The purpose of this Note is to provide a periodic refocusing of what my thoughts and beliefs about the topic of Personal Identity currently are. Previous versions can be found from the list below. This version has links to the various other Notes that expand further on the issues raised, and supply extensive reading lists. While very often these Notes are of the “promissory” variety, the links will remind me to improve them as needed.

1. What are we? This is one of the most important questions we need to ask ourselves. Just what kind of things are we? The question is closely related to a similar one: just what sort of adventures can individuals such as ourselves survive? This second question sheds light on the first for if there are certain contingencies that we think we would – or would not – survive, when a typical member of that kind would not – or would – survive, then that kind may not represent what we really think we are. Of course, we might be wrong in our estimations, but at least this will raise the question.
2. Why is this not a trivial question? If we look at a dog, say, and ask what it is, the answer to such a question is obvious – it’s a dog! It may be our pet – with a name – a particular individual, but when we ask what kind of thing it is, it’s a member of the species canis lupus. So, when we look at ourselves, the obvious answer is that we are human beings – specifically human animals, members of the species homo sapiens. That is the answer posited by the Animalists, amongst whose number – broadly speaking – I place myself, who accept the biological view of personal identity.
3. If this is true, then our persistence conditions – the necessary and sufficient conditions for us to continue in existence – are the same as those of other animals – the great apes, say, under which category we fall, biologically speaking. Why is this not the end of the story? Well, this is because – despite being a species of great ape – human beings are special in that we have enhanced cognitive capacities. We are morally accountable. In sum, we are persons, and have a “first person perspective” (FPP) on the world – something most philosophers deny to other animals – and care about our futures and – wantons apart – agonise over our past mistakes. Lynne Rudder Baker claims this perspective makes an ontological difference, rather than being – as I think – a special property of human beings that may or may not be had in particular cases. Baker accuses the animalists of not taking persons seriously. I might just note that there’s a facile and confusing answer to what we are, that is “people”. You may have noticed that I used the technical term “persons” as the plural of “person”. Some philosophers annoyingly use the term “people”, but this confuses the issue. When we say there are ten people in the room, while it is clear in normal circumstances what we mean – dogs don’t count, for instance – but if there happened to be a Klingon and a visiting angel, would they count as people or not? They are – we may suppose – persons, but they are not human persons
4. Since at least John Locke, this fact of our mental exceptionalism has tempted philosophers to say that it’s our psychological continuity that is more important for our identity-preservation than our physical continuity. This view still has its supporters – not only for those such as Dean Zimmerman and Richard Swinburne who believe in immaterial souls – but for the many who think that psychological continuity and connectedness is constitutive of the identity of persons. It is also implicit in the ideas of the Transhumanists who think that – come the Singularity – we might be capable of being uploaded to computers and thereby live almost forever.
5. Before proceeding further we have to say something brief and sketchy about identity and persistence. “Identity” – in the sense of “numerical identity” – is a relation a thing holds to itself and to nothing else. A is identical to B if A and B are the very same thing. It is an equivalence relation, being transitive, reflexive and idempotent; and, many of the sticking points in the philosophy of personal identity arise from this fact.
   1. It has nothing to do with “identity” as a sociological concept such as national identity, sexual identity or identification with a particular group.
   2. Also, John may be said “not to be the same person” since he took heroin, but he is still John and still the same individual; it’s just that his personality has changed.
   3. It also has nothing to do with “narrative identity” which is the story we tell about ourselves in an attempt to make sense of our lives.
   4. Finally, it has nothing to do with “exact similarity”: my television may be “identical” to yours, but that doesn’t mean I can have yours if mine breaks. They are – or were, when manufactured – exactly similar, but are distinct.
6. “Persisting” is what a thing does in continuing in existence. As we noted above, there are what are called “persistence conditions” – specific to a kind of thing – that set out what vicissitudes a thing can survive if it is to remain that very same thing. There are sometimes hard cases, and there can seem sometimes that there is an element of convention: is a particular club still the same clubs after it has lost all its original members, changed its name, and so on? But we can’t accept that our own existence is a matter of convention, though this could seem the case with the once-dominant psychological view of personal identity: just how much psychological connection could I lose with my former self – philosophers wondered – and still be me? However, things seem simpler and more objective for organisms, which persist despite exchanging material with the environment and changing many of their properties, provided they are caught up in a complex and hopefully long drawn-out event (or process) known as a “life”.
