Professor Shelly Kagan:
Let me start by reviewing the
problem that we were considering
last week.
We were raising a difficulty
for the personality theory of
personal identity according to
which the key to being the same
person is having the very same
ongoing,
evolving personality.
And the difficulty was
basically the problem of
duplication.
That it seemed as though we
could have more than one--call
it an individual--more than one
body,
that had the very same set of
memories, beliefs and so forth.
And that we have to ask
ourselves, "Well,
what should the personality
theory say about a case like
that?"
So imagine that over the
weekend, the mad scientist
copied my memories,
beliefs,
desires, fears,
ambitions, goals,
intentions and imprinted that
on somebody else's brain.
They did it last night at
midnight.
This morning, we woke up.
And we have to ask ourselves,
"Who's Shelly Kagan?
Who's the person that was
lecturing to you last week?"
Well, it doesn't seem plausible
in terms of the personality
theory to say that he's
Shelly Kagan,
and the one here today--Suppose
the other one's in Michigan.
If the one in Michigan's Shelly
Kagan but this one's not--After
all, although it's true that
he's got Shelly Kagan's
memories,
he woke up thinking he was
Shelly Kagan,
just like I woke up thinking I
was Shelly Kagan.
He woke up thinking about what
he was going to lecture on in
class today, just like I woke up
thinking about what I was going
to lecture in class today.
He remembered last week's
lecture just like I remembered
last week's lecture.
Well, no clear reason to
say--for the personality theory
to say--that he's Shelly Kagan
and I'm not.
After all, I've got the very
same set of memories,
beliefs, desires that he has.
But equally true,
and more surprisingly,
from the personality theory
point of view,
there's no reason to say that
I'm Shelly Kagan and
he's not.
After all, he's got all the
same memories,
beliefs and desires that I do.
It doesn't seem plausible to
say we're both Shelly
Kagan, because now we'd have to
then say Shelly Kagan's in two
places at the same time.
So the only alternative seems
to be to say that neither of us
is Shelly Kagan.
But if neither of us is Shelly
Kagan, then the simple original
personality theory was false.
Because according to that
theory, having the personality
is what it took to be Shelly
Kagan.
We both have it,
yet neither of us is Shelly
Kagan.
The personality theory must be
false.
So we revise the personality
theory to say,
the secret to personal identity
is having the same
personality--provided that
there's no branching.
Provided there's no splitting.
Provided there's only one best
competitor, not two equally good
candidates.
Given the no branching view,
the no branching rule,
we can say, in the ordinary
case,
look, there really wasn't
anybody imprinted with my
memories and desires in
Michigan.
I'm the only one around in the
earth right now with Shelly
Kagan's memories and desires.
Since there's no competitor,
and I've got the personality,
I'm Shelly Kagan.
I'm the very same person that
was here lecturing to you last
week.
That's what the personality
theory--It gives us the answer
we're looking for in the
ordinary case.
But in the science fiction
story where there's a duplicate,
it says, uh,
if there's branching,
the no branching rule comes in.
Neither of them is Shelly Kagan.
All right, so that's the best
way for the personality theory
to get revised to deal with this
problem.
The trouble was,
it seems the no branching rule
seems very counter-intuitive.
So think about it.
Here, right now I'm standing in
front of you saying I'm Shelly
Kagan, the guy who was lecturing
to you last week.
I believe I'm Shelly Kagan,
the guy who was lecturing to
you last week.
Am I Shelly Kagan?
Well, I've got Shelly Kagan's
personality.
So far so good.
Now all we have to decide is,
was the branching rule
satisfied or violated?
So all we have to know is,
is there somebody else
somewhere in the universe who's
got all my memories and beliefs
and desires?
Well, how in the world could I
know that?
Whether I, this person talking
to you right now,
is Shelly Kagan depends on
whether there's some duplicate
with all my memories in Michigan
or not?
It seems very counter-intuitive.
So although the personality
with no branching rule avoids
the problem of what to say about
duplicates,
by saying when there's
branching, neither of them is
Shelly Kagan,
the branching rule itself seems
very counter-intuitive.
We feel as though whether
somebody is me or not should
depend upon internal facts about
me in the earlier stages or this
stage and that stage,
not about what's happening
elsewhere, outside,
extrinsic to these things.
