Find Enlightenment

Identity And Universals: A Conceptualist Approach to Logical, Metaphysical, and Epistemological Problems of Contemporary Identity Theory
Chapter 5, Personal Identity
by Carolyn Ray

Date: 11 Nov 98
Copyright: Carolyn Ray

The natural way of doing this is to start from the things which are more knowable and obvious to us and proceed towards those which are clearer and more knowable by nature; for the same things are not 'knowable relatively to us' and 'knowable' without qualification....(Aristotle, Physics, 184a17-20).

But yet, when we will inquire what makes the same spirit, man, or person, we must fix the ideas of spirit, man, or person in our minds; and having resolved with ourselves what we mean by them, it will not be hard to determine, in either of them, or the like, when it is the same, and when not (Locke, Essay Concerning Human Understanding, II, xxvii, 15)

Person: RD = A living human being with a mind capable of memory, abstraction, environmental interaction, and causal efficacy with respect to bodily and psychological attributes, and persistent self-awareness with regard to all of these activities and traits.

The Procedure of this Chapter

Although I have stated the definition of 'person' above, I do not assume it in what follows; rather, I try to show how I arrived at it. I attempt to establish that the fact to which the concept PERSON refers is given in experience, and that scientific data and reason converge to corroborate, rather than contradict, this hypothesis. I begin by presenting a overview of the received view concerning the proper method for developing criteria of identity for persons, noting briefly some disagreements with that method. Then I briefly describe a naive view of persons, considering various attacks on that view, and considering the data that tend to contradict or support the attacks. Next, I present two apparent difficulties with the naive view: multiple personality syndrome and the subjects of "split-brain" operations. I evaluate the analyses of these cases, and then offer alternative analyses. I use the concepts developed in this discussion to deal with some commonly-proposed criteria and conditions of personal identity, and to deal with the objections thereto. Finally, I present criteria and conditions of personal identity from the naive point of view. This chapter will further set the stage for solving identity puzzles in logic and those concerning non-persons.

The Received View

The study of personal identity is usually conducted as though the most mysterious and least familiar case of persistence and reidentification is the case of persons. In other words, one of the very things that human beings think they have the least trouble reidentifying is the thing philosophers generally treat as the most unfathomable. The backdrop of this chapter consists of a confused mass of ideas that persistence is an illusion, that there is no self, that persons are not spatiotemporally continuous, that persons can be disembodied, that continuity of consciousness is not wherein personal identity consists, that we must not use the word 'memory' to define the word 'person,' that in fact that it does not matter whether we retain identity over time because all that matters is our projects. There is a great deal of interest, probably due to the difficulty of epistemology and the focus on metaphysics, in eradicating minds from all aspects of identity theory. The result is that personal identity theory is particularly odd, and prone to violations of the law of identity.

It is the received opinion that in order to develop criteria of identity for persons, one must first develop criteria of identity for "simpler" objects (see, e.g., Hirsch, Mills). Discussion frequently starts with rings, lumps of clay, or amoebae. Using the criteria developed for these simple objects, one then moves on to more complex objects such as ships, cats, and human bodies. The results of the analysis are then applied to persons. Even when the starting point seems to be persons themselves, it is often the case that persons are nevertheless being taken apart like ships, or divided like amoeba; then our alleged intuitions about these sci-fi operations are applied to real persons (see, e.g., Parfit, Unger, Kolak, Mills, Swinburne). But if we follow this track, not only personal identity but identity in general will seem incomprehensible. Even as analogies, non-persons and disassembled human bodies fail to be similar enough to persons in the essential respects to help us see what is true of them, and can only lead to loss of focus on the proper object of the study of personal identity.

I defend a different approach. I suggest that, before proceeding to non-person puzzle cases, we acknowledge our implicitly-held theory of personal identity--what are sometimes called "pretheoretic" convictions and premises--and acknowledge that our conceptual scheme is built upon these premises. The assumption of one's own continued identity is involved in any identity claim, overtly expressed or implicitly ascribed to, and it is in comparison to oneself that one makes judgments regarding the persistence of other things. It is therefore impossible to argue coherently against the "naive" view of persons--in fact this view is only naive in the sense that even naive people hold it, and it is profound in the sense that the fact taken by this view as obvious is a necessary condition for human knowledge.

Section I: The Naive View

In any discussion of persons, it is important to keep firmly in mind the fact that under most circumstances neither naive people nor philosophers have trouble determining whether they are confronted with a person at any given moment. It is also important to note that we have little trouble reidentifying persons with whom we are familiar. Rather than take this as evidence of just how naive we are, we should consider why this might be so, and why we are--apparently--so successful at it. In part, it is due to the fact that what is being determined is not whether an entity one meets on the street fits into a fixed category, but whether there are any important similarities between this entity and the entities (primarily, oneself) that one has already classified as persons.

You have a set of faculties that, taken together, you refer to as your mind. You direct some of the activities of your mind, such as deliberation; but some activities do not require your full conscious attention, such as comprehending music while focusing on reading. Other activities do not require your attention at all, such as sitting upright, and dreaming--these activities occur subconsciously.

The fact of personal identity is primary: it is self-evident to you that you exist, that you are conscious, that you remember. Personal identity cannot be demonstrated. To prove your own personhood and persistence to yourself or anyone else, you must assume them. Proof that you are not a persistent person relies on your ability to follow the argument, which requires sensation, perception, persistence, and memory. And these faculties are always embodied. Consciousness requires that there be something external to consciousness to be conscious of; and the only way to become conscious of something external is through sensory apparatus, which are part of a body.

There is no possibility of demonstrating "we are not what we believe." We know what we are, whether we can articulate all of our features or not. It is on the basis of self-knowledge that we are able to form the concept PERSON. To fundamentally change that concept requires denial of this knowledge--in other words, it requires one to contradict oneself, and thus reduces to an absurdity, even by the standards of logical possibilism. If one were to attempt to form or reform the concept PERSON solely on the basis of observations of others or on the basis of thought experiments, again one would fall into contradiction, for it is impossible to block out that internal knowledge which is the standard to which all other beings are compared. Moreover, attempting to deny that persons are as we think they are is again to fall into contradiction, since it is the way that we are that one depends upon in order to disprove it: we are rational, self-aware, unified, and persistent, and all of these ingredients are required to engage in the argument.

The fact that I have a body is given in every act of awareness--it is self-evident. Proving that I am embodied requires a body and denying it assumes I am embodied. There is nothing from which one might differentiate embodiment. Thus the question whether I am embodied or just a soul thinking myself to be embodied is misguided from the outset and cannot reasonably arise when all of this self-knowledge is kept in mind.

Upon looking around the world I do notice that there are objects that may be differentiated from all other objects according to certain characteristics. These objects first and foremost are like me. They are conscious, rational, etc. I can talk to them, make friends with them, have fights with them, remember them, and get remembered by them. They can integrate their past experiences with the present, can recognize things that they have learned. They are always associated with human bodies, and so I at first informally come to think of the term 'human being' as synonymous with 'person'. So a metaphysically necessary condition for the existence of a person is a functional body. And it is also an adequate epistemological criterion for judging whether the same person persists, since I can always judge, for example, who my friends are by which bodies I am facing.

However, there are entities to which the word 'human being' applies, while failing to meet the metaphysical conditions required to give rise to and sustain persons; for example, some kinds of brain damage result in human beings who cannot integrate new information with old memories. Perhaps it is more precise to say that they fail to be so similar in certain important respects to the things I call persons that I am tempted to not include them. Clearly, the persistence of the body is not a metaphysically sufficient condition for the persistence of the same (or even the existence of any) person: a person may cease to exist while the body persists. Contrary to common ways of thinking about criteria, this does not mean that the bodily criterion is inadequate; on the contrary, it is in virtue of this very criterion that we are able to judge that a person has died--how else would we know in the normal case?

I suggest that these facts cast grave doubts upon those inquiries into the nature of personal identity which seek to determine what the word 'person' means by examining case after case of what it does not mean. I suggest that the proper approach to personal identity puts persons back into the inquiry. Persons each take their own case as paradigmatic; unfamiliar individual human beings are identified as persons by comparison to an ever-expanding body of empirical data, but the standard is each person's own case. It is this inductive, everyday approach that I suggest is necessary for more complicated philosophical investigations. This approach is recommended by the conceptualist view of universals, in that it acknowledges that each of us must create his or her own concepts IDENTITY and PERSON, and that to do so requires that each of us observe the facts which give rise to them and pick out the important features--a factor that weighs heavily in its favor from a philosophical point of view. It is also tremendously successful--a factor that weighs heavily in its favor from a common-sensical point of view.

To counteract any temptation to lose sight of this personal knowledge as somehow inferior or tainted and to force the reader to focus on his or her own experiences, knowledge, and consciousness, I have been writing and will continue to write in the first and second person; to help give a sense of the force of the arguments in this chapter, I will use the reader as one of my primary examples.

Differentiating Ourselves By Means Of Contrast Objects

Metaphysically, our nature and the persistence of ourselves and other things is a fundamental assumption. We cannot proceed with our daily lives, acquire knowledge, etc., unless it is true that things, including ourselves, are some way, and endure for some time.

Suppose that some human being was not aware of or did not believe this fundamental fact. Suppose further that this human being attempted to live life in complete consistency with this denial. Such a human being would be unable to perform actions requiring extended planning, even extended thought; after all, if I cannot assume my own identity, then it must also be true that I cannot connect one thought to another. Future selves literally would not matter. Oliver Sacks describes such a being:

He remembered nothing for more than a few seconds. He was continually disoriented. Abysses of amnesia continually opened beneath him, but he would bridge them, nimbly, by fluent confabulations and fictions of all kinds. For him they were not fictions, but how he suddenly saw, or interpreted, the world. Its radical flux and incoherence could not be tolerated, acknowledged, for an instant--there was, instead, this strange, delirious, quasi-coherence, as Mr Thompson, with his ceaseless, unconscious, quick-fire inventions, continually improvised a world around him...

But does Mr Thompson himself know this, feel this?....Is he in a torment all the while--the torment of a man lost in unreality, struggling to rescue himself, but sinking himself, by ceaseless inventions, illusions, themselves quite unreal? It is certain that he is not at ease--there is a tense, taut look on his face all the while, as of a man under ceaseless inner pressure; and occasionally, not too often, or masked if present, a look of open, naked, pathetic bewilderment....

....What comes out, torrentially, in his ceaseless confabulation, has, finally, a peculiar quality of if it didn't really matter what he said, or what anyone else did or said; as if nothing really mattered any more (Sacks, Hat, pp. 111-112).

