necessarily consist in? This is the question of personal identity, and
it is literally a question of life and death, as the correct answer to
it determines which types of changes a person can undergo without
ceasing to exist. Personal identity theory is the philosophical
confrontation with the most ultimate questions of our own existence:
who are we, and is there a life after death? In distinguishing those
changes in a person that constitute survival from those changes in a
person that constitute death, a criterion of personal identity through
time is given. Such a criterion specifies, insofar as that is
possible, the necessary and sufficient conditions for the survival of
persons.
One popular criterion, associated with Plato, Descartes and a number
of world religions, is that persons are immaterial souls or pure egos.
On this view, persons have bodies only contingently, not necessarily;
so they can live after bodily death. Even though this so-called Simple
View satisfies certain religious or spiritual predilections, it faces
metaphysical and epistemological obstacles, as we shall see.
Another intuitively appealing view, championed by John Locke, holds
that personal identity is a matter of psychological continuity.
According to this view, in order for a person X to survive a
particular adventure, it is necessary and sufficient that there
exists, at a time after the adventure, a person Y who psychologically
evolved out of X. This idea is typically cashed out in terms of
overlapping chains of direct psychological connections, as those
causal and cognitive connections between beliefs, desires, intentions,
experiential memories, character traits, and so forth. This Lockean
view is well suited for thought experiments conducted from
first-person points of view, such as body swaps or
tele-transportation, but it, too, faces obstacles. For example, on
this view, it appears to be possible for two future persons to be
psychologically continuous with a presently existing person. Can one
really become two? In response to this problem, some commentators have
suggested that, while our beliefs, memories, and intentions are
experienced to be of utmost importance, they are not necessary for our
identity, our persistence through time.
A third criterion of personal identity is that we are our bodies, that
is to say, that personal identity is constituted by some brute
physical relation between, for example, different bodies or different
life-sustaining systems at different times. Although this view is
still somewhat unpopular, recent developments in personal identity
theory promise an ideological change, as versions of the so-called
somatic criterion, associated with Eric Olson and Paul Snowdon,
attract a continuously growing number of adherents.
The aim of this article is to (1) add precision to the problem of
personal identity, (2) state a number of theories of personal identity
and give arguments for and against them, (3) formulate "the paradox of
identity," which proposes to show that posing the persistence
question, in conjunction with a number of plausible assumptions, leads
to a contradiction, and (4) explain how Derek Parfit's theory of
persons attempts to answer this paradox.
1. Understanding the Problem of Personal Identity
The persistence question, the question of what personal identity over
time consists in, is literally a question of life and death: answers
to it determine, insofar as that is possible, the conditions under
which we survive, or cease to exist in the course of, certain
adventures. These adventures do not have to be theoretically as fancy
as the cases, to be discussed later, of human fission or brain swaps:
a theory of personal identity tells us whether we can live through the
acquisition of complex cognitive capacities in our development from
fetus to person, or whether we have survived car accidents if we find
ourselves in a persistent vegetative state. Furthermore, theories of
personal identity have ethical and metaphysical implications of
considerable magnitude: in conjunction with certain normative premises
they may support the justification or condemnation of infanticide or
euthanasia, or they could prove or falsify certain aspects of our
religious outlook, in deciding the questions of how and whether we can
be resurrected and whether we are possessors of souls whose existence
conditions are identical with ours. It is not surprising, therefore,
that most great philosophers have attempted to solve the problem of
personal identity, or have committed themselves to metaphysical
systems that have substantial implications with regards to the
problem, and that most religious belief systems give explicit answers
to the persistence question. Neither is it surprising that virtually
everybody holds a pre-theoretical theory of personal identity, if only
in the sense of having beliefs about afterlives and the meaning of
death. The task of solving the metaphysical problem of personal
identity essentially involves answering the question of how the
phenomenon or principle in virtue of which "entities like us" persist
through time is to be specified, under the widely but not universally
accepted premises that there is such a phenomenon or principle and
that it can be specified. We are concerned, in other words, with the
truth-makers of personal identity statements: what makes our judgment
that an entity X at time t1 and an entity Y at time t2 are identical
true, if X and Y are entities like us?
a. Criteria and the Identity Relation
Answers to the persistence question often provide a criterion of
personal identity. A criterion is a set of non-trivial necessary and
sufficient conditions that determines, insofar as that is possible,
whether distinct temporally indexed person-stages are stages of one
and the same continuant person. (A temporally indexed person-stage is
a slice of a continuant person that extends in three spatial
dimensions but has no temporal extension.) To say that C is a
necessary condition for E is to say that if E is the case, then C is
the case as well, and to say that C is a sufficient condition for E is
to say that if C is the case, then E is the case as well.
Consequently, to specify such a criterion is to give an account of
what personal identity necessarily consists in.
Let us distinguish between numerical identity and qualitative identity
(exact similarity): X and Y are numerically identical iff X and Y are
one thing rather than two, while X and Y are qualitatively identical
iff, for the set of non-relational properties F1…Fn of X, Y only
possesses F1…Fn. (A property may be called "non-relational" if its
being borne by a substance is independent of the relations in which
property or substance stand to other properties or substances.)
Personal identity is an instance of the relation of numerical
identity; investigations into the nature of the former, therefore,
must respect the formal properties that govern the latter. The concept
of identity is uniquely defined by (a) the logical laws of congruence:
if X is identical with Y, then all non-relational properties borne by
X are borne by Y, or formally "∀(x, y)[(x = y) → (Fx = Fy)]; and (b)
reflexivity: every X is identical with itself, or formally "∀x(x = x).
(Note that congruence and reflexivity entail that identity is
symmetric, "∀(x, y)[(x = y) → (y = x)], and transitive, "∀(x, y,
z)[((x = y) & (y = z)) → (x = z)]).
Grasp of the notion of numerical identity, to be sure, is essential to
our ability to distinguish between the events of picking out one thing
more often than once and picking out more than one thing. Although
exact similarity is, by congruence, a necessary condition for
synchronic personal identity, it is neither necessary nor sufficient
for diachronic personal identity, that is to say, the persistence of a
person over time: two person-slices at different times could be
qualitatively identical slices of different people or qualitatively
distinct slices of the same person. This is not to say, however, that
it is ruled out that lack of similarity over time may obliterate
numerical personal identity: depending on what personal identity
consists in, certain qualitative changes in a person's psychology or
physiology may kill the person. The question a criterion of personal
identity answers is: what kind of changes does a person survive?
This gives a distinctive sense to the claim that a criterion of
personal identity is to be constitutive, not merely evidential: in
order for a relation R to be constitutive for personal identity, it
must be the case that, necessarily, if some past or future Y stands in
an R-relation to X, then X is identical with Y. Hence, many elements
of our successful everyday reidentification practices, such as
physical appearance, fingerprints, or signatures, are inadequate if
considered as constituting ingredients of personal identity relations:
for example, if the man in the crowd is wearing a Yankees jacket, this
might be sufficient evidence for you to conclude that he is your
friend Larry. However, wearing a Yankees jacket is not what it is for
Larry to persist through time: neither did Larry come into existence
when he wore the jacket for the first time nor does he die when he
takes it off.
