Torin
Alter and Stuart Rachels
[Ratio XVII, September 2004, 241-255]
Abstract
Derek
Parfit's combined-spectrum argument seems to conflict with epistemicism, a viable
theory of vagueness. While Parfit argues for the indeterminacy of personhood,
epistemicism denies indeterminacy. But, we argue, the linguistically based
determinacy that epistemicism supports lacks the sort of normative or
ontological significance that concerns Parfit. Thus, we reformulate his
argument to make it consistent with epistemicism. We also dispute Roy
Sorensen's suggestion that Parfit's argument relies on an assumption that fuels
resistance to epistemicism, namely, that 'the magnitude of a modification must
be proportional to its effect.'
Epistemicism is the view
that vague concepts have sharp borderlines, but we cannot know where these
borderlines lie. On this view, there is an exact number of grains of sand that
make the smallest heap, but we cannot know what that number is.[1]
Derek Parfit simply assumes that epistemicism is false in presenting his
combined-spectrum argument, one of his main arguments for reductionism about
persons.[2]
On reductionism, personal identity need not be determinate--questions of the
form 'Is X the same person as Y?' can lack determinate yes-or-no answers. When
Parfit presented his argument, it was natural not to take epistemicism
seriously. Epistemicism is counterintuitive and had not yet been systematically
developed and defended. But now it has been.[3]
Thus, Parfit's argument seems vulnerable to an epistemicist challenge.
We think
this challenge can be met. Granted, epistemicism can be used to defend the
claim that personal identity is necessarily determinate. But the determinacy
that results derives from subtle features of linguistic practice and therefore
lacks the sort of normative or ontological significance that concerns Parfit.
His argument can be reformulated so as not to conflict with such determinacy,
as we will demonstrate. Therefore, epistemicism does not undermine his project.
We will
also defend Parfit's argument against a related objection due to Roy Sorensen.[4]
According to Sorensen, Parfit appears to assume the false principle that 'the
magnitude of a modification must be proportional to its effect'--a principle
that Sorensen thinks fuels resistance to epistemicism. We will show that
Parfit's argument depends on no such assumption.[5]
1. 'Reductionism' and
'Non-Reductionism'
Call
Parfit's claim that personal identity can be indeterminate the indeterminacy claim. This is only part of Parfit's reductionist
view. Two other parts are relevant here. One is the doctrine that, roughly
stated, a person consists merely in a brain, a body, and a series of interrelated
physical and mental events. We will call that doctrine ontological reductionism. Ontological reductionism contrasts with
the view that we are separately existing entities, such as persisting
immaterial Cartesian egos. The other relevant doctrine is that personal identity is not what matters.
In other words, what justifies my special anticipatory concern about my future
is not that the future person will be me. Parfit sometimes uses 'reductionism'
to refer just to ontological reductionism.[6]
But we will follow his broader usage, on which reductionism also includes the
indeterminacy claim and the doctrine that personal identity is not what
matters.
We will use
'non-reductionism' to refer to the antithesis of reductionism, in this broader
sense. Thus, non-reductionists believe: (a) the determinacy claim, that personal
identity is necessarily determinate; (b) ontological
non-reductionism, that it is not the case that a person consists merely in
a brain, a body, and a series of interrelated physical and mental events; and
(c) that personal identity is what matters; personal identity justifies special
anticipatory concern. According to Parfit, non-reductionism is the common-sense
conception of persons ('What We Believe Ourselves To Be'[7]),
whereas reductionism is true ('How We Are Not What We Believe'[8]).
2. The Combined-Spectrum
Argument
In Part
Three of Reasons and Persons, Parfit
first tries to prove ontological reductionism (and in particular that we are
not Cartesian egos); then he argues for other reductionist doctrines, given
ontological reductionism. The combined-spectrum argument figures in that latter
task.
