, is doing the same work as James's «legal title» handed from one herdsman to the next. James also relies on a metaphor of a herdsman branding cattle to talk about the present self's relationship to its past, and explains the metaphor with another, the idea of a perceived «warmth and intimacy» that the self feels.
In a similar vein Nozick introduces principles that govern entification. One such principle, which integrates his theory of personal identity with his theory of value, recommends defining yourself so as to increase your value, which he takes to be marked by organic unity. This principle could account for the born-again murderer, who despairs of creating an organic unity with his former self, preferring instead to «start over» in order to track value in his selfhood. The desire to rise above the moment, to avoid oblivion, expresses a related principle: Entify oneself so as to avoid oblivion, ceteris paribus. The person who weighs his uniqueness so heavily that he cannot wear Platonic glasses with reference to his future branches, in the Parfitian scenarios, takes advantage of the ceteris paribus clause. Nozick would not do so, and he presumes that his readers as well would wear Platonic glasses in such extraordinary cases, doing such things as dividing their wealth equally among the branches rather than giving it away.
A principle of rational prudence stems from the organic-unity principle, since a life united by treating each moment of one's life as of equal weight has more value-as-organic-unity than a life lived for the moment. What Rawls calls the Aristotelian principle also derives from tracking value in one's life. There is a tendency for human beings to seek to develop their more complex abilities. A principle emphasized by Nozick is precedent, which guides one towards choices that cohere with one's previous choices, which set parameters which set limits to what one can choose currently, without causing any particular choice. The model for this principle is stare decisis in the common law.
Refusing to wear Platonic glasses, Parfit reports that before he had formulated his Reductionist view he had «seemed imprisoned in myself»; his life seemed like a «glass tunnel».
Discounting for some rhetoric, this is a fair statement of difference between Parfit, refusing to wear Platonic glasses, whose life goes better by believing trivializing Reductionism, and other people, who believe in significant personal identity through time, and who would believe that they were continued by multiple equally-close branches, were branching to occur.
In a thought-experiment about «the Combined Spectrum», in which there are gradual physical and psychological changes in a person until he becomes more like Greta Garbo than himself, Parfit writes,
Parfit concludes his critique.
Although there is no general answer to the sorites question raised by the Combined Spectrum, individuals could give their own answers, possibly different from person to person, about where the cutoff point is. In this a person would be exercising his right, as a self-defining Real Self, to determine the metric of «close enough» in judging whether a continuer is close enough to be him. Self-definition is an addition to the closest-continuer theory that Nozick employs when that theory is applied to persons. Persons are self-defining entities, unlike other continuants through time, such as clubs and chairs. That the cut-off point might seem arbitrary from an external point of view is neither here nor there. The individual has a pressing reason to draw the line, namely the subjective utility of continued existence, which motivates a choice that would otherwise be arbitrary. Drawing the line here can be compared to choosing whether to provide for one's branches or give one's wealth away when the prospect of branching is nigh. How much weight must one attach to uniqueness to give the gloss of rationality to the choice the latter choice? There is no hard line. The subject has to make the decision by his own lights. The sorites problem reduces to an existential one.
Emotions and personal relations affect the decision value of a candidate hypothesis for belief. On the basis of the same evidence that is available to others, a mother whose son is on trial for murder arrives at a different belief from them, that her son is innocent. Nozick defends the rationality of the woman's belief on the grounds of his decision-value account, which allows the symbolic utility of believing her son innocent to have weight and, given that the credibility value of the the hypothesis of his innocence is sufficiently high, to lead her rationally to the belief in her son's innocence. He employs the following rule: «Believe a statement h if there is no alternative statement incompatible with h that has a higher credibility value than h does, and the credibility value of h is high enough, given the kind of statement that h is, and the expected utility of believing h is at least as great as the expected utility of having no belief about h.» (Nozick 1993, 89) He translates this into his decision-value account, which maximizes decision-value as the weighted sum of causal, evidential,and symbolic utility -- as follows: «Believe (an admissible) h only if the decision-value of believing h is at least as great as the decision-value of having no belief about h.» (Nozick 1993, 89) Nozick's rule for rational belief is closely related to a strategy employed by William James, to which I now turn.