Does the logic of the concept of identity impose further restraints on
the concept of personal identity? Some commentators believe that
identity is an intrinsic relation, that is, that if two person-stages
at different times are stages of one and the same person, that will be
true only in virtue of the intrinsic relation between these two stages
(cf. Noonan 1989; Wiggins 2001). Others hold identity to be
necessarily determinate, that is, that it is necessarily false that
sometimes there is no answer to the question of whether X is identical
with Y. These commentators typically reason as follows: suppose that
it is indeterminate that X is identical with Y. Since it is
determinate that X is identical with X, under the assumption that
congruence and predicate logic apply, X must be determinately
identical with Y. Therefore, by modus tollens, if X is not
determinately identical with Y, X is not identical with Y (cf. Evans
1985; Wiggins 2001). Consequently, the question does in fact have an
answer, and the claim that identity is indeterminate is
self-contradictory. This conclusion is strengthened, in the case of
personal identity, by the widely shared intuition that even if the
identity of some objects might be indeterminate, this could not be
true of the identity of persons: one cannot, it seems, be bit dead and
a bit alive in the same way in which one cannot be a bit pregnant. As
it turns out, however, there may be good reasons to deny both the
intrinsicness and the determinacy of personal identity (cf. 3.a.;
3.b.).
b. Personhood
While the formal properties of the concept of identity are necessary
constraints on our discussion, the truth of our identity judgments is
subject to material conditions of correctness, which these formal
properties cannot provide. These material conditions must be supplied
by the nature of the relata judged to stand in an identity relation.
The obvious suggestion is that, given that we are dealing with
personal identity, these relata are person-stages located at different
times. This proposal, however, violates the requirement that the
persistence question ought to specify its relata without presupposing
an answer: should we choose to accept a definition in the vicinity of
Locke's characterization of a person as a "thinking, intelligent
being, that has reason and reflection, and can consider itself as
itself, the same thinking thing in different times and places" (1689,
II.xxvii.9), then those criteria of personal identity that sanction
the identity of a person at one time with a non-person at another time
are categorically ruled out. Fetuses, infants, or human beings in a
persistent vegetative state, for example, plainly do not fulfill the
criteria envisaged by Locke. As a result, since these beings do not
possess cognitive capacities, if they do at all, that qualitatively
attain those of thinking beings, couching the persistence question in
terms of persons entails that none of us has ever been a fetus or
infant or ever will be a human vegetable (Olson 1997a; Mackie 1999).
To be sure, these initially baffling claims could be true. However,
since these are clearly substantial questions about our persistence,
we should not consider ourselves justified to settle the matter by
definition. Consequently, we should prefer vagueness over chauvinism
and pose the persistence question in terms of the wider notion of
human being, postponing the question of whether and in what sense the
notions of person and human being ought to be distinguished: for any
person X and any human being Y at different times t1 and t0/t2, if X
at t1 is numerically identical with Y at t0/t2, what makes this claim
necessarily true?
2. Theories of Personal Identity
In order to discover what your pre-philosophical attitude towards this
question is, ask yourself the following: what does a supernatural
being have to do in order to resurrect you after you die? Collect a
few possible answers and ask yourself whether the resulting being, the
freshly created being that is now a candidate for being identical with
you before you died, is in fact you. For example, do you believe that
1. …the supernatural being could have given you a body which bears
no physical continuity or causal relation to the one you possessed
before your death, or that it could have resurrected you, in some
sense or other, as a bodiless being?
2. …it could have given a new form or content to your psychology,
that is, that it is not necessary or sufficient for the "resurrected
you" to remember your actions or experiences and that there do not
have to be any causal connections between the actions and experiences
of you before you died and the"resurrected you"?
3. …the question of whether or not the resulting person is you
depends on the existence, in the resurrected person, of something that
one might call "a soul"?
If you believe any of these options, then you must also believe,
respectively, that
1. …a physiological criterion of personal identity is false.
2. …a psychological criterion of personal identity is false.
3. …the Simple View of personal identity is true.
Let us discuss these theories of personal identity in more detail.
a. The Simple View
Some commentators believe that there are no informative, non-trivial
persistence conditions for people, that is, that personal persistence
is an ultimate and unanalyzable fact (cf. Chisholm 1976; Lowe 1996;
Merricks 1998; Shoemaker & Swinburne 1984). While psychological and
physiological continuities are evidential criteria, these do not
constitute necessary and/or sufficient conditions for personal
identity. We must distinguish between two versions of this view.
Either it is non-reductive and wholly non-informative, denying that
personal identity follows from anything other than itself. This makes
the label Identity Mysticism ("IM") most appropriate (cf. Zimmerman
1998):
IM: X at t1 is identical to Y at t2 iff X at t1 is identical to Y at t2,
Identity Mysticism plays only an indirect role in contemporary
personal identity theory. Although it may be poorly understood, I
must, due to limitations of space, disregard the view here. IM is to
be distinguished from a more popular version of the simple view,
according to which personal identity relations are weakly reductive
(WR) and in independence non-informative (INI):
WR-INI: X at t1 is identical to Y at t2 iff there is some fact F1
about X at t1, and some fact F2 about Y at t2, and F1 and F2 are
irreducible to facts about the subjects' psychology or physiology, and
X at t1 is identical with Y at t2 in virtue of the fact that the
propositions stating F1 and F2 differ only insofar as that "X" and
"t1" occur in the former where "Y" and "t2" occur in the latter.
WR-INI is weakly reductive in the sense that, while the identity
relation in question can be reduced to a further domain, the further
domain itself typically exhibits elements of non-reducibility and/or
resistance to full physical explanation. In their most prominent
variants, these elements are due to references to souls, Cartesian
Egos or other spiritual or immaterial substances and/or properties.
Initially the idea underlying this claim may appear prejudicial;
ultimately it is based on a number of widespread but not universally
accepted beliefs about the naturalness of the world and the nature,
validity and theoretical implications of physicalism. According to
this general stance, either both psychological and physiological
continuity relations are fully reducible to a domain in which physical
explanations are couched, perhaps in terms of the basic elements of a
final and unified theory of physics, or they belong themselves to such
a domain.
WR-INI may entail IM but does not so necessarily: it is conceivable
that personal identity relations consist in something which is itself
neither identical with nor reducible to a spiritual substance nor
identical with nor reducible to aggregates or parts of psychologies
and physiologies. In fact, Descartes' own view that personal identity
is determined by "vital union" relations between pure Egos and bodies,
with the persistence of the Ego being regarded as sufficient for the
persistence of the person but the person not being wholly identifiable
with the Ego, could be a weakly reductive view of persons. It is
merely weakly reductive, however, because the identity of the
phenomenon that specifies the necessary and sufficient conditions for
personal identity does not itself follow from anything other than
itself. While a weakly reductive criterion of personal identity
relations is explicable in terms of the identities of phenomena other
than persons, the identities of these phenomena themselves are not
explicable in other terms: their identity may be, as we would suppose
"soul identity" to be, "strict and philosophical", and not merely
"loose and popular" (Butler 1736).