So, if you're not willing to
accept the no branching rule,
if it strikes you as a bizarre
thing to throw in to personal
identity,
maybe you need to reject the
personality theory.
Now during all of this,
the fans of the body view
typically are laughing.
They say this just goes to show
what a dumb theory the
personality theory is.
The whole problem with the
personality theory is that
personality is a bit like a
software.
It's like programs.
It's the various programs you
run on your computer along with
the various data files that you
have saved on your hard drive,
and so forth.
And those can be duplicated.
You have copy after copy after
copy.
You can have two copies of my
personality.
You could have 100 or 1,000.
The problem with--what drove
the personality theory into the
no branching rule,
implausible as it may be,
was the fact that your
personality is like software,
and it can be copied.
That's why, they say,
we should believe in the body
view.
If we accept the body view,
we avoid the duplication
problem.
Because, unlike software,
which can be literally copied,
as many as you want identical,
the body can't split.
Human bodies can't divide or
branch.
There's no way that there's
another body,
that the body on Thursday
became two bodies.
The body that was here on
Thursday didn't,
couldn't become two bodies.
So we avoid all the problem.
That's at least the kind of
claim that fans of the body view
often make in the face of this
difficulty for the personality
theory.
Well, now we need to ask,
is it really true?
Is it really true that bodies
don't face a duplication
problem?
Is it really true that human
bodies don't and couldn't split?
Look, the crucial word here is,
of course, "couldn't."
Personalities don't actually
split either,
right?
Although I've been giving
science fiction examples in
which the mad scientist
duplicates my memories and
beliefs and desires,
they've all been science
fiction examples.
If I can use science fiction to
talk about the possibility of
splitting, and use that against
the personality theory,
I'm entitled to use science
fiction examples to talk about
the possibility of bodies
splitting,
and ask, what kind of problem
that would raise for the body
theory?
Now, we are familiar with some
low-level examples of bodies
splitting.
Amoebas split, right?
You've got a single amoeba.
It's going along.
At a certain point--Let's draw
our amoeba splitting,
right?
You've got an amoeba split,
going along.
At a certain point,
it starts to look like that.
Then it looks like that.
And then boom!
You've got, well, it splits.
There's nothing in biology per
se that rules out cell division.
Indeed, on the contrary, right?
We know cells can split.
Now, human bodies,
unlike amoebas,
don't do that.
But maybe there's nothing in
biology that rules out the
possibility.
Suppose we open up the Yale
Daily tomorrow and we see
that the Yale Center for Amoebic
Studies has made this tremendous
breakthrough and has discovered
how to,
through the right kind of
injection or whatever,
cause a human body to replicate
and split in an amoeba-like
fashion.
Well, then we have to face the
problem of what to say in this
case of bodily branching.
Well, instead of pursuing that
example, let me give you a
slightly different example
that's been discussed a fair bit
in the philosophical literature.
This is actually a case that
one of the students in the class
asked about, I think it was last
week, if it wasn't even earlier.
And I said, "Great question.
Let's come back to it."
So here, at long last,
I'm making good on my
promissory note.
I'm going to come back to the
example that was raised before.
You'll recall that when we
talked about the body view,
I said the best version of the
body view doesn't require the
entire body,
to be the same body,
but the brain.
Follow the brain.
And indeed, it doesn't seem as
though we have to require the
entire brain,
just enough of the brain,
however much that turns out,
to house personality,
memories and so forth.
And then, I said,
suppose it was possible that
one hemisphere of your brain is
enough.
If there's enough redundancy in
the brain so that even if your
right hemisphere got destroyed,
your left hemisphere,
you still have all the same
memories, desires,
beliefs.
Good enough.
So now we worry about the
following case.
So I gave you a bunch of
examples, right,
where there are brains being
transplanted into torsos of
others.
So suppose, gruesome as it was,
this weekend I'm in some
horrible accident and my torso
gets destroyed and they keep my
brain on life support,
oxygenating it just long enough
to do some radical surgery into
some spare torsos.
Where'd the torsos come from?
Well, you had some living
people, but they had very rare
brain diseases and their brain
suddenly liquefied.