The
combined spectrum is a range of cases. These cases do not occur in succession;
they are just distinct possible futures. In the case at the near end of the
spectrum, a future person is fully continuous with me as I am now, both
physically and psychologically.[9]
In the next case, a few of my brain-and-body cells are replaced with Greta Garbo-like cells. The resulting person resembles me in
almost every way. But unlike me, that person enjoys acting, has a few
quasi-memories of living Garbo's life, and bears a
slight physical similarity to Garbo.[10]
In the next case, a greater number of my cells are replaced and the resulting
person is a bit more like Garbo. Thus the cases
involve an increasingly large number of cells replaced (always at once, never
gradually). At the far end of the spectrum, all of my cells are replaced, and
the resulting person is physically and psychologically indistinguishable from Garbo. The spectrum is 'combined' because it involves
physical and psychological changes.[11]
The
combined-spectrum argument can be put as follows. In the cases at the near end,
the resulting person is me, since I am very strongly connected, both physically
and psychologically, to that person. In the case at the far end, '[t]here would
be no connection, of any kind, between me and this resulting person. It could
not be clearer that, in this case, the resulting person would not be me.'[12]
Therefore, if our identity is necessarily determinate, there is a sharp
borderline in the spectrum: a case n such that in n I am the resulting person
but in n+1 I am not. If there is a sharp borderline, then (i)
'the difference between life and death could just consist in any of the very
small differences'[13]
between neighbouring cases in the spectrum. Of
course, it would not be a 'very small difference' if we were Cartesian egos and
the resulting persons were different
egos in cases n and n+1.
But as we mentioned, Parfit assumes ontological reductionism in this part of
the book. Parfit also thinks that if there is a sharp borderline, then (ii) 'we
could never have any evidence where the borderline would be.'[14]
Both (i) and (ii) are implausible. Together, they are
more implausible than the denial of an unknowable sharp borderline. Therefore,
our identity need not be determinate. In numbered steps (and slightly
simplified):
1.
If our identity is necessarily determinate, then there
is a sharp borderline in the combined spectrum, which entails that: (i) the difference between life and death consists in the
minor differences between certain
neighbouring cases; and (ii) such a line exists even
though we could never locate it exactly.[15]
2.
There is no such sharp borderline in the spectrum.
3.
So, it is not the case that our identity is
necessarily determinate.
Here and in the rest of our paper
we follow Parfit in assuming ontological
reductionism, and thus that persons are not Cartesian egos. But unlike Parfit,
we will henceforth omit premise 1's clause (ii), which states that the
borderline in question would be unknowable. We do this mostly because, in the
ensuing discussion, only (i) will be directly
relevant. Further, dropping (ii) does not seem to us to weaken the argument--in
fact, we think it makes the argument stronger. Without clause (ii), we get:
1.
If our identity is necessarily determinate, then there
is a sharp borderline in the combined spectrum, which entails that the
difference between life and death consists in the minor differences between certain neighbouring
cases.
2.
There is no such sharp borderline in the spectrum.
3.
So, it is not the case that our identity is
necessarily determinate.
Call that the simple formulation of the combined-spectrum argument. Premise 1 is
plausible and, for present purposes, may be granted. 3 follows from 1 and 2 by modus
tollens. That leaves 2.
3. Sorensen's Objection
Sorensen
challenges premise 2. As an epistemicist, he thinks that minor differences can
affect the application of any vague concept. He thinks, for example,
that one hair fewer can affect whether someone is bald. On his view, the
difference between life and death can consist in a minor difference, given that
'same person' is vague.
According
to Sorensen, Parfit appears to assume the
proportionality principle in denying that there is a sharp borderline in
the spectrum. This is the causal principle that 'the magnitude of a
modification must be proportional to its effect.'[16]
Sorensen thinks this principle fuels resistance to epistemicism.[17]
But as he says, it is false:
An
extremely tiny change in the velocity of an object can make the crucial
difference as to whether it achieves escape velocity and travels far out into
space, or fails to escape and crashes to earth. Of course, it is enormously
improbable that the impact of a particular raindrop on a rocket will make the
crucial difference. Likewise it is enormously unlikely that changing a brain
cell will make the crucial difference between life and death. The
proportionality principle virtually always provides the correct answer when
applied to any particular miniscule change. But its distributive reliability
does not entail its collective reliability.[18]
Parfit never explicitly invokes the
proportionality principle in defending premise 2, that there is no sharp
borderline in the spectrum. Does he rely on it implicitly?
