who am i philosophy essay

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Question of the Month

Who or what am i, the following answers to the question of the self each win a random book..

I am a living, breathing organism signified by the words ‘human being’. I am a material or physical being fairly recognisable over time to me and to others: I am a body. Through my body, I can move, touch, see, hear, taste and smell. The array of physical sensations available to me also includes pain, hunger, thirst, tiredness, injury, sickness, fear, apprehension and pleasure. In this way I experience myself, others and the world around me. However, there is another aspect of me not directly visible or definable. This is the aspect of me which thinks and feels, reflects and judges, remembers and anticipates. Words used to describe this aspect include ‘mind’, ‘spirit’, ‘heart’, ‘soul’, ‘awareness’ and ‘consciousness’. This part of me is aware that I can never be fully known or understood by myself or by others; it notices that although there may be some unchanging essence which is ‘me’, this same ‘me’ is also constantly changing and evolving.

So I am a physical body and an emotional and psychological (or spiritual) being. The two together make me a person. Being a person means that I have virtues and flaws, gifts and needs, possibilities and defeats. I am basically good, but I am capable of evil. I am neither an angel nor a monster. Being a person means that I am a social animal, needing connection, recognition and acceptance from others, while simultaneously knowing myself as isolated and solitary, with many experiences which are never fully shareable with others. However, I also realise that this paradoxical condition is a universal experience, and this enables the emergence of empathy and compassion for others as it affords glimpses of understanding and solicitude, mutuality and intimacy. Being a person means that I am like all other persons, but also unique. It also means that I can never provide a genuinely definitive answer to the question.

Kathleen O’Dwyer, Limerick, Ireland

Human beings are defined by a sense of personality, experiences and reason. We are often inclined to believe that the face we see in the mirror is us, a thing which has developed a personality through experiences. Here the body is merely a tool for the true self, the mind. It is however an error to conclude that the body is not significant for selfhood. Without a body a mind would not be able to make certain types of judgments.

The mind/brain utilizes the body to survive, calculate and function within various social contexts. It also favors order rather than chaos. The mind governing our body assigns mental places to various objects in the world. Through the use of language humanity has come to construct an image of the world that transcends one’s own immediate environment. This has enabled humans to develop complex means of social interaction. Thus we are physical beings capable of having non-physical thoughts that in turn construct and sometimes deconstruct the physical world .

David Tamez, Austin, TX

I would argue that the answer to this question is dependent on the idea of identity. The idea of identity is itself rather problematic in that it’s determined from subjective viewpoints, which can be divided into two types. The first is an internal creation of identity, formed by myself for myself. This is the picture I have of myself. The second is an external creation of identity, formed by someone else. These are the pictures that other people have of me. “I am a fool!” cries the self, while the other labels that person a genius (or vice versa ). Inevitably there will be clashes based on differing viewpoints. While not always so extreme as this example, it must surely be very rare that people will agree entirely on a person’s identity. In the same way that Einstein showed that time is dependant on viewpoint, so I think we can show that identity is relative, and by extension, the answer to the question ‘Who or what am I?’ becomes a matter of who is answering it. The question must then be asked, on what do we base these identities we assign other people or ourselves? It seems that assigning a particular identity to someone else occurs through a process of observation, watching and remembering a person’s actions, then placing a value on the information we have of that person from our past and present encounters. Our view of our own identity places the highest priority on the intentions and thoughts that precede our actions, in contrast to other people’s reliance on our actions. This can mean that the person we consider ourselves to be may not be the person we portray to others.

Anoosh Falak Rafat, Erith, Kent

Philosophy is about generalities, but this question demands particularity: who am I – a particular person in a particular time and place, related in particular ways to others? The usual answers are not of much philosophical interest: Bill, Patricia’s husband, Katy’s father. In each of these identities, however, I find two things: a state of interiority – feelings, thoughts, beliefs and desires with which only I am directly acquainted, and a social role – a relatedness to other human beings. So the question is two-fold: How does it feel to be me? and How do I function in a social context? Each of us must answer these questions for ourselves, but we can share our answers with others. The first-person point of view is an important starting point. We each have a life-story, of what has been and continues to be important to us, what the pivotal events were that brought us to the present moment. By comparing stories, we find such timeless human themes as love and hate, honor and degradation, loyalty and betrayal, inspiration and despair; and we learn how others have handled themselves in situations without ourselves having to undergo them. In this way human culture advances far more rapidly than biological evolution. By taking an ‘objective’ point of view toward our own subjectivity, we can transcend ourselves. We are not bound by chains of habit or instinct; we can see who we are and choose to change it. The ability to examine one’s own experience is something that distinguishes us from other animals. We have, in some measure, the ability to create ourselves. There are limits to what we can make of ourselves imposed by evolution, biology and culture, ut the ability to know those limits and find ways to work within them gives us the unique ability not only to discover, but to decide and create the answer to the question ‘Who am I?’

Bill Meacham, Austin, TX

If you look in the mirror, what is staring back at you? Flesh. Eyes. And underneath that? Bones. Blood. Brain. But then, what makes us different from animals? Is it, with Plato and Aristotle, the ability to reason and live virtuously? Possibly – so a soul, a consciousness. It is perfectly likely that our one defining feature is metaphysical. But higher mammals’ intelligence is too near ours to assume this is our single differentiation: the ability to communicate and love is reflected in dolphins and primates. So it is equally likely that being human comes down to our biological structure – our DNA and physiology – developing certain features that other animals lack, including hormones. Perhaps what we really are comes down to the rather annoying answer, “we are human.” But ‘human’ describes something that we cannot certainly define or grasp. The most we can do is ascertain that we are indeed different, a compilation of our multiplicity: we are evolved animals; the inhabitants of earth; the most widespread of colonists, and the most diverse of species. And when we look in the mirror, to question ourselves and stare at our flesh, our eyes, our bones, our blood, to philosophise and obey our brains – in short, when we define ourselves as human, that is what it is to be a person.

Amy Andrews, Nantwich, Cheshire

Half of our lives we behave like animals. Sleeping, feeding, drinking, pursuing sex and other bodily necessities, we do exactly what baboons, monkeys, and other animals do. Most of the rest of our available time is spend doing what the societies we live in want us to do, namely work to earn enough to pay for those necessities. The little time left over which we could call ‘time out’ is scarcely enough to keep up with what happens in the world around us, if we even are interested.

When I look at the mirror in the morning, the face which stares back at me is not me. It cannot be me, it is too old to be me. I am retired a long time already, and we all change considerably through the years. I call it an evolutionary process; but still, this face I see does not correspond with what I feel I am.

I am still looking for what Martin Heidegger called ‘Being’. I follow his idea about Dasein . Even living 50% of the time as an ape, I nevertheless feel the facticity of living in space and time, and have always tried to be authentic in my acts and the thoughts which motivate them, seeking an independence of mind and avoiding the general entrapment of following the crowd in the search for the Being of beings. I still consider it a lucky fact to have been ‘thrown into’ a world which is no doubt hostile, repetitive and extremely materialistic, and have accepted nothingness as the ultimate destination of my journey, yet I’m still asking the question ‘why is there something rather than nothing?’ I thought about all of this when I was a young man, and the answer to this question and so many other ones are still out of my reach, and the doubts about meaning of life permeate my mind today as strongly as when I was a student opening my eyes to the basic questions of Being. If this is so, why don’t I know the face in the mirror?