Nozick's example fine-tunes the Incline-the-Beam strategy employed by James in his defense of contra-causal free will in the chapter «Attention» from The Principles of Psychology. What he calls there the «effect theory» is the view that attention is always the effect of an antecedent cause; it represents a deterministic outlook. He opposes to it the `cause theory' according to which attention is an `original force'; it represents contra-causal free will. He argues that the evidence for determinism is not so compelling that it blocks his right to believe in contra-causal free will, a belief that makes better sense of his life than the effect theory. Dismissing Occam's Razor (parsimony) as adequate to reject the `cause theory', he characterizes the `original force' deepening and prolonging the stay in consciousness of innumerable ideas which would otherwise fade away more quickly, continuing:
When a person is continued uniquely by one person in the continuum who is «close enough» by the original person's metric, Incline-the-Beam favors continued personal identity. When there is branching and many continuants are close enough, the original person should wear Platonic glasses and divide his care equally over them. The law might give such continuants a special legal status, as bersons who are entitled to equal shares in the original person's property. (Never mind for now the issues that would arise about property that is not divisible.) When such branching includes continuants who are not close enough, the original person's care is not extended to them. This might be reflected for instance in wills that are designed to cope with such eventualities, according to which continuants deficient on some heavily weighted dimension are not to be regarded as bersons. As for those continuants who are on the fringe of the distinction between bersons and non-berson continuants, such cases could be decided by the courts. By definition, the original person would not know what to say about such continuants. So the decision could be made for social reasons in favor of regarding the marginals as bersons, or not. A line could be drawn by the courts, with the degree of arbitrariness that affects judicial discretion, sorting continuants on one side or the other of the classes of berson and non-berson. The legitimate scope of judicial discretion is not unlimited. Where there are only two bersons, for instance, and one has all the weighted dimensions of the person's identity and the other has very few, a judicial decision in favor of the the latter would be a mistake. To avoid such mistakes persons would have an extra reason to create wills that filter bersons from non-persons according to their metric.
Philosophy in Nozick's explanatory mode may hitch its wagon to a scientific star and see where that goes. Nothing like a proof will come of it, but an interesting possibility will have been explored. That is the intent in what follows. Some implications of no-collapse interpretations of quantum physics are explored, especially with reference to the question whether Parfit's or Nozick's account of personal identity is better suited to describe what happens when a person branches into parallel worlds.
Bersons exist in one world, the world in which they branch from a person, whereas many-worlds copies of a person exist in parallel worlds. They are similar however in that the case for wearing Platonic glasses with respect to bersons also applies to a person's copies in other worlds. Many-worlds dispenses with the «collapse of the wave function» in the orthodox interpretation, in which the various probabilities for a quantum superposition are unrealized except for the one that survives the collapse: there is just one future you, for instance. On many-worlds however there is no collapse. the various probabilities are actually realized. There is many-worlds branching, creating many copies of you in other worlds, in proportion to the prior-to-branching probability that your future would take that direction. One proponent of the «no-collapse» theory of quantum physics (as David Lewis dubbed it (Lewis 2004)) is quantum physicist David Deutsch, who seems to favor Nozick's «Platonic glasses» approach to branching. There are «multiple identical copies» of me in the multiverse. Which one am I? Deutsch answers, «I am, of course, all of them.»
The no-collapse theorist Lewis assumes too that one continues through one's branches. That is why he finds the prospect of quantum immortality so terrifying.
The Parfitian answer to the question about the branches would be, «The concept of personal identity doesn't apply.» This answer seems to be favored by several no-collapse theorists. (Wallace 2002, 22) But this creates an inconsistency, because they continue to refer to the branches as the same person, and they take issues like quantum immortality seriously, as Lewis does, when on Parfit's view there is no cause for concern, since the «immortal» won't be you.
Lev Vaidman writes,
Note that Vaidman in this passage is committed to both
1.There is more than one person Lev after a given quantum experiment,
2.There is no good answer to the question, «How many Levs are there after a given quantum experiment».