One might
say that the difference between life and death couldn't consist in any small
change in cells, since no small physical change could have large,
identity-altering psychological effects. That claim would be suspect, given the
possibility of threshold effects: a single cell replacement might result in a
large psychological change, just as a single raindrop might result in a large
change in a rocket's trajectory. Parfit, however, relies on no such argument.
He stipulates that the neural and
psychological differences between neighbouring
cases in the spectrum are minor. Therefore, he does not have to prove that there are only minor
psychological differences between any pair of neighbouring
cases; that assumption is true by hypothesis.
Perhaps
Sorensen thinks Parfit relies on the following argument:
1.
The magnitude of a modification must be proportional
to its effect. (the proportionality principle)
2.
In the combined spectrum, each individual modification
(i.e., each cell replacement and psychological change) is miniscule.
3.
So, the effect of each modification must be miniscule.
4.
Death is not miniscule.
5.
So, in the combined spectrum, no individual modification
can have as an effect that the original person dies.
But that
argument's emphasis on 'modifications' betrays a confusion. According to its
second premise, each modification in the combined spectrum is miniscule. But
some of the modifications are huge;
consider the case in which all of my cells are replaced with Garbo-like cells. The 'modifications' that pertain to Parfit's argument must be the differences between adjacent cases. In offering the proportionality
principle, Sorensen misinterprets the combined spectrum as being a series of
modifications, rather than a range of possible futures.
A better
argument can be formulated in terms of a revised proportionality principle:
1. Consider
modifications M1 and M2 and their respective effects E1 and E2. The difference
between E1 and E2 must be proportional to the difference between M1 and M2.
(the revised proportionality principle)
2. In the
combined spectrum, the difference between modifications in adjacent cases (e.g.,
between replacing none of my cells and replacing a few) is miniscule.
3. So, the
difference between these modifications' effects must be miniscule.
4. The
difference between life and death is not miniscule.
5. So, in
the combined spectrum, no adjacent modifications can be such that only one
causes death.
Sorensen's examples falsify
the revised proportionality principle. Therefore, the first premise of the
preceding argument is false.
But Parfit
need not rely on the revised proportionality principle or on any principle that
succumbs to Sorensen's examples. First, Parfit might not be relying on any
general principle at all; he may have rejected the idea of a sharp borderline
simply as an intuition, as something plausible in itself. Second, Sorensen's examples
involve causality beyond the initial
difference: a difference of one raindrop has enormous significance because it
causes a big change in the rocket's trajectory. In the combined spectrum,
however, there is no suggestion that the small differences in cells and
psychology result in further, significant changes in cells and psychology.
Rather, the issue is whether those differences in themselves could constitute, or guarantee, a difference in
personal identity. Thus, in rejecting a sharp borderline in the spectrum,
Parfit might appeal to something like the
following principle:
Trivial
differences in low-level phenomena cannot, in themselves, constitute or
guarantee non-trivial differences in high-level phenomena. For example, a tiny
change in bits of wood cannot, by itself, ensure that a table ceases to exist;
replacing a microscopic portion of a single brain cell cannot, by itself, make
it the case that a person ceases to exist.
Call that the constitution principle. It may need
revising, but something like it can serve Parfit's purposes. Alternatively, he
could appeal to a normative principle that he attributes to Bernard Williams:
Since
personal identity has great significance, whether identity holds cannot depend
on a trivial fact.[19]
Parfit describes this
principle as 'plausible.' Of course, he cannot accept it as stated, since he
denies that personal identity has great significance. But he can accept a conditionalized version: if personal identity has
great significance, then whether identity holds cannot depend on a trivial
fact.[20]
Even that version may need revising, as may the constitution principle. But
neither is refuted by Sorensen's examples of threshold effects.[21]
Sorensen
presents his objection in passing, while developing his epistemicist view.
Perhaps his objection was motivated by the suspicion that Parfit's argument
fits uneasily with epistemicism. That is a more serious concern, to which we
now turn.
4. The Objection from
Epistemicism
Epistemicists
contend that vagueness consists in ignorance: our necessary ignorance of sharp
boundaries. For example, they believe that there is an exact but unknowable
number of seconds past which a toddler is no longer a toddler. That view may
seem incredible, and until recently it was disregarded.[22]
But due primarily to Sorensen and Timothy Williamson, it must now be taken
seriously.
