Professor Shelly Kagan:
Last time, we turned to the
question of what the
metaphysical key to personal
identity might be.
What makes it be the case that
one person, some person that
exists in the future,
is the same person as me.
The first approach to this that
we considered was the soul
theory of personal identity:
the key to being the same
person is having the same soul.
Same soul, same person.
Different soul,
different person.
And the difficulty with that
approach, even if we bracket the
question whether or not there
are souls,
the difficulty with that
approach was that it seems as
though the soul could constantly
be changing while the
personality,
as we might call it,
stays the same.
I have the same beliefs,
memories, desires,
goals, preferences and so
forth.
But the soul underneath it all
keeps being swapped every five
minutes.
If the soul theory of personal
identity were right,
that would not be me.
I would be--Every five minutes
that person would die and we'd
have a new person,
despite having the same
personality.
Most of us find that a rather
difficult thing to believe,
that the person could be
constantly changing in this way,
without having any way at all
to tell.
And if we're not willing to
accept that implication,
it seems as though we need to
reject "the soul theory of
personal identity."
Now, I use this cumbersome
phrase because,
of course, I'm not here talking
about rejecting the existence of
souls.
What I'm considering right now
is the question whether sameness
of soul is the key to being the
same person.
And this is a--There's a
logical distinction here that's
worth drawing.
Even if you believe in souls,
you don't have to say that
having the very same soul is the
key to being the very same
person.
And trivially,
of course, if you don't believe
in souls, if you don't believe
that souls exist,
that you certainly can't appeal
to the existence of souls,
the continuity of soul,
the sameness of soul,
as the key to personal
identity.
But we might then ask,
"Well what's the alternative?"
Now, the natural alternative is
to say, "The key to being the
same person is not the sameness
of the soul,
whether or not it exists,
but rather having the very same
body."
And again, although I'm not
going to go on and on about this
point, it's worth noticing that
even if you do believe that
souls exist,
nothing stops you from
accepting the body theory of
personal identity.
Nothing rules out the
possibility that having the very
same body is the key to being
the very same person over time.
Even if you believe in souls,
you can accept the body theory.
And it certainly looks as
though if you don't believe in
souls, you have to accept the
body theory of personal
identity.
Now, as it turns out,
that appearance is deceptive.
There are still other
alternatives open to the
physicalist, but let's come to
that other alternative later.
Let's take a few minutes and
consider the nature of the body
theory, the body theory of
personal identity.
On this theory,
of course, the secret to being
the same person is having the
same body.
So when we ask,
well you remember last lecture
I was talking about how there'd
be somebody here lecturing to
you, philosophy,
on Tuesday.
Well, here somebody is.
Is that the same person?
Is the person who's lecturing
to you now the same person as
the person who was lecturing to
you before?
According to the body theory,
the answer is--turns on the
question, "Well,
is this the same body as the
lump of flesh and bone that was
here last week?"
If it is--and by the by it
is--if it is,
then it's the same person.
So am I the person who was
lecturing to you last week?
Yes, I am, because it's the
very same body.
That's what the body theory
says.
And unlike souls,
where it's all rather
mysterious how you could tell
whether soul swapping was taking
place or not,
it's not all that mysterious
how we check out to see whether
the same body's been around.
Even though you didn't do it,
you could have snuck into my
house, watched my body go to
sleep,
get up in the morning,
followed the body around over
the course of the day,
see it go to sleep again.
You could have tracked that
body through space and time and
said, "Hey look.
It's the very same body."
In the same way that we are
able to track in principle cars,
our earlier example,
and talk about yeah,
it's the same hunk of metal and
wire and rubber and plastic.
This is the same hunk,
same body.
All right, same body,
same person.
That's the body theory of
personal identity.
Now, if we accept the body
theory, then of course if we
turn to the question,
"Could I survive my death?"
Could I survive the death of my
body?"
at first glance,
it looks as though the answer's
going to have to be,
"Well, of course not."
Because when my body dies,
then, oh eventually the body
begins to decay.
It decomposes,
turns into molecules which get
absorbed into the soil or what
have you.