This seems flatly contradictory. Vaidman can have 1 on Nozick's «Platonic-glasses» account, or 2 on Parfit's reductionist account. This passage is instructive because it reflects common practice among MWI theorists, of paying lip service to Parfit's position, presumably because they accept his argument that the concept of identity does not apply in cases of branching, while speaking as though the concept of personal identity continued to apply when talking about the branched copies of oneself.
Copies need not be strictly identical in the sense of the identity of indiscernibles relativized to universes: All of my copies see a coin spinning in a coin toss, but an instant later half my copies see `heads' come up, the other half see `tails'. A distinction between copies, versions, and variants is at work here. Variants of me need not see the spinning coin. Versions of me see it though some of them see `heads' and some `tails'. Multiple copies of me all see the spinning coin. So if I toss heads and believe that I could have flipped tails, some version of me actually tosses the coin and sees tails. Variants of me don't flip the coin at all, underwriting the subjunctive, `I could have refrained from tossing the coin'. The generic sense of `copy' that includes copies in the narrow sense but also versions and variants may be singled out by capitalizing: my me-Copies comprise me-copies, me-versions, and me-variants. Not included are `me-outliers' such as the person who, instead of flipping the coin or refraining from doing so, shoots everyone in sight. That is not something I could have done. The transworld structure that is Me -- the set of me-Copies -- excludes the me--outliers.
Among philosophers Lewis is notable for associating no-collapse theory with the prospect of unwelcome immortality, writing «You who bid good riddance to collapse laws should shake in your shoes. Everett's idea is elegant, but heaven forfend it should be true! Sad to say, a reason to wish that it is false is no reason to believe that it is false.» (Lewis 2004, 21) He argues that in in life-and-death cases (like Schroedinger's Cat) we need to adjust the intensity rule, which departs from orthodox collapse interpretations by giving up chances of possible outcomes of a collapse in favor of the intensities of the possible outcomes. Chances correspond to the pre-collapse squared amplitudes of the branches, only one of which will become real. No-collapse theorists on the other hand think of their non-collapsing branches as having differing `intensities', again corresponding to the squared amplitudes of those branches.
The adjustment in the intensity rule that Lewis proposes is to apportion all our expectation to the branches where we survive. When we have life-and-death branching, first discard all the death branches, because there are no minds and no experiences associated with death branches. Only then divide expectations of experience between the remaining branches in proportion to their intensities. Since all causes of death are probabilistic, there will always be a branch in which you survive. Inevitably however you will end up a lonely geriatric wreck. Note that Lewis wears Platonic glasses in his description of the modified intensity rule. You are on all those branches that link your current self to the future wreck. That is why quantum immortality is a bad prospect for you.
David Papineau is notable for his confidence about the no-collapse theory. He sees no need to adjust the intensity rule. We can simply proportion expectations about the future directly to the intensities. He is serene about giving up chances in favor of intensities, though he prefers to think of chances as being theoretically reduced to intensities rather than eliminated and replaced by intensities. He doesn't share Lewis's concern that the intensity rule is unjustified as well as relatively new, observing that the chance rule can't be justified either, as shown by the history of attempts to justify induction since Hume.
Lewis thinks there is another reason why the lack of justification counts against the intensity rule more than the chance rule, namely its adjusting concern about branches according to their intensities, instead of treating them all equally: «All your future selves, on all your branches, are equally real, and equally yours. You will have experiences of all of them. Do they not deserve equal weight regardless of their intensities?» (Lewis 2004, 15))
And although both collapse- and no-collapse theories track probabilities of branchings, only the no-collapse theorist cares about all the branches, in Papineau's view, whereas the collapse-theorist cares only about the branch that becomes actual. If we really want what benefits one's post-collapse actual successor, isn't it odd that the collapse-theorist would adopt a principle that counsels maximizing benefit over all possible outcomes? As Papineau writes,
By contrast the no-collapse theorist has no problem on this score, since one will be succeeded by all one's possible successors, weighted by their intensities. Among one's successors is the miserable immortal, but this prospect is vanishingly small on either no-collapse or orthodoxy. There are far greater expectations of a normal life. Papineau defends this parity by rejecting Lewis's adjustment to the intensity rule, so that no-collapse can follow orthodoxy in assigning normal expectations to futures in which one is dead, in proportion to their intensities whether or not those futures contain one's live successors. He favors formulating the intensity rule in terms of expectations of what will happen whether experienced or not, rather than in terms of expectations of experience. So he does not follow Lewis in pruning dead branches, so to speak. He puts the point like this.