Epistemicism
supplies the non-reductionist with a clear response to the combined-spectrum
argument: there is a sharp borderline in the spectrum, albeit an
unknowable one. That there should be a sharp borderline is hard to believe. It
is also hard to believe that there is a sharp borderline in a typical sorites series, involving grains of sand and heaps, or
hairs and bald men, and so on. Epistemicism is hard to believe. But if it is
true, then there is an unknowable sharp borderline in all sorites
series. Epistemicism does not entail that there is such a borderline without
the further premise that 'same person' is vague (and likewise for related
concepts such as 'survives' and 'dies'). But epistemicists
can accept that premise, and therefore their
view would seem to provide a basis for rejecting the combined-spectrum
argument.[23]
In our
view, the objection from epistemicism must ultimately fail, for the following reason.
What is central to Parfit's view is that persons should be understood on the
model of heaps, nations, clubs, and other vague phenomena. Although Parfit
denies that the vagueness of persons is epistemic, he need not. He can accept
that there is an unknowable sharp borderline in the combined spectrum; he need
only reject a sharp borderline that has important implications for parts of
reductionism other than the indeterminacy claim. In the next section, we will
present a version of his argument that denies the existence of a normatively
relevant borderline: a borderline that has consequences for what matters in
survival. Later, we will present a version that denies the existence of an
ontologically based borderline: a borderline that is determined by the world
rather than linguistic practice.
5. The Normative Formulation
The simple
formulation of the combined-spectrum argument neglects the normative part of
non-reductionism--the doctrine that personal identity is what matters.
Non-reductionism does not entail merely that there is a sharp borderline in the
combined spectrum. It entails that there is a sharp borderline that is relevant to what matters--a
borderline that has implications for special anticipatory or prudential concern
in our survival. Here is a formulation of the argument that includes that idea:
1.
If our identity is necessarily determinate and
personal identity is what matters, then there is a normatively relevant sharp
borderline in the combined spectrum.
2.
There is no such sharp borderline in the spectrum.
3.
So, it is not the case that: our identity is
necessarily determinate and personal
identity is what matters.
Call that the normative formulation of the
combined-spectrum argument. If sound, it would show that the indeterminacy
claim follows from ontological reductionism combined with the doctrine that
personal identity is what matters.
As before,
the premise at issue is 2. 2 is plausible. Moreover, it can be defended with
the (conditionalized) normative principle mentioned
earlier: if personal identity has great significance, then whether identity
holds cannot depend on a trivial fact.
When Parfit
presented his argument, he may have had the normative formulation in mind. Why
does he think that the difference between life and death couldn't consist in
the minor differences between neighbouring cases in
the spectrum? His stated reason is that those minor differences are 'trivial'
(p. 239). The triviality could be normative or ontological. If he intends the former, then his point is that the
minor neural and psychological differences between neighbouring
cases can't justify special anticipatory or prudential concern in our survival.
On this reading, he tacitly assumes that the sharp borderline would have to be
normatively relevant. We will discuss another reason to think Parfit intended
the normative formulation in the next section. In section 7, we will consider
the alternative, ontological
reading.
The
normative formulation lets Parfit respond to the epistemicist without
challenging epistemicism, as follows: epistemicism may show that there is an
unknowable sharp borderline in the combined spectrum, but it does not show that
the borderline has normative relevance. So, we must now ask: can epistemicism
be used to establish the existence of a normatively relevant sharp borderline
in the spectrum? In terms of the above argument, does epistemicism support
thinking that the normatively relevant difference between life and death could
consist in the minor differences between neighbouring
cases?
We do not
think so.[24]
For epistemicists, minor changes in linguistic
practice can change the location of a sharp boundary. Williamson writes,
A slight
shift along one axis of measurement in all our dispositions to use 'thin' would
slightly shift the meaning and extension of 'thin'. On the epistemic view, the
boundary of 'thin' is sharp but unstable.
Suppose
that I am on the 'thin' side of the boundary, but only just. If our use of
'thin' had been very slightly different, as it easily could have been, then I
should have been on the 'not thin' side. The sentence 'TW is thin' is true, but
could very easily have been false without any change in my physical
measurements or those of the relevant comparison class.[25]
According to epistemicism,
the sharp boundary of 'same person' comes from linguistic practice, just as the
sharp boundary of 'thin' does. Thus, for the epistemicist, the source of the
sharp borderline in the combined spectrum is linguistic practice. Therein lies
the problem for showing that such a borderline has normative relevance: how
could what matters be whether I survive, if my survival depends on the
subtleties of linguistic practice? From the normative point of view, such
subtleties are arbitrary.