Nowadays, the Simple View is disparaged as a theory only maintained by
thinkers whose religious or spiritual commitments outweigh the reasons
that speak against their views on personal identity. This is due to
the fact that it is assumed that a theory of personal identity cannot
be weakly reductive without involving appeal to discredited spiritual
substances or committing itself either to the acknowledgment of yet
unrecognized physical entities or to an Identity Mysticism on the
level of persons. As a consequence, many philosophers think that the
problems that infiltrate dualism and Cartesian theories of the soul,
such as the alleged impossibilities to circumscribe the ontological
status of souls and to explain how a soul can interact with a body,
render the Simple View equally problematic. While I agree that the
options mentioned are exceedingly difficult to defend, I do not
understand why they have to be regarded as the only options available
to the Simple Theorist. Arguably, many respectable philosophical
ideologies, such as conceptualism or Neo-Kantianism, may issue in
theories of personal identity along Simple lines without appeal to
Cartesian Egos. (Note, however, that these ideologies, with regards to
the problem of the persistence of people, may also be, and in fact
have been, construed along physiological or psychological lines). This
suggests that we do not only need a better understanding, and above
all more promising articulations, of the Simple View, but also a new
taxonomy of theories of personal identity: the traditional division of
theories into Simple, Psychological and Physical, even if maintained
here by the author of this entry, may not be the best way of viewing
the matter.
b. Reductionism (1): General Features
Modern day personal identity theory takes place mainly within
reductionist assumptions, concentrating on the relative merits of
different criteria of identity and related methodological questions.
Reductionist theories of personal identity share the contention that…
Reduction: Facts about personal identity stand in an adequate
reduction-relation to sets of sub-personal facts SF1.SFn about
psychological and/or physiological continuities in such a way as to
issue in biconditionals of the form "X at t1 is identical to Y at t2
iff X at t1 and Y at t2 stand in a continuity-relation fully
describable by SFx."
Thus, any given set of sub-personal facts will impose demands, in
forms of necessary and sufficient conditions, upon the kinds of
adventures a subject can survive in persisting from t1 to t2. The sets
of necessary and sufficient conditions determined by these sets of
sub-personal facts constitute the various criteria of personal
identity. It must be noted that the biconditionals in question need
not to be understood in such a way as that circularity is an objection
to them: provided that concepts other than "person" feature in the
analysans, these biconditionals, by exhibiting connections with
collateral and independently intelligible concepts, may be genuinely
elucidatory even if the concept to be analyzed features on both sides
of the equation (cf. McDowell 1997; Wittgenstein 1922, 3.263).
Only when the concepts "person" and "personal identity" become the
target of what I shall refer to as an authentic reduction
circularities become vicious. The need for the distinction between
authentic and inauthentic reductions arises due to an equivocation
that ought not to confuse the present discussion: reductionisms in
personal identity theory often take forms, if regarded for example as
sets of supervenience claims, that are deemed, in other areas of
analytic philosophy, as distinctively non-reductionist. I shall speak
of authentic reductions if the ontological status of members of the
reduced category is, in a way to be made precise, diminished in favor
of the allegedly "more fundamental" existence-status of members of the
reducing category. The question of whether an authentic reductionism
about persons must claim that it is not only able to give a criterion
of personal identity without presupposing personal identity but also
that facts about persons are describable without using the concept
"person" is a matter of current controversy (cf. Behrendt 2003; Cassam
1989; 1992; Johnston 1997; McDowell 1997; Parfit 1984; 1999;
forthcoming; cf. also 2.d.).
In a search for the necessary and sufficient conditions for the
sustenance of personal identity relations between subjects, which type
of continuity-relations could SF describe? There are two main
contenders, physiological continuity-relations and physiological
continuity-relations, which I shall discuss in turn.
c. Reductionism (2): Psychological Approaches
Psychological Criteria of personal identity hold that psychological
continuity relations, that is, overlapping chains of direct
psychological connections, as those causal and cognitive connections
between beliefs, desires, intentions, experiential memories, character
traits and so forth, constitute personal identity (cf. Locke 1689,
II.xxvii.9-29; Parfit 1971a; 1984; Perry 1972; Shoemaker 1970;
Shoemaker & Swinburne 1984).
Two apparently physiological theories of personal identity are at
bottom psychological, namely (i) the Brain Criterion, which holds that
the spatiotemporal continuity of a single functioning brain
constitutes personal identity; and (ii) the Physical Criterion, which
holds that, necessarily, the spatiotemporal continuity of that which
sustains the continuous psychological life of a human being over time,
which is, contingently, a sufficient part of the brain that must
remain in order to be the brain of a living person, constitutes
personal identity (cf. Nagel 1971). These approaches are at bottom
psychological because they single out, as the constituting factors of
personal identity, the psychological continuity of the subject.
Consider a test case. Imagine there to be a tribe of beings who are in
all respects like human beings, except for the fact that their brains
and livers have swapped bodily functions: their brains regulate,
synthesize, store, secrete, transform, and break down many different
substances in the body, while their livers are responsible for their
cognitive capacities, basic integrated postural and locomotor movement
sequences, perception, instincts, emotions, thinking, and other
integrative activities. Imagine the brain criterion to be true for
human beings. Would we have sufficient reason to believe the brain
criterion to be true for members of the tribe in question as well, if
we were aware of all facts about their physiologies? I think not:
precisely because the brain criterion is true for human beings, a
liver criterion would have to be true for members of this tribe. There
is nothing special about the 1.3 kilograms of grey mass that we carry
around in our skulls, except for the fact that this mass is the seat
of our cognitive capacities.
We can further distinguish between three versions of the psychological
criterion: the Narrow version demands psychological continuity to be
caused "normally," the Wide version permits any reliable cause, and
the Widest version allows any cause to be sufficient to secure
psychological continuity (cf. Parfit 1984). The Narrow version, we may
note, is logically equivalent to the Physical Criterion.
One might think that brain criterion and physical criterion, to
varying degrees, combine the best of both worlds: both acknowledge the
vital function psychological continuity plays in our identity
judgments while at the same time admitting of the importance of
physiological instantiation. In fact, however, the opposite is the
case: the appeal to physiology introduces an unacceptable element of
contingency into the answers to the persistence question envisaged by
defenders of these criteria. A criterion of personal identity tells us
what our persistence necessarily consists in, which means that it must
be able to deliver a verdict in possible scenarios that is consistent
with its verdicts in ordinary cases. One scenario that has been widely
debated is the following:
Teletransportation
At t1, X enters a teletransporter, which, before destroying X,
creates an exact blueprint of X's physical and psychological states.
The information is sent to a replicator device on Mars, which at t2
creates a qualitatively identical duplicate, Y (cf. Parfit 1984). Our
alleged intuition: since Y at t2 shares with X at t1 all memories,
character traits, and other psychological characteristics, X and Y are
identical. Alleged conclusion: should teletransportation be reliable,
all proposed criteria but the Wide and Widest versions of the
Psychological Criterion are false.
Should teletransportation be unreliable, all criteria of personal
identity but the Widest version of the Psychological Criterion are
false. Consequently, should appeal to such scenarios as
Teletransportation be acceptable and should the intuition above be
widely shared, the brain criterion and physical criterion are false.
d. Quasi-Psychology
Many people regard the idea that our persistence is intrinsically
related to our psychology as obvious. The problem of cashing out this
conviction in theoretical terms, however, is notoriously difficult. I
have already said that psychological continuity relations are to be
understood in terms of overlapping chains of direct psychological
connections, that is, those causal and cognitive connections between
beliefs, desires, intentions, experiential memories, character traits
and so forth. This statement avoids two obvious problems.