Henry Back, Flagler Beach, Florida

The question ‘Who am I?’ can be answered only specifically. Anything else would be an abstraction that would liken me to others who share such characteristics. But that’s not who I am, that’s what I am. So here is a description of who I am in particular contexts. When I walk in the park, I am Friendly Human. I adopt a stance toward others of smiling, looking at them rather than averting my eyes, nodding and saying “Hello” and so forth. Doing so helps me feel safe and connected with them. Friendly Human is a strategy for being in the world which avoids hostility and harm. It includes deference and yielding. I step aside when encountering someone on a narrow path. By letting them pass, I avoid confrontation and disharmony. I get more enjoyment from the path by letting others have it. They pass, and I get to continue to meander as I wish. When I am Friendly Human I am not Worker, focused on accomplishing a task. I am not Competitor, focused on getting somewhere ahead of someone else. I am not Acquisitor, focused on getting what I want. Nor am I Intimate, focused on loving, understanding and enjoying my mate. I am just Friendly Human – a bit like a dog, but with more autonomy. Worker has a sense of self-importance, pleasure at doing something worthwhile, sometimes angry at obstacles, sometimes pleased at accomplishment. Competitor feels tense, anxious and angry. Acquisitor feels much like Worker, but when combined with Competitor, feels hostile. Intimate feels best of all. When I am Intimate, my guard is down; I delight in things my mate does; I let my thoughts and words flow freely; I bask in the warmth of love. By contrast, Friendly Human is peaceful and relaxed but a bit reserved: I am not anxious, angry or hostile, but neither am I completely unguarded. I keep to myself, engaging others briefly if they wish, or not at all. There is philosophical interest in this only to the extent that it illustrates the human capacity to adopt strategies for being in the world, and thereby define our own answers to the question ‘Who am I?’

Robert Tables, Blanco, TX

I’m a crowd, so I’m a ‘what’. There isn’t an ‘I’. As psychosynthesis says, I’m a collection of sub-personalities. More accurately, this thing is a collection of personalities, some shy, some noisy, pushy, sexy, boring, clever. This is the Many Selves model. The Gestalt view is similar: I/This is the continuous interaction and interrelatedness between myself and the environment of others and objects. Except on this theory there isn’t a ‘myself’ at the core, this I-ness is the constant flux. Even when alone, eyes closed in silence, there’s the flux of sensations and thoughts (coming from where?) In the Many Selves model all these Selves are interrelated, actors with a script they write as the play proceeds, with more parts than actors, so multiple roles are played. The problem is that, mostly we want to believe there is a core self or single I inside the sensations, so we can reinforce our Self Concept: “I am the sort of person who…” A fragmented self-concept is emotionally distressing.

I see the Self as a kaleidoscope. As with the Gestalt and the Many Selves models, the pattern is ever changing. Life and its activities is rotating the kaleidoscope, rather than me. My very limited control is to speed it up or slow it down. The constant ‘me’ I wake up as is the kaleidoscope briefly at rest before the environment begins to turn it. The kaleidoscope’s glitter are the few fixed aspects of me, such as gender, body, culture, etc. What’s new every time is the mood I wake up in or experience. Differences between people are simply different combinations of different bits. His bits are mainly red and angular – a spiky person; hers are mostly greenish and rounded, a softer personality. To a degree I can add or remove bits of glitter, choosing colour and shape, such as changing my behaviours and attitudes. But, as with a real kaleidoscope, this means opening up and getting inside, which we mostly resist. So I cannot say “I am.” I can only say “This thing I call Myself is like the image in rotating kaleidoscope” and “I am a Crowd.”

Tony Morris, Putney, London

To answer this question requires gaining some perspective on oneself. Not capable of devouring huge quantities of texts on Descartes’ cogito , Freud’s ego , Proust’s ‘true me’, Sartre’s ‘non-essence’ or Locke’s personal identity, I choose a different approach, related to a condition I have had since my teenage years: depersonalisation. For those of you unfamiliar with the disorder, it involves losing a sense of self – failing to recognise any physical connection with your own body. Sufferers regularly experience autoscopy, more commonly known as an out-of-body experience. A common technique for getting back in is to list the five senses and write what you are experiencing for each one, hopefully reconnecting yourself with yourself in the process. In more extreme cases sufferers have been known to self-harm, acute pain creating a faster and stronger reconnection.

When I am in a depersonalised state I know two things. First, I know that my physical body can function without my mind being in control, as I can observe this occurring. The body runs on the mind’s residuum. Second, as mentioned, I know that to reconnect I must experience a physical sensation, painful or pleasurable, the more intense the more effective. From this I can deduce that there are two entities present, the conscious and the physical, and the link that connects the two is sensation. So for me, the ‘Who’ is the consciousness and the ‘What’ is the body. But are we still the same person if we suffer from some degenerate disease, mental or physical? I’d like to end with a Joyce quote, which could shed more light on the problem than I have: “I am tomorrow, or some future day, what I establish today. I am today what I established yesterday or some previous day.”

S. E. Smith, Lancaster

I’m a book. Not literally, of course, but this is the metaphor that I’m going to use, so please bear with me.

I am a particular self. So, what makes a self particular? Its story. That is, the events and objects surrounding it, and its actions on, reactions to, and perceptions of them. You are you because you have lived your life, and I am me because I have lived mine. Even if I had a Siamese Clone we would still have different selves because he would perceive the world from a different viewpoint than me. An important aspect of this story about stories is that the story exists independently of me.

This means that I am a self plus a story. The situation is comparable to that of a book. Books have similar physical elements, like paper, binding, and ink. What makes them unique is the story that they contain. Even if The Iliad has the same font, paper, and glue as El Otoño del Patriarca , they are different books because one is about a Greek struggle and the other a Latin dictator. Likewise, I am different from you because my story is about a guy from Edmond and yours is not. And there you have it. You, me, the creepy guy down the hall – we all have similar selves, but I’m a one-of-a-kind story.

Matthew Hewes, Edmond, OK

I share a large genetic similarity with mice. And like mice I am also made of water and soil. Yet I have opposable thumbs and use language, narratives and imagination for almost everything in life. Because of all that, I think myself superior to a mouse. If I were like most humans I would carry that thought even further, and think that I was either the pinnacle of evolutionary development or the crowning achievement of a divine being’s creation, only slightly less divine than the supernatural being who created me. However, personally, I think none of those grand thoughts. I am a water molecule in an ocean. I am a grain of sand on a beach. I am a linguistic phrase in the novel of time. I am a “ha!” in the middle of a long belly laugh. And these thoughts are more comfortable, less stressful views of me than grand visions of me as the center and purpose of everything. I am a part of everything, but I am not in charge of everything, and that’s a relief. I’m here to do as best I can: my watery, grainy, languagey part of the story society is constantly creating about what it means to be alive. Towards that end I am a thought collector, and I hoard ideas and experiences like a mouse hoards cheese. From my collection I create a story, and with my opposable thumbs and language skills I share it.

Sue Clancy, Norman, Oklahoma

I want to answer your question by paraphrasing the originator of Psychosynthesis, Roberto Assagioli:

I have a body, but I am not my body.

I have emotions, but I am not my emotions.

I have a mind, but I am not my mind.

I have roles to play in life, but I am not any of them.

I am a centre of pure consciousness.

Ray Sherman, Duarte, CA

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To celebrate the launch of Mark Vernon’s book How To Be An Agnostic (Palgrave Macmillan) the next question of the month is: What is Truth? The prize is a signed copy of the book. Let us know what truth is and what it’s good for in less than 400 words, please. Subject lines or envelopes should be marked ‘Question Of The Month’, and must be received by 25th July. If you want a chance of getting a signed book, please include your physical address. Submission implies permission to reproduce your answer physically and electronically.

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Who am I? The Philosophy of Personal Identity

The various problems of personal identity pose difficult, yet essential questions for the entire field of philosophy as a whole.

Personal identity is a philosophical issue which spans a whole range of disciplines within philosophy, from the philosophy of mind, to metaphysics and epistemology , to ethics and political theory. There is no one problem of personal identity – they are rather a kind of philosophical problem that starts to emerge whenever we ask questions about what one ‘is’ most fundamentally.