And so, epistemicism alone cannot explain how
there could be a normatively relevant sharp borderline. Might epistemicism provide the non-reductionist with part of such
an explanation? We do not see how it could; again, from a normative viewpoint,
the borderlines it entails are arbitrary. We conclude that epistemicism does
not undermine the normative formulation of the combined-spectrum
argument.
On the
normative formulation, premise 2 denies that there is a normatively relevant
sharp borderline in the spectrum. Of course, if an epistemicist accepts this
premise, she cannot maintain that 'X is the same person Y in a normatively
relevant sense' has an indeterminate extension.
Rather, her position would be that this predicate fails to pick out a real
(moral/rational) feature of the world. On this view, whether X is the same
person as Y never matters, rationally or morally; what matters are benefits and
burdens, not how they are distributed. This seems the most reasonable view for
the epistemicist to take about the extension of 'X is the same person Y in a
normatively relevant sense': the alternative would be to take the predicate to
mark a sharp borderline in the spectrum, which is wildly implausible (given
ontological reductionism).
6. Parfit's Reply to a
Similar Objection
Parfit discusses an
objection that, like the objection from epistemicism, relies on semantic
considerations.[26]
Let us briefly relate his discussion to ours. Some philosophers think that the
notion of an identity claim that is neither determinately true nor
determinately false is incoherent.[27]
If they are right, then Parfit cannot maintain that our identity can be
indeterminate. In response, he emphasizes that their view about identity claims
is consistent with the idea that personal identity is not what matters. Parfit
describes the latter idea as 'the most important claim in the Reductionist
View.'[28]
Someone who accepts the idea can say, 'The view that identity can't be
indeterminate forces me to concede that there is some determinate line, but
such a line would have no rational or moral significance.' Of such a view,
Parfit writes, 'I regard this view as one version of Reductionism, the
tidy-minded version that abolishes indeterminacy with uninteresting stipulative definitions.'[29]
Similar things
can be said about the objection from epistemicism. A reductionist can say,
'Epistemicism forces me to concede that there is a determinate line in the
spectrum, but that line would have no rational or moral significance; for such a line would be determined by
linguistic facts that are, from a rational or moral viewpoint, arbitrary.'
Such a view may also be characterized as a version of reductionism--one that
incorporates a linguistically based determinacy that makes no difference to
what matters. Our normative formulation of the combined-spectrum argument can
be conceived as a working out of this response.
7. The Ontological
Formulation
A critic of
the normative formulation might say, 'By bringing in normative concerns, you
have distorted the argument's metaphysical orientation.' We think the normative
reading finds considerable support in Parfit's writings. But the argument can
also be revised to satisfy the objector.
According
to common sense, personal identity is always determinate, but not due to the
subtleties of linguistic practice. Consider a slight variation of an example given by Parfit.[30]
Suppose that someone whom I neither
know nor care about is about to undergo major neurosurgery. I ask the
surgeon whether the patient will survive. She replies, 'Yes, but only given
recent shifts in linguistic usage; thanks to them, the term same person now
correctly applies to the patient and the person who will wake up after the
operation.' Intuitively, the surgeon is evading my question. The idea that the determinacy
of our identity derives from arbitrary linguistic practice runs afoul of common
sense.
It is more
in keeping with common sense to say that 'person' refers to a natural kind,
where the distinction between persons always carves nature at a joint. So, if
non-reductionism is the theory of common sense, it holds the distinction
between persons to be ontologically based. The combined-spectrum argument may thus be conceived as attacking the idea that there is a sharp
borderline that is determined by the world, not by linguistic practice.[31]
In presenting this version, we will continue to assume ontological reductionism and thus that we are not Cartesian egos.
Consider:
1.
If our identity is necessarily determinate and the
source of that determinacy is ontological, then there is an ontologically based
sharp borderline in the combined spectrum.
2.
There is no such sharp borderline in the spectrum.