So now we've got some spare
torsos.
All right, so here we've got
Shelly Kagan.
His body gets destroyed.
And here's my brain.
Over here we've got Jones'
torso.
And over here we've got Smith's
torso.
Suppose we take,
call this one the left
hemisphere, and we stick it in
here, into Jones' torso.
We take this other hemisphere,
the right half of my brain and
we stick it into Smith's torso.
We connect all the wires,
all the neurons.
The operation's a smashing
success.
Both things wake up.
So here's Jones' torso with the
left half of SK's brain.
Smith's torso with the right
half of SK's brain.
They wake up.
We need some way to refer to
these people,
so we can start talking about
who they are.
Let me just call this top
one--Jones' torso with the left
half of Shelly Kagan's
brain--let's call him Lefty.
Smith's torso with the right
half of Shelly Kagan's brain,
let's call him Righty.
Okay, operation's a success.
Lefty and Righty both wake up.
They both think they're Shelly
Kagan, and so forth and so on.
And we ask ourselves,
according to the body view,
which one is Shelly Kagan?
What are the possibilities?
We could say Lefty is Shelly
Kagan and Righty is not.
Righty's an imposter.
But there's nothing in the body
view to give us a reason to make
that choice.
It's true that Lefty's got half
of Shelly Kagan's brain and
that's good enough.
But it's also true that
Righty's got half of Shelly
Kagan's brain and that seems
good enough.
So there's no reason to say
that Lefty is Shelly Kagan and
Righty isn't.
And similarly,
of course, there's nothing in
the body view to make us say
that Righty is Shelly Kagan and
Lefty isn't.
Well, if it's not one,
and not the other,
what are the remaining
possibilities?
We could, I suppose,
try to say they're both
Shelly Kagan.
And so Shelly Kagan continues,
that is to say his body
continues, that is to say his
brain continues,
that is to say enough of his
brain continues,
merrily on its way,
except now in two places.
And so from now on,
Shelly Kagan,
that single person,
is in two different places at
the same time.
Lefty goes to California.
Righty moves to Vermont.
From now on,
Shelly Kagan's bicoastal.
It doesn't seem right.
So what else can the body
theory say?
Well, the body theory could say
neither of them are
Shelly Kagan.
Shelly Kagan died in that
gruesome, horrible accident.
Although it's true that we now
have two people,
Lefty and Righty,
each of whom has half of Shelly
Kagan's brain,
and all of Shelly Kagan's
memories, for whatever that's
worth, neither of them is Shelly
Kagan.
We could say that as well.
But if we--and that seems the
least unpalatable of the
alternatives.
But if we say that,
then we've given up on the body
view.
Because the body view,
after all, said to be Shelly
Kagan is to have enough of
Shelly Kagan's brain.
And in this case,
both of Lefty and Righty seem
to have enough of Shelly Kagan's
brain.
What's the body theorist to do?
As far as I can see,
the best option for the body
theorist at this point is to
add--no surprises here--a no
branching rule.
The body theorist should say,
"The key to personal identity
is having the same body,
to wit, the same brain,
to wit, enough of the brain to
keep the personality
going--provided that there's no
branching,
no splitting,
no perfect competitors,
only one."
If the body view adds the no
branching principle,
then we can say,
look, in the case of this sort
of splitting--This example is
known in theto philosophical
literature as fission,
like nuclear fission when a big
atom splits into two.
So, in the fission case,
the body says,
the body theorist says,
in the fission case,
there's splitting,
there's branching.
So neither of them is going to
end up being Shelly Kagan.
But in the ordinary humdrum
case, here I am,
my body.
Why am I Shelly Kagan?
Because the brain in front of
you--you can't see it,
but it's in front of you--the
brain in front of you is the
very same brain as the brain
that you had in front of you on
Thursday.
Follow the body,
in particular follow the brain.
So in the ordinary case,
no splitting,
follow the brain.
In the special case where
there's splitting,
even if you follow the brain,
not good enough.
So the body theorist can avoid
the problem of fission,
avoid the problem of
duplication by adding the no
branching rule.
But of course,
the no branching rule didn't
seem very intuitive.