First, some attempts to cash out personal identity relations in
psychological terms appeal exclusively to direct psychological
connections. These accounts face the problem that identity is a
transitive relation (see 1.a.) while many psychological connections
are not. Take memory as an example: suppose that Paul broke the
neighbor's window as a kid, an incident he remembers vividly when he
starts working as a primary school teacher in his late 20s. As an old
man, Paul remembers his early years as a teacher, but has forgotten
ever having broken the neighbor's window. Assume, for reductio, that
personal identity consists in direct memory connections. In that case
the kid is identical with the primary school teacher and the primary
school teacher is identical with the old man; the old man, however, is
not identical with the kid. Since this conclusion violates the
transitivity of identity (which states that if an X is identical with
a Y, and the Y is identical with a Z, then the X must be identical
with the Z), personal identity relations cannot consist in direct
memory connections. Appeal to overlapping layers or chains of
psychological connections avoids the problem by permitting indirect
relations: according to this view, the old man is identical with the
kid precisely because they are related to each other by those causal
and cognitive relations that connect kid and teacher and teacher and
old man.
Second, memory alone is not necessary for personal identity, as lack
of memory through periods of sleep or coma do not obliterate one's
survival of these states. Appeal to causal and cognitive connections
which relate not only memory but other psychological aspects is
sufficient to eradicate the problem. Let us say that we are dealing
with psychological connectedness if the relations in question are
direct causal or cognitive relations, and that we are dealing with
psychological continuity if overlapping layers of psychological
connections are appealed to (cf. Parfit 1984).
One of the main problems a psychological approach faces is overcoming
an alleged circularity associated with explicating personal identity
relations in terms of psychological notions. Consider memory as an
example. It seems that if John remembers having repaired the bike,
then it is necessarily the case that John repaired the bike: saying
that a person remembers having carried out an action which the person
did not in fact carry out may be regarded as a misapplication of the
verb "to remember." To be sure, one can remember that an action was
carried out by somebody else; it seems to be a matter of necessity,
however, that one can only have first-person memories of experiences
one had or actions one carried out. Consequently, the objection goes,
if memory and other psychological predicates are not impartial with
regards to identity judgments, a theory that involves these predicates
and that at the same time proposes to explicate such identity
judgments is straightforwardly circular: it plainly assumes what it
intends to prove.
To make things clearer, consider the case of Teletransportation above:
if at t2 Y on Mars remembers having had at t1 X's experience on earth
that the coffee is too hot, then, necessarily, X at t1 is identical
with Y at t2. The dialectic of such thought experiments, however,
requires that a description of the scenario is possible that does not
presuppose the identity of the participants in question. We would wish
to say that since X and Y share all psychological features, it is
reasonable or intuitive to judge that X and Y are identical, and
precisely not that since we describe the case as one in which there is
a continuity between X's and Y's psychologies, X and Y are necessarily
identical. If some psychological predicates presuppose personal
identity in this way, an account of personal identity which
constitutively appeals to such predicates is viciously circular.
In response, defenders of the psychological approach have created
psychological concepts that share with our ordinary psychological
predicates all features except presumptions of personal identity: for
example, the concept of "quasi-memory" is exactly like ordinary memory
apart from the fact that "memory" is judgmental with regards to
personal identity whereas "quasi-memory" is not (cf. Shoemaker 1970).
While many commentators regard the appeal to quasi-memory, and
ultimately "quasi-psychology," as sufficient to solve the circularity
problem, some commentators think that personal concepts infiltrate
extensionally articulated psychological concept-systems so deeply that
any reductionist programme in personal identity is doomed from the
start (cf. Evans 1982; McDowell 1997).
e. Reductionism (3): Physiological Approaches
Opponents of the psychological criterion typically favour a
physiological approach. There are at least two of them: (i) the Bodily
Criterion holds that the spatiotemporal continuity of a functioning
human body constitutes personal identity (cf. Williams 1956-7; 1970;
Thompson 1997); and (ii) the Somatic Criterion holds that the
spatiotemporal continuity of the metabolic and other life-sustaining
organs of a functioning human animal constitutes personal identity
(cf. Mackie 1999; Olson 1997a; 1997b; Snowdon 1991; 1995; 1996). It is
not obvious that there is a straightforward relation between them, for
everything depends on how the notions of "functioning human body" and
"life-sustaining organs" are understood. If these notions are
understood similarly, the views are (close to) equivalent; the other
extreme, even if unlikely to be held, is that the notions are
understood differently, to the effect that they are incompatible (if,
for example, a functioning human body and its life-sustaining organs
could come apart). Physiological approaches have consequences many of
us feel uncomfortable with. Consider the following thought experiment:
Body Swap
X's brain is transplanted into Y's body. X's body and Y's brain
are destroyed, the resulting person is Z. Our alleged intuition: since
Z shares with X all memories, character traits, and other
psychological characteristics, X is identical with Z. Alleged
conclusion: the Bodily and the Somatic Criteria are false (cf. Locke
1689, II.xxvii.15; Shoemaker 1963).
Defenders of bodily criterion and somatic criterion typically bite the
bullet and argue that it is not the case that X and Y have swapped
bodies, but that Y falsely believes to be X, and therefore that Z is
identical with Y.
Since the psychological and physiological approaches are mutually
exclusive and, we may suppose in the current context, as candidates
for an adequate theory of personal identity jointly exhaustive, any
objection against the psychological approach is equally an argument
for the physiological approach. The initial implausibility of the
physiological approach is due to thought experiments that
traditionally permeate the personal identity debate and often favour
psychological considerations. Defenders of the somatic approach, most
notably Olson and Snowdon, have tried to shift the focus to real-life
cases in which descriptions along physiological lines look much more
promising. Consider:
Human Vegetable
X has at t1 a motor bicycle accident. The being Y that is
transported to the hospital is at t2 in a persistent vegetative state.
Our alleged intuition: X at t1 is identical with Y at t2. Alleged
conclusion: all views which postulate psychological continuity as a
necessary condition are false.
Fetus
Since a fetus does not possess the cognitive capacities necessary
to satisfy the demands of the Psychological Criterion, if the latter
is true, no person can be identical with a past fetus. Our alleged
intuition: Each of us is identical with a past fetus. Alleged
conclusion: all views which postulate psychological continuity as a
necessary condition are false.
A third problem for the psychological approach is that it implies,
supposedly, that we are not human animals (Ayers 1990; Snowdon 1990;
Olson 1997a; 2002a). The argument is simple:
Premise 1: Psychological continuity is neither necessary nor
sufficient for the persistence of a human animal.
Premise 2: The psychological approach claims that psychological
continuity is necessary and/or sufficient for our persistence.
A: for reductio:The psychological approach is true.
B: from 2, A: Psychological continuity is necessary and/or
sufficient for our persistence.
Premise 3: Psychological continuity cannot at the same time be (i)
necessary and/or sufficient for a thing's persistence and (ii) neither
necessary not sufficient for the same thing's persistence.
C: from 1, B, 3: None of us is identical with a human animal.