This may take years or decades
or even centuries,
but my body no longer exists
after death of my body.
And so how could I survive the
death of my body,
if for me to survive the death
of my body,
there's got to be somebody
who's me, and if being me
requires it being the same body,
my body would have to still be
around, but it's not.
That's what it looks like at
first glance.
But at second glance we see
that there's at least a logical
possibility of surviving the
death of my body.
All it takes is for my body to
be put back together.
Bodily resurrection.
Now I'm not going to here
pursue the question of,
"Do we believe bodily
resurrection occurs or will
occur?"
I'll note that there have been
religious traditions that have
taught and believed in this
possibility.
In particular,
it's probably worth mentioning
that early Christians believed
in something like the body
theory of personal identity and
believed in bodily resurrection
that would happen on Judgment
Day.
We can certainly understand the
possibility that God would
perform a miracle,
put the molecules back
together, turn the body back on.
Same body, same person,
come Judgment Day.
That's the possibility.
So it's at least worth
emphasizing the fact that even
if we don't believe in souls,
we could still believe in the
possibility of surviving one's
death, the death of one's body,
if we're willing to believe in
bodily resurrection.
Well, that's how it looks.
Now let's take a harder look.
Talking that way assumes that
when you put the body back
together, when God puts the body
back together on Judgment Day,
that that's still my body.
Is that right?
I'm inclined to think it is
right.
If God gathers up all the
various molecules that had
composed my body,
reassembles them in the right
order,
putting this calcium molecule
next to that hydrogen molecule
and so forth and so on,
reassembles them in the right
way--obviously if what He makes
out of my body's molecules is a
Cadillac,
then that's not my body--but if
He puts them together in the
right way, that seems like it
should be my body.
So here's an analogy to give
you a sense of what's going on.
Suppose I take my watch to the
jeweler because it stopped
working.
And in order to clean it and
fix it, repair it,
what the jeweler does is he
takes it apart.
He takes the rust off of the
gears, if there are still gears
in watches.
Imagine it's an old stop watch.
And he cleans all the pieces
and buffs them and polishes them
and then reassembles the whole
thing.
And a week later,
I come back and ask,
"Where's my watch?"
And he hands it to me.
Well, all well and good.
Now imagine some metaphysician
saying, "Wait a minute,
buster.
Not so quick.
That's not my watch.
Admittedly, it's composed of
all the very same pieces that
made up my watch.
Admittedly, all these pieces
are in the very same order as my
watch, but still that's not my
watch."
On the contrary,
it seems to me the right thing
to say about that example is,
"No, that is my watch."
My watch was disassembled for a
period of time.
Perhaps we should say my watch
didn't exist during that period
of time.
But it got put back together.
Now that's my watch.
If that's the right thing to
say about the watch--and it does
seem to me to be the right thing
to say about the watch--then God
could presumably do the same
thing on Judgment Day.
He could take our molecules,
which had been scattered,
put them back together and say,
"Ha!
That's your body."
And if the body theory of
personal identity is right,
well, that would be me.
So it seems to me.
But there's a different example
that we have to worry about as
well, which argues against this
proposal that the body could
decompose and then be
recomposed.
This is an example that's due
to Peter van Inwagen.
He's a contemporary
metaphysician,
teaches at Notre Dame.
Suppose that my son builds a
tower out of wooden blocks.
We have a set of wooden blocks
at home.
Suppose that he builds some
elaborate tower.
It's very impressive.
And he says,
"Please show it to mom when she
comes home."
And he goes to bed.
And I'm very good.
I'm cleaning up the house after
he goes to bed and oops,
I knock over the tower.
I say, "Oh my god,
he's going to be so angry.
I promised him I'd be careful."
So what I do is I take the
blocks and I put them back
together, building a tower in
the very same shape and the very
same structure,
the very same order as the
tower that my son had built.
And in fact I'm so
careful--perhaps the blocks are
numbered--I'm so careful that
every block is in exactly the
same position as in the case
where my son built it.
All right, I rebuild or I build
this tower and my wife comes
home and I say,
"Look what our son built.
This is the tower that our son
built."
Ah, that doesn't sound right.