The case of William Thompson is no science fiction thought experiment. It is reality for the victims of Korsakov's Syndrome, one symptom of which is complete anterograde amnesia (the inability to form new abstractions and memories) and frequently accompanied by retrograde amnesia (the loss of memories of the past). While the concept IDENTITY is not formed with reference to a contrast object, one can see from these cases of damaged human beings what life might be like if one had never been able to form this concept. Another of Sacks's Korsakov's Syndrome patients, Jimmie G., was able to remember things for a few minutes, sometimes long enough to complete a game of checkers. Unlike Thompson, he seemed to show a sense that there was something wrong, especially when confronted by facts that contradicted his image of himself as the nineteen-year-old he had been 40 years earlier. Jimmie was horrified to see the reflection of an old man in the mirror; Sacks distracted him by changing the subject, then walked out of the room:

Two minutes later I re-entered the room. Jimmie was still standing by the window, gazing with pleasure at the kids playing baseball below. He wheeled around as I opened the door, and his face assumed a cheery expression.

'Hiya, Doc!' he said. 'Nice morning! You want to talk to me--do I take this chair here?' There was no sign of recognition in his face.

'Haven't we met before, Mr G.?' I asked casually.

'No, I can't say we have. Quite a beard you got there. I wouldn't forget you, Doc!' (Sacks, Hat, p. 25).

Because the retrograde amnesia wiped out all memories formed after around 1945, Jimmie, who had been in the Navy until 1965, did not recognize technological developments made since that time; newspapers and television were available to him, but he had forgotten what he had learned and was no longer retaining any new information:

'What is this?' I asked, showing him a photo in the magazine I was holding.

'It's the moon,' he replied.

'No, it's not,' I answered. 'It's a picture of the earth taken from the moon.'

'Doc, you're kidding! Someone would've had to get a camera up there!'


'Hell! You're joking--how the hell would you do that?'

Contrasting ourselves with such human beings allows us to focus on some of the facts about ourselves that we take for granted: that we are able to self-consciously understand our relationship to our environment, to integrate our past with that environment and with the present, and to form new abstractions and memories. These features are surely part of what you mean when you refer to yourself, whatever you may think of William Thompson's or Jimmie G.'s personhood.


Memory is an important subject in personal identity; however, its importance is overlooked, and frequently disputed. Let us focus on this elusive idea. What are the facts that give rise to the concept MEMORY? Memory is not itself awareness; it is a sort of product of awareness and abstraction working together. When I acquired my first bicycle, I was aware of acquiring it. It is not correct to say that I am now aware of acquiring the bike; I need to distinguish one idea from the other. Thus, I am aware that I was aware of things of which I am not now aware, yet I can relate those experiences to myself in the present. It is this fact that gives rise to the concept MEMORY.

It should be apparent from the preceding documented cases that memory is a prerequisite for awareness of the fact that things have identity. Awareness of the fact of identity need not be something that the human being can state explicitly; but evidence of the awareness--or lack thereof--manifests itself in the behavior of the being. Human beings with the kinds of brain damage mentioned above exhibit behavior that, were we to conceptualize its assumptions, seems to assume that nothing, including themselves, endures. One might speculate that, though they too once recognized the fact of identity and implicitly formed the concept, they are no longer able to apply it--or perhaps it seems to them that this concept simply does not apply. Perhaps this accounts for their apparent fear, desperation, and confabulation: they sense that there is something terribly, fundamentally wrong with the world because they have distant memories of "how it used to be."

It is because of this lack of knowledge of itself as a being with identity that it also cannnot know other things to have an identity; without the ability to relate other things to oneself, one cannot retain any information about those things. It is therefore as though those things do not have an identity. In fact, it is as though they do not persist at all, and that which does not persist does not exist. This is just how the anterograde amnesiac behaves: it is as though things that he is not staring at at the moment do not exist.

Our contrast object helps us to understand how crucial is one's own persistence for the awareness of the identity of other things, and how crucial is memory for one's own persistence. Human beings are the measure, epistemologically, of the identity and persistence of things other than themselves. The amnesiac's estimate of the endurance of things other than himself reveals his estimate of his own endurance. To speak of the persistence of victims of retrograde and anterograde amnesia may be to speak merely of the persistence of a human body, or perhaps of that body and certain aspects of the things we call 'persons.' With that build up for memory, then, we turn to Locke's much-cited, and much-maligned, view of the person.

The Continuity Of Self-Awareness

Identity theorists do not always straightforwardly deny the self-evident fact of personal identity. The attack is usually more roundabout; and though it may not always be any author's intention, the combined result of such attacks is that the concept PERSON is chipped away until there is little left.

I quote Locke at length here, to clear up a particularly insidious rejection of the self-evident fact of personal identity.

This being premised, to find wherein personal identity consists, we must consider what person stands for:--which, I think, is a thinking intelligent being, that has reason and reflection, and can consider itself as itself, the same thinking thing, in different times and places; which it does only by that consciousness which is inseparable from thinking, and, as it seems to me, essential to it: it being impossible for any one to perceive without perceiving that he does perceive. When we see, hear, smell, taste, feel, meditate, or will anything, we know that we do so. Thus it is always as to our present sensations and perceptions: and by this every one is to himself that which he calls self: since consciousness always accompanies thinking, and it is that which makes every one to be what he calls self, and thereby distinguishes himself from all other thinking things, in this alone consists personal identity, i.e., the sameness of a rational being: and as far as this consciousness can be extended backwards to any past action or thought, so far reaches the identity of that person; it is the same self now it was then; and it is by the same self with this present one that now reflects on it, that that action was done. (Locke, Essay, II, xxvii, 11).

Locke does several things here: (1) He picks out the referents of the concept ("idea") PERSON: they think, reason, reflect, are intelligent, and are aware of their own spatiotemporal persistence ("can consider itself as itself, the same thinking thing, in different times and places"). (2) He argues that these things are able to be aware of their own persistence because they cannot help but be aware of being aware. (3) He argues that since awareness of being aware is that which a being refers to when it uses the word 'self,' this is what personal identity consists in. (4) He invokes memory ("as far as this consciousness can be extended backwards to any past action or thought") as the necessary condition of the person's persistence through time.

These details all seem sensible, but before we embrace them, a famous objection from Bishop Joseph Butler must be met:

One should really think it self-evident that consciousness of personal identity presupposes, and therefore cannot constitute, personal identity, any more than knowledge in any other case can constitute the reality which it presupposes (quoted in Locke, p. 458, note 1).

Butler is onto something important. It is true that consciousness of personal identity presupposes personal identity. The reason he gives is also true: awareness of any fact requires the existence of that fact. And since any particular person's understanding of personal identity requires that he or she acquired that understanding on the basis of his or her own case, personal identity must be taken as given.

This objection has had enormous influence in the history of personal identity theory. It is generally taken to show that continuity of consciousness cannot be what is meant by 'personal identity.' However, Butler has mistaken Locke's point, at least as it is stated above (see also Locke, Essay, II, xxvii, 17, for a similar formulation). Butler argues against the claim that personal identity consists of awareness of personal identity--which we might understand to be awareness of the person or of the self as a whole. But Locke actually claims that awareness of particular acts of awareness constitutes personal identity. Particular acts of awareness and the self-as-a-whole are not the same thing; and awareness of the latter is arguably a more advanced piece of conceptual knowledge, while the former is a basic given, a primary fact--and this seems to be precisely what Locke intends: "it being impossible for any one to perceive without perceiving that he does perceive." Moreover, memory of particular past acts of awareness combines with the awareness of particular present acts of awareness, and this is what we mean by the whole self. Thus, Butler's objection attacks a straw man, and Locke's theory, which I take seriously as part of the naive view, remains undamaged.

Echoing Butler in their criticisms of Lockean characterizations of persons, some identity theorists have claimed that the concept MEMORY cannot be used in a definition of personal identity. Memory implies that there is a rememberer, so the argument runs--in other words, the very self or person whose nature is being defined: "personal identity cannot be defined in terms of memory since one must already be in possession of the concept of personal identity, and be able to determine that it applies, in order to be in a position to operate with the concept of memory at all" (Noonan, Personal Identity, p. 14). This objection, too, misses the mark; we have already seen that Noonan is confounded by his conflation of metaphysics with epistemology, and here is a further result of that confusion. The passages from Locke to which Noonan objects do not appear to attempt a definition of personal identity at all. One need not be in possession of a sophisticated philosophical idea of persons, in order to have memories; and it is the having of memories, not the concept MEMORY, that Locke is talking about. A human being needs only an experience and the capacity to remember it to get the process of "person-formation" started. Infants, who do not have any concepts at all, certainly do not need the concept PERSON nor any notions about personal identity in order to remember; and very young toddlers can use the word 'remember' to tell you about their trip to the zoo, despite the fact that they cannot tell you anything about personal identity.

Removing the concept MEMORY from either the definition of 'person' or the characterization of personal identity obliterates the meanings of both 'person' and 'personal identity.' Memory--the fact, the function--must be operative in order for abstraction to take place; and the concept PERSON must be developed by abstraction. Thus, memory is metaphysically prior to--and is a necessary condition for--the existence of a person. Memory makes personal identity possible; therefore, it is a ghastly mistake to say memory presupposes personal identity.

What can we conclude about persons vis a vis memory? The fact of memory is self-evident, lies at the base of all knowledge, and leads to circularity and contradiction in proofs or denials of it (see also Butler, Dissertation on Personal Identity). Memory is a metaphysically necessary condition for personal identity; it makes one's existence as a person possible. It is also something that we can test fairly easily in others by asking the right questions; thus, memory is a useful epistemological criterion for reidentification of other persons, and that is because it is an epistemologically obvious and metaphysically necessary condition for personal identity. Furthermore, memory is a metaphysically necessary condition for our epistemological awareness of the identity not only of ourselves, but of the things that we compare to ourselves. Because of this causal relationship, which Noonan has reversed, the concept MEMORY helps to make the concept PERSON intelligible. We will put it right back where it belongs, into the definition of 'person,' and into the characterization of personal identity.

Is memory a sufficient condition for being a person? Obviously not. Dogs and rats remember. And in the absence of the ability to form new memories--the ability to understand the relationship between old memories, oneself, and the present--a human being with anterograde amnesia is very, very different from the sort of things we call 'persons.'

Section II: Unity Of Mind

An identity theorist might agree that fiction has no bearing on our concept PERSON but still worry about documented split-brain and "multiple personality" cases; these are sometimes offered as scientific proof of the falsity of the "naive" view that persons correspond one-to-one with human bodies (see, e.g., Parfit, Glover, Mills, Unger). Thus, to complete the examination of the concept PERSON, we must remove some suspicions about divided consciousness and multiple occupation.

In the first part of this section, I argue that the data concerning brain-damaged human beings provide contrast objects that help to show that personal identity and unity of consciousness are prerequisites of any inquiry and virtually all activities required for human life. The trend in philosophy is to avoid objectively assessing these cases on the grounds that real life can only provide messy complications to an otherwise neat theory of personal identity. I will argue that a sober evaluation of these unfortunate beings is crucial to a complete philosophical investigation of the concept IDENTITY. They provide contrast objects that can help us to talk about the boundaries that we normally draw between persons on the one hand and all other objects of our world on the other, and help us to say just what we mean by 'persistence.'