7. In the above I have assumed at least three things.
   1. Firstly, that “things” – or at least some things – exist. There’s a philosophical position known as “Process Metaphysics” (or “Naturalised Metaphysics”) that gives the focus to process rather than ontology, particularly in the case of organisms. I’m not sure how fatal this is to my approach, since I admit that animals are individuated by their lives, which are processes.
   2. Secondly, that we exist. This would seem hardly worth mentioning, other than that certain philosophers – nihilists – have argued that we (whatever we are) or – for similar reasons – various common things like hands – don’t exist.
   3. Finally, I assume that things do indeed persist, at least some of the time.
   I can’t really address these foundational issues here, but will just say a few words on the second issue. There are a lot of interconnected issues to do with the philosophy of time and change, in particular the problem of temporary intrinsics. How can the leaf that was green yesterday be the same leaf if it is brown today? How can the old bald bloke I am today be the same individual as the hirsute teenager all those years ago?
   1. Some philosophers – the exdurantists – say that there’s no relation of identity across time, but merely a weaker counterpart relation analogous to that between an individual and its counterpart in another possible world.
   2. Others – in particular Derek Parfit – have said that even if there is identity across time, it’s not what matters.
   In what follows, I assume that we exist and that we continue to exist self-identically across time and that this identity relation is important. We could not carry on our lives without these assumptions even if – philosophically-speaking – they were false; but I think they are true: I don’t want to distinguish the “strict and philosophical” from the “loose and popular” senses of identity first raised by Joseph Butler. I also assume the standard logic of identity and reject all heretical accounts that are invented from time to time as radical solutions to the difficult questions of persistence. In particular, I reject the view – known as occasional identity that – while (say) I am not identical to my younger self – yet I was that person, just not any more.
8. Now back to the main thread. Most Anglophone philosophers these days are physicalists (though maybe most non-philosophers are unreflective dualists). This gives physicalist philosophers a problem if they have hopes of post-mortem survival. If the human organism is totally destroyed – eg. by cremation, explosion, or eating of worms – just how does the very same individual get from this life to the next? Christian Materialists have had a go at thinking this through, and acknowledge the difficulties. Peter Van Inwagen attempted to show that it is at least logically possible by having God snatch away the dying body immediately pre-mortem, replacing it with a simulacrum. Dean Zimmerman – while himself a dualist – has suggested a “falling elevator” model to help out his materialist friends, whereby there is immanent causation (by some unknown natural or supernatural process) between the dying body and the resurrection one so that the dying individual escapes in the nick of time to the next world without loss of numerical identity. Others claim that God’s omnipotence is sufficient and is sovereign even over the laws of logic, so that problems raised by identity being an equivalence relation can be overcome by brute force. Maybe so, but without the constraints of logical possibility, we have no way of arguing the matter, so let’s not bother.
9. However, most Christian materialists prefer an alternative. They recognise that getting from here to the next world with temporal or spatial gaps raises difficult questions as to whether the numerical identity of the individual is preserved but adopt an alternative solution – the Constitution View. On this thesis, the person is distinct from the human animal – “just as” the statue is distinct from its constituting marble – so that the very same person – tagged by the unique “first person perspective” noted above – can be constituted first by its earthly body, and subsequently by its heavenly one.
10. Some Animalists have what they think of as a knock-down argument against the Constitution View. Eric Olson calls it the “Thinking Animal” argument. If the person and the animal are distinct things, albeit co-located, there are too many thinkers – because the animal can certainly think, as can the person, so we have two thinkers where we thought we had one – which is one problem; and there’s another – how do we know which we are, the person or the animal? I’m not impressed by this argument. There are several “multiple occupancy” conundrums that have been claimed at one time or another to deny the existence of things we are sure do exist. Dion and Theon, Tib and Tibbles, the “problem of the many” and so on. We just need to sort out our rules for counting. Also, the whole question of three- versus four-dimensionalism (4D) – whether a persisting thing is wholly present at a time – or whether only a temporal part is present, the thing as a whole being a “space-time worm” – bears on the question of counting. If different things can share stages – say the person and the human animal, or the statue and the clay – then we have to be careful how we count. In the case of a future fission – whereby two space-time worms share their past stages, but will ultimately diverge – we might not know how many to count at a time, but this will often not matter for practical purposes.