Whether or not I'm Shelly
Kagan, the guy that was
lecturing to you on Thursday,
depends on whether,
unbeknownst to me,
over the weekend,
somebody removed half of my
brain,
stuck it in some other torso,
sealed me all back up.
How could that matter?
Well, if you don't find the no
branching rule plausible,
you're in trouble as a body
theorist.
In fact, so what we see is,
the body theory is in exactly
the same problem,
exactly the same situation,
as the personality theory.
Indeed, the fission example is
a very nice case of how you
could have splitting for the
personality theory.
Here, before the accident,
was Shelly Kagan,
somebody who had my beliefs,
desires, memories,
goals, and so forth.
After the accident,
we've got two people,
Lefty and Righty,
or two entities,
Lefty and Righty,
both of whom have Shelly
Kagan's memories,
beliefs, desires,
goals, and so forth.
Splitting the brain shows how
you could, in fact,
have splitting of personality.
So the very same case raises
the very same problem for both
the body view and the
personality view.
And the only solution that I
can see, at least the best
solution that I can see,
is to accept the no branching
rule.
If you don't like the no
branching rule,
it's not clear what your
alternatives are.
Or at least,
it is clear what your
alternatives are;
it's not clear which
alternative would be any better.
Now during all of
this--problems for the
personality theory,
problems for the body
view--during all of this,
the soul theorist is having a
field day.
The soul theorist is saying,
"Look you guys,
you got into all this trouble
with splitting and so forth and
so on,
and needing to add the no
branching rule,
silly and implausible as that
seems,
you got into all that trouble
because of the problem of
splitting because personalities
can be split,
bodies can be split.
If only you had seen the light
and stuck to the soul theory of
personal identity,
all these problems could be
avoided."
Now, as you know,
I don't believe in souls.
But forget that issue for the
moment.
Let's just ask the question,
"Is it true that the soul
theory--if only there were
souls--is it true that the soul
theory would at least have the
following advantage?
It avoids these problems of
duplication and fission."
Well let's ask.
What should a soul theorist say
about the fission case?
So here's the gruesome accident.
My brain gets split apart.
One part gets put into Jones'
torso.
One part gets put into Smith's
torso.
After the operation,
Lefty wakes up thinking he's
Shelly Kagan.
Smith wakes up thinking he's
Shelly Kagan.
Lefty's got part of Shelly
Kagan's brain.
Smith's, or rather Righty's got
part of Shelly Kagan's brain.
What should the soul theorist
say about the case of fission?
Well, again,
remember, the soul theory says
the key to being the same person
is having the soul.
Why am I the person that was
lecturing to you on Thursday?
Because it's the very same soul
animating my body,
or what have you.
So, what does the soul theorist
say about the fission case?
I'm not quite sure,
because we have to turn to a
metaphysical question that we've
touched upon before,
namely, can souls split?
After all, the problem that
fission raises for the
personality theory,
in a nutshell,
is that personalities can
split, they can branch.
The problem for the body view
that fission raises,
in a nutshell,
is that bodies can split.
They can branch.
We need to ask about the
metaphysics of the soul,
can souls split?
And I don't know the answer to
that, of course.
So let's consider both
possibilities.
Possibility number one.
Souls, just like bodies,
just like personalities,
can split.
Suppose that's what happened.
So, there was a single soul
here, Shelly Kagan's soul,
but in the middle of this
gruesome operation,
gruesome accident and followed
by this amazing operation,
Shelly Kagan's soul split.
So there's one of the SK souls
over here and there's one of the
SK souls in the other case as
well.
Each one of Lefty and Righty
has one of the pieces of the
split Shelly Kagan soul.
All right, so now we ask
ourselves, "According to the
soul theory, which one is Shelly
Kagan?"
Well, you--By this point,
you can run through all the
possibilities yourself,
right?
We could say,
well, it's Lefty and not
Righty.
But there's nothing in the soul
theory that supports that claim.
They each have an equally
good--however good it may
be--they've got an equally good
piece of the original Shelly
Kagan soul.
So there's no reason to say
that Lefty is Shelly Kagan and
Righty isn't.
There's no good reason to say
Righty is Shelly Kagan and Lefty
isn't.