3.
So, it is not the case that: our identity is
necessarily determinate and the source of that determinacy is ontological.
Call that the ontological formulation of the
combined-spectrum argument. If sound, it would show that the indeterminacy
claim follows from ontological reductionism and the assumption that the source
of determinacy would be ontological.
As before,
the premise at issue is 2. 2 is plausible. Moreover, it can be defended with
the constitution principle mentioned earlier: trivial differences in low-level
phenomena cannot, in themselves, constitute or guarantee non-trivial
differences in high-level phenomena. It might be said that this principle begs
the question against epistemicism. But Parfit may appeal to an amplified
version of the constitution principle: trivial differences in low-level
phenomena cannot, in themselves, constitute or guarantee non-trivial, ontologically based differences in
high-level phenomena. The amplified principle does not conflict with
epistemicism, given epistemicism's linguistic
orientation.
Like the
normative formulation, the ontological formulation provides a response to the
objection from epistemicism: although epistemicism explains how there could be
a sharp borderline in the combined spectrum, it fails to explain how there
could be an ontologically based borderline. Rather, epistemicism posits a
borderline determined by the subtleties of linguistic practice. The conclusion
is the same as before: epistemicism, if true, undermines only the simple
formulation. Both revised formulations are consistent with epistemicism.
8. Conclusion
Parfit's
combined-spectrum argument does not rely on the proportionality principle,
which Sorensen rightly rejects. It does face an epistemicist challenge.
Epistemicism, if true, would undermine the simple formulation of the argument,
but it would not undermine the normative or the ontological formulation. The
point of the argument is not that the spectrum counts against the determinacy
of persons. The point is rather that it counts against any normatively relevant
or ontologically based determinacy. Parfit's argument, suitably sharpened,
survives the challenge.[32]
The
Department of Philosophy
[1] For
the epistemicist, this number may vary with context. But a full specification
of the context would still leave the number unknowable. See Timothy Williamson,
Vagueness, (New York: Routledge, 1994), p. 215; and Roy Sorensen, Vagueness and
Contradiction (
[2] Derek Parfit, Reasons and Persons (New York: Oxford University Press, 1984), pp. 23643. See also p. 232. And compare pages 2028 of Parfit, 'The Unimportance of Identity', in H. Harris (ed.), Identity (New York: Oxford University Press, 1995), pp. 1345.
[3] See Williamson, Vagueness; and Sorensen, Vagueness and Contradiction and Blindspots (New York: Oxford University Press, 1988).
[4] Blindspots, pp. 25052.
[5] Peter Unger rejects Sorensen's criticism on different grounds. See Unger's Identity, Consciousness & Value (New York: Oxford University Press, 1990), p. 203.
[6] See p. 268, fn. 7 of Derek Parfit, 'Experiences, Subjects, and Conceptual Schemes', Philosophical Topics 26 (1999), pp. 21770.
[7] Reasons and Persons, chapter 10.
[8] Reasons and Persons, chapter 11.
[9] We use 'connected' and 'continuous' in Parfit's sense. See Reasons and Persons, chapter 10, especially pp. 20409.
[10] For Parfit's notion of quasi-memory, see Reasons and Persons, pp. 220 and 226. The notion originates in Sydney Shoemaker, 'Persons and Their Pasts' American Philosophical Quarterly 7 (1970), pp. 26985.
[11] Parfit also discusses a physical spectrum and a psychological spectrum. See Reasons and Persons, pp. 231-236.
[12] Reasons and Persons, p. 238.
[13] Reasons and Persons, p. 239.
[14] Reasons and Persons, p. 239.
[15] We follow Parfit in using 'the difference between life and death' to refer to the difference between surviving and not surviving in the spectrum. Also, (i) could be formulated more formally as follows: 'there is a pair of cases in the spectrum, n and n+1, such that in n I am identical to the resulting person, but in n+1 I am not.' Although we will continue to use Parfit's formulation, we mean it to be equivalent to the more formal formulation.
[16] Blindspots, p. 251.
[17] Blindspots, pp. 25052.