In second part of this section, I argue that those persons suffering from what is known as "multiple personality syndrome" provide a different sort of contrast object--one that helps draw the distinction between a person and a person-ality. This distinction is neglected in the philosophical literature, though not without some good reason: the scientists who write about these phenomena do not distinguish consistently between the concepts PERSON and PERSONALITY, despite the fact that they frequently use the distinction, implicitly. I will argue that some scientists' use of these concepts is not based on more thorough acquaintance with the referents of those, but rather on their lack of philosophical sophistication in making distinctions.

The Split Brain

Philosophers are not alone in the study of personal identity. Neurologists, neurosurgeons, psychiatrists, and other scientists who study the biology and psychology of human beings have added some quite accessible literature to our bibliographies. This is a great boon. Instead of having to imagine what might happen if a human being's cerebral hemisphere is removed, we have actual case histories of such accidents and procedures. We can use this data to help us think about the concepts IDENTITY and PERSON.

Jonathan Glover has made some forays into the neurological literature in an attempt to understand personal identity. I take Glover as representative of identity theorists who are concerned with the scientific findings about brain damaged patients. Unlike those I refer to as the 'science fiction philosophers,' Glover in general attempts to remain within the bounds of available scientific data. Nonetheless, his representation of that data is not always accurate, and his conclusions conflict with the data. Let us first understand his view, and then see what can be made of it. I note in passing that nowhere in his book on personal identity does Glover explain what he means by the terms 'mind,' 'consciousness,' 'person,' 'unity,' 'divided person,' or 'divided consciousness;' hence, I will attempt to supply definitions that are based on the overall point of the text.

Glover advances three claims: (1) "our natural belief that a person has an indivisible unity is mistaken...Consciousness can be divided;" (2) "being a person requires self-consciousness;" and (3) "our natural beliefs about what our own unity consists in are mistaken" (Glover, I, p. 14). The first and third claims are typical of the literature and disputing them will help to show what is wrong with one of the most common approaches to personal identity. Let us examine Glover's claim that "our natural belief that a person has an indivisible unity is mistaken," for which he claims to have scientific evidence.

Some of the data that Glover considers come from experiments with the subjects of commissurotomy. In order to understand the results and evaluate the conclusions Glover draws from them, a brief introduction to the surgical procedure is in order.

Beginning in the 1940's, a number of operations to sever the cerebral commissures were performed on worst-case epileptics in the hope of eliminating seizures. The commissurotomies worked well for their intended purpose; the best news was that absolutely no side effects were evident to the patients themselves, their physicians, or their friends and relatives. The total perceived effect can be summed up as follows: before the operation, the patients had suffered debilitating seizures (ones that would occur so frequently as to prevent them from leading normal lives), and after the operation they proceeded to live average and neurologically uneventful lives, to the extent that the aftermath of such traumatic seizures permitted.

Neurologist Roger Wolcott Sperry found it incredible that one could sever 800 million nerve fibers without making any observable difference beyond the cessation of seizures. He designed an elaborate laboratory experiment to search for hidden side-effects. It is worth giving a complete description of the experimental set-up, some of which had to be obtained from sources other than Glover's presentation, as the details are important.

The experimenter covers one of the subject's eyes, and instructs him to focus the other eye on a dot on a projection screen; this prevents the natural orienting movements of the eye that normally would allow the subject to see the screen to the left and to the right of the dot. A picture is projected onto the screen, for 1/10 second, so that the dot is in the center of the picture. The result is that the eye does not have time to scan from left to right and thus the subject does not see the picture as a whole. The picture flashed is actually a stimulus chimera, which is formed by cutting in half pictures of different objects, and joining the left half of one to the right half of the other. The subject is instructed to say the name of what he sees. He is also instructed to feel for and pick up an object that corresponds to what he sees. Since looking for the object would involve the orienting movements of the uncovered eye, the objects and the subject's hands are hidden from his sight. In order to prevent tell-tale sounds from giving the patient clues as to what his hands are picking up, the table is carpeted (Trevarthen, 'Split,' 742).

These experiments showed conclusively that there was indeed a further effect. In unaltered brains, information about the external world is transmitted virtually instantaneously from one cerebral hemisphere to the other via the cerebral commissures. In commissurotomy subjects, it must be transmitted between the hemispheres via alternate routes, including the lower regions of the hemispheres and the brain stem structures and external relations of the body with stimuli and its own reactions thereto. In other words, in the absence of cues from other parts of his body under the experimental conditions, the commissurotomy subject is unable to pass certain kinds of information directly from one hemisphere to the other.

It had long been known that nerve cells responsible for scanning the right half of the visual field ran directly to the left cerebral hemisphere, and that nerve cells responsible for scanning the left half of the visual field ran directly to the right hemisphere. It had also long been known that the nerve cells in the left hand are connected directly to the right hemisphere, and the nerve cells in the right hand are connected directly to the left hemisphere. But it was not certain whether the cerebral commissures were functional in distributing messages among the hemispheres, or whether this distribution occurred solely through the lower brain regions. In fact, in both animal and human subjects who had undergone commissurotomy, "movements, alertness, and general motivation were entirely normal," to the extent that it was suspected that the commissures had no psychologically or neurologically interesting function apart from spreading epileptic seizures (Trevarthen, 'Split,'p. 741).

Sperry's experiment not only proved there was a side-effect, but did so spectacularly. It was found that, under the experimental conditions, a commissurotomy patient is unable to talk about information that enters the right hemisphere via visual stimulation, even though he can communicate it through manipulation of objects, and he is unable to communicate through manipulation of objects the information that enters the left hemisphere via visual stimulation. For example, suppose that a stimulus chimera composed of the left half of a cube and the right half of a ring is flashed on the screen. The subject's left hand, which is hidden from his view, is then presented with an assortment of 3-dimensional objects, such as a ring and a cube and some other easily distinguished objects (also hidden from view). If asked to find with his left hand the object that feels like what he saw, the subject's hand will pick up the cube--this information is fed from the left visual field into the right hemisphere, which controls the left hand. But if asked to say the name of what he saw, the subject will say the word 'ring'-- this information is fed from the right visual field into the left hemisphere, which controls speech.

If shown the object his hand picked up and asked to explain why he didn't pick up the object he named, he will confabulate--i.e., tell a plausible story that includes both objects, though these inconsistent results accompanied by story-telling occur with such regularity that it is clear he is just making the story up to make sense of the conflicting information. He might say, "I saw a ring, and that made me think of a box to put the ring in, so I picked up the cube."

Jonathan Glover takes this result as evidence for the notion that "consciousness" may "divide," and that the split-brain patient is a case of such division. He concludes that each hemisphere is "aware" of things that the other hemisphere is not "aware" of. We will see that there is good reason to object to this portrayal of the situation (in fact it begs the question in favor of divided consciousness and multiple occupancy), but for now let us presume that we know what he means by the terms in scare-quotes and grant the inference.

The facts concerning commissurotomy patients are often taken as sufficient reason to doubt the unity of consciousness. But Glover notes that there is yet another product of modern medicine that lends support to the doubt:

Some people have their left hemispheres surgically removed in adult those who know them they seem recognizably to be people with an inner life of their own.

It seems that, when the left hemisphere has been removed, the right hemisphere can be associated with consciousness. It is hardly likely that the presence in the same skull of a disconnected left hemisphere changes this. And so it is reasonable to see the disconnected right hemisphere of the split-brain patient as a centre of consciousness. If this is right, the experiments do demonstrate divided consciousness (Glover, I, p. 40).

A detailed look at Glover's argument is in order. I draw attention to key terms and phrases with italics.

1. A human being who has had the left cerebral hemisphere removed is judged by its associates to be a person with an inner life; such a person has a center of consciousness in the remaining right hemisphere.

2. A commissurotomy patient is a human being who has a disconnected hemisphere in his skull.

3. Therefore, a human being who has undergone commissurotomy is like a human being who has had one cerebral hemisphere removed.

4. But in the case of the split-brain patient, the left cerebral hemisphere is still present.

5. If a right hemisphere can support a center of consciousness, then surely a left hemisphere can support a center of consciousness.

5a. In addition, it is unlikely that the presence of a second hemisphere in the skull changes whether or not the first one can support on its own a center of consciousness.

6. The Sperry laboratory experiments provide independent evidence for the conclusion that it is possible for a split-brain patient to have two centers of consciousness.

7. Thus, there is reason to say that a split-brain patient has two centers of consciousness.

Because the type of argument and interpretation of scientific results that Glover presents is typical of and taken as crucial to personal identity theory, let us examine carefully each of the above propositions in turn.

1. A human being who has had the left cerebral hemisphere removed is judged by its associates to be a person with an inner life ; such a person has a center of consciousness in the remaining right hemisphere. So far I have been unable to find information on adult human beings who have had the entire left hemisphere removed (Glover does not supply any cases), although some very young children have undergone hemispherectomy, which removes the cerebral cortex covering one hemisphere. In their case, the plasticity characteristic of very young neurons allows the remainder of the brain to restructure and compensate for most of the damage, though the brain will never be completely normal (Bloom and Lazerson, Brain, pp. 296-297). But Glover appears to have in mind adults who have had this procedure done. It may be that a human being whose entire left hemisphere has been removed seems to have an inner life. But to some extent, so does a dog, or a rat; we do not impute personhood, or the kind of consciousness we associate with persons, to them on that account. I will not focus for the moment on what is meant by 'consciousness' here, but will merely point out the use of the term so that the progression of this argument is apparent. At any rate, this premise is more complex than it at first appears: it suggests that anything with something like consciousness is necessarily a person in the sense that we normally mean.

2. A commissurotomy patient is a human being who has a disconnected hemisphere in his skull. Glover's description of the facts of the commissurotomy is misleading: one pictures a human being limping along with one hemisphere doing the work of two, while the other sloshes loosely in the cranial cavity. Glover's implicit assumption is that when the commissures are cut, there are two separate organs or that the former single organ is now in pieces; this is most emphatically not the case. There is no "disconnected hemisphere" in the skull of the split-brain patient. Commissurotomy is more analogous to cutting a finger, than to cutting off a finger. The brain is an organ which may be viewed as having several regions; two of those regions, the two cerebral hemispheres, are directly connected to each other by the corpus callosum--but they are also connected through the brain stem, which is not in any way altered by commissurotomy. Thus we can immediately see that the next statement is false as well:

3. Therefore, a human being who has undergone commissurotomy is like a human being who has had one cerebral hemisphere removed. Again, we must assume that it is the human being whose cerebral hemisphere is removed in adult life that Glover has in mind. If so, then he fails to mention that the subject of cerebral hemisphere removal would be severely debilitated in a way that the commissurotomy patient is not. Data on human beings whose either right or left cerebral hemisphere has been only partially damaged is readily available. We could expect the subject of right hemisphere removal to be unable to recognize shapes (including printed words) and hence be unable to read or even to navigate its environment; visio-spatial disorders resulting from damage to the posterior of the right hemisphere can leave the patient unable to acknowledge the existence of the left half of the body, unable to dress, unable to recognize faces, and tending to walk into walls (if able to walk at all). They cannot be made to understand that there is a "left side" of the world--for them, only what is in the right half of their visual field exists. One of Sacks's patients, Mrs. S., suffered damage only to the back and lower portions of the right cerebral hemisphere and consequently lost the idea of "left":

....Sometimes she complains that her portions are too small, but this is because she only eats from the right half of the plate--it does not occur to her that it has a left half as well. Sometimes, she will put on lipstick, and make up the right half of her face, leaving the left half completely neglected...