11. I think the idea of a first-person perspective is important. It is this that provides the pull against animalism when linked to various thought experiments (TEs) that we’ll come on to presently. However, I still don’t like the Constitution View. My objection is that the FPP is a property of something else – like a smile – in this case of a human animal, though the smile might belong to a cat. You can’t take the very same smile from one cat and place on another (it would be at best an exactly similar smile) – let alone have a disembodied smile like that of the Cheshire Cat. Similarly, you can’t take the very same FPP from one body and plop it onto another. True, it might be a qualitatively exactly similar FPP, but not the same one. What’s to stop that FPP being plopped on several resurrection bodies? Which would be numerically identical to me, given that they can’t all be, in the absence of 4D?
12. What are the temptations for not sticking with the animalist approach – which ought these days to be the default position in the absence of anything more compelling? As noted, the apparent lack of rational expectation of an afterlife is one incentive to look elsewhere, so “elsewhere” is a favourite for those who can’t bear the thought of their selves expiring with their bodies. We’ve noted the Christian dualists and materialists, but what about the Transhumanists? There’s the relatively metaphysically uninteresting case of cryoscopy followed by repair and resuscitation; there we have material continuity, and no possibility of reduplication, though some might claim there is too much outside interference for identity to be preserved. But, what about the “hope” of “you” being uploaded to a computer? There seems to be an idea about that “we” are really software (or data), when we are clearly material beings. If we are software, it is said, then we might “run” on different hardware. I have two issues with this, apart from the immense technical obstacles to be overcome both in “scanning” the “real you” and providing a computer of sufficient power to run your program and the virtual world for you to experience, Matrix-like.
    1. Firstly, what sort of thing is a program? It’s an interesting question whether a program has persistence conditions. Is Windows 10 the same program as Windows 0? Whatever the answer to this question is, a program would seem to be a kind of universal rather than a particular, and “we” are particulars.
    2. This leads to the second issue – a reduplication objection. Say we developed a sophisticated program that could run on an open-ended number of exactly similar robots. No two of these would be numerically identical to one another – they would be distinct, though exactly similar. So, were the program to be a simulation of your brain, it could run – presumably – on an open-ended number of computers – and these computers (or computer partitions) would not be identical to one another, so none of them could be you, as you could only be one of them, and there’s no principled way of saying which. The same objection prevents Star Trek-like teletransportation – were it possible – being identity-preserving. I might also add that no “program” is – in itself – conscious, though a machine that runs it might conceivably be. Mind you, there are arguments here as well – originated by John Searle – at least for digital computers.
    Incidentally, the transhumanists seem to imagine unending computer life as a secular heaven, but it could just as easily be a secular hell.
13. So, I remain wedded to my view that we are human animals with the persistence conditions of such. “Person” is not a substance term, but an honorific that refers to some substance during some periods of its existence when it has the requisite mental and moral properties to qualify. “Person” is a Phase Sortal (like “teacher”) that – in the case of “person” – applies to most humans most of the time, but need not apply to all humans all the time. There are ethical consequences for this view, but they are not as dramatic as is sometimes urged. Non-persons don’t have moral responsibilities, as is already recognised for demented or infant humans, and all non-human animals. The obverse – that persons allegedly have no moral obligations towards non-persons – or that non-persons have no rights – is the sticking point, and ought to be reflected in a more humane treatment of all non-persons rather than that we might contemplate sending human non-persons as well as non-human non-persons to the slaughter-house.
14. So, what are the problems for animalists? There are several. Some – like the so-called “corpse problem” (is my corpse me – only dead – if not, where does it come from? It doesn’t have the persistence conditions of an organism) are probably relatively easy to overcome. Recently, I’ve discovered that animalists – like (but for different reasons) those who think we are essentially persons – allegedly have a “fetus problem”. Animalists – saying that we are essentially animals – have (it seems) to say that we were once foetuses – which appears to be what our animal once was. But was this fetus once a proper part of its mother? There’s work currently going on to suggest that this is so – and if so, just when did the new human animal come into existence? However, I don’t think any of this seriously threatens animalism. Maybe animalists should have considered the problem more than they have, but animals do come into existence sometime – presumably by the time of birth at the latest – and that’s enough for an animalist.
15. The real problems for animalism stem from the force of thought experiments such as the “brain transplant intuition”. An animalist seems forced to say that I would not “go with my brain” in the circumstance where my brain is transplanted into another body, when it seems to most people that I would. The alleged reason for this is that at least some animalists consider the brain to be “just another organ” that we might lose like we might lose a kidney, provided the animal is kept alive. Doubts about this have led some to think that we are not “really” whole human animals but proper parts thereof, maybe not brains as such, but brains and a few other bits. This does seem comical. Just how large am I – would I fit into a hat-box, as Olson asks?