Problems of personal identity were first posed in something like the form they take today, but underlying issues of personal identity have been a feature of the Western philosophical tradition since its inception. Plato , writing near the dawn of philosophical enquiry, and Descartes writing at the dawn of modern philosophy, both had a theory of what we were most fundamentally – namely, that we are souls. This illustrates that it is very difficult to undertake any extensive philosophical enquiry without coming up against some problems of personal identity.

Personal Identity: A Variety of Questions, a Variety of Answers

Some of the usual answers to the question of personal identity – ‘I am a human being’ or ‘I am a person’ or even ‘ I am a self ’ – are sufficiently vague as to be worthy of further philosophical analysis. Some of the problems of personal identity involve trying to define terms like ‘human’ or ‘person’ or ‘self’. Others ask what the conditions are for the persistence of a human or a person or a self over time; in other words, what it takes for a person or a self to persist.

Still, others ask what the ethical implications of these categories actually are, or whether what matters in an ethical sense has anything to do with what we are most fundamentally at all. In other words, some question whether personal identity matters . How we respond to one problem of personal identity is likely to (partly) determine how we respond to other problems of personal identity. It is therefore justified to think about personal identity in terms of general approaches to it as an issue, rather than specific responses to specific problems.

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Please check your inbox to activate your subscription, the ‘physical’ approach.

Before going through several problems of personal identity in depth, it is worth distinguishing some of those general approaches now. There are three broad categories of approach to personal identity. The first is what we can call the ‘Physical’ approach: this locates what we are fundamentally in something physical. Some theories of this kind say that what we are most fundamentally is our brains, or some part of our brains – be it a specific part, or just enough of our brains. The underlying thought here is generally that our minds only exist as they do because our brains are a certain way, and whilst losing (say) a finger or even an arm couldn’t possibly turn someone into a wholly different person, removing or altering their brain might. Other theories of this kind refer to a range of physical features, which together define us as a biological organism or a species.

The ‘Psychological’ Approach

A second approach to personal identity says that what we are, most fundamentally, is not any physical organ or organism, but something psychological . We can call these ‘Psychological’ approaches. We might be understood, as Hume did, as a succession of perceptions or impressions . We might also be understood as consecutive psychological connections. What differentiates these two is the view that certain kinds of mental states constitute relations which hold over a span of time. Memory is especially significant here. For instance, there is a relation between my mental state as I recall agreeing to write this article, and the time at which I agreed to write this article. The idea that what we are fundamentally relies on such connections is a highly intuitive one. If someone were to have their memories wiped, or switched out for someone else entirely, we could imagine calling into question whether the resultant person is the same as the one which existed before their memory was altered.

The ‘Sceptical’ Approach 

A third approach to personal identity calls into question the reality of the problems of personal identity, or is sceptical about our ability to answer them correctly. We can call these ‘Sceptical’ approaches. This approach says that there is no answer to questions concerning personal identity, or that they are the wrong way of asking questions about ourselves and our mental lives, or that whatever answer we give to these questions isn’t really important.

There are broadly three kinds of sceptical approaches. First, that which holds we ‘are’ nothing at all, most fundamentally. There is no core to our existence, no final kernel of truth about what we are which trumps all others – one influential statement of this view comes from Ludwig Wittgenstein’s Tractatus Logico-Philosophicus . Second, that which holds that there is no answer to this question because it is the wrong kind of question, focusing too much on the concepts by which we understand ourselves rather than the source of our mental lives. This approach might say that what we are most fundamentally is a question best left to the natural sciences. Third, that which holds that whatever we are fundamentally does not seriously affect how we should see the world, or morality.

The Ship of Theseus

This last view is worth considering in more detail, as we move on to consider specific problems of personal identity in more detail. Before exploring it further, it is important to clarify that personal identity is often considered a species of the yet-more-numerous problems of identity simpliciter . Perhaps the archetypal problem of identity is explained using an example, commonly called the ‘Ship of Theseus’ problem . The thought experiment is this: imagine a ship which, over time, has every plank, every mast, every patch of sail, indeed every single part of it replaced with a new component. Even if the shipbuilder or the captain tries very hard to make a like for like replacement, no two planks of wood are exactly alike. The questions this raises are these: is the ship with all of its component parts changed the same ship it was before a single component was removed? And, if it is not, then at what point did it become a different ship?

Enter the Teletransporter

This doesn’t even begin to cover some of the many interesting problems of identity, but it does begin to illustrate how problems of personal identity can be conceived in similar terms. Derek Parfit illustrated one such problem using an imaginary piece of technology known as a ‘Teletransporter’. This piece of technology obliterates every cell of one’s body and brain, traces it, and then replicates it somewhere else almost immediately. This is experienced by the person in the Teletransporter as something like a brief nap, after which they awake at their destination otherwise unchanged. Intuitively, if such a piece of technology existed, we might be inclined to use it. If I awake with my body and mind unchanged, what’s the harm?

Problems of Replication

That is, until Parfit changes the thought experiment and asks us to imagine what would happen if we were replicated instead. Now when we awake unaltered, there’s a version of me remaining unchanged back wherever I came from. How does that change my perception of this procedure? What if I were to awake from Teletransportation with a heart defect, but would know that my Replicant was going to be perfectly healthy, and so would be able to live my life as I had been up till that point. What all of this head-spinning, science fictional thinking is meant to elicit is the sense that how we respond to one problem of personal identity may be intuitive, but applying the same logic to other problems of personal identity might leave us with some quite perverse conclusions.

Reductionism – A Skeptical Solution?

Parfit’s response to all of this isn’t to offer his own, separate approach to the problems of personal identity. Rather, he argues that personal identity does not matter. What matters is not some fundamental kernel of the self, some criterion of personhood, or some other ‘deep’ fact about ourselves. What matters are the things we know to matter, namely the categories of our mental life that are self-evident. Our memories, our perceptions, and the ways in which we describe our lives to ourselves.

This approach to personal identity is often labelled ‘Reductionist’, but perhaps a better term would be ‘Anti-Contemplative’. It doesn’t advocate that we answer difficult questions by excavating deeper and deeper until we find what we are fundamentally. It suggests that this manner of reflection is unhelpful, and rarely offers us consistent answers. The problems of personal identity are endlessly fascinating, and far broader than can be summarized in one article. The relationship between the various problems of personal identity is itself a matter of debate.  Eric Olsen holds that “There is no single problem of personal identity, but rather a wide range of questions that are at best loosely connected”.

Personal Identity: Implications for Philosophy in General

This is, of course, another explanation for why no single conception of ourselves appears to meet all of the problems of personal identity. Equally, problems of personal identity raise a number of ‘ metaphilosophical ’ questions; that is, questions about the nature of philosophy itself and the methodology one should adopt when undertaking it. In particular, it raises the question of whether there is a natural hierarchy within philosophy in terms of which questions should be answered first, and thereby determine our answers to other philosophical questions.

It is often implicitly understood that while our conclusions about how our minds are can influence our conclusions about ethics, our conclusions about ethics cannot influence our conclusions about our minds. This kind of priority comes under question at the point where we start to take an – already convoluted and contradictory set of responses to questions about our minds – and engage with them not by attempting a somewhat ramshackle unified response, but rather asking what actually matters to us, both in the realm of ethical reflection and in the less reflective arena of our everyday lives.

Epistemology: The Philosophy of Knowledge

By Luke Dunne BA Philosophy & Theology Luke is a graduate of the University of Oxford's departments of Philosophy and Theology, his main interests include the history of philosophy, the metaphysics of mind, and social theory.

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Personal Identity

Personal identity deals with philosophical questions that arise about ourselves by virtue of our being people (or as lawyers and philosophers like to say, persons ). This contrasts with questions about ourselves that arise by virtue of our being living things, conscious beings, moral agents, or material objects. Many of these questions occur to nearly all of us now and again: What am I? When did I begin? What will happen to me when I die? Others are more abstruse. They have been discussed since the origins of Western philosophy, and most major figures have had something to say about them. (There is also a rich but challenging literature on the topic in Eastern philosophy: see the entry Mind in Indian Buddhist Philosophy .)