That's not the tower that our
son built.
That's a tower that I built.
This is a duplicate tower.
Sure, if my son were to wake up
and I didn't tell him,
he wouldn't know that it was a
duplicate.
But when you take a wooden
block tower apart and then put
the pieces back together,
piece for piece,
duplicate, you don't have the
very same tower that you started
out with.
That's what van Inwagen says
and, I've got to admit,
sounds right to me.
If I were to point to that
tower and say,
"Ari built that," I'd be saying
something false.
"That's the very same tower
that Ari built."
No, I'd be saying something
false.
So van Inwagen concludes,
if you have an object and you
take it apart and then put it
all back together again,
you don't have the very same
object that you started out
with.
So even if Judgment Day were to
come, and God were to reassemble
the molecules and resurrect the
body,
it's not the very same body
that you started out with.
And if having the very same
body is the key to personal
identity, it's not the same
person.
Come Judgment Day,
we've got a duplicate of me,
but we don't have me.
That's what van Inwagen would
say, if that's the way bodily
resurrection would work.
I don't know,
theology aside,
I don't know what to say about
the metaphysical questions.
When I think about the tower
case, I do find myself inclined
to say, with van Inwagen,
that's not the tower my son
built.
But when I think about the
watch case, I find myself saying
that is the very same watch.
Now, all I can do is invite you
to think about these two cases
and ask yourself,
what should we say here?
Of course, for those people who
think it really is the same
tower, no problem.
Then we say,
the watch and the tower,
in both cases,
it's the very same object when
it's reassembled.
Reassemble the body,
that'll be the very same body
as well.
For those people who say,
"Yeah, van Inwagen was right
about the tower,
and the same thing would be
true about the watch.
The reassembled watch isn't the
very same watch," then we have
to say bodily resurrection would
not be the very same
body.
So that wouldn't be me waking
up on Judgment Day.
The alternative is to try to
find some relevant difference
between the watch case and the
tower case.
Something that allows us to say
that "well, when you reassemble
the watch it is the same watch.
When you reassemble the tower,
it's not the same tower.
Here's the explanation of why
those two things work
differently in the reassembly
cases."
And then of course,
we'd have to further
investigate whether when you
reassemble a body,
is it more like the watch case
or is it more like the tower
case?
I just have to confess,
I don't know what the best
thing to say about these cases
is.
I find myself inclined to think
reassembled watch,
same watch.
Reassembled tower,
not same tower.
Maybe there's a difference
there.
I don't have a good theory as
to what the difference is.
Since I don't have a good
theory as to what the difference
is, I'm not in a good position
to decide whether a reassembled
body would be the same body or a
different body.
I don't know.
So there's metaphysical work to
be done here by anybody who's at
least interested in getting this
theory of identity worked out
properly.
Still, at least the possibility
that we could work this out is
still there.
So I suppose there's still at
least the possibility that
bodily resurrection would be
coherent in such a way that it
would still be the same body.
So if we accept the body
theory, could there be life
after death?
Could there be survival of the
death of my body?
Seems like, as far as I can
tell, it's still a possibility,
although there's some puzzles
here that I don't know how to
see my way through.
Mind you, that's not to say
that I myself do believe that
there will be a Judgment Day,
and on that day God will
reassemble the bodies.
But it at least seems like a
coherent possibility.
Let's refine the body view.
I've been suggesting that the
key here, the idea of whether
it's the same person or not,
is whether it's the same body.
But of course as we know in
thinking about familiar objects,
we don't need to have every
single piece of an object,
of an entity,
stay the same to have the same
thing.
So I think I previously talked
about the steering wheel in my
car.
Every time I drive the steering
wheel in my car,
I rub off some atoms.
But that's okay.
It's still the very same
physical object.
The steering wheel is--Having
the same steering wheel is
compatible with changing of a
few pieces.
The same thing is true for
bodies, right?
You get sunburned,
your skin peels,
you've lost some atoms in your
body.
It doesn't really matter.
It's still the very same body.
So if body is the key to
personal identity,
we don't have to worry about
the fact that we're constantly
gaining and losing atoms.
Yes, question?