Papineau concludes that no-collapse theory is as «healthy as could be» with regard to empirical confirmation, and that experimental evidence leaves «no room for anything except highly ad hoc alternatives.» In all circumstances simple enough for the interference effects that demonstrate non-collapse, like the two-slit experiment, those effects are detected. Furthermore the ad hoc accounts that posit collapse, under conditions too complex to test for interference, are «strikingly less elegant than Everett» and also require rejection of special relativity and the conservation of energy. (Papineau 2004, 168)
Lev Vaidman recommends what he calls the Behavior Principle, «We care about all our successive worlds in proportion to their measures of existence,» which avoids Lewis's problem: «I should not agree to play quantum Russian roulette because the measure of existence of worlds with Lev dead will be much larger than the measure of existence of the worlds with rich Lev alive.» (Vaidman 2002) However, he accepts at face value, unlike Papineau, the collapse theorist's care about possible future selves according to the probability of their occurrence. He doesn't see an advantage for MWI on this score, only equal care differently explained. Like Papineau though he is bullish about MWI.
When human beings become agents through reflexive self-awareness, they express their agency by having reasons for acting, to which they assign weights. Choosing the dimensions of one's identity is a special case, in which the assigning of weight to a dimension is partly self-constitutive. But all acting for reasons is constitutive of the self in a broader sense, namely, by its shaping one's character and personality in a manner analogous to the shaping that law undergoes through the precedent set by earlier court decisions. Just as a judge does not merely apply the law but to some degree makes it through judicial discretion, so too a person does not merely discover weights but assigns them; one not only weighs reasons but also weights them.
Set in train is a process of building a «framework» for future decisions that we are «tentatively committed to». The life-long process of self-definition in this broader sense is construed indeterministically by Nozick. The weighting is «up to us» in the sense that it is undetermined by antecedent causal factors, even though subsequent action is fully caused by the reasons one has accepted. He compares assigning weights in this deterministic sense to «the currently orthodox interpretation of quantum mechanics», (Nozick 1981) following von Neumann in understanding a quantum mechanical system as in a superposition or probability mixture of states, which changes continuously in accordance with quantum mechanical equations of motion and discontinuously via measurement or observation that «collapses the wave packet» from a superposition to a particular state. Analogously, a person before decision has reasons without fixed weights: he is in a superposition of weights. The process of decision reduces the superposition to a particular state that causes action.
This picture might better be understood as about unpredictability rather than indeterminism, since the currently much-discussed many-worlds interpretation of quantum mechanics is deterministic. (At any rate it's probably an overstatement to regard von Neumann's wave-packet-collapse view as the current orthodoxy.) Then the unpredictability might be due to the fact that the background field of more or less inchoate reasons that the agent fixes is insufficient by itself, without that fixing, to determine action. But the process as a whole would be deterministic. The telling analogy, as suggested above, would not be to the indeterminacy of quantum mechanics but rather to judicial discretion: A judge does not in «hard cases» discover the law but rather makes it, according to Hart's theory of judicial discretion; similarly the agent in character-forming decisions does not discover his reasons but rather fixes their weight. Neither judicial nor personal agency need be construed indeterministically. (Bratman 2002) On the other hand, the judicial model at the psychological level and quantum indeterminacy at the lower level of the brain's operations could combine to provide a contra-deterministic theory of free will that isn't liable to the objection that it renders free will random. This was Nozick's intent.