Knowing it intellectually, knowing it inferentially, she has worked out strategies for dealing with her imperception. She cannot look left, directly, she cannot turn left, so what she does is to turn right--and right through a circle. Thus she requested, and was given, a rotating wheelchair. And now if she cannot find something which she knows should be there, she swivels to the right, through a circle, until it comes into view. She finds this signally successful if she cannot find her coffee or dessert (Sacks, Hat, pp. 77-78).

If the left hemisphere were removed, we could expect the human being to be unable to work with language in the usual ways:

Further tests show that the right hemisphere is virtually unable to imagine the sound of a word for an object seen, even a very common one like an 'eye', so it cannot solve a test requiring silent rhyming 'in the head' (for example, 'eye' matches with 'pie', 'key' matches with 'bee'). It seems as if the habitual, and inherently favoured, dominance of the left hemisphere for speaking is tied in with a one-sided ability to predict how words will sound. The right hemisphere can know the meaning of a word from its sound, but it cannot make a sound image for itself from sight of the word, or from sight of the object the word stands for (Trevarthen, 'Split,' p. 744).

In addition, each cerebral hemisphere encompasses limbic system structures crucial to the formation of new memories: the hippocampus and the amygdala. And we saw in the chapter on thought experiments, loss of cerebral cortex in Alzheimer's victims eventually results in loss of long-term memories. With the entire cerebral hemisphere removed, it is not clear what would be left of the person. (For a brief excursion through the severe disabilities that arise for real human beings whose allegedly redundant or unimportant brain structures have been damaged or surgically cut or removed, see the Appendix.)

5. If a right hemisphere can support a center of consciousness, then surely a left hemisphere can support a center of consciousness. Now the equivocation on the word 'consciousness' combines with the lack of data to begin its work: Recall that in the first premise, we allowed the term 'consciousness' to mean what we, as conscious beings, usually mean by it; given the scant data I have just provided, it seems Glover must mean something different. If by 'center of consciousness' Glover means 'a cerebral hemisphere that can produce bodily responses to stimuli under experimental conditions without reference to concurrent information from the other cerebral hemisphere,' then there is some sense in which the right hemisphere supports a center of consciousness. Again, I shall leave this point without saying more here, for this is much work to be done to straighten out this tangle.

5a. In addition, it is unlikely that the presence of a second hemisphere in the skull changes whether or not the first one can support on its own a center of consciousness. This premise is supposed to appeal to parsimony in explanation. In Glover's words:

It is hard to accept that consciousness divides and unites when people enter and leave the experimental set-up. It is simpler to suppose that the operation just divides consciousness, rather than supposing that it somehow combines with the experimental conditions to cause a series of temporary divisions (Glover, p 41).

This "simpler" supposition involves ignoring the massive amount of evidence to the contrary provided by the patients' daily lives under ordinary circumstances. They can control and get feedback from both hands as easily as do normal people; they are completely coordinated in all of their endeavors, to the extent that no one--including the patients--suspected that anything was different about them. The experimental setup required to elicit the unusual effect is extremely elaborate. And the effect is temporary. It is, on the contrary, harder to suppose is that the elaborate experimental set-up expressly designed to aggravate the physical effects of commissurotomy does not combine with the commissurotomy to produce the mental effect.

6. The Sperry laboratory experiments provide independent evidence for the conclusion that it is possible for a split-brain patient to have two centers of consciousness. This proposition requires an implicit--and unwarranted--assumption that all stimulus-response is conscious. But there is an important distinction between stimulus-responses of which we are conscious and stimulus-responses of which we are not conscious; that distinction is blurred in Glover's argument. Stimulus-response is not identical to, nor even necessarily indicative of, awareness. Consider, for example, the blink of an eye at the approach of a speck of dust; this movement is usually performed without the awareness of the subject, even though some of the time people also blink voluntarily and deliberately. The important point to note is that the frequency with which eye blinking as a stimulus-response is accompanied by or even due to our awareness does not imply that awareness always accompanies or causes this action. There are two kinds of stimulus-response: conscious and unconscious.

Eye blinking is a quite simple function, and it might be objected that language comprehension, visual recognition, and the cooperation of the two is much too complex to be analogous. However, more complex examples can be produced. I am an amateur harpsichordist. I find that I am completely unable to verbally report on the notes that I play with my left hand. Moreover, unless I have learned the bass line separately, I am unable to hear, while I am performing, the entire bass line although I am aware of a greater "fullness" to the music than I would hear if I played the right hand alone. I am not only completely unable to state verbally the names of the notes that I am playing (even though I read music and know the names of the notes on the scale), but I am unable to hum the bass line from memory. The recognition of the position of the notes on the page "triggers" the movement of my fingers to the corresponding position on the keyboard, and (most of the time), an intelligible bass line is produced that others can hear, and which I could easily hear if I listened to a tape of my performance. This is all despite the fact that the music that I play is predominantly contrapuntal, which usually results in a bass line that is linear and quite melodious itself--in other words, "hummable."

One possible response to this as a counterexample to Glover's conclusion that consciousness may divide is that I have simply shown that my consciousness is divided, and quite possibly that I, and many other musicians, have some sort of brain damage. However, such a response would lead straight to the conclusion that pretty much every human being's consciousness is multiply splintered. Every normal human being is regularly engaged in a variety of activities that may have demanded conscious attention at one time but are now automatic. For the musically disadvantaged, I supply a list of automated actions for consideration, all of which could be used instead of my music example to stress that successful response to the environment need not indicate conscious awareness: balancing and standing up straight while reading at the bus stop; walking (or bike-riding or driving) while talking and chewing gum; scratching an itch while enjoying a concert; touch-typing a paragraph while working out the details of the paragraph; staying inside the highway lane and responding to signs and signals while monitoring the car's speed and conversing with a passenger. Ask yourself what inner ear sensations you have had to monitor and what muscular contractions and relaxations you have had to enact in order to stay upright for the past five minutes, and you may perhaps find it easier to believe that the split-brain subject could respond to some stimuli without being conscious of it.

7. Thus, it is reasonable to say that a split-brain patient has two centers of consciousness. We have seen that Glover has not given us much reason to believe his conclusion that the split-brain patient has two centers of consciousness; on the contrary, his discussion and the data highlight the important fact that normal persons regularly engage in all manner of behavior and stimulus response without awareness of the response or the behavior. To bring them out, let us depart into a discussion of consciousness, keeping Glover's assertions in mind. Let us apply our standard method and ask, "What facts in reality give rise to the concept CONSCIOUSNESS?

We have already seen that the fact of consciousness is a self-evident fact. But as we develop and use the concept, we can find contrast objects from which to differentiate conscious beings, and begin to worry about what sorts of things are similar enough to the conscious things we already know about (principally, ourselves) to be included in the concept. The concept and its definition are important for making these distinctions.

The claim that there is consciousness of an event refers to a complex set of facts. What are those facts? I can distinguish the feeling of doing something or having something happen to me while I observe, from the feeling that something happened while I was unable to observe. For example, I have attempted to remind my brother of morning phone conversations I had with him; he cannot remember them at all, because it turns out that he was asleep during those "conversations." I can succeed in reminding him of conversations that he has forgotten because he had those conversations while he was awake. It would make no sense to protest to my brother that, since he did actually respond to my queries and comments during those conversations in the wee hours, he was in fact conscious of our conversation. Nor would it make sense to suggest that while half of his mind was aware of the conversation, the other half was not, suggesting two centers of "consciousness."

I can also distinguish the different states that human beings can be in, by observing from the outside how they interact with their environment; I see a similarity in behavior--especially linguistic behavior--among those human beings who not only respond to the environment, but can reflect and report on experiences, as differentiated from those human beings who cannot do this. For example, I can distinguish between someone who is drugged and someone who is sober on the basis of what each does when slapped: the sober one will respond and be able to report having experienced the event; the drugged one will not. It would make no sense to say to the drugged person, "Of course you were conscious of being slapped; you just did not know it at the time, and cannot be reminded of it now." If an event happens to someone but she cannot report having experienced it (and there are no memory problems that can be detected), she is said to not have been conscious of it.

And it is the fact that I can engage in some acts consciously while I engage in others subconsciously or unconsciously that gives rise to the concept MIND. There is a difference between 'unity of consciousness' and 'unity of mind,' if 'consciousness' is taken to name the faculty of awareness. The mind engages in all sorts of subconscious and unconscious functions, including the integration of information from two slightly impaired post-commissurotomy hemispheres. Thus, at least under experimental conditions, the commissurotomy subject has separate stimulus-responses, but never has divided consciousness--as is demonstrated by the fact that under experimental conditions, the hemispheres "correct each other" by a frown or a nod of the head--a phenomenon known as 'cross-cuing.' The commissurotomy subject's mind is only divided in the sense that it engages in both conscious and subconscious processes simultaneously--just like ours.

Conscious Subprocessors?

Recall that Glover claims that there are two centers of consciousness for a given commissurotomy patient. Can we make sense of this idea? I contend that to claim that there is consciousness is precisely to claim that there is something which is conscious. Let us say, for the sake of clarity, that I have undergone commissurotomy. If Glover claims that there is conscious subprocessing occurring within the confines of my body, but that no one I know of is conscious of it, then he must mean that there is something other than me that is conscious in its own right; so there are two conscious beings in this body--it is simply that one of them cannot communicate with me or anyone else, and it only makes its appearance known by responding to simple stimuli. If that is not his claim, but rather that I am the one conscious of these things, then he is claiming that I am conscious of things I am not conscious of, which is absurd.

In fact, no one in this body is aware of the processes I perform without being aware that I perform them. This is the fact that gives rise to the concept SUBCONSCIOUS. This is a quite ordinary feature of the life of a person, as we are beginning to see. Part of what the concept PERSON includes is the fact of unconscious and subconscious processes: i.e., processes that my nervous system is able to accomplish without my awareness of them. One is the "memory search" which apparently continues even after conscious focusing has ceased. Another is "pent-up" emotions which can arise because of inadequately resolved situations, and which later cause behavior that the actor does not herself understand. Another is the regulation of temperature and heart rate. This is all part of what gives rise to the concept PERSON. In fact, so much of what our nervous systems do is inaccessible to our direct awareness that we would probably be unlikely to categorize a thing as a person if it did not show signs of subconscious processing--if it not only did not dream, but did not have flashes of insight, never started out of a doze with a remembered name, could not hold a conversation while walking or while driving a car, had to concentrate in order to shave and bathe, had to go through a mental checklist in order to recognize a familiar face, had to pay attention to balance and movement, etc. Such a creature would be very dissimilar to the things that we call 'persons,' since engaging in all those activities consciously would prevent it from doing all the things the normal human being is free to do with its conscious attention.