The topic is sometimes discussed under the problematic term self . This term is sometimes synonymous with ‘person’, but often means something different: a sort of unchanging, immaterial subject of consciousness, for instance (as in the phrase ‘the myth of the self’). It is often used without any clear meaning and will be avoided here.

After surveying the main questions of personal identity, the entry will focus on our persistence through time.

1. The Problems of Personal Identity

2. understanding the persistence question, 3. accounts of our persistence, 4. psychological-continuity views, 6. the too-many-thinkers objection, 7. animalism and brute-physical views, 8. wider themes, other internet resources, related entries.

There is no single problem of personal identity, but rather a wide range of questions that are at best loosely connected and not always distinguished. Here are the most familiar:

Characterization. Outside of philosophy, the term ‘personal identity’ commonly refers to properties to which we feel a special sense of attachment or ownership. My personal identity in this sense consists of those properties I take to “define me as a person” or to “make me the person I am”. (The precise meaning of these phrases is hard to pin down.) To have an “identity crisis” is to become unsure about my most characteristic properties—about what sort of person I am in some deep sense. To ask about it is to ask, in the expectation of a deep and revealing psychological answer, Who am I? My individual personal identity contrasts with my gender, ethnic, and national identity, which consist roughly of the sex, ethnic group, or nation I take myself to belong to and the importance I attach to it.

This sort of personal identity is contingent and temporary: the way I define myself as a person might have been different, and can vary from one time to another. It is a subset, usually a small one, of someone’s properties. It could happen that being a philosopher and a parent belong to my identity but not being a man or a cyclist, while someone else has the same four properties but feels differently towards them, so that being a man and a cyclist belong to his identity but not being a philosopher or a parent. Someone may not even need to have the properties belonging to her identity: if I become convinced that I am Napoleon, being an emperor could be one of the properties central to the way I define myself and thus (perhaps) part of my identity, even though I’m deluded and have never been an emperor.

What determines someone’s personal identity in this sense is sometimes called the characterization question (Schechtman 1996: 1). (Glover 1988: part 2 and Ludwig 1997 are useful discussions.)

Personhood. What is it to be a person, as opposed to a nonperson? What have we people got that nonpeople lack? The question often arises in connection with specific cases: we may ask, for example, at what point in our development from a fertilized egg there comes to be a person, or what it would take for a chimpanzee or a Martian or a computer to be a person, if they could ever be. An ideal account of personhood would be a definition of the word ‘person’, filling the blanks in the formula ‘Necessarily, x is a person at time t if and only if … x … t …’.

The most common answer is that to be a person is to have certain special mental properties. Locke, for instance, said that a person 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” (1975: 335; Baker 2000: ch. 3 is a detailed account of this sort). Others propose a less direct connection between personhood and these special mental properties: that to be a person is be capable of acquiring them, for example (Chisholm 1976: 136f.), or to belong to a kind whose members typically have them when healthy and mature (Wiggins 1980: ch. 6). (A very different answer is mentioned in section 6 below.)

Persistence. What does it take for a person to persist from one time to another—to continue existing rather than cease to exist? What sorts of things is it possible, in the broadest sense of the word ‘possible’, for you to survive, and what sort of event would necessarily bring your existence to an end? What determines which past or future being is you? Suppose you point to a child in an old class photograph and say, “That’s me.” What makes you that one rather than one of the others? What is it about the way she relates then to you as you are now that makes her you? For that matter, what makes it the case that anyone at all existing back then is you? This is sometimes called the question of personal identity over time , as it has to do with whether the earlier and the later being are one thing or two—that is, whether they are numerically identical. An answer to it is an account of our persistence conditions .

Historically this question often arises from the thought that we might continue existing after we die (as in Plato’s Phaedo ). Whether this could happen depends on whether biological death necessarily brings our existence to an end. Imagine that after your death there really will be someone, in this world or the next, who resembles you in certain ways. How would she have to relate to you as you are now in order to be you, rather than someone else? What would the Higher Powers have to do to keep you in existence after your death? Or is it even possible? The answer to these questions depends on the answer to the persistence question.

Evidence. How do we find out who is who? What evidence bears on the question of whether the person here now is the one who was here yesterday? One source of evidence is first-person memory: if you remember doing some particular action (or seem to), and someone really did do it, this supports the claim that that person is you. Another source is physical resemblance: if the person who did it looks just like you—or better, if she is in some way physically or spatio-temporally continuous with you—that too supports her being you. Which of these sources is more fundamental? Does first-person memory count as evidence all by itself, or only insofar as we can check it against physical facts? What should we do when these considerations support opposing verdicts?

Suppose Charlie’s memories are erased and replaced with accurate memories (or apparent memories) of the life of someone long dead—Guy Fawkes, say (Williams 1956–7). Ought we to conclude on these grounds that the resulting person is not actually Charlie, but Guy Fawkes brought back to life? Or should we instead infer on the basis of physical continuity that he’s just Charlie with new memories? What principle would answer this question?

The evidence question dominated the anglophone literature on personal identity from the 1950s to the 1970s (Shoemaker 1963, 1970 and Penelhum 1967 are good examples). It’s important to distinguish it from the persistence question. What it takes for you to persist through time is one thing; how we ought to evaluate the relevant evidence is another. If the criminal had fingerprints just like yours, the court may rightly conclude that he is you, but having your fingerprints is not what it is for a past or future being to be you: it’s neither necessary (you could survive without any fingers at all) nor sufficient (someone else could have fingerprints just like yours).

Population. The persistence question is about which of the characters introduced at the beginning of a story have survived till the end of it. But we can also ask how many are on the stage at any one time. What determines how many of us there are right now? If there are eight billion people on the earth at present, what facts—biological, psychological, or what have you—make that the right number?

You may think the number of people at any given time (or at least the number of human people) is simply the number of human organisms there are then. But this is disputed. Some say that cutting the main connections between the cerebral hemispheres results in radical disunity of consciousness so that two people share a single organism (Nagel 1971; for skeptical views see Wilkes 1988: ch. 5 and van Inwagen 1990: 188–212). Others say that a human being with multiple personality could literally be the home of two or more thinking beings (Wilkes 1988: 127f., Rovane 1998: 169ff.; see also Olson 2003, Snowdon 2014: ch. 7). Still others argue that two people can share an organism in cases of partial twinning (Campbell and McMahan 2016; see also Olson 2014).

The population question is sometimes called the problem of “synchronic identity”, as opposed to the “diachronic identity” of the persistence question; but these terms need careful handling. They are apt to give the mistaken impression that identity comes in two kinds, synchronic and diachronic. The truth is simply that there are two kinds of situations where we can ask how many people (or other things) there are: those involving just one moment and those involving an extended period. To make matters worse, the term ‘synchronic identity’ is sometimes used to express the personhood question.

Personal ontology. What are we? What properties of metaphysical importance do we human people have, in addition to the mental properties that make us people? What, for instance, are we made of? Are we made entirely of matter, as stones are, or are we partly or wholly immaterial? Where do our spatial boundaries lie, if we are spatially extended at all? Do we extend all the way out to our skin? If so, what fixes those boundaries? Do we have temporal as well as spatial parts? Are we substances—metaphysically independent beings—or is each of us a state or an activity of something else?

