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
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“This is Washington’s axe. The handle’s been replaced
three times and the head’s been replaced twice.”
Ship of Theseus
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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
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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
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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:
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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=B
B=C
but
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 9year-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
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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
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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:
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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