Well, would it be better to say
they're both Shelly
Kagan, as long as you've got a
piece of Shelly Kagan's soul,
of the original soul,
then you just are Shelly Kagan?
In which case,
Lefty and Righty are both
Shelly Kagan,
and Shelly Kagan is now
bicoastal, one in California,
one in Vermont,
one part of him?
That doesn't seem very
satisfying.
What's the alternative?
The alternative,
it seems, for the soul
theorist, is to say,
neither of them is
Shelly Kagan.
Neither of them is Shelly
Kagan, then Shelly Kagan died.
But how can we say that if we
accept the soul theory?
They both have pieces of Shelly
Kagan's soul.
The soul split.
Well, maybe what the soul
theorist would have to do at
this point is accept
the--da-ta-da--the no branching
rule.
"Ah," says the soul theorist,
"Follow the soul--unless the
soul splits, in which case
neither of them is Shelly
Kagan."
Well, the trouble is,
we didn't find the no branching
rule very plausible.
It seemed counterintuitive.
But at this point,
you begin to wonder,
maybe we just need to learn to
live with it.
If the personality theory needs
the no branching rule,
and the body theory needs the
no branching rule,
and the soul theory needs the
no branching rule,
maybe we're just stuck with the
no branching rule,
whether or not we like it.
And if we're stuck with it,
then of course it's not an
objection against any one of the
theories that uses it.
Well, this is all what we would
say as soul theorists if we
think souls can split.
But we need to consider the
possibility that souls can't
split.
Maybe the soul theorist has an
alternative available to it
that--available to him that the
other theories don't have.
Suppose Shelly Kagan's soul
cannot split.
What does that mean?
It means, when my brain gets
split, my soul is going to end
up in Lefty or in Righty,
but not in both.
If a soul can't split,
you can't end up with pieces of
the soul or the remnants of the
soul in both.
The soul is a unified simple
thing.
Now, I don't actually know
whether it's true that simple
things can't split.
Metaphysically,
I'm not sure whether that's a
possibility or not.
But let's just suppose--look,
Plato argued the soul was
simple.
He didn't actually convince me
of that, but suppose we thought
souls are simple,
and we think simple things
can't split.
It would follow,
then, that souls can't split.
Suppose we accept all that
metaphysics.
Then the question is just,
which one is Shelly Kagan?
Well, it depends which one
ended up with Shelly Kagan's
soul.
We can't say,
they both have a piece.
One of them will have it,
the other one won't.
And you want to know which
one's Shelly Kagan?
The one that actually ends up
with Shelly Kagan's soul.
If Lefty ends up with Shelly
Kagan's soul,
then Lefty is Shelly Kagan and
Righty is an imposter.
He thinks he's Shelly Kagan,
but he's not,
because he doesn't have Shelly
Kagan's soul.
Lefty has it.
If Righty's got Shelly Kagan's
soul, then Righty is Shelly
Kagan and Lefty is the imposter.
Now, looking at the situation
from the outside,
we might be unable to tell
which one is really Shelly
Kagan.
Because we won't be able to
tell, looking at it from the
outside, which one really has
Shelly Kagan's soul.
Although it will be true,
whichever one really does have
Shelly Kagan's soul is Shelly
Kagan.
But we don't know which one
that is.
Interestingly,
and somewhat more surprisingly,
looking at it from the inside,
we won't be able to tell
either.
Lefty will say,
"Give me a break.
Of course I'm Shelly Kagan.
Of course I've got Shelly
Kagan's soul.
Of course I'm the one."
But Righty will also say,
"Give me a break.
Of course I'm Shelly Kagan.
Of course I've got Shelly
Kagan's soul.
Of course I'm the one."
If souls can't split,
one of them is mistaken.
But there's no way for them to
know which one is the one that's
deceived.
Now, that may not be a problem
that you're unwilling to
swallow.
As we've seen,
all the views here have their
difficulties.
Maybe that's the difficulty
you're prepared to accept.
What's the right answer in
fission?
It depends on who's got Shelly
Kagan's soul.
No way to tell.
But still, that's the answer to
the metaphysical question.
Question?
Student: What happens if
neither of these had Shelly
Kagan's soul?
Professor Shelly Kagan:
The question was,
"What if neither of these have
Shelly Kagan's soul?"