Here are some of the main proposed accounts of what we are (Olson 2007):

• We are biological organisms (“animalism”: van Inwagen 1990, Olson 1997, 2003a).
• We are material things “constituted by” organisms: a person is made of the same matter as a certain animal, but they are different things because what it takes for them to persist is different (Baker 2000, Johnston 2007, Shoemaker 2011).
• We are temporal parts of animals: each of us stands to an organism as your childhood stands to your life as a whole (Lewis 1976).
• We are spatial parts of animals: something like brains, perhaps (Campbell and McMahan 2016, Parfit 2012), or temporal parts of brains (Hudson 2001, 2007).
• We are partless immaterial substances—souls—as Plato, Descartes, and Leibniz thought (Unger 2006: ch. 7), or compound things made up of an immaterial soul and a biological organism (Swinburne 1984: 21).
• We are collections of mental states or events: “bundles of perceptions”, as Hume said (1978 [1739]: 252; see also Quinton 1962, Campbell 2006).
• There is nothing that we are: we don’t really exist at all (Russell 1985: 50, Unger 1979, Sider 2013).

There is no consensus or even a dominant view on this question.

What matters in survival. What is the practical importance of facts about our persistence? Why does it matter ? If you had to choose between continuing to exist or being annihilated and replaced by someone else exactly like you, what reason would you have to prefer one over the other? And what reason do you have to care about what will happen to you, as opposed to what will happen to other people? Or is there any such reason? Imagine that surgeons are going to put your brain into my head and that neither of us has any choice about this. The resulting person will be in terrible pain after the operation unless one of us pays a large sum in advance. If we were both entirely selfish, which of us would have a reason to pay? Will the resulting person—who will think he is you—be responsible for your actions or for mine? (Or both, or neither?) These questions are summarized in the phrase what matters in survival .

The answer may seem to turn entirely on whether the resulting person would be you or I. Only I can be responsible for my actions. The fact that some person is me, by itself, gives me a reason to care about him. Each person has a special, selfish interest in her own future and no one else’s. Identity itself (numerical identity) is what matters in survival. But some say that I could have an entirely selfish reason to care about someone else’s future for his own sake. Perhaps what gives me a reason to care about what happens to the man people will call by my name tomorrow is not that he is me, but that he is then psychologically continuous with me as I am now (see Section 4). If someone else were psychologically continuous tomorrow with me as I am now, he would have what matters to me and I ought to transfer my selfish concern to him. Likewise, someone else could be responsible for my actions, and not for his own. Identity itself has no practical importance. (Sosa (1990) and Merricks (2022) argue for the importance of identity; Parfit (1971, 1984: 215, 1995) and Martin (1998) argue against.)

That completes our survey. Though some of these questions may bear on others, they are largely independent. Many discussions of personal identity leave it unclear which one is at stake.

Turn now to the persistence question. Few concepts have led to more misunderstanding than identity over time. The persistence question is often confused with others or stated in a tendentious way.

It asks roughly what is necessary and sufficient for a past or future being to be someone existing now. If we point to you now, and then describe someone or something existing at another time, we can ask whether we are referring to two different things or simply referring twice to one thing. The persistence question is what determines the answer to such queries. (And there are precisely analogous questions about the persistence of dogs, rocks, and other things.)

Here are three common misunderstandings of this question. Some take it to ask what it means to say that a past or future being is you. This would imply that we can answer it simply by reflecting on our linguistic knowledge—on what we mean by the word ‘person’, for example. The answer would be knowable a priori. It would also imply that all people must have the same persistence conditions—that the answer to the question is the same no matter what sort of people we considered. Though some endorse these claims (Noonan 2019b: 84–93), they are disputed. What it takes for us to persist might depend on whether we are biological organisms, which we cannot know a priori. And if there could be immaterial people—gods or angels, say—what it would take for them to persist might differ from what it takes for a human person to persist. In that case our persistence conditions could not be established by linguistic or conceptual analysis.

Second, the persistence question is often confused with the question of what it takes for someone to remain the same person —as in this passage from Bertrand Russell (1957: 70): “Before we can profitably discuss whether we shall continue to exist after death, it is well to be clear as to the sense in which a man is the same person as he was yesterday.” If Baffles were to change in certain ways—if she lost much of her memory, say, or changed dramatically in character, or became severely disabled—we might ask whether she would still be the person she was before, or instead become a different person. This is not a question about persistence—about numerical identity over time. To ask whether Baffles is the same person that she was before, or to say that she is a different person from the one she used to be, presupposes that she herself existed at the earlier time. The question arises only when numerical identity is assumed. To ask about Baffles’ persistence, by contrast, is to ask not whether she is still the same person, but whether she still exists at all.

When we speak of someone’s remaining the same person or becoming a different one, we mean remaining or ceasing to be a certain sort of person. For someone no longer to be the same person is for her still to exist, but to have changed in some important way. This typically has to do with her individual identity in the sense of the characterization question—with changes in respect of those properties that “define someone as a person.”

Third, the persistence question is often taken to ask what it takes for the same person to exist at two different times. The most common formulation is something like this:

• If a person x exists at one time and a person y exists at another time, under what possible circumstances is it the case that x is y ?

This asks, in effect, what it takes for a past or future person to be you, or for you to continue existing as a person . We have a person existing at one time and a person existing at another, and the question is what is necessary and sufficient for them to be one person rather than two.

This is narrower than the persistence question. We may want to know whether each of us was ever an embryo, or whether we could survive in an irreversible vegetative state (where the resulting being is biologically alive but has no mental properties). These are clearly questions about what it takes for us to persist. But as personhood is most commonly defined (recall Locke’s definition quoted earlier), something is a person at a given time only if it has certain special mental properties at that time. Embryos and human beings in a vegetative state, having no mental properties at all, are thus not people when they’re in that condition. And in that case we cannot infer anything about whether you were once an embryo or could exist in a vegetative state from a principle about what it takes for a past or future person to be you.

We can illustrate the point by considering this answer to question 1:

Necessarily, a person x existing at one time is a person y existing at another time if and only if x can, at the first time, remember an experience y has at the second time, or vice versa.

That is, a past or future person is you just if you (who are now a person) can now remember an experience she had then, or she can then remember an experience you’re having now. Call this the memory criterion . (It too is often attributed to Locke, though it’s uncertain whether he actually held it: see Behan 1979.)

The memory criterion may seem to imply that if you were to lapse into an irreversible vegetative state, you would cease to exist (or perhaps pass to the next world): the resulting being could not be you because it would not remember anything. But no such conclusion follows. Assuming that an organism in a vegetative state is not a person, this is not a case involving a person existing at one time and a person existing at another time. The memory criterion can only tell us which past or future person you are, not which past or future being generally. It says what it takes for someone to persist as a person , but not what it takes for someone to persist without qualification. So it implies nothing about whether you could exist in a vegetative state or even as a corpse, or whether you were once an embryo. As stated, it’s compatible with your surviving with no memory continuity at all, as long as this happens when you are not a person (Olson 1997: 22–26, Mackie 1999: 224–228).

No advocate of the memory criterion would accept this. The view is intended to imply that if a person x exists now and a being y exists at another time—whether or not it’s a person then—they are one just if x can now remember an experience y has at the other time or vice versa. But this not an answer to Question 1: what it takes for a person existing at one time and a person existing at another time to be one rather than two. It’s an answer to a more general question: what it takes for something that is a person at one time to exist at another time as well, whether or not it’s a person then:

• If a person x exists at one time and something y exists at another time, under what possible circumstances is it the case that x is y ?

Those who ask Question 1 are commonly assuming that every person is a person essentially : nothing that is in fact a person could possibly exist without being a person. (By contrast, no student is a student essentially: something that is in fact a student can exist without being a student.) This claim, “person essentialism,” implies that whatever is a person at one time must be a person at every time when she exists, making Questions 1 and 2 equivalent.

But person essentialism is controversial (Olson and Witt 2020). Combined with a Lockean account of personhood, it implies that you were never an embryo: at best you may have come into being when the embryo that gave rise to you developed certain mental capacities. Nor could you exist in a vegetative state. It rules out the brute-physical view described in the next section. Whether we were once embryos or could exist in a vegetative state, or whether we are people essentially, would seem to be substantive questions that an account of our persistence should answer, not matters to be presupposed in the way we frame the debate.

