All the world's a stage, and all the men and women merely players; they have their exits and their entrances, and one man in his time plays many parts.
I.
Introduction
Mark Johnston has argued that four-dimensionalist theories of persistence have “surprising, repellent and perhaps even disastrous, implications for our ordinary moral outlook.”[1] In response, Alex Kaiserman has argued that these disastrous implications afflict only one kind of four-dimensionalism, namely, worm theory, but that they do not afflict the alternative stage theory.[2] In this post, I argue that given some plausible premises having to do with pain and moral status, stage theory does not in fact escape the problem raised by Johnston.
II. The
Personite Problem and the Stage Theory Solution
The
problem raised by Johnston against four-dimensionalism is that it is committed
to the existence of personites. Some standard four-dimensionalist
terminology is needed in order to precisely define a personite.[3] Take parthood-at-t
as an undefined primitive relation that is reflexive and transitive. Two
objects overlap at a time iff there is something which is a part of both
of them at that time. A thing x is a fusion at t of class S
iff (i) every member of S is a part of x at t and (ii)
every part of x at t overlaps at t some member of S.
Things x and y coincide at t iff they overlap at t
exactly the same objects. Lastly, x is an instantaneous temporal part
of y at t iff (i) x exists at, but only at, t, (ii)
x is part of y at t and (iii) x overlaps at t
everything that is part of y at t. From here, four-dimensionalism
itself can be defined as follows:
Four-Dimensionalism: Every object has an instantaneous
temporal part at every time at which it exists.
Now, let
us say that something is a person-stage iff it is an instantaneous
temporal part of a person. Let R be the relation between person-stages that
secures personal identity through time.[4] Then we can define worm
theory and stage theory (with respect to persons) as follows:
Worm
Theory: Persons
are maximal R-interrelated fusions of person-stages.
Stage
Theory: Persons
are person-stages.
We can now
define a personite as follows:
Personite: If x is a person, then y
is a personite of x iff y is a temporally continuous non-maximal
R-interrelated fusion of two or more person-stages, each of which is R-related
to every instantaneous temporal part of x.
Now, the personite problem can be characterized as follows. Given that I am a person, there are a very large number of personites associated with me. There is a personite that existed over the first ten years of my life and then ceased to exist, another personite that has existed over the last ten minutes of my life and still exists, a personite that will exist in an hour and go out of existence thirty seconds later, and so on. If these personites have moral status, then things like prudential self-sacrifice, making onerous promises for the good of others, and punishing criminals become (deeply) morally wrong.[5] For instance, deciding to undergo substantial short-term sacrifices in order to gain a great long-term benefit for yourself is wrong as it subjects all of the many personites that exists over and only over the interval of sacrifices to great hardship without any benefit. Indeed, hardship is all that such personites will ever go through! Johnston’s argument that personites have moral status can be formulated as follows[6]:
- For all possible worlds w and possible objects x, if x is a person in w then x has moral status in w.
- For all possible worlds w and v and possible objects x and y, if x in w is a duplicate[7] of y in v, then x has moral status in w iff y has moral status in v.
- For all personites x, there are a possible object y and a possible world w such that y is a person in w and y in w is a duplicate of x in the actual world.
- Therefore, all personites have moral status.
In
response to this argument, Kaiserman grants (1) and (2) but argues that if
stage theory (as opposed to worm theory) is true, then (3) is false. For
according to stage theory, a person is a person-stage, not a fusion of (two or
more) person-stages. Thus, there is no possible person that is a duplicate of an
actual personite.[8]
Thus, (3) is false, and the inference to (4) is thereby blocked. The stage
theorist has eluded the personite problem.
I now turn
to a critical evaluation of Kaiserman’s stage-theoretic response to the
personite problem.
III. Critique
of the Stage Theory Solution: The Problem of Pain
What I
want to argue is that stage theory has a problem with accounting for pain, and
the most plausible solution to this problem exposes stage theory to the
personite problem. The upshot is that even if Kaiserman has escaped from one
particular argument for the personite problem, he has not escaped the problem
itself. The main idea is this: Pain takes time. More precisely, for humans at
least, there is a minimum duration of time such that if a pain is shorter than
this duration, then a human cannot experience it.[9] One way to understand this
is that a human experience of pain is temporally extended. Now, here is a
plausible thesis: a temporally extended experience can only be had by a
temporally extended experiencer. It follows that if humans experience pain,
then humans are temporally extended.
This is
where stage theory runs into a problem. For according to stage theory, persons
are person-stages, and person-stages are instantaneous (i.e., temporally unextended)
entities. It follows that persons—human ones at least—cannot experience pain.
But humans clearly do experience pain! If this is so, then humans cannot
be person-stages. Given a four-dimensionalist, stage-theoretic ontology, what,
then, could humans be? I submit that the most plausible answer is that humans
are fusions of human person-stages such that the fusion is sufficiently
temporally extended to be able to have a human experience of pain. The upshot
of this is that humans are then by definition personites.[10]
Now, here
is another fact about humans: they undergo physical suffering.