Premise 2 is implied by the psychological approach. The thought
experiments that support premise 1 have already been given: since the
human animal each of us is has been a fetus and could end up as a
human vegetable, the thought experiments Fetus and Human Vegetable
above demonstrate that psychological continuity is not necessary for
human animal identity. A variant of Body Swap shows that psychological
continuity is not sufficient for human animal identity. Suppose X's
brain to be transplanted into Y's skull and X's body and Y's brain are
destroyed. Suppose further that the resulting being Z is
psychologically continuous with X. In this case, it does not seem to
be the case that the surgeons transplant the human animal X from one
head to another. Rather, it seems, the human animal Y receives a new
organ, namely a brain. Consequently, psychological continuity is not
sufficient for human animal identity and premise 1 holds. Premise 3
seems to be obvious, because its being false would entail that one and
the same being can outlive itself, which is absurd. The defender of
the physiological approach now argues that
Premise 4: We are human animals.
C: from B, 4: The psychological approach is false.
Premise 5: Physiological and psychological answers to the
persistence question are mutually exclusive and jointly exhaustive.
Conclusion: The physiological approach is true.
It may be argued that premise 4 is not a matter of metaphysics but of
biological classification. The underlying problem, however, is that it
seems undeniable that there is a human animal located where each of us
is. If this human animal has persistence conditions different from
those that determine our persistence, then there must be two things
wherever each of us is located. This conclusion raises important
questions and problems a psychological approach must address.
3. The Paradox of Personal Identity
One of the most influential thought experiments in recent personal
identity theory is the case of fission, which I shall now discuss.
a. Fission
Fission
X's brain is removed from X's body and X's body is destroyed. X's
brain's corpus callosum, the bundle of fibres responsible for
retaining the capacity of information-transfer between the two brain
hemispheres, is severed, leaving two (potentially) equipollent brain
hemispheres. The single lower brain is divided and each hemisphere is
transplanted into one of two qualitatively identical bodies of the
fission outcomes Y1 and Y2. Our alleged intuition: since both Y1 and
Y2 share with X all psychological characteristics, both are candidates
for being identical with X: either, in the absence of the other, would
have been identical with X. Alleged conclusion: either, on pain of
violating the transitivity of identity, the Psychological Criterion is
false or the question of whether two person-stages X at t1 and Y1 at
t2 are temporal parts of the same person depends on facts concerning
not only X and Y1 but also, in this case, Y2. In the latter case, a
"closest continuer" clause and/or a "no-branching" proviso must
complement a psychological continuity analysis (cf. Nozick 1981;
Parfit 1984; Wiggins 1967).
Fission scenarios emphasise the difficulty of deciding whether a
thought experiment is acceptable or not. They assume the possibility
of commissurotomy or brain bisection, that is, the perforation of the
corpus callosum, and hemispherectomy, that is, the surgical removal of
the cerebral cortex of one brain hemisphere. Commissurotomy was used
in epilepsy treatment in the 50's (cf. Nagel 1971) and
hemispherectomies too have been performed in the past. However,
fission cases additionally assume the possibility, in some sense or
other, of dividing the subcortical regions, and in particular the
single lower brain. This is not physically possible without damaging
the upper brain functions (cf. Parfit 1984). Many commentators regard
fission to be an acceptable challenge to theories of personal
identity. Wilkes disagrees: she thinks that our ignorance about what
actually happens in these cases jeopardises the theoretical relevance
of fission scenarios (cf. 1988). The question of whether or not
physically impossible but logically possible scenarios are acceptable
remains to be answered.
Should fission be an acceptable scenario, it presents problems for the
the psychological approach in particular. The fission outcomes Y1 and
Y2 are both psychologically continuous with X. According to the
psychological approach, therefore, they are both identical with X. By
congruence, however, they are not identical with each other: Y1 and Y2
share many properties, but even at the very time the fission operation
is completed differ with regards to others, such as spatio-temporal
location. Consequently, fission cases seem to show that the
psychological approach entails that a thing could be identical with
two non-identical things, which of course violates the transitivity of
identity. Some commentators have attempted to save the psychological
approach by appeal to the so-called "multiple occupancy view," that
is, the claim that, despite appearances, X was two people, namely Y1
and Y2, all along (cf. Lewis 1976; Noonan 1989; Perry 1972). Combined
with a four-dimensionalist or temporal part ontology, this view is not
as absurd as it initially seems, but it is certainly controversial.
Others have acknowledged, as a consequence of fission scenarios, that
psychological continuity is not sufficient for personal identity.
These commentators typically complement their psychological theory
with a non-branching proviso and/or a closest continuer clause. The
former states that even though X would survive as Y1 or Y2 if the
other did not exist, given that the other exist, X ceases to exist.
This proviso avoids the problem of violating the transitivity of
identity. It is hard to believe, however, because it entails that I
can kill you without you ever noticing: if I knock you unconscious,
transplant one of your brain hemispheres into a different body, and
drop you off at home before you wake up, then, if the transplant is
successful and the psychological approach with non-branching proviso
is true, you are dead. We could avoid this problem by adding a
closest-continuer or best candidate clause, stating roughly that the
best candidate for survival in a fission scenario, that is, the
fission outcome which bears the most or the most important
resemblances to the original person X, is identical with X. One of the
problems with this suggestion is that it assumes that personal
identity is an extrinsic relation. It thereby violates another
important principle, namely the so-called "only X and Y rule," which
states, roughly, that if two person-stages at different times are
stages of one and the same person, that will be true only in virtue of
the intrinsic relation between these two stages (cf. Noonan 1989;
Wiggins 2001). While this principle is not necessarily sacrosanct, it
is desirable to avoid violating it.
b. The Paradox
The upshot of the preceding discussion is that we find ourselves in a
perplexing situation. Let the underlying assumption be that there is a
criterion of personal identity. The starting point of the debate has
been that
Premise 1: A criterion of personal identity captures all those
aspects of our existence that are necessary and sufficient for our
persistence.
Premise 2: Our persistence is determinate.
A: from 1, 2: A criterion of personal identity determines for
every possible past event e0 and future event e2, within the
boundaries of an adequate delineation of the modality in question,
whether a person X at t1 is identical with the being that has
participated in e0 and the being that will participated in e2.
Premise 3: Personal identity relations are factual: criteria of
personal identity are determined neither by conventions, norms, or
other social or personal preferences, however basic, nor by analytic
matters about the meaning of concepts. Their truth is, literally, a
matter of life and death.
B: from A, 3: There is a factual relation R between a person X at
t1 and a being Y at t0/t2 which, for every possible scenario,
determines whether X at t1 is identical with Y at t0/t2.
Now, if we agree with the tentative conclusion that there is, at
present, no satisfactory simple view of personal identity, then we
assent to the claims that
Premise 4: IM and WR-INI are, with respect to a specification of
the necessary and sufficient conditions for personal identity,
inadequate.
Premise 5: The distinction between IM and WR-INI on the one hand
and the reductionist views sketched in I.A.4 on the other is
exclusive.
C: from 4, 5: The only feasible candidates for R are relations of
physiological and/or psychological continuity.
Since B demands that R holds for every possible scenario, within the
limits of an adequate delineation of the modality in question, a
criterion of personal identity must deliver compatible judgments on
the thought experiments sketched above. However, since these thought
experiments deliver conflicting intuitions about which criterion is
true, it cannot be the case that more than one such criterion is true.
