Personal identity
Michael Lacewing
enquiries@alevelphilosophy.co.uk
© Michael Lacewing
Two kinds of identity
• Qualitative identity: two things are identical in
their properties
• Numerical identity: there is just one thing (a=a)
• If one thing changes its qualities, does it remain
the same thing?
– ‘He was a different person after the cancer
scare’
– Who was? Change presupposes numerical identity
• Personal identity: what are the criteria for being
the same (numerically identical) person over
time?
One mind?
• Dualism: I am a mental substance; as long as
the substance persists, I do
• Materialism: there is only matter - does this
mean that I persist as long as my body does?
• Psychological theory: personal identity is
continuity in psychological properties - even
if these are transferred to another body
Locke’s theory
• I am united by memory: I am the same person as I
was at times I remember
– Reid: But I can’t remember every moment from the past
– Overlapping chains of memory
• What of sleep? Shoemaker: causal dependence not
just on memory but persistence through sleep
• Extend from memory to many psychological states
An objection
• The teletransporter
malfunctions!
– Both Kirks have overlapping chains of
psychological states; are both Kirk or
neither? We have qualitative
identity, but not numerical
– Not both: One person cannot be or
become two people
– Not neither: the same causal
relation holds as in normal cases;
whether Kirk is Kirk can’t depend on
whether another Kirk exist…?
• Something other than
psychological continuity is
needed for personal identity
Bodily theory
• Psychological continuity isn’t enough,
there must be continuity in matter
• Williams: more than 50% of my brain
• Animalism: we are animals, not simply
embodied minds; personal identity
means continuing as the same organism
• Teletransportation doesn’t keep
identity - it produces a replica
Brain transplants
• Is animalism or
Williams right? If your
brain is switched with
another brain, which
body are you ‘in’? Your
original one or the one
with your brain in?
• Your brain and mine are
both ‘erased’ and then
reprogrammed with
each others
psychological states;
now which body are
you ‘in’?
Was I that baby?
• I have almost no psychological
continuity with the baby
whose body became mine
• So was I ever a baby?
• Option 1: we are essentially
animals, and only persons for
some time
• Option 2: we are essentially
persons, and start to exist
after the animals whose bodies
we are ‘in’