Student: What about
someone who loses a huge amount
of weight?
Professor Shelly Kagan:
Good.
The question was,
"What about somebody who loses
a huge amount of weight?"
They feel different.
People treat them different.
What about that case?
Well, I think if we're doing
metaphysics, as opposed to
psychology--Psychologically,
we understand why losing weight
might make a real difference as
to how you feel about yourself.
And we might even say,
loosely, it's as though she's a
whole new person.
But strictly speaking,
we don't think it is literally
a whole new person.
It's not as though we say,
"Poor Linda died when she
entered the spa.
Or a week into the spa when she
dropped those 50 pounds.
Somebody else who remembers all
of Linda's childhood,
some imitator came along."
We don't say "different person."
We say "same person,
lost a lot of weight."
Now that's not a problem for
the body view,
because on the body view,
the question is,
is it the same body?
And what we want to say is,
of course, look,
just like it's still your body
even if you break your arm.
Even though--It's still your
body after you've eaten dinner,
and so now some molecules have
been absorbed into your body
that weren't there before.
It's still your body after you
lose some molecules,
even a lot of molecules.
There can be changes in your
body that are compatible with it
still being the same body.
Now, we might worry about
the--Which changes?
Are all the changes,
it's certainly not as though
any change will do.
I mean, suppose what happens is
Linda goes to bed and what we do
in the middle of the night is we
take away that body and put some
new body there.
Well that 100% change,
that's clearly too much.
Change of some small
percentage, from eating,
not a problem.
Change from a somewhat larger
percentage of losing a fair bit
of weight doesn't seem to be a
problem.
So which changes in bodies make
for a different body and which
changes in body make for the
same body?
And in particular,
how should we run that if we're
thinking about the body as the
key to personal identity?
I think if we have that
question in front of our minds,
we're going to want to say not
all parts of the body are
equally important.
You lose a fair bit of weight,
some fat from your gut,
not a problem.
Here's one of my favorite
examples.
In the Star Wars movies,
Darth Vader whips out his light
saber and slashes off the hand
of Luke Skywalker.
"Luke, I am your father."
"No!"
Then the hand goes, right?
The very next scene--this has
always amazed me--the very next
scene, Luke's got an artificial
hand that's been attached to his
body and they never even mention
it again.
No one says, "Oh, poor Luke.
He died when Darth Vader cut
off the hand."
It seems pretty clear that not
all parts of the body matter.
You can lose a hand and still
survive.
Same body, except now without a
hand.
Suppose Darth Vader had aimed a
little higher and cut off Luke's
entire arm.
It would still be Luke.
It would still be Luke's body.
Suppose, even worse,
Darth Vader slices off both
arms and both legs.
It would still be Luke.
It would still be Luke's body,
though now without arms and
legs.
What part of the body,
if any, is essential?
Well here's a proposal.
It seems to me we'd say
something rather different if
what happened was that what got
destroyed was Luke's brain.
Suppose that Darth Vader uses
the force--the dark side of the
force of course--Darth Vader
uses the dark side of the force
to destroy,
to turn into pea soup,
Luke Skywalker's brain.
Now I think we might want to
say, "Well look,
no more Luke."
And if what happens is they
drag out some replacement brain,
it's still not Luke.
At least, that's a possible
version of the body view.
According to this version,
which I take to be the most
promising, the best version of
the body view,
the crucial question in
thinking about personal identity
is whether it's the same
body--but not all parts of the
body matter equally.
The most important part of the
body is the brain.
Well, why the brain?
No surprise there,
because of course the brain is
the part, we now know,
the brain is the part of the
body that is the house of your
personality,
your beliefs,
your desires,
your fears, your ambitions,
your goals, your memories.
That's all housed in the brain.
And so that's the part of the
brain that's the key part of the
body for the purpose of personal
identity.
That's what I'm inclined to
think is the best version of the
body view.
We find examples of this
thought, that the brain is the
key, in odd places.
So let me actually share one
with you.
This was something from the
Internet that my brother sent to
me some years ago.
It purports to be from a
transcript from an actual trial
in which a lawyer's cross
examining the doctor.
