Professor Shelly Kagan:
We've been looking at Plato's
arguments for the immortality of
the soul, and so far I have to
say I haven't found them very
compelling arguments.
In a minute,
I'm going to turn to an
argument that at least strikes
me as more interesting.
It's more difficult to pin down
where it goes wrong.
But before we do,
I want to make a last couple of
comments about the argument we
were considering at the end of
last class.
That was the argument from
recollection.
You recall the basic idea was
that although objects in the
ordinary familiar empirical
world are not perfectly just,
perfectly round,
what have you,
they're able to remind us of
perfect justice,
perfect roundness and the like.
And when Plato asked himself,
"How could that be?"
the answer he gives is,
"Well, it's got to be that we
were previously acquainted with
the forms before our life in
this world."
And that shows that the soul
must be something that existed
prior to the creation of the
body.
That's the argument from
recollection.
And at the very end of class I
suggested that,
look, even if we were to grant
to Plato that in order to think
about justice,
circularity,
what have you,
we had to somehow grasp the
forms, and even if we were to
grant to Plato that nothing in
this world is perfectly round or
perfectly just,
it's not necessarily correct to
say, "So the only possible
explanation of what's going on
is that these things in the
empirical world remind us of our
prior acquaintance with the
forms."
It could be that what goes on
is, when we bump up against
something that's partially just
or partially beautiful or
partially round--imperfectly
round--what happens is,
those things sort of trigger
our minds in such a way that we
begin to think about the forms
for the very first time.
So it might be,
in order to think about justice
and roundness,
we have to grasp the forms.
But it could be that we only
grasp the forms in this life,
for the very first time.
Exposure to the things that
participate in the forms may
nudge our minds or our souls in
such a way that at that
point--given that exposure--we
begin to grasp the forms.
It's as though the ordinary
earthly objects,
we bump into them or they bump
into us, and they get us to look
upwards to the heavenly Platonic
realm.
I don't mean literally upwards.
It's not as though these
things--the number three--is up
there.
But if you accept the metaphor,
running into things in the
empirical world gets our minds
to start thinking about,
for the first time,
the heavenly realm of the
Platonic forms and ideas.
That would be just as likely a
possibility as the alternative
explanation that what's going on
is that ordinary empirical
objects are reminding us of our
prior acquaintance.
Perhaps these ordinary objects
act like letters of
introduction,
getting us to,
helping us to,
think about the forms for the
very first time.
Well, if that's right,
then of course,
we don't have any good reason
to follow Plato when he says,
"It must be the case that the
soul existed prior to the--prior
to birth."
Now, the objection I've just
raised is not an objection that
Plato raises in the
Phaedo,
but he does raise a different
objection.
Remember our concern isn't,
strictly speaking,
with the question,
"Did the soul exist before our
birth?
Did the soul exist before our
bodies?"
but rather, "Is the soul
immortal?"
And so, having now given the
argument from recollection,
Plato envisions two of
Socrates' disciples,
Simmias and Cebes,
responding, objecting,
by saying, "Look,
even if the soul existed before
birth,
it doesn't follow that it
exists after death.
And that's, after all,
what we really want,
are wondering about.
We want to know,
will we survive our deaths?
Is the soul immortal?
And you haven't yet shown that
Socrates," they object.
Could be that it existed
before, but won't exist
afterwards.
But very nicely--it's quite
elegant structure at this
point--Socrates puts together
the two arguments that we've
just been rehearsing--the
argument from recollection and
the argument that came before
that,
the one that I dubbed "the
argument from recycling."
Remember, the argument from
recycling says,
when you build something,
you build it out of parts,
and when that thing falls apart
you go back to the parts.
All right.
So the prior parts get recycled.
The soul, we now say--based on
the argument from
recollection--the soul is one of
our prior parts.
The soul existed before we were
put together,
or before we were put together
with our bodies.
If you then combine the
argument from recycling and say,
the parts that existed before
are going to exist afterwards,
it must follow that if the soul
existed before,
it will exist afterwards as
well.
And so we've got the
immortality of the soul after
all.
Now, bracket the fact that,
as I just explained,
I don't myself find the
argument from recollection
persuasive.
I don't think we've got any
good reason to believe--based on
the sort of things that Plato is
drawing our attention to--I
don't think we've got any good
reason to believe that the soul
existed before we were born.
But even if we grant him that,
we shouldn't be so quick to
conclude, on the basis of
combining the argument from
recollection and the argument
from recycling,
that the soul will continue to
exist after the death of our
bodies.
After all, take a more
familiar, humdrum example.
Cars are built out of non-cars,
right?
Cars get built out of engines
and tires and steering wheels.
And the engine is not a car;
the steering wheel is not a car.
So you build the car out of its
parts.
Now, the engine is a
prior-existing part.