Three main sorts of answers to the persistence question have been proposed. Psychological-continuity views say that our persistence consists in some psychological relation, the memory criterion mentioned earlier being an example. You are that future being that in some sense inherits its mental features from you—beliefs, memories, preferences, the capacity for rational thought, and so on—and you are that past being whose mental features you have inherited in this way. There is dispute over what sort of inheritance this has to be—whether it must be underpinned by some kind of physical continuity, for instance, and whether it requires a “non-branching” restriction—and about what mental features need to be inherited. (We will return to some of these points.) But most philosophers writing on personal identity since the early 20th century have endorsed some version of this view: e.g. Dainton 2008, Hudson (2001, 2007), Johnston (1987, 2016), Lewis (1976), Nagel (1986: 40), Parfit (1971; 1984: 207; 2012), Shoemaker (1970; 1984: 90; 1997; 1999, 2008, 2011), Unger (1990: ch. 5; 2000).

A second answer is that our persistence consists in a physical relation not involving psychology: you are that past or future being that has your body, or that is the same biological organism as you are, or the like. Call these brute-physical views. (Advocates include Ayers (1990: 278–292), Carter (1989), Olson (1997), Snowdon (2014), van Inwagen (1990: 142–188), and Williams (1956–7, 1970).)

Some try to combine these views, saying that we need both mental and physical continuity to survive, or that either would suffice without the other (Nozick 1981: ch. 1, Langford 2014, Madden 2016, Noonan 2021).

Both views agree that there is something that it takes for us to persist—that there are informative, nontrivial, necessary and sufficient conditions for a person existing at one time to exist at another time. A third view, anticriterialism , denies this. Psychological and physical continuity are evidence for persistence, it says, but do not always guarantee it and may not be required. The clearest advocate of this view is Merricks (1998; see also Swinburne 1984, Lowe 1996: 41ff., 2012; Langford 2017; for criticism see Zimmerman 1998, Shoemaker 2012). There is also debate about how anticriterialism should be understood (Olson 2012, Noonan 2011, 2019a).

Most people—most Western philosophy teachers and students, anyway—feel immediately drawn to psychological-continuity views. If your brain were transplanted, and that organ carried with it your memories and other mental features, the resulting person would be convinced that he or she was you. This can make it easy to suppose that she would be you, and this would be so because of her psychological relation to you. But there is no easy path from this thought to an attractive answer to the persistence question.

What psychological relation might it be? We have already mentioned memory: a past or future being might be you just if you can now remember an experience she had then or vice versa. This proposal faces two historical objections, dating to Sergeant and Berkeley in the 18th century (see Behan 1979) but more famously discussed by Reid and Butler (see the snippets in Perry 1975).

To see the first objection, imagine that a young student is fined for overdue library books. As a middle-aged lawyer she remembers paying the fine, but in her dotage she remembers her law career but has entirely forgotten not only paying the fine but all the other events of her youth. According to the memory criterion the student is the lawyer and the lawyer is the elderly woman, but the elderly woman is not the student. This is an impossible result: if x and y are one and y and z are one, x and z cannot be two . Identity is transitive; memory continuity is not.

The second objection is that it seems to belong to the very idea of remembering that you can remember only your own experiences. To remember paying a fine (or the experience of it) is to remember yourself paying. That makes it uninformative to say that you are the person whose experiences you can remember—that memory continuity is sufficient for us to persist. It’s uninformative because we could not know whether someone genuinely remembers a past experience without already knowing whether she is the one who had it. Suppose we ask whether Blott, who exists now, is the same as Clott, whom we know to have existed in the past. The memory criterion tells us that Blott is Clott just if Blott can now remember an experience Clott had then. But Blott’s seeming to remember one of Clott’s experiences counts as genuine memory (the objection goes) only if Blott actually is Clott. So we would already have to know whether Blott is Clott before we could apply the principle that is supposed to tell us whether she is. (There is, however, nothing uninformative about the claim that memory connections are necessary for us to persist—that you could not survive without being able to remember anything, for example.)

One response to the first objection (about transitivity) is to modify the memory criterion by switching from direct to indirect memory connections: the old woman is the young student because she can recall experiences the lawyer had at a time when the lawyer remembered the student’s life. The second problem is commonly met by replacing memory with “quasi-memory”, which is just like memory but without the identity requirement: even if it’s impossible to remember doing something you didn’t do but someone else did, you could still “quasi-remember” it (Penelhum 1970: 85ff., Shoemaker 1970; for criticism see McDowell 1997).

But there remains the obvious problem that there are many times in our pasts that we cannot remember or quasi-remember at all, and to which we are not linked even indirectly by an overlapping chain of memories. There is no time when you could recall anything that happened to you while you dreamlessly slept last night. The memory criterion has the absurd implication that you have never existed at any time when you were unconscious, and that the person sleeping in your bed last night was someone else.

A better solution replaces memory with the more general notion of causal dependence (Shoemaker 1984, 89ff.). We can define two notions, psychological connectedness and psychological continuity. A being is psychologically connected , at some future time, with you as you are now just if she is in the psychological states she is in then in large part because of the psychological states you are in now (and this causal link is of the right sort: see Shoemaker 1979). Having a current memory (or quasi-memory) of an earlier experience is one sort of psychological connection—the experience causes the memory of it—but there are others. The important point is that our current mental states can be caused in part by mental states we were in at times when we were unconscious. For example, most of your current beliefs are the same ones you had while you slept last night: they have caused themselves to continue existing. You are then psychologically continuous , now, with a past or future being just if some of your current mental states relate to those he or she is in then by a chain of psychological connections.

That would enable us to say that a person x who exists at one time is the same thing as something y existing at another time just if x is, at the one time, psychologically continuous with y as it is at the other time. This avoids the most obvious objections to the memory criterion.

It still leaves important questions unanswered, however. Suppose we could somehow copy all the mental contents of your brain to mine, much as we can copy the contents of one computer drive to another, thereby erasing the previous contents of both brains. Whether this would be a case of psychological continuity depends on what sort of causal dependence counts. The resulting being (with my brain and your mental contents) would be mentally as you were before, and not as I was. He would have inherited your mental properties in a way—but a funny way. Is it the right way? Could you literally move from one organism to another by “brain-state transfer”? Psychological-continuity theorists disagree. (Shoemaker (1984: 108–111, 1997) says yes; Unger (1990: 67–71) says no; see also van Inwagen 1997.)

A more serious worry for psychological-continuity views is that you could be psychologically continuous with two past or future people at once. If your cerebrum—the upper part of the brain largely responsible for mental features—were transplanted, the recipient would be psychologically continuous with you by anyone’s lights, and any psychological-continuity view will imply that she would be you. If we destroyed one of your cerebral hemispheres, the resulting being would also be psychologically continuous with you. (Hemispherectomy—even the removal of the left hemisphere, which controls speech—is sometimes carried out as a treatment for severe epilepsy: see Shurtleff et al . 2021.) And it would be the same if we did both at once, destroying one hemisphere and transplanting the other: the recipient would be you on any psychological-continuity view.

But now suppose that both hemispheres are transplanted, each into a different empty head. (We needn’t pretend that the hemispheres are exactly alike.) The two recipients—call them Lefty and Righty—will each be psychologically continuous with you. The psychological-continuity view as we have stated it says that any being who is psychologically continuous with you must be you. It follows that you are Lefty and also that you are Righty. But that again is impossible: it cannot be that you and Lefty are one and you and Righty are one, but Lefty and Righty are two. Yet they are: there are clearly two people after the operation. One thing cannot be numerically identical with two different things. We can see this in another way by asking how many people there are in the whole story, from start to finish. If you are both Lefty and Righty, the answer is one: the only person in the story is you. Yet seeing as Lefty is not Righty, the answer must be at least two. Your being both Lefty and Righty would imply that the number of people in the story is both one and more than one.