Dominant Hemispheres

I conclude the discussion of the commissurotomy subjects and all the philosophical troubles they have contributed to with a brief discussion of hemisphere specificity. Part of Glover's problem in interpreting the data is that he makes too much of the term "dominant hemisphere." He is not alone; it is common in the literature to understand the dominant hemisphere to be the one that does all the important work, with the other hemisphere running little subprograms and playing slave to it--helpful, but redundant and negligible. The stage is immediately and illegitimately set for the "transplant" of the adult right hemisphere into another body. However, because the functions of the hemispheres are not only different but complementary, the neurologist's term 'dominant' is a loaded one in the hands of a philosopher who is arguing that consciousness may divide. Glover treats hemisphere specificity differently depending on the case at hand, and if he would commit himself to one view or the other, true or false, the puzzles would disappear: either the functions of the brain are hemisphere specific and thus one needs both hemispheres in order to be what we ordinarily think of as conscious and as persons; or the functions of the brain are not hemisphere specific, and the brain can make do without one of its hemisphere with no loss of person. He cannot have it both ways.

Nor do the functions of the brain divide neatly between the two hemispheres. For example, while the capacity to form memory resides in portions of the brain stem, long-term memories seem to be widely distributed throughout the brain, including the brain stem, with memory for certain kinds of things (shapes, for example) being localized for the most part in the right hemisphere, and memory for certain other kinds of data (words, for example) being localized in the left. The most obvious, most parsimonious explanation for the split-brain patients' alternate-route compensation for the severed corpus callosum is that one human hemisphere is inadequate to deal effectively with the world, as is amply corroborated by brain damaged human beings. Indeed, the patient's confabulation under experimental conditions indicates that there is only one center of consciousness, that it is localized in those regions of the brain responsible for language use, and that no one at all was conscious of the stimuli to and responses from the right hemisphere. (See also, Carlson, Physiology, p. 5, for similar conclusion).

Finally, Trevarthen offers this opinion concerning just how isolated from each other the hemispheres are:

Evidently, the semi-conscious appreciation of the location and orientation of major features in outside space, mainly picked up from dynamic transformations of the visual image, is not divided by commissurotomy. Indeed, the general background or context of body coordination and orienting must be intact for commissurotomy subjects to retain the freedom of action and coherence of awareness they ordinarily exhibit. To this degree the operation does not divide the agency of the subject, or the experience of whole-body action. The two halves of the neocortex are kept in functional relationship, coordinated through ascending and descending links with the sub-hemispheric regions of the brain stem (Trevarthen, "Split-Brain," p. 743).

Let us take stock. It begins to appear that to define the word 'person,' we must account for subconscious processes, at least by using the concept MIND, which includes both conscious and subconscious processes, and that a metaphysically necessary condition for the existence of a person is both conscious and subconscious processors.

But we are not done with multiple occupancy yet. In the next section, I deal with the psychological phenomenon known as 'multiple personality.'

Multiple Personality

Multiple personality is another exciting phenomenon for identity theorists. The condition appears to provide proof that persons do not necessarily correspond one-to-one with normal human bodies. Like the oddities of the condition of commissurotomy patients, this syndrome is difficult to express in conventional language, and this difficulty shows up even in skeptical descriptions. Charles Rycroft, a psychoanalyst whose views on the syndrome are quite conservative, says that in multiple personality "the subject maintains for a considerable length of time some line or course of action in which he appears not to be actuated by his usual self--or alternatively, his usual self seems not to have access to the recent memories that one would normally expect him to have." The subject "appears to change from one person to another" (Rycroft, p. 197).

Since 'multiple personality' is a household term, and since others (e.g., Wilkes, Real, pp. 100ff) provide detailed and diagramed accounts and philosophical analyses, I will not go into any detail about cases in this work. Although my conclusions about the syndrome may be controversial, the distinctive details of individual cases do not make a difference to them. In my descriptions of the basic symptoms, I will attempt to avoid question-begging by referring to the subject-in-a-state.

Human beings who experience multiple personality syndrome exhibit at different times two or more fairly coherent sets of personality traits, each for some extended period of time. These periods are sometimes referred to as "fugues" or "states." They are also referred to in more question-begging ways: "Personality X took over the body from Personality Y," or worse, "Person Z took possession of the body from Person P." Sometimes, but not always, what happens to the subject in one state seems to be forgotten by the subject in a different state. For example, Mary Reynolds, studied by William James, was a somber, melancholy, shy, fearful person until the age of 19; she suddenly became cheerful, social, reckless, and fearless, and acted as though she had forgotten her family and friends. Thenceforth, she experienced such reversals repeatedly. When she was somber, she recognized her family again, and was distressed to hear stories of what she had been doing when reckless; when she was cheerful, she treated her family as strangers, and was amused by stories of what she had been doing when shy (Rosenfield, Strange, pp. 123ff). Christine Beauchamp, Morton Prince's patient, sometimes could remember what she had been doing when she was in certain states but not in others.

Apparently, the psychoanalytic jury is still out on the question of what exactly the phenomenon amounts to. Rycroft believes that the extreme rarity and bizarreness of the condition indicate that it is actually a "social and psychiatric artefact" which only occurs when society is prepared to accept the notion of more than one personality per body and when the diagnosing psychiatrist believes in it. His argument hinges on the fact that the great majority of cases reported date from between 1840 and 1910--"from after demoniacal possession had ceased to be a plausible, scientifically respectable explanation of sudden, extraordinary changes in personality until the time at which psychoanalytical ideas began to have an impact" (Rycroft, 'Dissociation,' p. 197). He speculates that the fact that people were unaware of the phenomenon of transference, especially the tendency of the patient to produce symptoms to please the physician, made it easy for them to believe some stories that today would seem silly to trained psychoanalysts. Rycroft thinks the real problem is rather deception and self-deception.

I make no attempt to deny that this syndrome occurs. Whatever the explanation, these are the facts that give rise to the concept DISSOCIATION. However, when interpreting the data for use in identity theory, it is crucial not to be swept away by the terminology. What can be said about persons, given multiple personality syndrome? To answer that, we have to ask, "To what in reality does the concept PERSONALITY correspond?"

I have argued that each conscious subject forms the concept PERSON on the basis of his or her own internal awareness, and then extends the concept to other beings as it is inferred that are similar in that they too have this internal awareness. Unlike the concept PERSON, the concept PERSONALITY is formed on the basis of observations of others. We notice that other beings have their own peculiar ways of behaving and responding to the environment and other beings. One person may become enraged by a traffic jam and swear loudly to himself, while his passenger responds by looking with interest at the other drivers and the scenery. The former may be shocked and disoriented by unusual situations, while the latter takes them in stride or responds with curiosity. We do not always observe these kinds of styles immediately, without prompting, in ourselves; sometimes others must point them out to us and give names to our traits: moody, pensive, shy, picky, friendly. It is to these observable traits that we refer when we speak of a person's person-ality. We freely apply the concept PERSONALITY to animals as well; even those who would have a hard time saying "Dogs are people too" would describe a dog as having a certain personality. My rats have very different personalities: Silhouette is sweet, affectionate, undignified, social, and impervious to commands yet easily cowed; Oreo is aloof, reserved, sneaky, persistent, and domineering yet obedient. To personify an animal is to impute to it the same motivations and thoughts that persons have; but to describe it as having a personality is merely to acknowledge that it responds to its environment in some particular style.

Normal human beings may drift smoothly out of one personality and into another in the course of a day as their environment changes. It is common for people to be well-behaved and cooperative, even jovial, at work, where it is required that they stifle feelings of anger, resentment, and vengefulness--and yet be openly furious and abusive to their families at home, where such behavior may be tolerated. These "states" can persist for longer periods. If pressure and tension are steadily or increasingly applied long-term, a person may remain irritable, nervous, and prone to outbursts of rage--all which symptoms may disappear suddenly when the pressure is removed. The person may not remember what was said in rage, and may even have no idea how much time has elapsed.

My intention is not to recount the development of split personality syndrome, nor to explain it away. Rather, I think that we should attempt to see it as an extreme form of the variations to which even normal human beings are subject. Personality is the format or style in which a human being responds to its environment. Each person responds to the environment in some format, and, rarely, in more than one disjoint format. The difference between a human being with multiple personality disorder and a normal human being on this view is that the normal human being has smooth transitions between formats, whereas a human being suffering from multiple personality disorder exhibits sharp, jerky transitions and will maintain a certain format for extended periods. In addition, the normal human being is not surprised to hear about something that she did, and in fact usually knows it; the human being suffering from multiple personality disorder does not know at any given time what sorts of behavior he is capable of.

Israel Rosenfield offers a particularly comprehensible and demon-free analysis of split personality syndrome. Rosenfield's view is that a human being suffering from multiple personality disorder has no personality which is fully adequate--or, in my terms, no format which is by itself well-suited to the business of dealing with an environment--and the mind responds to this fact by turning from one format to another, abruptly, in search of a "fit" which it can never find, each personality being limited by its very nature as a fragment. Multiple personality disorder is never such that any one personality is a complete response-format. We can find evidence of this in the fact that it is common for the person to be unable to feel pain in one its formats, and in the fact that cheerfulness and recklessness are not tempered by prudence: the prudent pain-feeler is set aside as one "thing," and the cheerful daredevil as another. Because neither personality is acceptable, each is disowned, and frequently declared a thing apart by the bestowal of a name (Rosenfield, Strange, pp. 120ff).

Thus we can see that multiple personality disorder admits of unsensational and metaphysically parsimonious interpretations, which happen to fit quite nicely with the nature of human beings as we know it and have been discussing it here. To regard these as cases of distinct persons associated with a single body is an unwarranted restructuring of the conceptual scheme. I suggest that the term 'multiple personality' is unfortunate, and that 'split personality' has more appropriate connotations: the format in which a person responds to the environment is split into smaller sets.

Again let us take stock. I have claimed that each person knows what a person is from his or her own case, and that other beings get included under the concept PERSON on the basis of similarity to that case. I have gone some way toward the characterization of persons on the basis of my own case and cases that are similar to mine, and on the basis of differentiation from cases of damaged human beings and differentiation from the mere forms of expression of the person via personality traits. Now we are in a better position to tackle the epistemological criteria by which the persistence of the person is judged, usually referred to as 'criteria of personal identity,' and the metaphysically necessary and/or sufficient conditions for being the same person.

