- Nozick advances a general view about all judgements of identity over time. To be the same thing as some past thing is to be that thing's closest continuer. Nozick's view is Reductionist. He claims that there can be various kinds of continuity between some past person and various present persons. The present person whom we judge to be this past person is the present person who has the greatest continuity with this past person. On this view, the fact of personal identity over time just consists in the holding of such continuities. It does not involve any Further Fact. And Nozick explicitly compares personal identity with the identity over time of a certain group of philosophers, the Vienna Circle. This is like my comparison with the history of a club.
- Though Nozick's view is in these ways Reductionist, he rejects the version of Reductionism that I defend. He writes:
One philosophical approach to a tangled area of complicated relationships of varying degree, rather than trying to force these into somewhat arbitrary pigeonholes, rests content with recognizing and delineating the underlying complicated relations. Concerning personal identity, it might say that future selves will have varying degrees of closeness to us-now in virtue of diverse underlying relations and events, such as bodily continuity, psychological similarity, splitting or fusion; and that the real and whole truth to be told is of the existence and contours of these underlying phenomena. Why impose any categorization — the closest continuer schema being one — over this complexity?
- He then explicitly rejects my view, continuing:
The underlying level itself, however, also will raise similar problems. For example, in what way is something the same body when all of its cells other than neurons, as well as the particular molecules composing the neurons, are replaced over time? Should we speak again only of the complicated relations that underlie this level? We cannot avoid the closest continuer schema, or some other categorization, by restricting ourselves to the full complexity of the underlying relations. . . . Eventually we are pushed to a closest continuer schema or something similar at some level or other … If it becomes legitimate, because necessary, to use the schema at some level, then why not simply begin with it?
- This disagreement is unnecessary. I do not deny that we make judgements about the identity over time of many different kinds of thing. And I accept Nozick's Closest Continuer Schema as an account of how we make many such judgements. My claims are these. Since personal identity over time just consists in the holding of certain other relations, what matters1 is not identity but some of these other relations. And the logic of identity does not always coincide with what matters2. When what matters3 takes a branching form, or holds to intermediate degrees, judgements of identity cannot plausibly be made to correspond with what matters4. In these cases we should not apply the Closest Continuer Schema in an attempt to achieve such correspondence. As Nozick writes, we would then be forcing what matters5 'into somewhat arbitrary pigeonholes'. In these cases we should simply describe the ways in which, and the degrees to which, these other relations hold. We should then try to decide how much, in different ways, these relations matter. Nozick's objection to this view, quoted above, seems to be that we cannot avoid making some judgements about identity. But this is an objection only if we add the claim that, if we describe some cases by making or denying judgements about identity, we must describe all cases in this way. I can see no reason to accept this claim.
- In his claim about what matters6, Nozick again seems to reject Reductionism. He writes that, on his view, 'I will care equally about my closest continuer, whatever its degree of closeness happens to be (provided it is close enough)'. If he considered my Combined Spectrum, Nozick would probably withdraw this claim. In the cases in the middle of this Spectrum, there would be a resulting person who would have some proportion of the cells in my brain and body, and who would be in some ways psychologically continuous with me as I am now. But this resulting person would also have many new and dissimilar cells, and he or she would also be in many ways psychologically continuous with Greta Garbo. At the far end of this Spectrum, this future person would be in no way related to me. If I accept Nozick's view, I care equally about such a future person, provided that he or she is closely enough related to me. I regard all of the cases in the first part of this Spectrum as being just as good as ordinary survival. As we move along this Spectrum, the future person would be less and less closely related to me. But I am equally concerned about this person, provided that the degree of closeness is close enough.
- On this view, I must decide just what degree of closeness counts as close enough. I am must again draw a sharp line on this Spectrum. If my relation to some future person is just on the near side of this line, this relation is as good as ordinary survival. If my relation to some future person is just beyond this line, I should be less concerned. But the future person in the second of these cases would differ hardly at all from the person in the first case. The differences would be only that a few more cells would be replaced, and there would be some small psychological change, such as a new desire to be alone. Though these are the only differences, I should care less about what happens to this second person.
- This pattern of concern seems to me irrational. How can it have such importance whether just a few more cells would be replaced, or whether there would be one more small psychological change? Nozick's view treats this Spectrum as if it involves, at some point, a discontinuity. But this is false. Since the Spectrum is smooth, involving all of the degrees of continuity, why care equally in all the cases in the first part of the Spectrum, and then suddenly care less? This would be rational only if identity is some further fact which holds completely in the first part of this spectrum, and then suddenly fails to hold. But Nozick does not believe that there is any such further fact.
- Nozick suggests another way in which his pattern of concern might be defended. He thinks it can be rational to adopt what he calls the Platonic mode of caring about something. In this mode, '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'. Even though it is not true that we are beings whose continued existence must be all-or-nothing, it can be rational to care about our identity as if this was true. As Nozick admits, this involves 'an unrealistic overestimate of actuality, a seeing of it through Platonic glasses'. The alternative is to make '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…’
- Is this a sufficient defence of Nozick's pattern of concern? Can it be rational for his concern to correspond, not to the actual truth about his life, but to what he would have liked the truth to have been? Given the distinction between theoretical and practical rationality, Nozick's pattern of concern is defensible. I therefore withdraw my objection stated above. There is again no disagreement. If Nozick reacts to reality, not as it is, but as he would like it to be, this is theoretically irrational. But if this kind of wishful thinking is more deeply satisfying, it can be practically rational for him to try to make himself, in this way, theoretically irrational.
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