From this it follows that
Premise 6: Physiological and psychological criteria of personal
identity are incompatible, that is, R cannot be a conjunction of
physiological and psychological relations as well as issuing in
determinate and compatible solutions to each thought experiment.
Now, if we are also prepared to accept the
Big Assumption: A criterion of identity must accept all alleged
conclusions of the thought experiments sketched in I.A.5
then we must conclude that
D: from B, 6A:Neither physiological nor psychological continuity
is both necessary and sufficient for personal identity.
The problem with D is that, in conjunction with premises 2, 4, and 5,
it reduces the underlying assumption that there can be an informative
criterion of personal identity ad absurdum. This argument I shall
refer to as the Paradox of Personal Identity.
One should refrain from drawing precipitate conclusions from its
defining characteristic as a paradox, that is, the fact that denying
any of its premises leads to a conclusion that either violates our
intuitions or, in the case of 4, 5, and C, commits one to a
philosophically disreputable stance. Rather, the Paradox should be
regarded as the starting point of any discussion of personal identity,
in the sense that taking a stand on its individual premises bestows
the various criteria of personal identity with their distinctive
features. However, given that the paradox obliges us, in one way or
other, to revise our pre-philosophical beliefs, a theory of personal
identity should aim at meeting what I will refer to as the Adequacy
Constraint AC on theories of personal identity, which demands that
AC: We ought to sanction a substantial revision of our
pre-philosophical views of our metaphysical nature only on the
conditions that (i) we receive an explanation of the unreliability of
our intuiting faculties that in this domain outweighs our grounds for,
and in other domains is compatible with, believing in their
reliability; (ii) we receive an approximate demarcation of the extents
to which we have to abandon our pre-philosophical beliefs and to which
we can and we cannot have knowledge about ourselves.
How is the Paradox to be resolved? A, B, C, and D are deductions, and
premise 1 is plausible on independent grounds. If identity is
determinate, then premise 1 is true. Consequently, those arguments
that deny the possibility of vague objects and indeterminate identity,
in addition to our intuition that our own identity must be
determinate, work in favor of 1. Note that, should personal identity
be indeterminate, we might still be able to give a criterion of
personal identity, even though such a criterion would then fall short
of giving full necessary and sufficient conditions, since in some
imaginary case it does not apply.
The denial of premise 3 seems to entail that we have, in a deep sense,
an influence on whether we survive a given adventure, namely by
possessing a particular normative, experiential, or attitudinal
background. This contention may contradict our intuitions more than
any thought experiment could. Since I have decided to assume premises
4 and 5, only premises 2 and 6 and the Big Assumption remain. Could
one deny premise 6? Given that the determinacy and factuality premises
are accepted, I find it hard to believe that we could: if a hybrid
view were determinately true, a human being could die twice, once when
her psychological and once when her physiological capacities cease to
function. As a result, most commentators accept 6 but choose to accept
a particular criterion in the vicinity of either side of the
psychology-physiology divide. This implies that the Big Assumption
must either not entail D or be rejected, which can be argued, always
assuming that AC is being met, in three ways:
(a) One could define "adequacy of modality" in such a way as to
exclude precisely those thought experiments which are problematic for
a given criterion. There are two problems with this proposal: first,
it is difficult to see how such a definition of adequacy of modality
could not be ad hoc. And secondly, the suggestion is insufficient, for
some thought experiments circumscribing physically possible scenarios,
such as Human Vegetable, trigger incompatible intuitions as well.
While some commentators think that Y is identical with X despite X's
loss of cognitive capacities, others regard Y as a living grave stone,
nurtured merely for sentimental reasons, in commemoration of the
deceased X.
(b) One could deny premise 2 instead, arguing that if personal
identity is indeterminate, then our preferred criterion of personal
identity does not have to deliver verdicts in all thought-experimental
scenarios. This move has the further benefit that we do not have to
quarrel with the alleged conclusion of another thought experiment, the
combined spectrum:
Combined Spectrum
A spectrum of possible cases is imagined: at the near end, the
normal case, X at t1 is fully psychologically and physiologically
continuous with Y at t2, while at the far end X at t1 is neither
psychologically nor physiologically continuous with Y at t2. In the
intermediate cases, X at t1 is approximately halfway psychologically
and physiologically continuous with Y at t2. Our alleged intuition:
towards the near end of the spectrum X at t1 is identical with Y at t2
and towards the far end of the spectrum X at t1 is not identical with
Y at t2. There could not even in principle be evidence for the
existence of a sharp borderline between the cases in which X at t1is
and the cases in which X at t1is not identical with Y at t2. Hence, it
is implausible to believe that such a borderline exists. Alleged
conclusion: personal identity is indeterminate.
Epistemicists like Timothy Williamson (cf. 1994) deny that we should
render it implausible that there is such a sharp borderline merely
because we are necessarily ignorant of its existence. Vagueness,
according to epistemicism, consists precisely in our necessary
ignorance of such sharp boundaries. The other problem is that even if
personal identity is indeterminate, the claim cannot by itself
establish one criterion over others: in order to do so, it would have
to exclude those thought experiments that challenge opposing criteria
while leaving untouched those that supposedly establish the preferred
criterion. It is doubtful, however, that the indeterminacy of personal
identity can be exploited selectively, for physiological and
psychological continuity relations are equally indeterminate in a
particular range of cases (cf. Parfit 1984). Furthermore, in those
cases in which they are not, for example Body Swap, Human Vegetable,
and Fetus, appeal to indeterminacy does little to remove the
contradictory intuitions that these cases trigger. Consequently,
unless one holds that personal identity is categorically indeterminate
whenever the physiological and psychological features of a human being
come apart, appeal to indeterminacy cannot establish the rejection of
the Big Assumption in such a way as to avoid the Paradox's conclusion.
(c) The most common strategy is to bite the bullet and some or other
allegedly absurd conclusion of the thought experiments. The defender
of the Psychological Criterion must hold that we are not identical
with a past fetus or infant, and that we will not have survived if
fallen into a persistent vegetative state. Defenders of a
Physiological Criterion, on the other hand, must commit to the
consequence that if X's head is grafted onto Y's body, then the
resulting person is Y and not X, even though this person shares all
psychological features with X before the operation.
The problem with this strategy is that, if accepted, we seem to be
unable to decide on a criterion of personal identity on the basis of
intuitions at all, on pain of unjustifiably favoring one's own over
other people's intuitions. On the assumption that we are unable to
hierarchically structure these conflicting intuitions, we have a
classical stand-off: there are two sides to the coin of personal
identity and appeal to intuition plainly underdetermines preferring
one side over the other. The problem is that human beings are organic
material objects, the persistence of which is determined by these
objects' following a continuous trajectory between space-time points.
The further question of whether or not human beings are essentially
organic material objects depends on the question of whether
psychological properties render human beings to be sufficiently
dissimilar from such objects so as to "deserve" their own identity
criterion. The fear underlying the Paradox of Personal Identity, then,
is that there may be no metaphysical fact to the matter as to whether
the antecedently specifiable differences between human beings and
other organic or inorganic material objects count as sufficient in
order for us to have persistence conditions different from these
objects. It does not seem as if any possible thought experiment,
irrespectively of how unequivocal our intuitions about it, could
redeem this fear. Personal identity theorists, therefore, ought to
offer a more comprehensive account of the ontological status of
persons and their relation to the constituents that make them up.