Psychological-continuity theorists have proposed two different solutions to this problem. One, sometimes called the “multiple-occupancy view”, says that if there is fission in your future, then there are two of you, so to speak, even now. What we think of as you is really two people, who are now exactly similar and located in the same place, doing the same things and thinking the same thoughts. The transplant operation merely separates them (Lewis 1976, Perry 1972, Noonan 2019b: 141–144).

The multiple-occupancy view is usually combined with the general metaphysical claim that people and other persisting things are composed of temporal parts (often called “four-dimensionalism” or “perdurantism”; see Hudson 2001, Sider 2001a, Olson 2007: ch. 5). The idea is that for each part of a person’s life, there is a thing just like the person except that it exists only at that time. That thing is a temporal part of the person: it stands to the person as the first half of a football match stands to the match. On this account, the multiple-occupancy view is that Lefty and Righty coincide before the operation by sharing their pre-operative temporal parts or “stages”, then diverge by having different temporal parts located afterwards. They are like two roads that coincide for a stretch and then fork, sharing some of their spatial parts but not others. Much as the roads are just like one road where they overlap, Lefty and Righty are just like one person before the operation when they share their temporal parts. Even they themselves can’t tell that they are two. There are two coinciding people before the operation because of what happens later, just as there may be coinciding two roads here because of what’s the case elsewhere. Whether we really are composed of temporal parts, however, is disputed. (Its consequences are explored further in section 8.)

The second and more commonly proposed solution abandons the claim that psychological continuity by itself suffices for us to persist, and says that a past or future being is you only if she is then psychologically continuous with you and no other being then is. (There is no circularity in this. We need not know the answer to the persistence question in order to know whether people existing simultaneously are two or one: that comes under the population question.) So neither Lefty nor Righty is you: they both come into existence when your cerebrum is divided. If both your cerebral hemispheres are transplanted, you cease to exist—though you would survive if only one were transplanted and the other destroyed. Fission is death. (Shoemaker 1984: 85, Parfit 1984: 207; 2012: 6f., Unger 1990: 265).

This proposal, the “non-branching view”, has the surprising consequence that if your brain is divided, you will survive if only one half is preserved, but you will die if both halves are. That looks like the opposite of what we should expect: if your survival depends on the functioning of your brain (because that’s what underlies psychological continuity), then the more of that organ we preserve, the greater ought to be your chance of surviving.

In fact the non-branching view implies that transplanting one hemisphere and leaving the other in place would also be a fatal case of fission. Its consequences are especially surprising if brain-state transfer counts as psychological continuity: in that case, even copying your total brain state to another brain without doing you any physical harm would kill you.

These consequences are not just hard to believe, but also mysterious. Keeping half your brain functioning is normally sufficient for your survival, on a psychological-continuity view. Why then would you not survive if the other half too were kept functioning, separate from the first? How could an event that would normally ensure your survival destroy you if accompanied by a second such event (Noonan 2019b: 128–141)?

The non-branching view is largely responsible for the interest in the question of what matters in survival. Faced with the prospect of having one of your hemispheres transplanted, there is no evident reason to want the other one to be destroyed. Most of us, it seems, would rather have both preserved, even if they go into different heads. Yet on the non-branching view that is to prefer death over continued existence. This leads Parfit and others to say that that is precisely what we ought to prefer. We have no reason to want to continue existing, at least for its own sake. What you have reason to want (assuming that your life is going well) is that there be someone in the future who is psychologically connected or continuous with you, whether or not she is you. The usual way to achieve this is to continue existing yourself, but on the non-branching view it’s not necessary.

Likewise, even the most selfish person may have a reason to care about the welfare of the beings who would result from her undergoing fission, whether or not either of them would be her. The non-branching view suggests that the sorts of practical concerns you ordinarily have for yourself can apply to someone other than you. More generally, facts about numerical identity—about who is who—have no practical importance. All that matters is who is psychologically connected or continuous with whom. Psychological-continuity views are often said to be superior to brute-physical views in accounting for what matters in survival. Fission cases threaten this claim. (Lewis 1976 and Parfit 1976 debate whether the multiple-occupancy view can preserve the conviction that identity is what matters practically.)

Another objection to psychological-continuity views is that they rule out our being biological organisms (Carter 1989, Ayers 1990: 278–292, Snowdon 1990, Olson 1997: 80f., 100–109). This is because no sort of psychological continuity appears to be either necessary or sufficient for a human organism to persist.

We can see that it’s not necessary by noting that each human organism persists as an embryo without psychological continuity. And we can see that it’s not sufficient by imagining that your brain is transplanted. In that case the recipient would be uniquely psychologically continuous with you, and this continuity would be continuously physically realized. Psychological-continuity views imply that she would be you. A person would go with her transplanted brain. But it doesn’t seem that any organism would go with its transplanted brain. It looks as if the operation would simply move an organ from one organism to another, like transplanting a liver. It follows that if you were an organism, you would stay behind with an empty head, contrary to psychological-continuity views.

Psychological-continuity views do not merely rule out our being essentially or “fundamentally” organisms, but our being organisms at all. They say that each person has the property of persisting by virtue of psychological continuity: of being such that psychological continuity (perhaps with a non-branching restriction) is both necessary and sufficient for it to continue existing. But no organism has this property. (Or at least no human organism does, and we are clearly not non-human organisms.) Or again: every person would go with her transplanted brain, but no organism would do so. And if every person has a property that no organism has, then no person is an organism.

This is said to be a problem for psychological-continuity views because healthy, adult human organisms appear to be conscious and intelligent. Suppose they are. And suppose, as psychological-continuity views seem to imply, that we ourselves are not organisms. Three awkward consequences follow.

First, you are one of two intelligent beings sitting there and reading this entry: there is, in addition to you, an organism reading it. More generally, there are two thinking beings wherever we thought there was just one, a person and an organism distinct from it.

Second, we would expect the organism not just to be intelligent, but to be psychologically indistinguishable from you. That would make it a person, if being a person amounts to having mental special properties (as on Locke’s definition)—a second person in addition to you. In that case it cannot be true that all people (or even all human people) persist by virtue of psychological continuity, contrary to psychological-continuity views. Some—those who are organisms—would have brute-physical persistence conditions.

Third, it’s hard to see how you could know whether you yourself were the nonanimal person with psychological persistence conditions or the animal person with brute-physical ones. If you thought you were the nonanimal, the organism would use the same reasoning to conclude that it was too. For all you could ever know, it seems, you yourself might be the one making this mistake.

We can illustrate this epistemic problem by imagining a three-dimensional duplicating machine. When you step into the “in” box, it reads off your complete physical (and mental) condition and uses this information to assemble a perfect duplicate of you in the “out” box. The process causes momentary unconsciousness but is otherwise harmless. Two beings wake up, one in each box. The boxes are indistinguishable. Because each being will have the same apparent memories and perceive identical surroundings, each will think, for the same reasons, that he or she is you—but only one will be right. If this happened to you, it’s hard to see how you could know, afterwards, whether you were the original or the duplicate. (Suppose the technicians who work the machine are sworn to secrecy and immune to bribes.) You would think, “Who am I? Did I do the things I seem to remember doing, or did I come into being only a moment ago, complete with false memories of someone else’s life?” And you would have no way of answering these questions. In the same way, psychological-continuity views raise the questions, “What am I? Am I a nonanimal that would go with its brain if that organ were transplanted, or an animal that would stay behind with an empty head?” And here too there seem to be no grounds on which to answer them.