So can we conclude then that
from the fact that--argument
from recycling:
parts get reused,
get rebuilt,
when cars get destroyed,
the parts are still around--can
we conclude from the argument
from recycling and the fact that
the engine is a prior-existing
part from which the car was
built,
that the engine will continue
to exist forever after the
destruction of the car?
No, obviously you can't
conclude that at all.
Sometimes when cars get
destroyed the engine gets
destroyed right along with it.
And of course,
even if--in many cases--the
engine continues to exist for a
while after the destruction of
the car,
it certainly doesn't follow
that the engine is immortal,
that it continues to exist
forever.
Engines will eventually
decompose and turn back into
atoms.
So from the mere fact that the
engine was a part that existed
before the car existed,
and the further fact that when
the car breaks down,
it decomposes back into parts,
it certainly doesn't follow
that all of the parts that
existed prior to the existence
of the car will be around
forever.
That would just be false.
So even if we were to give
Socrates the assumption
that--the thesis that--the soul
existed before we were put
together,
before we were born,
it still wouldn't follow that
the soul will continue to exist
after we're taken back apart.
The soul might eventually decay
just like the engine will
eventually decay.
What we need,
to really become convinced of
the immortality of the soul,
is not the mere suggestion,
even it was--even if we were
convinced--is not the mere
suggestion that the soul was
around before our birth.
We need to believe that the
soul, unlike an engine,
can't itself be destroyed,
can't itself decompose,
can't fall apart.
That's what we need if we're
really going to become convinced
of the immortality of the soul.
Now, as I remarked previously,
one of the amazing things--not
amazing but one of the really
attractive things about Plato's
dialogues is,
you raise an objection and it
often seems as though Plato
himself, whether or not he
explicitly states the objection,
seems aware of the objection,
because he'll go on to say
something that is responsive to
it.
And again, that makes sense if
you think of these dialogues as
a kind of pedagogical tool to
help you get better at
philosophizing.
So the very next argument that
Plato turns to can be viewed,
I think, as responding to this
unstated objection--well,
I stated it,
but Plato doesn't state it in
the dialogue--the worry that
even if the soul was one of the
parts,
even if the soul was already
around before we were born,
how do we know it can't come
apart?
How do we know the soul can't
be destroyed?
Since what we want to know is
whether the soul is immortal,
how do we know it can't break?
Plato's next argument then
tries to deal directly with this
worry, and it's a quite
interesting argument.
I'll give it another--a new
label--I'll call it the
"argument from simplicity."
Socrates turns to a discussion
of what kinds of things can
break and what kinds of things
can't break;
what kinds of things can be
destroyed, and what kinds of
things can't be destroyed.
He thinks about examples;
he surveys examples and tries
to extract a kind of
metaphysical principle from
this.
And then, as we'll see,
he's going to use this
principle to convince us--or to
try to convince us--that the
soul is immortal,
it's indestructible.
Well, lots of things can be
destroyed.
Here's a piece of paper.
It can be destroyed Right?
Why was it that this was the
sort of thing that could be
destroyed?
Well, the straightforward
answer is the piece of paper had
parts.
And in breaking it,
in ripping it,
what I literally did was I
ripped one part from another.
To destroy the piece of paper,
I take its parts apart.
Here's piece of chalk.
The piece of chalk can be
broken.
What am I doing?
Taking its parts apart.
The kinds of things that can be
destroyed have parts.
They are composite.
They are composed of their
parts.
Bodies can be destroyed because
you can take a sword to it and
go sweep, sweep,
sweep and chop it into pieces.
Composite things can be
destroyed.
Things that have parts can be
destroyed.
Now, what kind of things can't
be destroyed?
Well, it won't surprise you
that when Plato looks for an
example of something that's
eternal and indestructible,
his mind immediately starts
thinking about the Platonic
forms.
Take the number three.
The number three can't be
destroyed, right?
Even if nuclear explosion took
place and everything on Earth
got atomized and destroyed
through some bizarre science
fiction chain reaction,
like they're always doing in
movies, the number three
wouldn't be touched.
The number three wouldn't be
fazed.
It would still be true that
three plus one equals four.
You can't hurt the number three.
You can't alter or destroy
perfect circularity.
Why not?
Well, it doesn't have any parts.
That's the thought.
Things like the Platonic forms
are eternal, and they're
eternal, changeless,
and indestructible,
because they are simple--simple
here being the metaphysical
notion that they're not composed
of anything.
Anything that's built up out of
parts you could,
at least in principle,
worry about the parts coming
apart and, hence,
the thing being destroyed.
But anything that's simple
can't be destroyed in that way.
It has no parts to take apart.
So the kinds of things that can
be destroyed are the things with
parts, and those are the sorts
of things that change,
right?
Even if they're not destroyed,
what's a tip off to something
being composite?
The fact that it changes.
Suppose I take a bar of metal
and I bend it.
I haven't destroyed it,
but I've changed it.
I'm able to change it by
rearranging the relationships
between the various parts.