Then they're both imposters.
That's a little bit like the
case we worried about when we
started thinking about the soul
view, right?
What if last night God
destroyed my soul and put in a
new soul?
Then Shelly Kagan died.
If Shelly Kagan's soul does not
migrate to Lefty or Righty,
neither of them is Shelly
Kagan, according to the soul
theory.
What happened to Shelly Kagan?
Well, if the soul got
destroyed, Shelly Kagan died.
If the soul didn't get
destroyed, maybe somebody else
that we weren't even looking at
is Shelly Kagan.
So as I say,
the soul theory can at least
give us an answer that avoids
the no branching rule.
If souls are simples and
simples can't split,
there's no possibility of
having two things with a
relevant soul.
So we don't need to add,
in this ad hoc fashion,
the no branching rule.
That's an advantage for the
soul theory, if only we believed
in souls.
It is an advantage.
But I need to point out that
there's another disadvantage
that the fission case raises for
the soul theory.
So let's just suppose that
metaphysically God tells us that
it's Lefty that has Shelly
Kagan's soul.
Then of course it's Lefty that
is Shelly Kagan.
Righty is an imposter.
Righty believes he's Shelly
Kagan, he has all the memories
of Shelly Kagan,
all the desires of Shelly
Kagan,
but he's not Shelly Kagan
because he doesn't have Shelly
Kagan's soul.
Lefty happens to have it.
That's a nice answer to the
problem of fission,
but notice the problem it
raises for the argument for
believing in a soul in the first
place.
Way back at the start of the
semester when we asked,
"Why believe in souls?"
one important argument was,
or really family of arguments
was, you need to believe in
souls in order to explain why
bodies are animated,
why people are rational,
how they can have
personalities,
how they can be creative,
and so forth.
In order to explain
consciousness and
self-awareness.
Whatever it was,
fill in your favorite blank,
fill in the blank in your
favorite way.
The claim was,
you needed to believe in souls
in order to explain all that.
But if that's right,
what's going on in Righty's
case?
Righty is aware.
Righty is conscious.
Righty is creative.
Righty has free will.
Righty makes plans.
Righty's got personality.
Righty is rational.
Righty's body is animated.
According to the soul-theory
argument for soul,
rather, according to the
argument for souls,
you needed to believe in souls
in order to explain how you
could have a person.
But now Righty's a person
without a soul,
because we just hypothesized,
oh, Shelly Kagan's soul's up
there.
So at the very same moment that
positing the nonsplitting of
souls seems to solve the fission
problem of duplication,
it yanks the rug out from
underneath the soul theorist by
undermining one of the types of
arguments for believing in the
soul in the first place.
After all, if Righty can be a
person, admittedly not Shelly
Kagan, but a person--conscious,
creative, rational,
so forth, aware--without a
soul, then maybe the same thing
is true for us,
which is of course what the
physicalist says.
Let me mention one other
possibility, because it's quite
intriguing.
Suppose the soul theorist
answers that last objection by
saying, "Ain't ever going to
happen."
Yeah, it would be a problem for
believing in souls if Righty
could wake up without one.
But since we stipulated that
Shelly Kagan's soul is going to
end up in Lefty,
Righty is not going to wake up.
Alternatively,
it might have been that Righty
woke up, but Lefty doesn't wake
up, doesn't survive the
operation.
Suppose we did these sort of
brain transfers all the time and
the following thing always
happened.
Transfer the entire brain,
the patient wakes up.
Transfer one hemisphere,
the patient wakes up.
Transfer both hemispheres,
one patient or the other wakes
up, but never both.
If that happened,
we'd have a great new argument
for the existence of a soul.
What could possibly explain why
either hemisphere of the brain
would normally be enough,
as long as we don't transfer
both?
When we transfer both,
one hemisphere might work
sometimes, sometimes the other
hemisphere, but never both.
What could possibly explain
that?
Souls could explain that.
If souls can't split,
it can only follow one half of
the brain, and that's why we'll
get somebody that's got one
half,
sometimes the other half,
but never both halves.
So there's a kind of empirical
argument for the existence of
the soul if we found those kinds
of results.
Of course, that's a big "if."
