How do people persist through time?: Professor Nicholas Jones

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How do people persist through time?

Prof Nicholas Jones

What matters in survival? Am I the same person as I was when I was 2 years old? These are all questions about the metaphysical problem of personal identity. To begin, let us look at what metaphysics and personal identity is:

Metaphysics – the study of the nature/structure of reality.

Personal Identity – what is the connection between a single person at different stages in their life, these stages will be signified with the letter ‘t’. (e.g. I exist at t1, am I the same person at t2?)

To begin, we’ll consider two thought experiments: the first one (the split-brain) is Nick’s one in the lecture and the second (the teletransporter) is one developed by Derek Parfit.

I’ll only illustrate Nick’s case 4 here:
You go into a room, and doctors remove your brain and find that the left and right hemispheres are identical. Suppose these doctors then put them into two bodies: call one of those persons lefty and the other of those persons righty. Your memory, brain structure and attitude are all identical. Which one are you? Are there two of you? Do you still exist?

A similar thought experiment is presented by Derek Parfit:

You’re on a spaceship and there is a teleportation device to Mars. This teleportation device operates like this: it copies, destroys and rebuilds your body atom by atom identical to what was on the spaceship. It works normally for a while, but as you go down to Mars once more, the device malfunctions. It copies, rebuilds but does not destroy. Now, there are two copies of you – one on Mars, the other on the spaceship. Call one A, the other B. Which one are you? Are there two of you? Do you still exist?

Attempting to figure out these questions will help us get a little further in solving this philosophical problem.

I’ll provide some of the views on this – maybe you have your own, feel free to explore and think this through:

Parfit’s Psychological Relations.

Parfit’s answer is to claim that the questions ‘do you still exist?’ or ‘which one am I?’ are empty questions. The reason being that there was never a single you that existed in the first place. It’s like asking which party is the Russian Social Democratic Labour Party, the Bolsheviks or Mensheviks? That is, there is no identical relation between you before splitting and you after splitting. All that is needed is a psychological relation – which is the collection of memories and behaviours that belong to your person. So, there is no need for a singular identity, all that is required is just a psychological relation. The more of me, the better!

David Lewis is always divided!

David Lewis provides an alternate view. He still thinks identity matters, after all, many still want to say that the person you were when you began reading this is the same person as now! He agrees with Parfit that a psychological relation is a necessary part of answering the problem of personal identity but proposes a way for identity to still be present. He says that there were always two different people present and what the splitting cases did was to reveal that there were two people. You were always split, it just happened that for some period of time, these two people occupied one space.

Further reading

Derek Parfit on Personal Identity video
David Lewis (1976). “Survival and Identity” in Amelie Rorty (ed.), The Identities of Persons. University of California Press. Reprinted with postscripts in Lewis (1986)
Philosophical Papers Volume I. OUP