PHIL1003 Lecture Notes - Lecture 11: Mental Substance, Personal Identity, Mental Property
Personal Identity
• The question
o You will have changed a lot physically, emotionally and
psychologically since you were 5,
o Yet you are still, in a very real sense, the very same person
o The question is, what does it take for a person to persist as the
very same person over time?
• Some central distinctions
o Qualitative Identity: two things are qualitatively identical if and
only if they share all the same qualities (barring occupying the
same space and time)
o Numerical Identity: two things are numerical identical if they are
on and the same thing.
▪ This does not infer qualitative identity, as it can span over
time; a thing can be the same thing but with different
qualities.
▪ What is it that makes someone at time 1 numerically
identical to a person at time 2?
o Evidence: what constitutes evidence that person at t1 (P1) =
person at t2 (P2)
▪ Evidence of P1 being P2 need not be necessary or sufficient
for P1 = P2.
o Criteria: what constitutes criteria that P1 (person at t1) = P2
(person at t2)
▪ Suppose feature X is the criteria, feature X offers both
necessary and sufficient conditions for constituting a
person. If P1 = P2, then X obtains. If X obtains, then P1 = P2.
▪ P1 is numerically identical to P2 only if X obtains. X is
essential to Ps identity.
▪ If P1 = P2 but X does not obtain, or if P1 ≠ P2 and X is
obtained, then the criteria for personal identity fails.
o Personal identity vs. identity of inanimate objects, biological
objects
▪ Ship of Theseus example
▪ Biology: what makes the cat the same as the kitten it once
was?
▪ We are concerned with the question of what makes a
person – the thing to which we normally ascribe mental
properties such as self-consciousness, feeling, wishing,
thinking, desiring (and on the basis of which we bestow
special ethical status) – the numerically same person as the
person it once was.
• Why do questions of personal identity matter?
o Survival after bodily death: it may give a measure of comfort to
suppose that a theory of personal identity, which allows for
survival after death, is even logically possible.
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