[18] Blindspots, p. 251. In the proportionality principle, the contrast between modification and effect can be read in two ways: (a) size of cause vs. size of effect; or (b) amount of intrinsic change vs. that change's intrinsic (moral or rational) significance. As we understand Sorensen, he intends the (a)-version. But his rocket example does not fully clarify which version he has in mind. The rocket's plunging to Earth is a sizeable effect (in terms of the region of space-time it occupies), which suggests the (a)-version. The plunging also has great moral and rational significance (astronauts die, NASA loses money, etc.), which suggests the (b)-version. But he gives other examples that favor the (a)-version. For example: 'A banana peel can elicit spectacular acrobatics from a lumbering pedestrian, a pebble in the fuel line of a truck can bring it to a halt . . .' (Sorensen 1988, p. 252). Such events do not typically have great moral or rational significance.
[19] Reasons and Person, p. 267. See Bernard Williams, Problems of the Self (Cambridge: Cambridge University Press, 1973). Parfit discusses the Williams principle in the chapter following the chapter in which he presents the combined-spectrum argument.
[20] Parfit seems sympathetic to a reductionist analogue of the Williams principle: 'This Reductionist View also meets the analogue of Requirement (2) [i.e., of the Williams principle] On this view, what is important is relation R: psychological connectedness and/or continuity, with the right kind of cause. Unlike identity, this relation cannot fail to hold because of a trivial difference in the facts. If this relation fails to hold, there is a deep difference in the facts' (Reasons and Persons, p. 271).
[21] We take no stand on whether either principle is true. Our point is only that, if Parfit is relying on any general principle (which might not be the case) it is not the proportionality principle. We offer the constitution principle and the conditionalized Williams principle as candidates.
[22] There are notable exceptions, such as James Cargile, 'The Sorites Paradox', British Journal for the Philosophy of Science 20 (1969), pp. 193202. For historical antecedents of the view, see Williamson, Vagueness, chapter 1.
[23] The epistemicist need not accept this premise. For the sake of argument, however, we will assume that she does. We have not addressed whether in Parfit's argument 'our identity', 'same person', etc., refer to classical identity or some weaker relation. We believe that our arguments do not depend on how that issue is resolved. But there are complications. In particular, if in Parfit's argument 'our identity' expresses classical identity, then Williamson would likely deny that the term is vague. (See Vagueness, chapter 9, section 2.) If the relevant terms are not vague, then the objection from epistemicism does not even get off the ground.
[24] It is worth bearing in mind that, even if the differences between neighbouring cases in the spectrum were extremely small, the epistemicist would claim that there is a sharp borderline. Suppose neighbouring cases n and n+1 differ only in this respect: in n+1 one one-trillionth more of a single neuron is replaced. Our question would then be whether such an extremely minor difference could make a great normative difference.
[25] Vagueness, p. 231. The view Williamson expresses in this paragraph has a conventionalist flavor. Epistemicism is independent of conventionalism. In fact, Sorensen expresses reservations about conventionalist approaches to meaning (and about the related view that 'meaning is mind dependent'; see Vagueness and Contradiction, pp. 19-20). But we know of no developed version of epistemicism that would avoid objections like those we adduce against Williamson's version. Thus, for simplicity, we will assume that he speaks for all epistemicists. It may be possible to formulate a coherent version of epistemicism to which our objection would not apply. On such a view, (a) vague terms have precise extensions and (b) those extensions are determined by the world and not by linguistic practice or any other human activity. But this paper concerns epistemicism as it has been defended.
[26] Reasons and Persons, pp. 24041.
[27] Some attribute the argument to Gareth Evans ('Can There Be Vague Objects?', Analysis 38 (1978), p. 208), and Nathan Salmon (Reference and Essence, Princeton: Princeton University Press, 1981, pp. 24346) offers a version. Both the argument and the attribution to Evans are controversial. For criticisms of the argument, see John Broome, 'Indefiniteness in Identity', Analysis 44 (1984), pp. 612. For criticisms of the attribution, see David Lewis, 'Vague Identity: Evans Misunderstood', Analysis 48 (1988), pp. 12830.
[28] Reasons and Persons, p. 241.
[29] Reasons and Persons, p. 241.
[30] Reasons
and Persons, p. 233.
[31] Parfit emphasizes this point in 'The Unimportance of Identity'.
[32] Torin Alter thanks the Research Advisory
Committee of the