And you'll see.
I don't actually know whether
it's true or not,
whether it's just somebody made
it up.
But it purports to be true.
Q: Doctor,
before you performed the
autopsy, did you check for a
pulse?
A: No.
Q: Did you check for
blood pressure?
A: No.
Q: Did you check for
breathing?
A: No.
Q: So then it is
possible that the patient was
alive when you began the
autopsy?
A: No.
Q: How can you be so
sure, doctor?
A: Because his brain was
sitting on my desk in a jar.
Q: But could the patient
have still been alive
nevertheless?
A: It is possible that
he could have been alive and
practicing law somewhere.
The point--The reason that this
is funny, other than of course
the obvious moral,
which is that lawyers are
morons, is that of course.
Why is it so clear the lawyer's
got to be a moron?
Because of course we think,
look, lose a hand,
the guy could still be alive.
Lose an arm, lose a leg.
Lose the brain,
he's not alive.
So again this is,
this is hardly philosophical
proof, but it shows that we're
drawn to the thought that the
key part of the body is the
brain.
Now, think about what the
implication of holding that
view.
Suppose we adopt that version
of the body view.
If I get a liver transplant,
so here I am and we take out my
liver and we put Jones' liver
inside.
I've gotten a liver transplant.
It's still me.
Suppose we rip out my heart and
put Jones' heart in here.
I've gotten a heart transplant.
It's still me.
Suppose we rip out my lungs and
put in Jones' lungs.
I've gotten a lung transplant.
It's still me.
Suppose we rip out my brain,
put in Jones' brain.
Have I gotten a brain
transplant?
No.
What's happened is that
Jones has gotten a
body transplant.
Or, as we might put it,
a torso transplant.
If we accept this version of
the body theory,
we say the crucial part of the
body for personal identity is
not sameness of torso.
The crucial part of the body is
sameness of brain.
Just like "follow the soul" was
the answer if we believe in the
soul theory of personal
identity,
if we believe in the brain
version of the body theory of
personal identity,
same person or not?
Follow the brain.
Same brain, same person.
Different brain,
different person.
As I've now been saying several
times, I think that's the best
version of the body view,
although not all body theorists
believe that.
As you know from reading your
Perry, the assigned reading,
his Dialogue on Personal
Identity and Immortality,
the heroine of that story,
Gertrude--Gertrude actually
thinks the key part of the body
is the torso.
Follow the torso,
follow the person.
That's what she thinks.
I'm inclined to say, no.
In those moods,
when I accept the body theory,
I'm inclined to think,
no, follow the brain.
Gertrude would presumably say
you get a brain transplant,
you got a brain transplant,
because it's the same torso.
I want to say,
as a fan of the brain theory,
you get a brain transplant,
what's really happened is
somebody else has gotten a torso
transplant.
Follow the brain.
How much of the brain?
Do we need all of the brain?
Well, just like we didn't have
to follow the parts of the body
that aren't essential for
housing the personality,
we might ask ourselves,
"Do we need all of the brain to
house the personality?"
Research suggests that there's
a fair bit of redundancy in the
brain.
You can lose portions of the
brain and still have a perfectly
functioning, P-functioning
person.
Some of you may know that there
have been experiments in which,
for one reason or the other,
the two halves of the brain
have been separated.
And you often end up there
with, well, something closer to
two persons being housed within
one skull,
because they can often still
communicate in various ways.
We don't quite get that.
I gather that the best research
suggests we don't really have
complete redundancy with
hemispheres.
But suppose that we did.
Let's be science-fictiony.
Suppose that,
as a kind of backup security,
what evolution has done is
produced so much redundancy in
the brain that either half of
the brain would suffice.
All right, so think about our
brain transplant example.
So there's an accident with
Jones and Smith.
Jones' torso gets destroyed.
His brain is fine.
Smith's brain has gotten
destroyed.
His torso is fine.
We take Jones' brain;
we put it in Smith's torso.
We hook up all the wires,
as it were.
The thing wakes up.
Who is that?
Jones' brain, Smith's torso.
Follow the brain.
That's Jones that woke up.
Version two.
Horrible accident.