This is the “too-many-thinkers” or “thinking-animal” objection to psychological-continuity views. The most common defense against it is to say that, despite sharing our brains and showing all the outward signs of consciousness and intelligence, human organisms do not think and are not conscious. There simply are no thinking animals (Shoemaker 1984: 92–97, Lowe 1996: 1, Johnston 2007: 55; Baker 2000 offers a more complex variant).

But although this is easy to say, it’s hard to defend. If human organisms cannot be conscious and intelligent, it would seem to follow that no biological organism could have any mental properties at all. This threatens to imply that human organisms are “zombies” in the philosophical sense: beings physically identical to conscious beings, with the same behavior, but lacking consciousness (Olson 2018). And it leaves us wondering why organisms cannot be conscious. The best proposed answer is given by Shoemaker (1999, 2008, 2011), who argues that it is because organisms have the wrong persistence conditions, but it’s highly controversial.

A second option is to concede that human organisms are psychologically indistinguishable from us, but try to explain how we can still know that we are not those organisms. The best-known proposal of this sort focuses on personhood and first-person reference. It says that not just any being with mental properties of the sort that you and I have—rationality and self-consciousness, for instance—counts as a person (contrary to anything like Locke’s definition). A person must also persist by virtue of psychological continuity. It follows that human animals are not people (thus avoiding the second awkward consequence, about personhood).

Further, personal pronouns such as ‘I’, and the thoughts they express, refer only to people in this sense. So when your animal body says or thinks ‘I’, it refers not to itself, but to you, the person. The organism’s statement ‘I am a person’ does not express the false belief that it is a person, but the true belief that you are. So the organism is not mistaken about which thing it is: it has no first-person beliefs about itself at all. And you’re not mistaken either. You can infer that you are a person from the linguistic facts that you are whatever you refer to when you say or think ‘I’, and that ‘I’ (in its typical uses, at least) never refers to anything but a person. You can know that you are not the animal thinking your thoughts because it’s not a person, and thus what you refer to when you say or think ‘I’. This avoids the third, epistemic version of the too-many-thinkers problem. (See Noonan 1998, 2010, Olson 2002; for a different approach see Brueckner and Buford 2009.)

The too-many-thinkers objection is based on the assumption that psychological-continuity views rule out our being organisms. Some question this assumption: they suggest that human organisms do persist by virtue of psychological continuity. Even if you are an organism, the transplant operation would not move your brain from one organism to another. Rather, it would cut an organism down to the size of a brain, move it across the room, and then give it new parts to replace the ones it lost. This view is sometimes called “new animalism” (Madden 2016, Noonan 2021; see also Langford 2014, Olson 2015: 102–106).

Animalism says that we human people are organisms. This does not imply that all organisms, or even all human organisms, are people: as we saw earlier, human embryos and animals in a vegetative state are not people on the most common definitions of that term. Being a person may be only a temporary property of us, like being a student. Nor does it imply that all people are organisms: it is consistent with there being wholly inorganic people such as gods or intelligent robots. Animalism is not an answer to the personhood question. (It is consistent, for instance, with Locke’s definition of ‘person’.)

For the most part, both animalists and their opponents say that organisms persist by virtue of some sort of brute-physical continuity with no psychological element. So most animalists accept a brute-physical account of our persistence. And most advocates of brute-physical views take us to be organisms.

The most common objection to brute-physical views (and, by extension, to animalism) focuses on their implication that transplanting your brain into my head would not give you a new body, but would give me a new brain. You would stay behind with an empty head (e.g. Unger 2000; for an important related objection see Johnston 2007, 2016). Animalists generally concede the force of this, but take it to be outweighed by other considerations: that we appear to be organisms, for example, that it’s hard to say what sort of non organisms we might be, and that our being organisms would avoid the too-many-thinkers problem. And animalism is compatible with our beliefs about who is who in real life: every actual case in which we take someone to survive or perish is a case where an organism does so. Psychological-continuity views, by contrast, conflict with the appearance that each of us was once a foetus. When we see an ultrasound picture of a 12-week-old foetus, we ordinarily think we’re seeing something that will, if all goes well, be born, learn to speak, and eventually become an adult human person, yet no person is in any way psychologically continuous with a 12-week-old foetus.

And the objection may be less compelling than it first appears (Snowdon 2014: 234). Suppose you had a tumor that would kill you unless your brain were replaced with a healthy donated organ. This would have grave side-effects: it would destroy your memories, plans, preferences, and other mental properties. It may not be clear whether you could survive it, even if the operation were successful. But is it really obvious that you could not survive it? Maybe it could save your life, though at great cost. And this might be so, the argument goes, even if the new brain gave you memories, plans, and preferences from the donor. But if it’s not obvious that the brain recipient would not be you, then it’s not obvious that it would be the donor. A brain transplant might be metaphysically analogous to a liver transplant. Again, the claim is not that this is obviously true, but only that it’s not obviously false. And in that case it’s not obvious that a person must go with her transplanted brain. (Williams 1970 argues in a similar way.)

The debate between psychological-continuity and brute-physical views cannot be settled without considering more general matters outside of personal identity. For instance, psychological-continuity theorists need to explain why human organisms are unable to think as we do. This will require an account of the nature of mental properties. Or if human organisms can think, psychological-continuity theorists will want an account of how we can know that we are not those organisms. This will turn on how the reference of personal pronouns and proper names works, or on the nature of knowledge.

Some general metaphysical views suggest that there is no unique right answer to the persistence question. The best-known example is the ontology of temporal parts mentioned in section 5. It says that for every period of time when you exist, short or long, there is a temporal part of you that exists only then. This gives us many likely candidates for being you—that is, many different intelligent beings now sitting there and reading this. Suppose you are a material thing, and that we know what determines your spatial boundaries. That should tell us what counts as your current temporal part or “stage”—the temporal part of you located now and at no other time. But that stage is a part of a vast number of temporally extended objects (Hudson 2001: ch. 4).

For instance, it’s a part of a being whose temporal boundaries are determined by relations of psychological continuity (Section 4) among its stages. That is, one of the beings thinking your current thoughts is an aggregate of person-stages, each of which is psychologically continuous with each of the others and with no other stage. If this is what you are, then you persist by virtue of psychological continuity. Your current stage is also a part of a being whose temporal boundaries are determined by relations of psychological connectedness . That is, one of the beings now thinking your thoughts is an aggregate of person-stages, each of which is psychologically connected with each of the others and to no other stage. This may not be the same as the first being, as some stages may be psychologically continuous with your current stage but not psychologically connected with it. If this is what you are, then psychological connectedness is necessary and sufficient for you to persist (Lewis 1976). What’s more, your current stage is a part of an organism, which persists by virtue of brute-physical continuity, and a part of many bizarre and gerrymandered objects (Hirsch 1982, ch. 10). Some even say that you are your current stage itself (Sider 2001a, 188–208). And there would be many other candidates.

The temporal-parts ontology implies that each of us shares our current thoughts with countless beings that diverge from one another in the past or future. In that case it’s not evident which of these things are us. Of course, we are the things we refer to when we say ‘I’, or more generally the referents of our personal pronouns and proper names. But these words would be unlikely to succeed in referring to just one sort of thing—to only one of the many candidates on each occasion of utterance. There would probably be some indeterminacy of reference, so that each such utterance referred ambiguously to many different candidates. That would make it indeterminate what things, and even what sort of things, we are. And insofar as the candidates have different histories and different persistence conditions, it would be indeterminate when we came into being and what it takes for us to persist (Sider 2001b).

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animalism | identity | identity: relative | Locke, John | mind: in Indian Buddhist Philosophy | personal identity: and ethics | temporal parts | zombies

Acknowledgments

Some material in this entry appeared previously in E. Olson, ‘Personal Identity’, in The Blackwell Guide to the Philosophy of Mind , edited by S. Stich and T. Warfield, Oxford: Blackwell, 2003.

Copyright © 2023 by Eric T. Olson < e . olson @ shef . ac . uk >

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