Recommended Reading

Hume, D. A Treatise of Human Nature Book I, Pt IV, Sec. VII.

Williams, B. (1970) ‘The Self and the Future’ in Philosophical Review 79. pp. 161-80. (Included in Perry and Bratman Introduction to Philosophy, 2^nd ed.)

Reid, T. Essays on the Intellectual Powers of Man Essay 3, Ch. IV. (in Perry/Bratman, 2^nd ed.)

The General Problem of Identity

We’re going to be talking about the identity of persons, but it’s worth noticing that the problem that we have with this concept is related to a general problem of claiming an identity between objects in a world of changes.

The River

The ancient Greek philosopher Heraclitus claimed that we can’t step into the same river twice, because diferent waters wash over the feet of the person on those two occasions. What is it then that makes us call it the same river? It is usually assumed that for a river at one time to be the same as a river at another time means that an observer would have noticed a continuity in experiences featuring the river. If a river changes its course it does not lose its identity as long as a continuous series of river-states through time link its old and its new states. Against this continuity view we can still observe that the water in the river is constantly changing and there will only in rare cases be a continuous connection to be traced between water portions.

Quantum Identities

In Quantum Mechanics the particles are allowed to exist only in discrete states: orbital levels in an atom are determined by the distribution of discrete quanta of energy in the system. If an electron in one level gains or loses energy it jumps instantaneously from one position to another without passing through any other positions. There is no continuity here, and there is nothing we can use to distinguish this electron from any other electron. How is it then that we can say that the particle in the second case is identical to the particle in the first case? Would we make such a claim if a billiard ball struck by a cue disappeared and another billiard ball appeared simultaneously elsewhere on the table? If not, why not?

The Ship of Theseus

Each of the planks of the ship of Theseus are removed in turn and replaced by new planks. The old planks are stored on a distant island. When the last plank is replaced we should admit that the ship has retained its identity despite being composed of entirely different materials. The interesting thing now is that if the original planks are taken from storage and put back together we have to wonder whether this too is not the same ship as we began with. If not, then we have to have a explanation for why we can't move something by disassembly, transportation and reconstruction (like moving a house). This example has been used to argue against the transitivity of identity.

The Problem of Personal Identity

Personal Identity through Time

A child is conceived, grows to maturity, marries and bears children in turn, then dies. We can imagine that every part of a person (like fingernails, hair, spleen, etc.) traces a continuous line through time and space for as long as that part exists. However, even something we assume to be permanent part of the person, like their head, changes its appearance and its constitution as it passes from one end to the other of the line. Probably no part/instant of the person is identical in that sense at both ends of the line. Each molecule of the child is replaced so that the substance of the adult is altogether different. Moreover, the entity at birth resembles the entity at death only in a very rough outline. Nevertheless we have no difficulty in ascribing identity (in theory at least) to the individuals which we can indicate at each point of this progress.

The Transporter

In Star Trek they have a device that they claim allows a person to be transported at the speed of light from one place to the other. This device they call a transporter, and it works by scanning the person to be transported, converting them into a type of information, projecting that information across space, and reconstructing the person at the other end. The tricky thing is, and probably one of the reasons that Dr. McCoy was so dubious about the whole process, is that no part of the original person is transported. So another way of looking at what’s being done is to say that one person is destroyed at the origin and another person is created at the destination. It just happens that the new person at the destination at the time of construction has all the same memories and characteristics as the late person at the time of deconstruction.

Splitter!

You may recall that in one episode, the crew of the Enterprise (NCC 1701-E) returned to a site where they’d had a transporter malfunction. It turned out that Commander Ryker had materialised as per usual, but his information had not been cleared from the pattern buffer and another materialisation occurred at the same time. This second materialisation was another exact copy of original Ryker. So are there one, two, or three Rykers in this story?

[Show film of Mary and the teleporter.]

Who Cares?

You may initially wonder why we should care about this stuff. Well, the principal answer is that we rely upon notions of identity in order to tell us how to behave towards people. If I promised yesterday to do something for you, we don’t think that I am excused from keeping that promise because you have eaten today and thus are constructed of different matter from the person I made the promise to, and are thus a different person from that person. That’s obvious, but there are other less obvious problems we need to solve. For example, a very old man is discovered to be a person wanted for crimes against humanity committed as a very young man in the WWII period. Is it reasonable that he should be held accountable for those actions now?

Two Possibilities

There are two criteria which people have most often suggested are the proper ones to use for deciding upon identities

Bodily Continuity

We saw how this would work in the previous example about personal identity through time. We think that someone X at time t₁ is the same person as someone Y at time t_n>1 if there is a continuous series of other persons at all times between t₁ and t_n that we are convinced are identical with each other, and X is at one end of that series and Y is at the other end. If we are able to discover such a continuity we are likely to accept identity because we take identity to be a transitive relation.