Jones' torso has been destroyed
and the left half of his brain
has been destroyed.
But the right half of his brain
is still there.
Smith's torso is fine,
but his entire brain has been
destroyed.
We take the right half of
Jones' brain,
put it into Smith's torso,
hook up all the wires the right
way, the thing wakes up.
Who is it?
It's Jones.
Follow the brain,
and more particularly,
follow however much of the
brain it takes to have enough of
the brain there to still give
you the memories,
beliefs, desires,
and so forth and so on.
If it were true--it probably
isn't true, but if it were
true--that half of the brain was
enough, then half the brain
would be enough.
That would be Jones that woke
up.
Question?
Student: [inaudible]
Professor Shelly Kagan:
Great.
The question was,
"On this theory,
what do we say about the case
where we take the two halves of
Jones' brain,
split them, put them in two
different torsos.
They both wake up.
Would they both be Jones?"
That's a wonderful question.
It's a wonderful case to think
about and, indeed,
I am going to come back to it.
But I just want to bracket it
for the time being.
But it's a great question to
keep in mind as you think about
the plausibility of the body
theory.
All right, so I'm inclined to
think that the best version of
the body theory has to do with
following the brain.
So one thing that a
physicalist, who does not
believe in souls,
one thing that a physicalist
could say is,
"What's the key to personal
identity?
The body.
Sameness of body."
And then I'm inclined to think
the best version of the body
view is the brain view.
So that's something that a
physicalist can say.
And for that matter,
it's something that a soul,
somebody who believes in souls,
could say as well:
even though there are souls,
that may not be the key to
personal identity.
Maybe sameness of body is the
key to personal identity.
That's something a physicalist
or dualist can say.
But, and this is not--to make
good on a promissory note I
offered earlier,
it's not the only view
available to physicalists or,
for that matter, dualists.
Even if there are no souls,
we don't have to say that the
key to personal identity is the
sameness of the body.
We could instead say the key to
personal identity is the
sameness of the personality.
After all, go back to the
Lockean worries about the soul
theory of personal identity.
It seemed very hard to believe
that it isn't the same person
when the memories and beliefs
and desires and goals and
ambitions and fears are all the
same,
even if a soul is constantly
changing.
It seems as though we wanted to
say same person.
Why?
Roughly speaking,
because it's the same
personality.
And with the body view,
when I started arguing a few
moments ago that the best
version of the body view was the
brain view,
why did that seem plausible?
Why didn't we say that Luke
died when he lost his wrist?
Because the brain,
after all, was the part of the
body that houses the
personality.
Enough of the brain was good
enough, I said.
What counts as good enough?
Enough to keep the personality.
Well, if what we think is
really important here is the
personality, why don't we just
say the key to personal identity
is the personality?
Let's just say it's me,
provided that there's somebody
who's got the same set of
beliefs, desires,
goals, memories,
ambitions, fears.
To coin a word,
the same "personality."
So the secret to personal
identity on this new proposal
isn't sameness of body,
it's sameness of personality.
Now, it's important to bear in
mind that this view is perfectly
compatible with being a
physicalist.
After all, we're not saying
that in order to have
personalities you need to have
something nonphysical.
As physicalists,
we can still say that the basis
of personality is that there are
bodies that are functioning in
certain ways.
But for all that,
the key to the same person
could have to do with the
personality rather than the
sameness of bodies.
Of course, normally the way you
get the same personality is by
having the same body.
Still, if we ask,
"What's doing the metaphysical
work here?
What's the key to being the
same person?"
we can say sameness of body
gave us the same personality,
but it was sameness of
personality that made it be the
very same person.
Could there be some way to get
sameness of personality while
not having sameness of body?
Maybe.
Suppose that we had some
disease.
The doctor tells me the
horrible news that I'm going to
have some disease that's going
to eventually turn my brain into
pea soup.
But luckily,
just before it does it,
they can take all of my
personality and put it into an
artificial replacement brain.
So there'll be --just like you
can have artificial hearts,
artificial livers,
you can have artificial brains,
which will get imprinted with
the same personality.
Same memory,
same beliefs,
same desires,
same fears, same goals.
