PERSONAL IDENTITY

What is personal identity

Am I the same person as I was when I was born? when I was a child? ten years ago? yesterday?

Is there a single self linking all these “person stages”, or are there just a succession of selves?

What kind of adventures could a person undergo without losing their identity? E.g. total amnesia, brainwashing, brain implants (remember the cyborg question?), brain transplant, teleportation?

Numerical identity vs. qualitative identity

Qualitative identity: two objects have exactly the same properties. Jenny and Sue are wearing the same dress.

Numerical identity: A and B are one and the same. Clark Kent is the same person as Superman. Jenny and Sue are in love with the same man.

Personal identity is about numerical identity: not, “am I the just the same as I was 10 years ago?”, but rather “am I the same person, or are there two people involved – one that existed 10 years ago but no longer, and me now?”

Heraclitus: “You cannot step into the same river twice.” The river is constantly changing (i.e. qualitatively different), so it is not the same river (i.e. numerically different).

Identity of objects

Washington’s axe

“This is Washington’s axe. The handle’s been replaced three times and the head’s been replaced twice.”

Ship of Theseus

Ancient Greek puzzle: a ship has been repaired so many times that there are no planks left at all from when the ship was first built. Is it still the same ship?

Hobbes’s addition: what if all the original planks were gathered up and the ship was rebuilt with them? Which ship now would be the original ship?

Identity of persons

What makes A at time T1 the same person as B and time T2? E.g. what makes me the same person as a little 9-year-old girl in the U.S. many years ago?

The animal approach

Adult me is a stage in the life of an animal that was born in Oklahoma, USA, many years ago. 9-year-old me was another stage in the life of that same animal. A caterpillar is a stage in the life of a butterfly.

Animals, like the Ship of Theseus, are constantly changing, and there may be no cells in common between the puppy and the adult dog it grows into. But the puppy and the adult dog are recognized as the same being.

Animals are the same if their bodies change gradually and the various stages are connected through an underlying design (DNA) and a continuous life process.

Problems with the animal approach

Body switching

Locke’s thought experiment, a prince and a cobbler switch bodies/minds

Surely, identity follows the mind. The prince is now in the cobbler’s body and vice versa.

Brain transplant

Identity travels with the brain?What about part of the brain?

Psychological approaches

1) The memory criterion

A is B if A can remember B’s experiences or thoughts.

I can remember being 9, so I am the same person I was when I was nine

Memory criterion paradox

I can remember getting glasses when I was nine, but I can’t remember what I did the day before I got glasses. But the day I got glasses, I could remember what I did the day before. So:

A = Kelly today B = the 9-year-old Kelly the day she got glasses C = the 9-year-old Kelly the day before she got glasses

According to the memory criterion:

A = BB = Cbut

A ≠ C

Solution?

Memory continuity criterion

If A is connected by a chain of memories to B, then A is B

Kelly today is connected by a shared memory with 9-year-old Kelly who is connected by a shared memory with 3-year-old Kelly who is connected by a shared memory with 2-year-old Kelly. Therefore Kelly today is the same person as 2-year-old Kelly.

Remaining problems for the memory criteria

Am I the same person as when I was a baby, if there is no chain of memory connecting me?

If you experience a short episode of amnesia, were you a different person during that period of time?

Are you a different person when you’re asleep?

Locke:

“if the same Socrates waking and sleeping do not partake of the same consciousness, Socrates waking and sleeping is not the same person. And to punish Socrates waking for what sleeping Socrates thought, and waking Socrates was never conscious of, would be no more right, than to punish one twin for what his brother-twin did, whereof he knew nothing, because their outsides were so like, that they could not be distinguished; for such twins have been seen.”

2) Psychological continuity

Person A is person B if they are connected by psychological continuity. I.e. if there are a chain of causal psychological connections between A and B.

E.g. my current psychological state depends on the psychological state of my brain when I was sleeping last night. For example, the memories and personality and mental capabilities that were part of my brain last night when I was asleep are still (for the most part) part of my brain right now. I am who I am partly because of what I was last night, last year, and when I was two.

Problem:

Psychological continuity may exist beyond the relationship between one’s past self and one’s present self. E.g. I am what I am partly because of my parent’s psychological states when I was growing up. Thoughts and ideas were transferred from their minds to my mind, causing my mind to develop a certain way.

Solution? The causal connection must be of the right kind – the normal causal connection between psychological states in a mind.

Is that a cop-out?

Problem cases

Brainwashing and total amnesia

If you had total amnesia (could remember nothing of your previous life) and were brainwashed so that you were psychologically radically different than before, would you be the same person?

On the animal approach: yes On the psychological approach: no

Fission: Hemispherectomy and half brain transplants

Tom’s brain is divided into two halves and transplanted into two different bodies. The right hemisphere is transplanted into a new body and called Righty. The left hemisphere is transplanted into a new body, called Lefty. According to the psychological criterion, they both should be the same person as Tom. But lefty is not righty.

Teleportation

John is on Planet Zorgon and wants to go back to his spaceship. He steps into a teleporter. The teleporter makes an exact duplicate of John’s body (and brain), destroys John’s body on Zorgon and rebuilds his body on the spaceship. The duplicate of John on the spaceship remembers everything that John did up until the time John stepped into the teleporter. He is also psychologically identical to John. He thinks he is John. Is he right?

What if John’s original body is not destroyed?

Brain implants

If your brain was implanted gradually with artificial parts that retained the same function as your brain, would you retain your identity? What if your entire brain was replaced gradually in that way? On the animal approach or the psychological approach? What if your brain was replaced suddenly rather than gradually?

Skepticism about personal identity

There is no personal identity. You are not the same person you were when you were a child, as you were last year, or yesterday, or when you walked into the lecture room. Any change makes us a different person.

Problems:

Moral responsibility: how can we blame anyone (or praise anyone) for anything “they” did, when it was not “them”, but their predecessor. I am not the person who stole the money yesterday, so don’t punish me.

Concern for our future selves: Why should I go to class? It won’t be me who graduates, but a different person. Why buy food, if it won’t be me who eats it?

Perhaps the relationship between A at T1 and A’ at T2 is not one of identity, but it is still a special relationship. Special enough that A’ can be punished for the actions of A and A cares deeply about the welfare of A’.

Suggested Readings

Derek Parfit, “What we believe ourselves to be” in Reasons and Persons, pgs. 199-217, on reserve in the Philosophy Department office

Adam Morton, “Identity through

Time” in Problems in Philosophy, pgs. 407-415, on reserve in the Philosophy Department office