Many of us think that we could have done otherwise, just as circumstances were when we chose to act. This doesn't consort well with another belief that we are likely to have, that determinism (at some level, such as the neurophysiological) is true. One way of relieving the tension between the two beliefs is offered by the Everett or many-worlds interpretation of quantum physics, introduced in the previous section. The self is distributed over many worlds, in virtue of which the subjunctive `I could have done otherwise' is true. It's true because I actually do otherwise in another world. David Lewis's modal realism makes a similar claim and is viewed by Deutsch as akin to the many-worlds hypothesis. However, Papineau puts this comparison in perspective.
Return to Parfit's Combined Spectrum of changes in me. Insofar as the changes are physically possible, they are present in the multiverse. In addition to copies of me in worlds close or similar to this one, there are versions of me in remote worlds. In addition to the me-copy that writes this sentence, there is the me-version that is a thinking beetle (if packing my psychology into a beetle body is a physical possibility). I belong to the Distributed Self that includes the various Real Selves in the sundry worlds as copies or instantiations. The Distributed Self is a trans-world set of Real Selves, whereas a Real Self is a particular in a particular world. As for which actual changes in me in this world are consistent with my continuation, that is for me (my Real Self) to decide. Different Real Selves in my Distributed Self may decide differently. After all, I am free.
Nozick favors a version of James's «cause» theory of attention, which he calls originative free will, as opposed to the compatibilist free will favored by determinists (which James labeled «soft determinism»). Nozick speculates that the brain is a quantum computer, in effect, enabling originatively free choices according to a «precedent» model of the relationship between current and past choices, as described above. Bratman has shown how the appeal of this model remains on a compatibilist or «soft determinist» view. What doesn't survive in Bratman's transfer is the intuition that many people have, that they could have done otherwise when they chose such-and-such, just as circumstances were. This seems to require something like Nozick's reference to quantum phenomena. John Searle for instance, in order to save the intuition, has recently converted to a defense of free will as underlain by quantum phenomena in the brain.
However, there is a another way of saving the intuition which is compatible with a deterministic universe, and it is arguably required in general, in order to justify counterfactual inferences about oneself and others. This is the Everett or many-worlds or multiverse interpretation of quantum physics, which justifies the subjunctive `I could have done otherwise' by reference to a parallel world in which I actually do otherwise. The `I' in question is a kind or set rather than a particular, and the particulars of that kind are called «copies» of the person. If this is correct, then Reductionism is doubly repudiated. Not only is there a Deep Self, namely the reflexively self-aware self and its construct, the Real Self, but also there is a Distributed Self, the self as distributed over many worlds.
The Deep Self rescues after a fashion the intuition about free will, namely, that, on everyday occasions of free action, just as circumstances were, one could have chosen otherwise. For one did do otherwise in other universes; members of your copy consort did do what you-copy did not. This is different from the rescue anticipated by the idea that one's brain is a quantum machine that creates moments of indeterminism that enable free choice. On the many-worlds view the brain may be a classical computer processing information according to deterministic laws that hold complete sway in the multiverse (the many worlds as a whole). But one is still free; one could have done otherwise on many an occasion; for one did do so, thanks to one's copies in other universes. One's Distributed Self was free, or one's Real Self was free qua member of a Distributed Self.
The Distributed Self is somewhat appealing as a solution to the problem of rescuing the free-will intuition in a deterministic universe. Those who accept compatibilism or «soft determinism» don't take seriously the intuition, so they won't recognize a problem. They will «analyze» I could have done otherwise in a compatibilist formula like I would have done otherwise if I had so chosen, or perhaps abandon analysis as doomed to failure and simply reject the intuition. Those who see a problem will reject the formula, insisting that it leaves out one's freedom, just as circumstances were when one chose as one did, to choose otherwise. A many-worlds metaphysics offers a solution. The many worlds as a whole make up a system deterministically governed by natural law, but in any given universe a person is probabilistically related to his or her copies in other worlds. Some of them do otherwise, supporting the intuition that one could have done otherwise.