A transitive relation is one that obeys the rule: if A is related as R to B, and B is related as R to C, then A is related as R to C. For example 2 < 3, 3 < 4 and ‘<’ is transitive, so 2 < 4. Or Aloysius is fatter than Bertrand, and Bertrand is fatter than Cyril, and ‘fatter than’ is transitive, so Aloysius is fatter than Cyril. In the case of the series of persons mentioned above we have:

if          A₁ = A₂

                            A₂ = A₃

                           …

                           A_n-1 = A_n

            Then     A₁ = A_n

(Note that ‘=’ and identity is more thn just transitive it’s also commutative, so A = B if and only if B = A, and so the same sequence of identifications will show us that A_n = A₁.)

Of course we have to ask what makes us think that we can discover any such equivalences between persons no matter how closely temporally connected. That just looks like a dodge.

Another way of thinking about it is to say that if we see that X is very similar to Y in facial features, sounds like Y when he speaks, walks with the same peculiar gait as he does, and so on; then we’re likely to make that identification. But this is even less likely to be unambiguous than the previous ‘method’. We’re going to have difficulties with identical twins for example, and worse difficulties with the split Rykers. We may even be fooled by impostors.

Generally when there is any doubt that a person whom we believe to be Bob (Bob₂) is actually identical to Bob (Bob₂), we test to see whether the internal Bob₂ is the same as the internal Bob₁ by asking questions and seeing whether that Bob₂ remembers what Bob₁ should remember or whether Bob₂ has the character that Bob₁ should have.

Psychological Continuity

Generally when there is any doubt that a person whom we believe to be Bob (Bob₂) is actually identical to Bob (Bob₂), we test to see whether the internal Bob₂ is the same as the internal Bob₁ by asking questions and seeing whether that Bob₂ remembers what Bob₁ should remember or whether Bob₂ has the character that Bob₁ should have. In most occasions, of course, these physical and mental criteria are going to agree, but in the cases where they disagree what are we going to believe.

There’s a famous example due to Locke ((ed. Nidditch, P. H.) Essay Concerning Human Understanding Book II, Chap. XXVII, Sec. 15, ll.10-14 )

For should the Soul of a Prince, carrying with it the consciousness of the Prince’s past Life, enter and inform the Body of a Cobler as soon as deserted by his own Soul, every one sees, he would be the same Person with the Prince, accountable only for the Prince’s actions: But who would say it was the same Man?

Locke is actually talking about the possibility of the transmigration of souls, but we can adapt the idea in the natural way to consider the possibility of an exchange of personalities between bodies. We can imagine the situation where the physiology of the Cobbler contains the psychology of the Prince and vice versa. The Cobler-body wakes up in the morning looks in the mirror and says ‘That’s not me!’ That body contains memories of being the Prince, and now displays all the other psychological characteristics of the Prince, such as courage, snobbishness, solitariness, slight depression, etc. Meanwhile, across town in the palace, a similar situation, mutatis mutandis, is playing out with the Prince-body seeming to believe that it doesn’t belong here.

Locke claims that the body that contains the memories of the Prince has the best (only) claim to be addressed as the Prince. In Locke’s opinion the identity of a person follows the chain of memories. It is the memories that the Prince has that make the Prince the person he is.

Problems with the Memory Criterion

1.             Our memories are not complete. What happens to the person whose memories are missing? For example, Bob can’t remember how he got home on Saturday night because he became tired and emotional. Did he cease to exist at some point? What if I can’t remember before some particular date? Does that mean I am a different person from the person who existed before that date? In response to this, it has often been urged that identity on the memory criterion should appeal to the transitive nature of identity and we should say that someone persists through time if there is a series of person/instants through time each of whom/when has a suitable subset of the memories of the immediately preceding person/instant.

2.             Memory can be inaccurate. Just because I think that I have memories of being Napoleon Buonaparte this doesn’t make me identical with that little Corsican upstart. This isn’t just an objection that memory is an unreliable criterion by which to determine identity; the real point is that it is meaningful to say that our memories are inaccurate. For what can that mean but that my memory of certain events is not a memory of events that really occurred and they are thus not memories of my experiences. But, then, what makes them my experiences is the fact that they occurred to me rather than that I have a memory of them. And so it seems that we must have a criterion of identity that is separate from, independent of, and possibly contradictory to the memory criterion. Here people often return to a bodily continuity view for a closer look, or they wonder about continuous non-bodily entities that may play the unifying role that underlies/explains the truth of identity statements – something like the self, for example.

3.             David Hume (who has something intelligent to say in every field of philosophy) made the remark that we should be leery of attributing our personal identity to some sort of Self conceived as a psychological entity, because there may not be any such thing. He says (Treatise of Human Nature Bk. I, Pt. IV, Sec. VI):

For my part, when I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never can observe any thing but the perception.

As a consequence, we have no justification in suposing there is a continuing thing to play the role of constant experiencer, but only that there are experiences. But if there is nothing that can be the self, and if there needs to be a non-bodily thing – a self – to ground our personal identity (where memories cannot do so), then there can be no personal identity.