Section III: Criteria and Conditions of Personal Identity

In what follows, I take Harold Noonan's critique of various kinds of criteria of personal identity as my point of departure, and consider his criticisms to be objections to my own view. I will use his arguments as contrasts to my own to bring out the full meaning of each.

Noonan surveys and neatly summarizes standard proposed metaphysical conditions and epistemological criteria of identity and follows them with standard objections to motivate each of the remaining proposals. You may recall that he sees his project as strictly metaphysical; however, since there are both metaphysical and epistemological questions to be raised, I will attempt to deal simultaneously with both in a well-delineated a manner, to emphasize both the connection between these two kinds of questions and also the conflations to which such discussions are susceptible. Noonan's formulations of the criteria will be briefly stated, along with what he takes to be unanswerable arguments against them.

The bodily criterion: "P2 at time t2 is the same person as P1 at time t1 if and only if P2 has the same body as P1 had"(Noonan, p. 3).

....though it is undeniable that in our everyday experience personal identity is constituted by bodily identity, it seems all too easy to imagine possible cases in which this is not so. But if such cases are indeed possible then personal identity cannot, as a matter of logical or conceptual necessity, consist in bodily identity....

....Imagine, then, that in the twenty-first century it is possible to transplant brains, as it is now possible to transplant hearts, and let us suppose that the brain of a Mr. Brown is transplanted into the skull of a Mr. Robinson...." (Noonan, Personal Identity, pp. 3-4 [emphasis Noonan's]).

Throughout the history of philosophy, the most reasonable objection to the idea that the body is an ingredient of personal identity has been inspired by religious considerations: If personal identity consists in bodily identity, then perhaps there is no immortal soul, and various religious texts are false. I say that this is the most reasonable objection because, superstition being part of the everyday lives and epistemological frameworks of prescientific people, it precludes any questioning to the contrary. The sort of case which has led most contemporary philosophers to think that the bodily criterion of personal identity must be rejected is unreasonable; given that our culture is immersed in information from the sciences, it is disconcerting that the doctrine of logical possibility has been able to undermine the specification of criteria of identity to this extent. Having dealt with the problems of science fiction philosophizing already, we are free now to criticize other aspects of the objection.

1. The apparent philosophical simplicity of the objection is misleading: it assumes a great deal about the nature of persons. I will not argue against the assumptions, since the onus of proof is on anyone who would construct such objections; I will simply state them, in order to make it clear what sorts of commitments are required to make the objection run. (1) It is assumed that the brain alone carries the entire person, self-contained, within its confines. The person and the body are two separate entities, glued together by means of the brain; and while the person may somehow be attached to the part of the body that lies inside the skull, it is in no metaphysically necessary way attached to the rest of the nervous system nor to the rest of the body. (2) It is assumed that the alleged person in the disembodied brain would live without the body whence it came; the person may be packed up in its brain and shipped off to another place. (3) It is assumed that the alleged person would take up residence in the new body; not only is the person separate from the body, but it is not picky about which body it gets stuck to. I contend that this objection can only begin to sound plausible given a new brand of dualism, despite the very physical and technological facade: the immaterial soul, unimpeded by the extraneous body, may ride in its material brain to a new body.

2. One ought to notice straight away how Noonan states this alleged "criterion" of identity. He states it as an biconditional, an 'if and only if' statement. This is because he is trying to get at the (metaphysical) essence of personal identity, what "personal identity consists in." He is also motivated by the search for a definition, which he thinks, in deference to modern logical theory, must be stated in the form of a biconditional. Here is what the statement says, broken into its component parts:

(M1) If P2 at time t2 is the same person as P1 at time t1, then P2 has the same body as P1 had

(E1) If P2 has the same body at t2 as P1 had at t1, then P2 is the same person as P1.

Yet this way of putting it is doomed to failure even without any science fiction. We can agree with the first statement, M1: Sameness of person is a metaphysically sufficient condition for sameness of body, and sameness of body is a metaphysically necessary condition for sameness of person. This statement certainly coheres with the naive view. However, why would anyone agree with the second statement, E1, which, if we are to believe Noonan's professed interest in metaphysics, says that sameness of body is a metaphysically sufficient condition for sameness of person, and that sameness of person is a metaphysically necessary condition for sameness of body? Clearly, death is a counterexample, and, arguably, many cases of brain damage are as well. If one of the conditionals is false, then so is the biconditional; noting this fact, we begin to uncover the problems with representing either criteria or conditions of personal identity as biconditionals (we shall see more in a moment).

And yet, we can feel the pull of the biconditional: it almost seems that, in one direction, it states the metaphysical conditions, and in the other direction, it states the criteria: the second conditional statement, above, which I have labeled 'E1', for 'epistemological' would then have it that ascertaining sameness of body entitles the judgment of sameness of person. We can even make use of the necessary "condition": the judgment of sameness of person necessitates ascertaining sameness of body--or something like that. However, Noonan does not make this distinction, and indeed it seems a dangerously confusing, equivocal way of putting things. What I think he really wanted to get at here, and in the rest of the "criteria" he discusses, is that sameness of body is a metaphysically necessary condition for the persistence of a person, and that it is also an adequate epistemological criterion for judging sameness of person.

Since we have no reason to think that the brand of dualism that seems to be emerging here is true, nor that such operations are possible, this objection gives us is no reason to reject the sameness of body as a metaphysically necessary condition for the persistence of a person, nor as an epistemologically adequate criterion of reidentification of persons over time.

One better objection to the epistemological criterion might be that it frequently happens, as we have now seen, that the body continues to function (walking around, talking) and even some personality traits remain, yet it is not clear that a person remains (since the responses to the environment are not at all similar to the way we, as paradigm cases, respond). William Thompson might be considered a counterexample to the bodily criterion of reidentification. This motivates us to try Noonan's next criterion.

The Brain Criterion: "P2 at t2 will be the same person as P1 at t1 just in case P2 at t2 has the same brain as P1 at t1"(Noonan, p. 5).

The human brain has two very similar hemispheres....

Let us suppose that half of a man's brain is destroyed and then the remaining half transplanted into another body with consequent transference of memories, personality, and character traits. Here we can neither appeal to the original Bodily Criterion of personal identity nor to the Brain Criterion to justify the judgement that the surviving person is the brain hemisphere donor....if we accept that a person goes where his brain goes it cannot make any difference if his brain in fact consists of only one brain hemisphere combining the functions usually divided between two (Noonan, pp. 5-7 [emphasis mine]).

One notable point is that justification of judgment has started to creep in to the objections to metaphysical conditions. Noonan has told us, as part of the initial conditions, that the person has been transferred to a new body; yet he objects to the metaphysical conditions on the grounds that we cannot justify our judgment that the person has been transferred to a new body. Why would we need to justify that? It is given; and if we plug that given premise into the metaphysical end of the biconditional, we get to conclude that we have the same brain. Noonan's metaphysical facade is beginning to wear thin. As is usually the case with science fiction thought experiments, the wild scenario is the hypothesis; we are told exactly what to think about the hypothesis from the very beginning. This is no test of a condition at all.

It is worth once again breaking down this biconditional, because the objection turns out to be very strange.

(M2) If P2 at t2 is the same person as P1 at t1, then P2 at t2 has the same brain as P1 at t1

(E2) If P2 at t2 has the same brain as P1 at t1 then P2 at t2 is the same as person as P1 at t1

Again, if E2 really were a metaphysical claim, no one would agree with it; brain death and just plain death are counterexamples. Thus, if we are not to interpret Noonan as attacking a straw man, we have to read it as an epistemological claim. And in fact, Noonan does attack the "criterion" on epistemological grounds this time. So he must be attacking E2 here. But if that is true, how did he do it? He gave us that it is the same person; he allegedly gave us as well that it is not the same brain. If this really is an attack on E2, then it is an attack by denial of the antecedent, which is a fallacious argument. Moreover, if the attack is on E2, then he has not attacked M2, which is the only reasonable metaphysical claim in sight, and which is the parallel of the statement he attacked when criticizing the bodily "criterion." So what about M2?

Noonan says that the problem with the brain criterion is that personal identity can be preserved without brain identity. What makes him say this? M2 says that sameness of person is sufficient for sameness of brain. And, as we just noted, we have been given that it is the same person. Do we not have sufficient reason to conclude that it is the same brain? His other statements certainly support this: since the hemispheres, according to his view of neuro-physio-psychology, are substitutable and therefore dispensible, loss of one hemisphere should not be very important. It would be analogous to a hand losing one finger, or a human being losing an arm. We do not think that someone has a different hand simply because she lost a finger. When he dealt with the bodily criterion, it seemed that an almost Lockean metaphysical condition of sameness of body was operative--he thought that we had sameness of body (though it had lost a brain) without sameness of person, and sameness of person without sameness of body; but here, that same condition is not operative. How can such a distinction be justified? I suspect that it is due to a commitment to the idea that the body is not really involved in all this person-business. Only the brain counts, and as the life of the party, it cannot afford to lose some parts and still retain its identity; however, the person's identity is not to be thwarted either by the loss of a mere body, nor by the loss of half of a mere brain. In other words, the scent of dualism is getting stronger.

A more realistic objection to the epistemological statement E2 might be that, as Noonan mentions, sometimes people do lose parts of their brains to stroke. One woman of my acquaintance suffered stroke to one hemisphere, and her personality was just as irritable and domineering as ever, but she was completely paralyzed, did not recognize her associates, showed little awareness of her surroundings, and habitually repeated one phrase ("The name...the name," ) with increasing volume and insistence until someone did something--it did not matter what--for her. It was not clear to her family that any person persisted there. (And, as is usually the case, contra Noonan, what was left of her brain never compensated for the damage.) So here we have a case of Lockean brain-and-body persistence, yet apparently do not have persistence of person. Yet we are tempted, on both the brain and bodily epistemological criteria E1 and E2, to say that it is the same person.

Can we say anything reasonable about the discussion of the brain criterion? The persistence of the brain is apparently a metaphysically necessary condition of personal identity. We have a great deal of scientific and personal evidence for this view, and no evidence against. As an epistemological criterion for reidentification, it could conceivably be useful; for example, in a murder involving mutilation, samples of brain tissue might be used to identify the victim. Unless new technology becomes available, ordinary people will simply have to assume that the same brain is in the same body, just as they have always done, and thus, epistemologically, this criterion collapses into the bodily criterion.

In these preceding two "criteria," Noonan appears to be missing his true target, and it is because he thinks he needs to specify necessary and sufficient conditions in terms of a biconditional. In turn, the biconditional form leads him to (1) believe that he has to make up an example that will result in personal identity without identity of the human body, rather than simply use real cases of body or brain identity without personal identity, and (2) conflate metaphysics with epistemology, by equivocating on the relation, 'if___then___'. But we can see that there is no need for this struggle. It is very easy to come up with real cases that make us wonder about both the conditions and the criteria.