We obviously can't do that.
This is a science fiction story.
But at least it allows you to
see how the body and the
personality could come apart.
And so we could have same
personality without literally
the same brain.
If personality is the key to
personal identity,
that would still be me.
Hold off again for a few
minutes, at least,
on the question,
"So what should we believe
here, the body,
the personality view?"
Let's try to refine the
personality theory.
So again, the point I was just
emphasizing was even if we
accept the personality theory,
this doesn't threaten our being
physicalists.
We can still say the reason
that we've got the same
personality in the normal case,
is there's some physical
explanation of what houses the
personality.
But for all that,
the key to personal identity is
same personality.
Notice, by the way,
that somebody who believes in
souls could also accept the
personality theory of personal
identity.
Locke believed in souls.
He just didn't think they were
the key to personal identity.
So you might think, "Oh no.
The physicalist is wrong when
the physicalist says that
personality--memory,
belief, consciousness,
what have you--is housed or
based in the body.
It's based in an immaterial
soul."
Dualists could say that.
And yet, for all that,
the dualist could consistently
say, "Still, same soul is not
the key to personal identity.
Same personality is the key to
personal identity.
If God replaces my soul every
10 minutes, as long as He does
it in such a way as to imprint
the very same personality on the
soul,
it doesn't matter any more than
it didn't matter whether or not
some of my body parts were
changing."
So the personality theory of
personal identity can be
accepted by physicalists and it
can be accepted by dualists.
So, just to keep score,
right now we've got three basic
theories of personal identity on
the table.
The soul theory,
the key to personal identity is
the same soul.
The body theory,
the key to personal identity is
the same body.
Where the best version,
I think, is the brain version
of the body theory.
And the personality theory,
the key to personal identity is
having the very same
personality.
Well again, we've got to be
careful about refining this.
Just like we all agreed,
I suppose, that you can have
the very same body,
even though some of the parts
come and go,
atoms get added,
other atoms get knocked off.
We can say, we'd better say,
that you can have the very same
personality even if some of the
elements in your personality
change.
After all, we defined the
personality in terms of it being
a set of beliefs and memories
and desires and goals and fears
and so forth.
But those things are constantly
changing.
I have all sorts of memories
now that I didn't have when I
was 10.
I have memories of getting
married, for example.
I wasn't married when I was 10.
So does the personality
theorist have to say,
"Uh-oh, different personality.
That kid no longer exists.
That person died,
got married and the memories
died."
If we say that,
we have very,
very short lives.
Because after all,
right now I've got some
memories that I didn't have two
hours ago.
I have some memories I didn't
have 20 minutes ago.
If every time you got a new
memory you had a new personality
and the personality theory said
having the very same personality
was the key to survival,
then none of us survive more
than a few seconds.
Well, the answer presumably is
going to be that the best
version of the personality
theory doesn't require item for
item having the very same
beliefs,
memories, desires, and so forth.
But instead requires enough
gradual overlap.
Your personality can change and
evolve over time.
So here I am as a 10 year old
child.
I've got certain desires,
certain memories.
As the year goes by,
I get some new memories.
I lose some of my goals.
I no longer--When I was 10,
when I grew up I wanted to be a
trash collector.
That was my first chosen
profession.
At some point I gave up that
desire.
I didn't want to be a trash
collector anymore.
I wanted to be,
I kid you not,
I wanted to be a logician when
I was a teenager.
I wanted to study symbolic
logic.
So at a certain point I gave
that up.
So my memories,
my desires were changing,
but they all changed gradually.
I lost some old memories.
I don't remember everything I
knew or remembered when I was
10.
When I was 10,
I had pretty vivid memories of
kindergarten.
Now I have very sketchy
memories of kindergarten.
Still, it wasn't abrupt.
It was gradual.
There was this slow evolution
of the personality.
And so when the personality
theorist says the key to
personal identity is the same
personality,
they don't' mean literally the
very same set of beliefs and
desires.
They mean, rather,
the same slowly evolving
personality.
Here's an analogy.
Suppose I had a rope that
stretched from that end of the
room all the way across to this
end of the room.