Please don't go away thinking
that what I just said is,
here's a new argument for the
soul.
We don't do brain transfers,
let alone have a half-a-brain
transfers.
We don't have any experiments
that suggest one half wakes up,
but not the other half.
All I'm saying is that if
someday we found that,
at that point,
we'd have an argument for the
soul.
Well again, let me put away the
soul theory again.
I was exploring it because it's
interesting to think about its
implication.
But since I don't believe in
souls, I want to choose between
the body view and the
personality view.
Both of them,
as we saw in the face of
fission, needs to accept a no
branching rule.
If they're going to survive
thinking about this case at all,
we need to throw in a no
branching rule.
Whether or not you find the no
branching rule hard to believe,
if both views are stuck with
it, well, then we're stuck with
it.
So let's try to choose between
the personality theory with the
no branching rule and the body
theory with the no branching
rule.
Which of these should we accept?
Which of these is the better
theory of personal identity?
Answer, "I'm not sure."
Over the course of my
philosophical career,
I have moved back and forth
between them.
There was certainly a long
period of time in which I found
the personality theory,
that is, the personality theory
with a no branching rule,
to be the better and more
plausible theory.
And it certainly has any number
of advocates on the contemporary
philosophical scene.
But at other times in my
philosophical career,
I have found the body theory,
that is to say,
the body theory with the no
branching rule,
to be the more plausible
theory.
And it is certainly the case
that the body theory has its
advocates among contemporary
philosophers.
For what it's worth--and I
don't actually think that what
I'm about to say is worth all
that much--I'm going to share
with you my own pet belief.
These days I'm inclined to go
with the body theory.
I'm inclined to think that the
key to personal identity is
having the same body,
as long as there's no
branching, as long as there's no
splitting.
But it's certainly open to you
to decide that you think no,
no, the personality theory is
the stronger view.
I can't settle the question.
I don't have any more
philosophical arguments up my
sleeve on this issue.
But I do have another point
that's worth considering.
Although I'm inclined to think
that the body theory may be the
best view about what's the key
to personal identity,
I'm also inclined to think it
doesn't really matter.
We've been posing the following
question.
We've been asking,
"What does it take for it to be
true that I survive?"
And it may be that what we
should conclude is,
whatever the best answer to
that question is,
it's not the question we should
really have been thinking about.
We weren't going to be in a
position to see that until we
went through all the stuff we've
been going over for the last
couple of weeks.
But now that we're here,
we're in a position perhaps to
raise the question,
should we be asking what it
takes to survive?
Or should we be asking about
what matters in survival?
Now, in posing this question,
I'm obviously presupposing that
we can draw a distinction
between the question,
"Do I survive?
Is somebody that exists in the
future, whatever,
me?"
and the question,
"What was it that I
wanted, when I wanted to
survive?
What was it that mattered in
ordinary survival?"
And it might be that these
things can actually come apart.
To see this,
suppose we start by thinking
again about the soul view.
Suppose there are souls.
I don't believe in them,
but let's imagine.
Suppose there are souls.
And suppose that souls are the
key to personal identity.
So somebody is me if they've
got my soul.
Or, to put it more
straightforwardly,
next week the person that's me
is the person with my soul.
I survive as long as there's
somebody around with my soul.
A hundred years from now,
am I still around?
Well, if my soul's still
around, that's me.
That's what the soul theory
says.
And suppose it's the truth.
Now, consider the following
possibility.
Suppose that people can be
reincarnated.
That is to say,
at the death of their body,
their soul takes over,
animates, inhabits,
gets connected to a new body
that's being born.
But, unlike the kind of
reincarnation cases that get
talked about in popular culture
and various religions where,
at least under the right
circumstances,
you can remember your prior
lives, let's imagine that when
the soul is reincarnated,
it's scrubbed completely clean,
no traces whatsoever of the
earlier life.
No way to retrieve it.
No karmic similarities of
personality or anything,
just starts over like a blank
slate.
Like a blackboard that's been
completely erased,
we now have the very same
blackboard, and now we start
writing new things on it.
Imagine that that's the way
reincarnation worked.
So somebody asks you,
"Will you still be around in
1,000 years?"
The answer's going to be,
yes, because my soul will be
reincarnated.