The physical criterion: "A person at t2 is the same person as a person at t1 iff the person at t2 has enough of the brain of the person at t1 to be the brain of a living person." This criterion is suggested by Wiggins (1967) and Parfit (1984) as a way out of the alleged problem with the brain criterion. The objection to the physical criterion is recounted by Noonan as follows:

We can imagine, [Williams] says, the removal of the information from a brain into some storage device...whence it is then put back into the same or another brain. It seems clear...that we should not dream of saying that he did not, at the later stage, really remember....

Moreover, Williams says, it seems pretty clear that under these circumstances a man should be counted the same if this were done to him, and in the process he were given a new brain....But, if so, the Physical Criterion of personal identity must, of course be abandoned (Noonan, pp. 8-9)

Paradoxically, Noonan interprets Williams to mean that the physical criterion is as worthless as the bodily criterion and for the same reasons. But this version of Williams's Reduplication Argument is meant to show why reference to the same body must always be made in criteria of personal identity. If it is logically possible to make one copy of a person, then it is logically possible to make two; if we can copy Mary Smith back into one brain, we can copy her into as many brains as we have on hand. But it is absurd to say that Mary Smith embodied here is identical with Mary Smith embodied over there. So it turns out that 'Mary Smith' actually picks out a person type, not a person, and there is no problem. Thus, the objection to the bodily criterion fails (Williams, "Are Persons Bodies," pp. 80-81). As we have seen in the discussion of metaphysics and epistemology, the Reduplication Argument is meant to show that there is something wrong with the objection, not that there is something wrong with bodily or physical epistemological criteria of any sort.

It serves poetic justice to let Williams himself answer the objection to the physical criterion, since Noonan falsely accuses him of providing that very objection. But another response can be given, without sci-fi: the objection presumes a psychological criterion to the exclusion of a physical criterion. It does so without argument, and thus begs the question whether any kind of physical criterion is inadequate as a criterion of identity.

Can we get any value out of this discussion of the Physical condition/ criterion, which does not seem to be very different from the Brain condition/criterion? As Noonan has stated it here, the metaphysical condition says that we have the same person only if we have enough of the brain to have a person. But as near as I can tell, this says no more than that we have the same person only if we have a person. So it says that as long as the thing is still a person, then it is the same person. I think there is actually something epistemologically interesting here for the Naive View as seen in a conceptualist light. If we create our concepts, and identity is concept-relative, then, as long as the thing fits the definition of the concept, we consider its identity as a thing of that kind to be retained. And if it loses major features stated in the definition, then it ceases to be the same thing in virtue of ceasing to be a thing of that kind. I will test this principle with non-persons in the next chapter.

The memory criterion: "P2 at t2 is the same person as P1 at t1 just in case P2 at t2 is linked by continuity of experience-memory to P1 at t1" (Noonan, p. 12). We have focused on this principle in two contexts already: the conflation of metaphysics and epistemology, and the Lockean characterization of persons and their identity. Just for review and convenience, here is the biconditional broken down:

(M3)If P2 at t2 is the same person as P1 at t1 then P2 at t2 is linked by continuity of experience-memory to P1 at t1.

(E3) If P2 at t2 is linked by continuity of experience-memory to P1 at t1 P2 at t2 is the same person as the person as P1 at t1

Noonan clearly argues against E3, since he worries that we cannot be sure of the truth of E3's antecedent unless we are sure about the truth of its consequent. I argued that memory-as-faculty is a metaphysically necessary condition for the persistence (indeed, for the very existence) of a person, and that it is not a metaphysically sufficient condition for the either the persistence or the existence of a person. Here, I will deal only with the problem of verification, which Noonan offers as part of the circularity objection. How can we deal with the fact that sometimes particular memories are not veridical but only apparent? In fact I have many, many memories that are false. Some of them have caused me to get the wrong answers on tests; others have led me to commit sins of omission (I thought I mailed those thank-you notes, but I did not). My identity is not in doubt because of false memories like these. But some false memories involve believing that I did what someone else did. For example, what if I remember myself taking care of my brother when he was sick, when it was really my sister who did it?

I do not believe that it matters, especially given the way the condition/criterion is worded here. What matters is that I remember being aware of being aware of seeing my brother sick, of getting food for him, of adjusting the room temperature, listening to him complain; I do not remember being my sister. Being my sister involves a lot more than just the few experiences I seem to remember of taking care of my brother. Regardless of whether I am correct about who did the action, I am the first-person referent of my memory. This is a metaphysically necessary condition of personal identity, because it is a metaphysically necessary condition of being a person.

But what about delusional people? Can overlapping chains of memories, alone, be used as an epistemological criterion of reidentification, if I really do start to think I remember being my sister? How can my assertions be tested? How can I know I am not my sister? And how can anyone who does not know us, find out?

This is precisely the distinction that the concept DELUSIONAL marks. I cannot tell, without someone else's help, whether I am mistaken in this regard. Nor can people who do not know us. Making the distinction requires knowledge about me, and possibly about her too if some other oddness about my behavior does not give me away (such as talking about how my sons are going to be home from school soon and I have to get their dinner ready, despite the fact that it she, not I, who has sons).

Three points of paramount importance are highlighted by this discussion: (1) Failure of the epistemological criterion to guarantee accurate conclusions regarding the reidentification of someone does not entitle one to any skepticism with regard to the necessity and priority of the metaphysical condition. (2) Each of us knows, first-hand, that persons are more than just memories, or even the faculty of memory; that is why the epistemological criterion can fail in some cases. Nevertheless, (3) failure of the epistemological criterion in unusual cases does not entitle one to complete skepticism with regard to the usefulness (or even with regard to the the requirement) for the epistemological criterion of self-reidentification. Memories and the faculty of memory are the criterion that we use to reidentify ourselves, implicitly, at every waking moment--it is people who lose their memories, or whose memories do not square with the present, who begin to doubt their identity. Recall, if you can, Jimmie G., who at the age of 50 remembered only incidents that had happened before he turned 19:

'Neurologist? Hey, there's something wrong with my nerves? And "here"--where's "here"? What is this place anyhow?'

'I was just going to ask you--where do you think you are?'

'I see these beds, and these patients everywhere. Looks like a sort of hospital to me. But hell, what would I be doing in a hospital--and with all these old people, years older than me. I feel good, I'm strong as a bull. Maybe I work here...Do I work? What's my job?...No, you're shaking your head, I see in your eyes I don't work here. If I don't work here, I've been put here. Am I a patient, am I sick and don't know it, Doc? It's crazy, it's scary...Is it some sort of joke?' (Sacks, Hat, p. 26)

The best objection that can be given to the memory criterion is the usefulness of all of the other criteria--and at that, they do not constitute a reason for discarding the memory criterion; they merely serve to point out that much more goes to make up our identity as persons than memory, and that these too can be used as criteria of personal identity, either in conjunction with memory or in lieu of it.

The psychological continuity criterion: "P2 at t2 is the same person at t1 if and only if P2 at t2 is psychologically continuous with P1 at t1"(Noonan, p. 13) Noonan invokes again the distorted version of Bernard Williams's Reduplication Argument to reject this principle. The psychological continuity criterion allegedly fails because we can imagine

...the case in which, via Williams's brain-state transfer device, Robinson's brain is put into a state information-theoretically equivalent to Brown's. Again the defender of the Psychological Continuity Criterion must regard the case as a clear example of personal identity. But if this could happen to Robinson it could also happen simultaneously to his friend Smith. Once again, then, the Reduplication Argument can be brought to bear. For its happening simultaneously to Smith would leave the intrinsic relations between Brown and Robinson wholly unaffected.

Consequently the defender of the Psychological Continuity Criterion of personal identity cannot afford just to ignore Williams's Reduplication Argument. He must respond to it (Noonan, Personal, p. 16).

Predictably, I reject the objection, not only on the grounds that it is based on sci-fi, but on the grounds that it muddles Williams's argument so thoroughly as to make it unreidentifiable. Noonan also objects on the grounds of circularity (because memory is involved in psychological continuity), but I have dealt with that issue already. However, it should be noted that such an objection really can only be taken seriously if one has explicit or implicit commitments to dualism. Where are these "people" who are being put into transfer devices? Originally, they were "in" their brains, and then they got recorded into machines, and then transferred into other brains. Sometimes this situation is put forth as an implication of the quintessential materialist view, or the mind-brain identity theory. But nothing strikes me as less "material" than a "being" who needs no particular physical substrate--not even any particular kind of substrate--for its existence.

What can we do with the psychological continuity criterion as stated above? It is not entirely clear that we are talking about metaphysical conditions at all, at this point. Rather, we are talking about what it would take to convince people to include a being under the concept PERSON, and recall that the paradigm case is oneself. Otherwise, psychological continuity, as a metaphysically necessary condition, just reduces to the memory condition. Why? In cases where people have lost the ability to form memories, most of these other sorts of connections do not hold either: they cannot plan, so there is no connection between intentions and actions; but there are connections between, for example, Jimmie G's childhood experiences and his adult character traits.

Psychological continuity, as Noonan defines it (links between an intention and a later act, between childhood experiences and adult character traits, persistent beliefs, etc.), certainly seems to be a metaphysically necessary condition for the persistence of a person. If none of these features were to remain, then, even if some similar responses to the environment, as in the case of the woman whose stroke left some of her personality intact but robbed her of all other psychological features, there would be little reason to consider that being like us in enough ways to call it a person, let alone the same person. Do all of the connections have to hold, in order for a being to remain similar enough to the paradigm case? Obviously not; many people overcome some of their childhood experiences quite thoroughly and have unrelated character traits, for example; and people change their beliefs. Like memory, which might consist of overlapping chains of connections, the psychological condition could demand no more than loose connections without excluding oneself-- the paradigm case of persons.

Psychological continuity is a metaphysically sufficient condition for the persistence of a person, but only in virtue of the fact that psychological features are necessarily embodied. It can even be a sufficient condition for reindentification: consider the work of homicide profilers, which involves linking known suspects of a certain psychological type and signature style to a certain kind of murder.

The closest continuer criterion or best candidate criterion A person at t2 is the same person as a person at t1 iff the person at t2 is psychologically continuous with the person at t1 and there is no rival candidate at t2 who is also psychologically continuous with the person at t1. Noonan thinks that the "intuitive" objection to the best candidate theory is the split-brain transplant case.

Suppose I am told that my brain is to be divided into two and the two halves transplanted into different bodies. Then according to the Revised Psychological Continuity Criterion I know that I will not survive and that two new people will be created by the fission. However, if I can persuade someone to destroy the right brain hemisphere before it is transplanted, thus eliminating the plurality of candidates, I will survive and be identical with the recipient of the left-brain hemisphere. survival is logically dependent upon the non-existence of someone...who would not be me even if he were to exist. But how can my survival be thus logically dependent on the non-existence of someone else? (Noonan, p. 17).