Very same rope at that end as
this end.
What makes up a rope?
Well as you know,
ropes are basically bundles of
fibers, very thin fibers that
have been woven together in a
certain way.
But the interesting thing is
the fibers themselves aren't
actually all that long.
They might be a couple of
inches or at most a foot or so.
And so no single fiber
stretches all the way across the
room.
Or even if some fibers did,
most of the fibers don't.
Does that force us to say,
"Ah, so it's not the very same
rope at the end as at the
beginning"?
No.
We don't have to say that at
all.
What we want to say is,
"It's the same rope as long as
there's this pattern of
overlapping fibers."
Certain fibers end,
but most of the fibers are
continuing.
Some new fibers get introduced.
They continue for a while.
Eventually maybe those fibers
end, but some new fibers have
been introduced in the meantime.
As long as it's not abrupt.
Imagine I take my scissors and
cut out a foot in the middle.
Then we'd say there isn't the
right kind of pattern of overlap
and continuity.
Now we really do have two
ropes--one rope here,
one rope there.
But if, in contrast,
there is the right kind of
pattern of overlap and
continuity,
same rope, even though,
even if no single fiber makes
it all the way across.
Something analogous needs to be
said by the personality
theorist.
Even if I have few or no
memories identical to the ones
that I had when I was 10,
that's okay.
We can still say it's the same
personality, the same evolving
personality, so long as there's
a pattern of overlap and
continuity.
New memories get added,
some memories get lost.
New goals get added,
some goals get lost.
New beliefs get added,
some beliefs get lost.
There might be few beliefs,
desires, goals that made it all
the way through.
But as long as there's the
right kind of overlap and
continuity, same personality.
All right, so what have we got?
Three views--soul view,
body view, personality view.
Three rival theories about the
key to personal identity.
Now, which of these is right?
Well, I don't myself believe in
souls, it's hardly going to
surprise you to learn that I
don't think the soul theory of
personal identity is right.
For me, the choice boils down
to the choice between the body
theory of personal identity and
the personality theory of
personal identity.
Of course, in real life,
they go hand in hand.
In ordinary cases at least,
same body, same personality.
Both theories are going to say
it's the very same person.
And if you believe in souls,
you are likely to think,
same soul as well.
In ordinary cases,
you have the same soul,
same body, same personality,
same person.
To think about which one of
these is the key to personal
identity, we need to think about
cases,
maybe somewhat fantastical,
science-fictiony,
in which they come apart.
Cases in which bodies and
personalities go their own ways,
as it were.
So that's what I'm going to do.
I'm going to tell you a story
in which your body ends up one
place and your personality ends
up someplace else.
And I'm going to invite you to
think about which of these two
resulting end products is me.
If you could figure out which
one's you, that would tell you
whether you think the body
theory is the right theory or
the personality theory is the
right theory.
Now, what's going to be our
guide?
I'm going to,
rather gruesomely--not in real
life, a science fiction
story--I'm going to torture one
of the two end products.
I'm going to ask you,
"Which one do you want to be
tortured?"
Or to put the point more
properly, which one do you want
to not be tortured?
Because I'm going to assume,
I'm going to take it,
that it's important to you that
you not be tortured.
So by seeing who you want to
keep safe, this will help you
see which one you think is you.
Of course, I've got to be sure
that you're thinking about this
in the right way.
Like some of you are probably
good, moral individuals and you
don't want anybody to be
tortured.
I say, "Ah, I'm about to
torture Linda over there."
You say, "No, no.
Don't torture Linda."
Still, if I were to say to you,
"I'm about to torture you."
You'd say, "No, no!
Don't torture me!"
and there'd be some extra
little something when you said
that, right?
So I want to invite you to keep
that extra little something in
mind when we tell the stories,
which we won't get to until
next time, when we tell the
stories next time,
and I say,
"Okay, who do you want to be
tortured, this person or that
person?"
The question is,
from that special egoistic
perspective that we're all
familiar with,
which is the one you really
care about?
That's going to be our guide to
deciding what's the key to
personal identity.
But to hear the stories,
you've got to come back next
lecture.
