(intro music)
This is a lecture on personal identity,
as this problem arises in the case of John Locke,
a British philosopher of the seventeenth century.
Hi, my name is Michael Della Rocca,
I'm a professor of philosophy at Yale,
and I've been a professor here at Yale for
what seems to me to be an unbelievably long period of time,
since 1991.
It's unbelievable to me that I've spent so much time at Yale
doing this one job that I love,
and it's also unbelievable to me because
it's hard to see what it could be,
in virtue of which I today,
the person speaking to you right now,
am the same person as this inexperienced person
who came to Yale right out of graduate school in 1991.
I'm that same guy,
but what is it, in virtue of which I'm the same person
as that inexperienced young philosopher in 1991?
There've been many changes over that period of time.
I've gained or lost weight, mostly gained weight,
over that period of time.
I've read a lot of books.
I've taught a lot of classes.
Many changes.
I've had a family during that period of time.
But through all these changes it seems that
the same person, me, has persisted.
What can make it the case
that the person now speaking to you here
is the same as, is identical to,
the young person who began teaching at Yale in 1991?
This is one question that arises
when one considers the problem of personal identity
over time, and it is a question that philosophers
have long struggled to answer.
And there is, of course, no consensus
as to the best answer to this question,
the question of what it is, in virtue of which,
an earlier person is identical to a later person.
It is this question that I want to shed light on today,
by looking at the example of John Locke's theory.
But before I do that, I want to say a bit,
and this is relevant to our topic,
a bit about the nature of philosophical problems in general,
and about what it is to make progress
on philosophical problems.
Many of the most central problems of philosophy,
including the problem of personal identity
that we are going to talk about today,
they've been with us for hundreds, if not thousands, of years.
And there is, as I said, no consensus
as to the solution of these problems.
This might seem frustrating and dispiriting,
because if there is no progress on these problems,
then why do we bother addressing these problems at all?
This is a challenging question.
Indeed, it's a question, it's a philosophical question,
about the nature of philosophy itself.
Why do we continue to pursue philosophical problems
when most of the main, important philosophical problems
have not been resolved over the years?
One thing I'd like to suggest is that in philosophy,
the problems are often more important
than the solutions, if indeed there are any solutions at all.
And this is because the problems in philosophy
are ways of seeking understanding about ourselves
and about our place in the world around us.
And any development that helps us to see
an old problem in a new light,
any development that opens up a new possible position
with regard to an existing philosophical problem,
is a development that increases our understanding,
not only of the philosophical problem,
but also, and thereby,
it increases our understanding of ourselves.
And that's an important kind of philosophical progress.
We can make philosophical progress
by understanding an old philosophical problem
in a new light.
We thereby learn something important about ourselves,
even if we have not gone all the way
toward answering definitively a philosophical problem.
That's a phenomenon I want to illustrate today
in our discussion of personal identity over time,
because I think John Locke made precisely
that kind of progress with regard to
a longstanding philosophical problem,
in his very original account of personal identity.
Let me say a bit about John Locke.
He's, as I mentioned, a British philosopher.
He lived from 1632 to 1704.
He's perhaps more famous
for his work in political philosophy.
He had a very important influence on political thought
at the time and down to the present.
But he also wrote some important works in metaphysics
and epistemology, and it's
one aspect of his metaphysical views
that we're considering today:
the problem of personal identity over time.
In his account of personal identity over time,
he hit upon an insight that put the entire problem
in an entirely new light,
and opened up a new area of research,
of philosophical research, into the nature of persons.
This was, I think, an important kind of
philosophical progress, and many philosophers today
who work on personal identity are very much indebted
to Locke's development in this field.
And it's his insight that I want to examine today.
Now, in general form (I'll just talk about the problem
in general now without mentioning Locke in particular,
but we'll turn to Locke in a moment),
in a general way, the problem of personal identity
takes the following form.
Let's call the person who started teaching at Yale in 1991,
me, let's call that person "A."
A is going to be my very unimaginative name for a person.
The earlier person is the person A,
the person who started teaching at Yale in 1991.
And the person speaking before you right now
is this new person.
This person is called "B."
It's also me, and we want to say that
A is the same as, the same person as,
is identical to, person B.
