The unimportance of being any future person
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Derek Parfit’s argument against the platitude that identity is what matters in survival does not work given his intended reading of the platitude, namely, that what matters in survival to some future time is being identical with someone who is alive at that time. I develop Parfit’s argument so that it works against the platitude on the intended reading.
KeywordsPersonal identity Division Fission Indeterminacy Survival What matters
A second, weaker reading focuses on one’s relation, more generally, to a future time:
The Strong Reading of the Platitude
Person \(P_1\) has at \(t_1\) reasons for prudential concern for the well-being of person \(P_2\) at \(t_2\) if and only if \(P_1\) is identical with \(P_2\).
The most influential argument against the platitude is Derek Parfit’s division argument. It’s based around the following case, called My Division:
The Weak Reading of the Platitude
Person \(P_1\) has at \(t_1\) reasons for prudential concern for some person’s well-being at \(t_2\) if and only if \(P_1\) is identical with some person who is alive at \(t_2\).
To distinguish between the people resulting from the division, call the one with the left half of my brain Lefty and the one with the right half Righty.3 Let \(t_1\) be a time when I am alive before the division and \(t_2\) be a time when Lefty and Righty are alive afterwards.
My body is fatally injured, as are the brains of my two brothers. My brain is divided, and each half is successfully transplanted into the body of one of my brothers. Each of the resulting people believes that he is me, seems to remember living my life, has my character, and is in every other way psychologically continuous with me. And he has a body that is very like mine.2
I have at \(t_1\) reasons for prudential concern for the well-being of each one of Lefty and Righty at \(t_2\).7
Lefty is not identical with Righty.8
It is not the case that I am identical with both Lefty and Righty.
As Jens Johansson points out, however, the division argument does not refute the platitude on the weak reading.9 On the weak reading, the platitude might still hold in conjunction with (1), (2), and (3) if I am identical with one of Lefty and Righty but it’s indeterminate which one of them I am identical with.10 Yet Parfit’s stated target seems to be the platitude on the weak reading rather than the strong one.11 Hence, if the division argument can’t be extended so that it also works on the weak reading, it would be less interesting.
Lefty is identical with Old Lefty.
There is no person P alive at \(t_3\) who is not identical with Old Lefty such that either I am identical with P or I have at \(t_1\) reasons for prudential concern for the well-being of P at \(t_3\).
I have at \(t_1\) reasons for prudential concern for the well-being of Old Lefty at \(t_3\).
I am identical with Old Lefty.
I am identical with Lefty.
I am identical with Lefty but not with Righty.
The Strong Indeterminacy Reading of the Platitude
Person \(P_1\) has at \(t_1\) reasons for prudential concern for the well-being of person \(P_2\) at \(t_2\) if and only if it is not false that \(P_1\) is identical with \(P_2\).
These readings are compatible with the conjunction of (1) and (3). So they are not open to Parfit’s division argument. And, on these readings, (7) doesn’t follow from (5) and (6). Hence the extended division argument is blocked too. The main problem with these readings, however, is that they don’t seem to fit the common-sense platitude that identity—rather than indeterminate identity—is what matters in survival.17 The platitude is based on the prima facie compelling idea that prudential concern is concern for oneself, rather than concern for everyone of whom it’s not false that they are oneself.
The Weak Indeterminacy Reading of the Platitude
Person \(P_1\) has at \(t_1\) reasons for prudential concern for some person’s well-being at \(t_2\) if and only if it is not false that \(P_1\) is identical with some person who is alive at \(t_2\).
Here, I follow Parfit (1995, p. 28) in taking the platitude to be that ‘it is the fact of identity which [...] give us our reason for concern about our own future’, that is, identity is ‘not what makes our survival good, but what makes our survival matter, whether it will be good or bad.’ On this take on the platitude, being identical with a future person needn’t in itself be a good or bad thing; rather it provides a reason to be prudentially concerned about the future. Kagan (2012, p. 162), on the other hand, takes the platitude to be that identity is what we want in survival. On this alternative take, being identical with a future person is in itself a good thing or something we want for its own sake. The difference between these two takes, however, will not be crucial for our discussion.
Following Strawson (1970, p. 186).
- 4.Parfit (1984, pp. 253–254). Parfit (1995, p. 41) adds that, even if this may not be true,
we can suppose that, through some technological advance, it has been made true of me. Since our aim is to test our beliefs about what matters, there is no harm in making such assumptions.
See Parfit (1984, pp. 256–257) for some arguments in favour of (2).
Thomson (1987, p. 230) calls this possibility ‘The Narrow Scope Position’, which is defended by Williams (2008, p. 151). This possibility requires that a disjunction can be true even though each disjunct is indeterminate. This is possible given, for example, supervaluationism or epistemicism about indeterminacy. Moreover, note that the platitude on the weak reading could also hold in conjunction with (1), (2), and (3) if (i) I’m identical with Lefty but not with Righty or (ii) if I’m identical with Righty but not with Lefty. But (i) and (ii) seem arbitrary, as we shall discuss later, given the symmetry between my relation to Lefty and my relation to Righty. The possibility that I’m identical with one of Lefty and Righty but it’s indeterminate which one I am identical with, on the other hand, doesn’t suffer from such arbitrary asymmetry.
- 11.Parfit (1995, p. 44) claims that
we should revise our view about identity over time. What matters isn’t that there will be someone alive who will be me.
In a few days, there will be no one living who will be me. It is natural to assume that this is what matters.
One might perhaps object that the fact that Lefty survives longer than Righty is a relevant asymmetry. Note, however, that Lefty needn’t survive much longer than Righty. Supposing that they both survive for several decades, it seems that Lefty’s surviving a few moments longer than Righty cannot be relevant to whether I’m identical with Lefty or to whether I’m identical with Righty.
Ehring (1999, pp. 330–331).
- 17.Ehring (1999, pp. 331–332) argues that this discrepancy might be due to a conceptual limitation of our common-sense thinking:
The explanation is simply that commonsense tends to recognize only two truth-values and, hence, tends to run “not being false” into “being true.”
I wish to thank Richard Yetter Chappell, Gregory Currie, David Efird, Stephen Holland, Christopher Jay, Jens Johansson, Barry Lee, Mary Leng, Paul Noordhof, Christian Piller, Tom Stoneham, Robert Trueman, and an anonymous referee for valuable comments.
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