In addition to appealing to the free-will intuition, the multiverse metaphysics also appeals to what might be called the distributed-care intuition: when you are deliberating over whether to do a or b, you care about your future whether you decide one way or another. But on a single-world metaphysics the course not taken is a mere unrealized possibility. It would counsel therefore that one's care should be focused exclusively on one's actual self, the possibility that is realized by the collapse of the wave function. If this is wrong, as it is on Papineau's account summarized above, it is because the action one chose has a reality greater than mere «unrealized possibility». The Everett interpretation articulates this reality: one cares about a copy of you that performs that action, the action you passed up. Otherwise your pattern of care would be irrational, as would your belief that you categorically could have done otherwise on occasions of putatively free action.
Given a multiverse or many-worlds outlook, basic ideas about the universe are either vindicated or undermined by the multiverse hypothesis. For instance, counterfactual conditionals refer to nearby parallel worlds when they stipulate what a thing would do under conditions that do not actually obtain; one-worlders implicitly collapse what things can do into what they actually do. Consider a coin toss. The identical worlds in which I (copies of me) see it spinning become branched; in fifty-percent of those worlds versions of me see `heads', and in fifty percent they see `tails'. This actual distribution of worlds is what licenses the inference, about this world, that if the coin hadn't turned up `heads' it would have turned up `tails'. Instead of its being a basic fact that my observing `heads' collapses probabilities into an actual outcome of the coin toss, those probabilities are grounded in actual universes in which both outcomes are represented.
Knowledge is a trans-universe structure, as one might expect because knowledge supports counterfactual implications, as revealed for instance in Nozick's tracking account of knowledge. Nearby parallel worlds are united by a common history of knowledge acquisition, which may be spelled out in broadly Popperian, conjecture-and-refutation terms. The resulting epistemological niche lends stability and reliability to knowledge in each universe. Moral knowledge is a part of this niche. Life is a similar trans-universe structure, molded by natural selection rather than rational criticism. What distinguishes genuine replicating DNA from junk DNA is that the former but not the latter is representative of a niche of replicators that extends across worlds. Indeed personal identity is inseparable from such a niche, which Deutsch picks out with the word «copies». A person is a set of copies in nearby parallel worlds. This comes out in his analysis of free will: `I could have chosen otherwise' is analyzed as `Other copies of me chose otherwise'. And in the denouement to a dramatic chapter that rehearses interference experiments from a multiverse viewpoint, he writes of his copies, «Many of those Davids are at this moment writing these very words. Some are putting it better. Others have gone for a cup of tea.» (Deutsch 1997)
Not only are persons spread out through worlds, but they, like everything else, are quantized through time in any given world. Time is a series of moments, and a person who exists at a moment exists there forever in four-dimensional space-time, rather than being transformed continuously through the flow of time. Such change and flow are mythical, Deutsch argues. The argument doesn't strictly require the multiverse hypothesis, but rather space-time physics since Newton has implied that the openness of the future is an illusion, and consequently causation and free will are illusions. What the multiverse adds is a reduced account of common sense's ideas of causation and free will. Although an effect can't be changed by its cause, the counterfactuals that causal statements support are true. If the cause hadn't occurred, the effect would not have occurred. For the multiverse, which is «to a first approximation» a very large number of co-existing and slightly interacting space-times, includes universes in which the cause doesn't occur and its effect doesn't occur. And although the «me-copy» in this space-time could not have done otherwise, there are me-copies in other worlds that actually do otherwise. There is a branching of these me-copies that validates my sense that my future is open, in contrast to space-time physics. However, the open future of common sense is a myth. There is no flow of time dividing the actualities of the past from the unactualized potentialities of the future.
Since «other times are just special cases of other universes», the temporal granularity of personhood through time is a special case of being spread out through worlds. In addition to one's identically time-stamped copies at a moment across parallel worlds transversely, there are the differently time-stamped copies across parallel worlds longitudinally, linked by natural law so as to give the individual's experience of one world and a continuous self. The implications for the theory of personal identity are not yet clear, but I have argued that endorsing Parfit's Reductionist view would be premature. Your `copies' in parallel worlds, like branching bersons in this world, are close enough to you to be you, even though the concept of personal identity does not strictly apply.
University of Alberta
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