4. Parfit and the Unimportance of Personal Identity
Derek Parfit proposes a theory of the ontological status of persons,
which promises to answer the problem of fission and the paradox of
personal identity. While I cannot do justice to the complexities of
Parfit's theory, which has been the focal point of debate since 1970,
it is worth mentioning its main features.
Although Parfit affirms the existence of persons, their special
ontological status as non-separately-existing substances can be
expressed by the claim that persons do not have to be listed
separately on an inventory of what exists. In particular, persons
themselves are distinct from their bodies and psychologies, but the
existence of a person consists in nothing over and above the existence
of a brain and body and the occurrence of an interrelated series of
mental and physical events. These are the foundational claims of
Parfit's constitutive reductionism. Consider an analogy: Cellini's
Venus is made of bronze. Although the lump of bronze and the statue
itself surely exist, these objects have different persistence
conditions: if melted down, Venus ceases to exist while the lump of
bronze does not. Therefore, they are not identical; rather, so the
suggestion, the lump of bronze constitutes the statue. The same is
true of persons, who are constituted by, but not identical with, a
physiology, a psychology, and the occurrence of an interrelated series
of causal and cognitive relations.
Now, how does this relate to the fission case? We must first note that
Parfit believes (i) that our persistence consists in physical and/or
psychological continuity; (ii) that personal identity is indeterminate
in some cases, that is, that sometimes there is no right-or-wrong
answer to the question of whether somebody has ceased to exist in the
course of a certain adventure (see 3.b.); (iii) that what prudentially
matters in survival is psychological continuity; (iv) that personal
identity relations must respect the remaining formal properties of
identity. This means that in the fission case Y1 and Y2 cannot be
identical with X because the transitivity of identity is violated:
therefore, X dies in the fission case. It further means, however, that
X has two Parfitian survivors, Y1 and Y2, which is, according to
Parfit, as good (or even better) than being identical with Y1 and/or
Y2. This is the upshot of Parfit's claim that what prudentially
matters is psychological continuity: for all we should care, from a
purely rational point of view, it is good enough for us to be
psychologically continuous with one or more future persons and
consequently it would be irrational for us to prefer our own continued
existence to death by fission. Generally, according to Parfit,
psychological continuity with any reliable cause matters in survival,
and since personal identity does not consist merely in psychological
continuity with any reliable cause, personal identity is not what
matters in survival.
5. References and Further Reading
ANTHOLOGIES
* Bermúdez, Jos‚ Luis; Marcel, Anthony & Eilan, Naomi eds. (1995),
The Body and the Self (Cambridge, MA & London: The MIT Press)
* Blakemore, Colin & Greenfield, Susan eds. (1987), Mindwaves
(Oxford: Blackwell)
* Charles, David & Lennon, Kathleen eds. (1992), Reduction,
Explanation, and Realism (Oxford: Clarendon)
* Cockburn, David ed. (1991), Human Beings, Royal Institute of
Philosophy Supplement, Vol. 29 (Cambridge University Press)
* Dancy, Jonathan ed. (1997), Reading Parfit (Oxford: Blackwell)
* Davies, Martin & Stone, Tony eds. (1995), Folk Psychology: The
Theory of Mind Debate (Oxford: Blackwell)
* Harris, Henry ed. (1995), Identity (Oxford: Clarendon)
* Lovibond, Sabina & Williams, Stephen G. eds. (1996), Essays for
David Wiggins: Identity, Truth, and Value (Oxford: Blackwell)
* Macdonald, Graham F. ed. (1979), Perception and Identity: Essays
Presented to A. J. Ayer, with His Replies (Ithaca, New York: Cornell
University Press)
* Martin, Raymond & Barresi, John eds. (2003), Personal Identity
(Oxford: Blackwell)
* Perry, John ed. (1975), Personal Identity (Berkeley & Los
Angeles, CA: University of California Press)
* Rorty, Am‚lie O. ed. (1976), The Identities of Persons (Berkeley
& Los Angeles, CA: University of California Press)
BOOKS AND ARTICLES
* Ayers, Michael (1991), Locke: Epistemology and Ontology, 2 vols.
(London & New York: Routledge)
* Baker, Lynne Rudder (1997), "Why Constitution Is Not Identity,"
The Journal of Philosophy, Vol. 94, No. 12, 599-621
* Baillie, James (1993), "Recent Work on Personal Identity,"
Philosophical Books, Vol. 34, No. 4, 193-206
* Behrendt, Kathy (2003), "The New Neo-Kantian and Reductionist
Debate," Pacific Philosophical Quarterly Vol. 84, No. 4, 331-50
* Blackburn, Simon W. (1984), "Has Kant Refuted Parfit?," in Dancy
ed. (1997), pp. 180-201
* Butler, Joseph (1736), "Of Personal Identity," First
Dissertation to The Analogy of Religion (reprinted in Perry ed.
(1975), pp. 99-105)
* Campbell, John (1992), "The First Person: The Reductionist View
of the Self," in Charles & Lennon eds. (1992), pp. 381-419
* Cassam, Quassim (1989), "Kant and Reductionism," Review of
Metaphysics, Vol. 43, No. 1, 72-106
* Cassam, Quassim (1992), "Reductionism and First-Person
Thinking," in Charles & Lennon eds. (1992), pp. 361-80
* Cassam, Quassim (1993), "Parfit on Persons," Proceedings of the
Aristotelian Society, Vol. 93, 17-37
* Cassam, Quassim (1997), Self and World (Oxford University Press)
* Chisholm, Roderick M. (1976), Person and Object (Chicago & La
Salle, IL: Open Court)
* Crane, Tim (2001), Elements of Mind (Oxford University Press)
* Doepke, Frederick C. (1996), The Kinds of Things: A Theory of
Personal Identity Based on Transcendental Argument (Chicago & La
Salle, IL: Open Court)
* Evans, Gareth M. (1982), The Varieties of Reference, ed. John
McDowell (New York: Oxford University Press)
* Evans, Gareth M. (1985), Collected Papers, ed. Antonia Phillips
(Oxford: Clarendon)
* Garrett, Brian (1991), "Personal Identity and Reductionism,"
Philosophy and Phenomenological Research, Vol. 51, No. 2, 361-73
* Garrett, Brian (1995), "Wittgenstein and the First Person,"
Australasian Journal of Philosophy, Vol. 73, No. 3, 347-55
* Garrett, Brian (1998), Personal Identity and Self-Consciousness
(London: Routledge)
* Geach, Peter (1967), "Identity," Review of Metaphysics, Vol. 21,
No.1 (reprinted in his (1972), Logic Matters (Oxford: Blackwell), pp.