A is identical to B.
But what is it, in virtue of which
the identity between A and B obtains?
This question can be broken down roughly
into two further questions.
This doesn't capture the complete content
of the "in virtue of" question that I raised,
but it's a large part of the content.
And the two questions are these:
"What are the necessary conditions
"for A to be identical to B?"
and "What are the sufficient conditions
"for A to be identical to B?"
Let me say a bit more about those two questions,
'cause they'll guide us throughout our discussion today.
The first question asks,
"What relation is required,
"in order for A to be the same as B?
"What relation must obtain
"in order for them to be identical?"
The form that the answer to this question would take
would be to find a certain relation
which is such that if A is identical to B,
then A and B stand in this relation.
So we're looking for a relation
that's a necessary condition for personal identity over time.
That's the first question.
The second question, about the sufficient conditions
for personal identity over time,
asks what is enough for a person at one time
to be identical to a person at another time?
What is enough, what is sufficient, for A
to be identical to B?
The form that an answer to this question would take
would be to find a certain relation,
perhaps another relation, a relation which is such that
if A and B stand in this relation, then A is identical to B.
So a necessary condition for personal identity
is a condition which is such that
if A is identical to B, then A and B stand in this relation,
and a sufficient condition for personal identity
is a condition such that
if A and B stand in this relation, then they're identical.
Now when you have both the necessary
and the sufficient conditions of the identity
of the earlier person A and the later person B,
when you have both sets of conditions,
then you have a full account of personal identity over time,
or at least you have the beginnings of such an account.
Now, the problem of personal identity over time
is addressing those two questions.
It's a more specific version of
the general problem of identity over time
for objects in general.
You can ask the question not just about
personal identity over time, but "What is it for a dog
"to be identical over time?
"What is it for an earlier dog to be
"identical to a later dog?"
There was a dog that was my dog last year.
His name was Jade, and that dog is identical
to a dog that is with me today.
What is it, in virtue of which the dog Jade,
the earlier dog Jade, is identical to the dog before me now,
the later dog.
That's the question of dog identity over time.
Similarly, we might ask about the identity of artifacts.
What makes the table that I'm sitting at now,
what makes this table now, identical to a table
that was in my office last week?
It's the same table, we want to say.
What is it, in virtue of which the table before me now
is identical to the table that was in my office last week?
We all think that there are such identity claims
that are true, but what is it that makes these claims true?
So the problem of personal identity over time
is a specific version of a general problem
about the identity of objects over time.
The question can arise in any area of philosophy
concerning any kinds of objects,
but specifically we're interested in the problem here
of personal identity over time.
And this focus makes sense, because
persons are really important to us.
I mean, dogs are important too, don't get me wrong.
But persons are especially important to us.
Tables, of course, are important to us,
but it's persons that we have a special interest in,
and we really want to know
what makes us the persons that we are.
What is it, in virtue of which we as persons
can persist over time?
The whole question of our practices concerning ourselves
seems to be premised on views about
personal identity over time.
The reason why I'm interacting with my friend right now
and I enjoy interacting with him or her
is that I think that the person I'm interacting with
right now is identical to the person that I grew up with
in Brooklyn many years ago.
It's the same person before me now
who I went to Coney Island with in Brooklyn many years ago.
And so there's a presupposition of identity over time
that guides this interaction that I have
with this person right now, because I believe
there's an identity claim that's true about this person.
Our practices of moral praise and blame
also seem to require certain presuppositions about
personal identity over time.
It doesn't seem right or fair
to blame someone before me now for a certain crime
or a certain bad action if the person before me now
is not identical to
the person who performed that bad action last week
or last year or whatever.
Practices of moral blame seem to presuppose
personal identity over time,
and similarly for moral praise.
More generally, planning for the future
seems to presuppose beliefs in personal identity over time.
I may have a certain plan that I want to go to
a certain concert tomorrow night,
because I believe that the person who will go to the concert
will be identical to me.
So I'm making up plans for myself in the future,
and that seems to presuppose a belief about
the persistence of a certain person over time.
So, all of our practical, day-to-day claims
in daily life presuppose, it seems,
a belief about some kind of personal identity over time.
That's one of the reasons why this question about
personal identity over time is so important.
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