16. My view is as follows. I am currently (thankfully) a whole human animal. My wife worked in the NHS with amputees, and I think it is right to say that they also are whole human animals, though they lack parts that most of us have. No doubt they could lose more parts – and some diabetics sadly do. So, we might view a “brain in a vat” – one ready for transplant – as a “maximally mutilated” human animal. Maybe – in the case of a brain transplant – a prior animal has fissioned (divided into two) when the brain is extracted and we now have a case of the fusion of two animals (the brain from one fusing with the body of the other). It might be argued that our identity-logic isn’t quite up to deciding who is who in such circumstances, but the stakes seem high enough to demand an answer, for which read on.
17. I doubt whether the transhumanist hopes of augmenting our physical or mental attributes by effectively converting us into cyborgs is much of a threat to animalism. We don’t worry about our spectacles or our mobiles phones making us any less mammalian. Closer integration with AI applications is only the next step for the extended mind.
18. So, is there any purchase in thought experiments that putatively have my first person perspective persisting in cases where there is no identity preservation. Could it be the case that “it seems to me” that I have survived some vicissitude – a cerebrum transplant, say – but I am mistaken? Some philosophers argue that this happens every night – I go to sleep, and when I wake up I just assume that I am identical to the individual who got into bed, but how do I know? I might be intellectually convinced by third parties – those other than the sleeper and the waker – one way or another, but how would this affect how it seems to me? Take the teletranportation case. Because of the reduplication objection (unless we are 4-dimensionalists), we should say that numerical identity is not preserved. But – if the technology works, and I am the teletransportee – the individual (or 77 duplicates) would (all) wake up convinced they were me, yet they must be deceived. Thankfully, reduplication is not a problem for whole-brain transplants, but it is for idempotent half-brain transplants, though I think the identity problem there occurs during the fissioning process rather than when the half-brains are implanted.
19. I continue to think that there is a distinction to be made between forward and backward psychological continuity, though I don’t see how third parties – or even first or second parties – could tell the difference. It makes all the difference to me if I go to sleep and someone else wakes up thinking they are me – as against the normal case where I go to sleep and I wake up. In the former case – for me – there’s just an endless nothingness, of which I know nothing, while in the latter case my experiential life carries on. However, backward psychological continuity – what it feels like looking back – is the same for a survivor and one who only thinks he’s survived.
20. In the case of the split brain transplant, however, how is it all supposed to work, experientially? Neurosurgery is – even today – carried out on substantially conscious patients, as that way there’s a quick feedback loop to tell the surgeon whether he’s destroying any important areas of cognitive function. What would it be like to “fission”? Maybe I lack the imagination, but it seems to me that my First Person Perspective would go along with whatever was the dominant hemisphere, assuming this “seat of consciousness” is initially located in one hemisphere or the other. If it is not, then it would presumably be destroyed and two new ones would be created in this miracle operation. Either way, this would sit comfortably with the logic of identity which would not be violated, as at most one of the recipients would be me. I can imagine being ripped apart psychologically, but I can’t imagine going two ways.
21. Of course, there are physical and metaphysical issues with the whole idea of brain transplants – the physical structure of the brain reflects “its” body, and mental faculties are not fully localised, so it’s not just the immensely complex task of “wiring up” the brain to its new body that presents a challenge. Half-brain transplants are even more problematical as in the TEs the brain stem is not split, but only the cerebra are supposed to be transplanted. It’s not clear to me whether there is pervasive confusion here and that these thought experiments are underspecified to the degree of incoherence. Some philosophers – eg. Kathleen Wilkes – think TEs are unhelpful in the philosophy of personal identity, and that our concepts are not up to being probed in this way. I’m not so sure – the TEs are about us, not our concepts.
22. There is finally the question whether there is any such thing as “the Self”, which is what is supposed to have this FPP. Some contemporary philosophers argue that the Self is an illusion that the brain generates. Others – such as David Hume – have argued; and others – such as Galen Strawson – do argue that when they introspect they find no evidence of a persisting Self. I don’t know where they are coming from, as I can’t think of anything more certain. But a Buddhist-inspired “no-self” view makes the animalist’s task easier, if maybe less interesting.