238-47)
* Gordon, Robert M. (1995), "Folk Psychology as Simulation," in
Davies & Stone eds. (1995), pp. 59-73
* Heal, Jane (1995), "Replication and Functionalism," in Davies &
Stone eds. (1995), pp. 45-59
* Hirsch, Eli (1991), "Divided Minds," The Philosophical Review,
Vol. 100, No. 1, 3-30
* Hume, David (1739), A Treatise on Human Nature, ed. Norton,
David F. & Norton, Mary J. (Oxford University Press)
* Johnston, Mark (1992), "Constitution Is Not Identity," Mind,
Vol. 101, No. 401, 89-105
* Johnston, Mark (1997), "Human Concerns Without Superlative
Selves," in Dancy ed. (1997), pp. 149-79
* Locke, John (1689), An Essay Concerning Human Understanding, ed.
Woolhouse, Roger (London: Penguin, 1997)
* Lowe, E. Jonathan (1991), "Real Selves: Persons as Substantial
Kinds," in Cockburn ed. (1991), pp. 87-108
* Lowe, E. Jonathan (1996), Subjects of Experience (Cambridge
University Press)
* Martin, Raymond (1998), Self-Concern: An Experiential Approach
to What Matters in Survival (Cambridge University Press)
* McDowell, John (1997), "Reductionism and the First Person," in
Dancy ed. (1997), pp. 230-50
* Merricks, Trenton (1998), "There Are No Criteria of Identity
Over Time," No–s, Vol. 32, No.1, 106-124
* Moore, Adrian W. (1997), Points of View (Oxford: Clarendon)
* Nagel, Thomas (1971), "Brain Bisection and the Unity of
Consciousness," Synthese, Vol. 22, 396-413
* Nagel, Thomas (1986), The View From Nowhere (Oxford: Clarendon)
* Noonan, Harold W. (1989), Personal Identity (London: Routledge)
* Noonan, Harold (1993), "Constitution Is Identity," Mind, Vol.
102, No. 405, 133-46
* Nozick, Robert (1981), Philosophical Explanations (Oxford: Clarendon)
* Olson, Eric T. (1997a), The Human Animal: Personal Identity
Without Psychology (Oxford University Press)
* Olson, Eric T. (1997b), "Relativism and Persistence,"
Philosophical Studies, Vol. 88, No. 2, 141-62
* Parfit, Derek A. (1971a), "Personal Identity," The Philosophical
Review, Vol. 80, No. 1, 3-27
* Parfit, Derek A. (1971b), On "The Importance of Self-Identity","
The Journal of Philosophy, Vol. 68, No. 20, 683-90
* Parfit, Derek A. (1976), "Lewis, Perry, and What Matters," in
Rorty ed. (1976), pp. 91-107
* Parfit, Derek A. (1982), "Personal Identity and Rationality,"
Synthese, Vol. 53, 227-41
* Parfit, Derek A. (1984), Reasons and Persons (Oxford University
Press; revised reprint, Oxford: Clarendon, 1987)
* Parfit, Derek A. (1986), "Comments," Ethics, Vol. 96, No. 4, 832-872
* Parfit, Derek A. (1987), "Divided Minds and the Nature of
Persons," in Blakemore & Greenfield eds. (1987), pp. 19-26
* Parfit, Derek A. (1995), "The Unimportance of Identity," in
Harris ed. (1995), pp. 13-45 (reprinted in Martin & Barresi eds.
(2003), pp. 292-318)
* Parfit, Derek A. (1999), "Experiences, Subjects, and Conceptual
Schemes," Philosophical Topics, Vol. 26, Nos. 1-2, 217-70
* Peacocke, Christopher (1983), Sense and Content: Experience,
Thought, and Their Relations (Oxford: Clarendon)
* Perry, John (1972), "Can the Self Divide?," The Journal of
Philosophy, Vol. 69, No. 16, 463-88
* Shoemaker, Sydney (1963), Self-Knowledge and Self-Identity
(Ithaca, New York: Cornell University Press)
* Shoemaker, Sydney (1970), "Persons and Their Past," American
Philosophical Quarterly, Vol. 7, No. 4, 269-85 (reprinted in Shoemaker
(1984), pp. 19-48)
* Shoemaker, Sydney (1984), Identity, Cause, and Mind (Cambridge
University Press; expanded edition, Oxford University Press, 2003)
* Shoemaker, Sydney (1985), "Critical Notice of Reasons and
Persons," Mind, Vol. 94, No. 375, 443-53
* Shoemaker, Sydney (1997), "Parfit on Identity," in Dancy ed.
(1997), pp. 135-48 (revised version of his 1985)
* Shoemaker, Sydney (1999), "Self, Body, and Coincidence,"
Aristotelian Society Supplementary Volume 73, 287-306
* Shoemaker, Sidney & Swinburne, Richard (1984), Personal Identity
(Oxford: Blackwell)
* Snowdon, Paul F. (1991), "Personal Identity and Brain
Transplants," in Cockburn ed. (1991), pp. 109-26
* Snowdon, Paul F (1995), "Persons, Animals, and Bodies," in
Bermúdez, Marcel & Eilan eds. (1995), pp. 71-86
* Snowdon, Paul F (1996), "Persons and Personal Identity," in
Lovibond & Williams (1996), pp. 33-48
* Strawson, Peter F. (1959), Individuals: An Essay in Descriptive
Metaphysic (London & New York: Methuen)
* Strawson, Galen (1999), "Self, Body, and Experience,"
Aristotelian Society Supplementary Volume 73, 307-32
* Swinburne, Richard G. (1973-4), "Personal Identity," Proceedings
of the Aristotelian Society, Vol. 74, 231-47
* Thompson, Judith J. (1997), "People and Their Bodies," in Dancy
ed. (1997), pp. 202-29
* Unger, Peter (1979), "I Do Not Exist," in Macdonald ed. (1979), pp. 235-51
* Van Inwagen, Peter (1990), Material Beings (Ithaca, New York:
Cornell University Press)
* Wiggins, David R. P. (2001), Sameness and Substance Renewed
(Oxford University Press)
* Wilkes, Kathleen V. (1988), Real People: Personal Identity
Without Thought Experiments (Oxford: Clarendon)
* Williams, Bernard A. O. (1956-7), "Personal Identity and
Individuation," Proceedings to the Aristotelian Society, Vol. 57,
229-52 (my references are to reprint in Williams (1973), pp. 1-18)
* Williams, Bernard A. O. (1970), "The Self and the Future,"
Philosophical Review, Vol. 79, No. 2, 161-80 (reprinted in Williams
(1973), pp. 46-63)
* Williams, Bernard A. O. (1973), Problems of the Self:
Philosophical Papers 1956-1972 (Cambridge University Press)
* Williams, Bernard A. O. (1978), Descartes: The Project of Pure
Enquiry (Hardmondsworth: Penguin Books)
* Williamson, Timothy (1994), Vagueness (London & New York: Routledge)
* Wittgenstein, Ludwig (1922), Tractatus Logico-Philosophicus,
transl. D.F. Pears & B.F. McGuiness (London: Routledge and Kegan Paul,
1961)
* Wittgenstein, Ludwig (1953), Philosophical Investigations,
transl. G.E.M. Anscombe (Oxford: Blackwell)
* Wright, Crispin (1983), Frege's Conception of Numbers as Objects
(Aberdeen University Press)
* Zimmerman, Dean W. (1998), "Criteria of Identity and the
"Identity Mystics"," Erkenntnis, Vol. 48, Nos. 2-3, 281-301
No comments:
Post a Comment