Plausibly, physical suffering entails pain (though the reverse is likely not
true). If this is right, then physical suffering requires temporal extension as
well so that person-stages cannot physically suffer. So, given that humans are (most
plausibly understood as) personites and given that humans suffer, it follows
that personites (human ones at least) suffer. From here, we can observe a
plausible principle of moral status: Anything that can suffer has moral status.[11] The conclusion is that
(human) personites have moral status. The personite problem has returned to the
stage.
What might
the stage theorist—Kaiserman in particular—say in response to this argument?
Consider the following two objections:
Objection
1: Although each
person-stage lacks temporal extension, the same person persists across the
person-stages, across an extended temporal interval. Thus, it would seem that a
(human) person can experience pain even assuming that temporal extension is
required in order to do so.
Objection
2: Even if the
argument for personites having moral status on stage theory is sound, it does
not follow that personites have full and equal moral status, and this
was Johnston’s contention.[12]
In
response to the first objection, I would argue that while persons ‘persist’
according to stage theory, they do not really persist.[13] What I mean is that while
stage theory provides truth conditions for our ordinary language statements
about the persistence of persons, these truth conditions do not consist in
persons really persisting any more than the mereological nihilist’s truth
conditions for ordinary language statements about ‘composite objects’ consists
in there really existing composite objects. On stage theory, each person (which
just is a person-stage) of necessity exists only for an instant.[14] To say that a person persists
from a time t1 to a later time t2 is to say
that there exists a person-stage (person) S1 at t1
and a numerically distinct person-stage (person) S2 at t2,
and S1 and S2 stand in an appropriate
counterpart relation. So, no person really exists in a temporally extended way.
Perhaps the stage theorist can say that while no individual person-stage
experiences pain, a number of them collectively experience pain. But
this collectivity sounds suspiciously like a fusion of two or more
person-stages, which just is a personite. Thus, in my view, the objection does
not succeed.
Finally, in response to the second objection, I am inclined to concede the point that my argument does necessarily not show that personites have full and equal moral status. I think it is plausible, for instance, that some non-human animals can suffer and yet have lesser moral status than we do. Nevertheless, given the sheer number of personites (and consequently the sheer quantity of potential suffering) involved, I think that there is still a significant personite problem that remains for the stage theorist. So, while I am willing to concede that Kaiserman has potentially lessened the personite problem for stage theory, I nevertheless maintain that he has in any case not eliminated it. Even if he has lessened it, however, the extent to which he has lessened it bears further investigation.
Moreover, as Alex Pruss has pointed out to me, what goes for pain plausibly goes for all conscious states so that (human) consciousness in general requires temporal extension. If this is right, then on stage theory, human persons turn out not to be conscious while (human) personites turn out to be conscious. Consequently, it would seem that human personites actually have more moral status than human persons, and this makes the personite problem even worse for stage theory than it is for worm theory. Further, it is plausible to think that whatever cannot be conscious isn't even a person in the first place so that person-stages cannot be human persons. If this is correct, then stage theory fails on grounds wholly independent of the personite problem. I conclude that stage theory is simply inadequate as a theory of persons.
References
Johnston,
M. (2016). Personites, Maximality and Ontological Trash. Philosophical
Perspectives, 30(1), 198–228. https://doi.org/10.1111/phpe.12085
Kaiserman,
A. (2019). Stage theory and the personite problem. Analysis, 79(2),
215–222. https://doi.org/10.1093/analys/any074
Koons, R.
C., & Pickavance, T. H. (2017). The Atlas of Reality: A Comprehensive
Guide to Metaphysics. Wiley
Blackwell.
Parfit, D.
(2012). We Are Not Human Beings. Philosophy, 87(1), 5–28. https://doi.org/10.1017/s0031819111000520
Pruss, A.
R. (2025, August 8). Consciousness and the open future. Alexander
Pruss’s Blog. https://alexanderpruss.blogspot.com/2025/08/consciosuness-and-open-future.html
Sider, T.
(1997). Four Dimensionalism. Philosophical Review, 106(2),
197–231. https://doi.org/10.2307/2998357
[1] Johnston (2016), pp. 199.
[2] Kaiserman (2019).
[3] This terminology is provided by
Kaiserman (see pp. 215-216). Similar definitions can be found in Sider (1997).
[4] Kaiserman lists psychological
continuity and bodily continuity as possible candidates for R.
[5] For detailed discussion of these
issues, see Johnston (2016), pp. 207-210.
[6] This formulation is taken from
Kaiserman (2019), pp. 217. For Johnston’s original formulation, see Johnston
(2016), pp. 203-204.
[7] Following Kaiserman (2019), say
that for all possible objects x and y and possible worlds w
and v, x in w is a duplicate of y in v
iff x instantiates exactly the same intrinsic properties in w as y
does in v (pp. 217).
[8] Cf. ibid., pp. 218.
[9] This idea comes from Pruss (2025).
[10] On this view, one might then say
that human persons (person-stages, according to stage theory) are proper
parts of human beings (personites, according to my argument). For
discussion of the view that human persons are proper parts of human beings,
see, e.g., Parfit (2012), pp. 14.
[11] As Johnston (2016) notes, Peter
Singer, among others, defends this thesis (pp. 203).
[12] Ibid., pp. 210.
[13] This point about the
stage-theoretic account of persistence is also made by Koons & Pickavance
(2017), pg. 571.
[14] Ibid.
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