I have gone on at length about the objections to the Naive View that could not arise without logical possibilism and sci-fi. Here we have an example of a condition/criterion of identity which could not arise without this theory and its method. Without the science fiction, I have no idea what it would mean for there to be a "closest continuer." Since I consider the method to be invalid, I will not deal with the hypothesis.

I consider Noonan's treatment of metaphysical conditions and epistemological criteria to be, if not always the most accurate, at least representative of the prevailing views on the matter. I will now use some of the concepts developed in this section to recap the Naive View and give criteria and conditions in accordance with its premises and in accordance with conceptualism.

Section IV: The Naive Epistemological Criteria and Metaphysical Conditions

The reason that Noonan's work with conditions and criteria of identity has been important in this work is that they help to bring out the fact that, whatever we can say about metaphysical conditions, we cannot say that there is one and only one thing wherein personal identity. It is not clear how we would say essentially wherein persons consist. But this is not a bad result, because to make such claims is not part of the conceptualist project. Noonan is engaged in a realist project. Whether he is a realist or not, his approach to personal identity indicates at least a concession to the realist view of the world: that things have real essences independent of any conscious subject's mental integrations, and that those essences must be described so that we can find wherein things consists, and, hence, wherein their identity consists. The fact that he confuses the necessary and sufficient metaphysical conditions with adequate criteria for reidentification shows that he sees this project in realist terms: recall that the realist sees questions of identity as soluble in terms of essences that remain constant throughout change and that supply, in virtue of being essential, the criteria of reidentification. Thus, we can more fully appreciate, given Noonan's difficulties, what is wrong with the realist's approach to identity.

The conceptualist project, as I hope has become clear throughout this chapter, is to ask why this concept PERSON arose in the first place--what are the facts in reality that made it seem like a worthwhile concept to form? I have answered that question in the presentation of the received view, and by contrasting the referents of the concept described in the received view with the various contenders for individual personhood as set forth by other theorists. Now I will finish this portion of the conceptualist project by reiterating the epistemological criteria for reidentification at which I have arrived throughout the discussion, and saying just a little about what it could mean to say that these are adequate criteria.


Epistemologically, sameness of body is an adequate criterion for reidentification of a person. In part this is due to the fact that persons are always embodied. I get this fact primarily from knowing my own case, but I see that many other bodies behave in ways that are similar to what I know myself to be. When I go to a party, and I want to find the people, I pick out the human bodies. If I start talking to a body I know, and it stares blankly and responds, "The name...the name," then I know that I have in fact reidentified the same person by reference to body, but that the person whose body that was is in all likelihood gone. Thus, body is obviously not a metaphysically sufficient condition even for the existence of a person, let alone its persistence. I could also be wrong in my reidentification: I could mistake a stranger for a high school pal because their faces are so similar. But the mere fact that I could be wrong sometimes does not make body an inadequate criterion for almost all situations; nor can I simply erase that criterion from my list as error-prone and begin using another. Rather, in such situations, I must also consult memory.


Epistemologically, sameness of memory is an adequate criterion for reidentification of a person. It is how I reidentify myself at all times. If we want to test our reidentification of someone else, we can ask telling questions about past events. If I am at that party and a man I do not recognize introduces himself as one of my college sweethearts, I will determine the accuracy of this claim by checking his memories. I can be wrong in this determination; he could lie skillfully. I can be uncertain of my own identity because of amnesia, or even wrong in the rarest of cases. In such cases, if I am able to formulate the question, I must ask others for help; and they will make the determination with reference to my body and with reference to what memories I still do have. The mere fact that these kinds of mistakes are possible does not justify eliminating memory as an adequate criterion for most situations similar to these, and certainly does not justify removing it from the list: in certain situations, I must also verify sameness of body. But historical memory is a metaphysically necessary condition of the persistence of a person, and the faculty of memory combined with historical memory is a metaphysically sufficient condition. Note that the sufficiency of the metaphysical condition does not guarantee accuracy of judgment.


Because a person must express itself in some way, personality is a metaphysically necessary condition for being a person: a being which does not respond to its environment in any way is not very similar to the paradigm case. It is not a sufficient condition for personhood: other animals have manners of responding to the environment, and victims of split personality syndrome have more than one discrete response format. Personality can, in some kinds of cases, be an adequate criterion of reidentification, and homicide profilers are not the only people who use it. Suppose that you and I are trying to verify that my roommate is the same person who sits in front of you in your optics class. You never really get a good look at her, so we cannot rely on a bodily criterion, and you certainly are not acquainted with her memories. But she has distinctive personality traits which reveal themselves in her before- and after-lecture conversations with the other people in your class. If we describe these to each other, it is likely that we will be able to make the reidentification. Reidentification on the basis of personality can be wrong, and it is much more error-prone than the memory and bodily criteria; but rather than dismiss it as inadequate, we must recognize that it is adequate in many cases, and that it is exceedingly helpful when added to the list of criteria we are building.


Is continuity of psychological connections a necessary condition for the persistence of a person? What counts as a psychological connection? We can agree with Noonan that the following all count as psychological connections: the connection between an intention and a later action; links between childhood experience and adult character, personality, and beliefs; and the persistence of certain beliefs. If these are the sorts of things that count, then surely we must also include all manner of conscious learning, such as the vocabulary that the subject develops, physical skills, and enduring defects in both. It is to all of these that I, as a conscious subject, refer when I refer to myself-as-a-whole. What would it mean for a human being to be without these things? I think we can safely conclude that the result would be even worse than Jimmie G and WilliamThompson: there would be nothing more than a body, perhaps with some automatic functionality. Is such a thing in any way like the things that we classify under the concept PERSON? Obviously not. When I call myself a 'person,' I do not merely refer to my automatically functioning body.

But persons change. They overcome childhood experiences, modify their personalities, change their beliefs, fail to carry out intended actions. We are not justified on these grounds to claim that the person has not persisted, however; for a persistent person is exactly what the concepts OVERCOME and MODIFY refer to. This is not mere question-begging. When I refer to myself, I am referring to something that changes. To say that a new person has come into existence with each change or with a set of such changes is to drop the context in which the concept PERSON was formed in the first place: the way that a person is includes alteration. Let us try a thought experiment that may provide a helpful contrast object. Suppose that I have adopted a stance of philosophical skepticism with regard to the kind of thing that I know I am, and I assert, "Thoughts are fleeting, and when I look inside myself, all I find are fleeting thoughts. So I might be like a fleeting thought as well: I am not permanent; I come into existence over and over, and dissipate just as quickly." Then the question immediately arises, from what is the flux of thought being distinguished? If it was picked out and compared, against what was it picked out, and to what was it compared? There must have been something persistent. And that persistent thing is the fact that gives rise to the concept SELF. To deny that this is so is also to deny that the subject of the claim 'I am not permanent' succeeds in referring--at which point one would be reduced to babbling.

Dealing With Borderline Cases

Derek Parfit attempts to convince us that the identity of a person can be indeterminate on the basis of the fact that there is a certain type of nonpersonal borderline case: a club the members of which stop meeting, and then begin meeting again. What are we to say? We could maintain that it is the same club, since a club is only its members; or we could deny it, since it stopped doing for a while what clubs do. So "is it the same club?" is an empty question; the club's identity is indeterminate. We can construct a thought experiment in which I have a replica, and I am about to die and my replica will live: I can either say that this would be as bad as death, or I can say that it would be as good as survival, but I do not know which to say. So my identity is indeterminate in the same sense (Parfit, Reasons, pp. 213-215). Naturally, I claim that such cases are utterly irrelevant to the study of the identity of persons, as opposed to the fictional study of fictional persons; but in addition, I claim that such puzzles arise because personal identity is taken, not as a given fact, but as an idea which, if it is about a fact at all, must be explained.

Could the identity of a person ever be indeterminate? To answer this question, we must first ask ourselves "What facts of reality give rise to the concept "DETERMINATE?" Immediately we know that there is a persistent, conscious subject involved: someone is trying to find the limits or boundaries of something. The conscious subject may be trying to find out, for example, whether a given entity is the same person the subject once knew. If one is unable to say for sure, then, with respect to the wondering conscious subject, the issue is not one that can be determined. It is indeterminate.

What about the object of the determination? Is it, in fact, limitless, boundless, by its very nature? Is it no particular way--i.e., does it have no identity? To say so is a contradiction. Everything is some way. But whether any given conscious subject can know how it is is not guaranteed by this fact. Would it be possible, as Parfit has it, to "know everything there is to know," yet not be able to determine whether this is the same person? Again, this is a contradiction: it says, in effect, "We know everything there is to know but there is something that we do not know." If, on the other hand, we know a lot, but still cannot make the determination, then we have a borderline case.

Like any concept, the concept PERSON is open-ended, in the sense that it is possible that a new entity may not share all of the properties of the entities already subsumed under that concept but still be similar enough to warrant being grouped with those entities for some specific purpose. This last qualification is important; many perceptual-level similarities are more or less given; but with regard to higher-level concepts, it is always with some purpose in mind that we take things to be similar. For example, for the purpose of most medical procedures, children can be taken to be similar enough to adults; for many legal purposes, they cannot. Now consider the case of Jimmie G. Is this entity to be included in the same class as ourselves? Looks and personality aside, he does not seem to be doing the same sorts of things that we take it as given that we do, and it is from our own case that we form the concept PERSON. Yet he does not seem to fit in any other categories we have either. We might then consider Jimmie G a borderline case. But there are still determinate things to say about the identity of the entity called 'Jimmie G.' His spatiotemporally continuous path can be traced; the same mostly-functioning body is in existence; and it was a person at one time, whether that person is still in existence now or not. So we can reidentify the person by means of a body criterion and by means of a memory criterion. But we can find enough dissimilarities to exclude him from the class of persons, although we do not have another class in which to put him, until we create one. Perhaps we should simply create a narrower class, subsumed by the class referred to by the concept HUMAN but distinct from the class referred to by the concept PERSON.

Concluding Remarks

I have dealt in this chapter with persons, the most knowable case of identity and persistence. When identity theorists treat the case of persons as an application of their theory of identity--or worse, as a special case--they treat it in effect as the most unknowable case of identity, persistence, and reidentification. In doing so, they miss

important facts that can not only help to solve puzzles about the identities of nonpersons, but prevent many of them from arising in the first place. For it is always with reference to a persistent, conscious subject with its own identity that judgments concerning the identity of nonpersons are made. If personal identity claims are taken as derivative cases of such judgments, then the subject of the judgments is eliminated, and the judgments themselves become mysterious, free-floating "propositions," the "meaning" of which we lowly conscious subjects must struggle to learn from bare reality itself without reference to any mind. I will support this claim throughout the following pages, as I apply this emerging theory of identity to nonperson puzzles; but as a segue, let us note that the question of whether a person's identity can be indeterminate arises because of the standard approach to identity that takes personal identity as a special application of an already established theory of identity.

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