In 1,000 years there'll be
somebody that has the very same
soul that's animating my body
right now.
Of course, that soul won't
remember being Shelly Kagan.
It won't have any memories of
its prior life.
It won't be like Shelly Kagan
in any way in terms of Shelly
Kagan's desires or ambitions or
goals or fears.
It won't be that--We can see
why that personality emerges
through karmic cause and effect
in any way that are a function
of what I was like in my life.
It'll be Shelly Kagan,
because it's Shelly Kagan's
soul, but with no overlap of
personality, memories,
anything.
Then I want to say, who cares?
The fact that I will survive
under those circumstances
doesn't give me anything that
matters to me.
It's no comfort to me to be
told I will survive,
because after all,
the soul is the key to personal
identity,
if there's no similar
personality, no memories,
no beliefs, no retrievable
memories of past lives.
Then who cares that it's me?
If you can feel the force of
that thought,
then you're seeing how the
question "Will I survive?"
can be separated out from the
question "What matters?"
What do we care about?
Bare survival of my soul,
even though that is the key to
personal identity--if it
is--bare survival of my soul
doesn't give me what I want.
It's no more comforting or
satisfying than if you said,
"You know this knucklebone?
After you die,
we're going to do knucklebone
surgery and implant that
knucklebone in somebody else's
body.
And that knucklebone is going
to survive."
And I say, "Oh,
that's very interesting that
that knucklebone will be around
100 or 1,000 years from now.
But who cares?"
And if the knucklebone theory
of personal identity gets
proposed and somebody said,
"Oh, yes, but you see,
that person now with that
knucklebone will be you,
because the key to personal
identity is having the very same
knucklebone."
I say, "All right, so it's me.
Who cares?"
Bare knucklebone survival does
not give me what matters.
Now, the knucklebone theory of
personal identity is a very
stupid theory.
In contrast,
the soul theory of personal
survival is not a stupid theory.
But for all that,
it doesn't give me what I want.
When you think about the
possibility of bare survival of
the scrubbed,
clean, erased soul,
you see that survival wasn't
really everything you wanted.
What you wanted--at least what
I want, I invite you to ask
yourself whether you want the
same thing--what I want is not
just survival,
but survival with the same
personality.
So even if the soul theory is
the correct theory of
personality, it's not enough to
give me what matters.
What matters isn't just
survival.
It's survival with the same
personality.
Let's consider the body view.
Suppose that the body theory of
personal identity is correct.
And to be me,
there's got to be somebody
there that's got my body.
Let's suppose the brain version
of the theory is the best
version.
And so next year,
there's going to be somebody
that's got my brain.
But let's imagine that the
brain has been scrubbed clean.
All memory traces have been
completely erased.
We're talking complete
irreversible amnesia,
complete erasure of the brain's
hard drive.
No traces of desires and
memories and intentions and
beliefs to eventually be
recovered if only we have the
right surgery,
or procedure,
or psychotherapy,
or what have you.
It's gone.
Now, that thing that wakes up
after this complete irreversible
amnesia will no doubt eventually
develop a personality,
a set of beliefs,
memories.
Nobody knows who it is,
so they call it,
they find it wandering on the
streets.
They call it John Doe.
John Doe will eventually have a
bunch of beliefs about how the
world works, make some plans,
get some memories.
According to the body theory,
that's me.
And if the body theory is
correct, well by golly,
it is me.
And all I can say in response
to that is, it's me,
but who cares?
So what?
I'm not comforted by the
thought that I will still be
around 50 years from now,
if the thing that's me doesn't
have my personality.
Mere bodily survival isn't
enough to give me what I want.
I want more than mere bodily
survival.
I want to survive with the same
personality.
So even if the body theory of
personal identity is the right
theory, what I want to say in
response to that is,
"So what?"
If the really crucial question
is not "Do I survive," but "Do I
have what I wanted when I wanted
to survive?"
the answer is the body theory
doesn't give it.
I don't just want to survive.
I want to survive with the same
personality.
Should we conclude,
therefore, that the key to the
important question--namely,
"What matters?"--the answer to
that question,
should we conclude,
is, same personality?
That's a question we'll have to
take up next time.
 