My body is constantly changing
because the relationships
between my arms and my head and
so forth, my muscles are moving.
You rearrange the parts,
the thing changes.
Oh, but that means it's got
parts and could be destroyed.
So we've got some nice
generalizations.
Things that change have parts;
things with parts can be
destroyed.
What are the kinds of things
that you can change and destroy?
Those are the familiar
empirical objects that we can
see: pieces of paper,
bodies, pieces of chalk,
bars of metal.
In contrast,
on the whole other side,
you've got things that are
invisible, like the number
three--nobody sees the number
three--things that are
invisible,
that never change.
The number three never changes,
right?
The number three is an odd
number.
It's not as though,
oh, today it's odd but maybe
tomorrow it'll be even.
It's eternally an odd number.
Three plus one equals four
today, yesterday and forever.
These facts about the number
three will never change.
The number three is changeless.
So the forms are eternal;
they're invisible;
they are changeless.
They're simple,
and simple things can't be
destroyed;
forms can't be destroyed.
You put all this together;
these are the sorts of thoughts
that Socrates assembles,
and I've got the initial
thoughts up there on the board.
All right.
So premise number one,
only composite things can be
destroyed.
Premise number two,
only changing things are
composite.
So if you put one and two
together, you'd get:
only changing things could be
destroyed.
And now add three,
invisible things don't change.
Well, if you've got to be the
kind of thing that can change in
order to be composite and you've
got to be composite in order to
be destroyed,
invisible things don't change,
follows four,
invisible things can't be
destroyed.
That's the metaphysical thesis
that Socrates comes to by
thinking about cases.
And that's the crucial premise
or sub-conclusion for the
immortality of the soul,
because then Socrates invites
us to think about the soul.
Is the soul visible or
invisible?
He says, pretty obviously,
"it's invisible."
But if invisible things can't
be destroyed,
the soul can't be destroyed.
So one, two and three got us
four, invisible things can't be
destroyed, but five,
the soul is invisible so six,
the soul can't be destroyed.
That's my best attempt at
reconstructing the argument from
simplicity.
It's not as though Plato
himself spells it out with
premises and conclusions like
that,
but I think this is fairly
faithful to the kind of argument
he means to put forward.
And in a moment I'll turn to
evaluating whether that's a good
argument or not.
But I think it's a pretty
interesting argument;
it's an argument worth taking
fairly seriously.
Except, I've got to confess to
you that Socrates doesn't quite
conclude the way I would've
thought he would've concluded.
So I've had the argument
conclude six,
the soul can't be destroyed.
But what Socrates actually says
is--his actual conclusion
is--"And so the soul is
indestructible or nearly so."
That's rather an odd
qualification,
"or nearly so."
The conclusion that Socrates
reaches from his examination of
change and invisibility and so
forth and so on,
and compositeness versus
simplicity, is that "the soul is
indestructible or nearly so."
Now, adding that qualification
opens the door to a worry.
The worry gets raised by Cebes
who says, even if we grant that
the soul is nearly
indestructible,
that's not good enough to get
us immortality.
And he gives a very nice
analogy of somebody who's--a
coat, which could outlast the
owner but isn't immortal.
Or the owner could go through
several coats;
but still at some point the
owner's going to die as well.
The owner is far more immortal,
in that sense,
closer to immortality.
And I've gone through many
coats in my life,
but for all that,
I'm not indestructible.
If all we've got is the mere
fact that the soul is "nearly"
indestructible,
it takes a whole lot more work
to destroy it,
maybe it lasts a whole lot
longer;
maybe it goes through a whole
lot of bodies being reincarnated
a half-dozen,
or a dozen, or hundred times
before it wears out and gets
destroyed.
That's not enough to give us
the immortality of the soul.
That's the objection that Cebes
raises.
And one of the oddities is
that, as far as I can see,
Socrates never responds to that
objection.
Raises the objection--that is,
Plato raises the objection in
the voice of Cebes--but
Socrates, on Plato's behalf,
never answers the objection.
It's hard to say what exactly
is going on.
It might be that Plato's
worried that he hasn't really
shown that the soul is immortal
afterwards.
Maybe this argument from
simplicity isn't really as good
as it needs to be.
And maybe that explains why
Plato then goes on to offer yet
another argument.
After all, if this argument
really did show the immortality
of the soul, why would he need
to offer a further
argument?--The argument from
essential properties,
which we'll be turning to later.
So maybe Plato just thought
there wasn't a good answer to
Cebes' objection.
But I want to say,
on Plato's behalf,
or at least on behalf of the
argument,
Socrates should never have
concluded the argument with this
odd qualifying phrase that the
soul is "indestructible or
nearly so."
He should've just said the soul
is indestructible,
full stop.
After all, if we have premises
one, two, and three--only
composite things can be
destroyed,
only changing things are
composite, invisible things
don't change--if you put those
together,
you get four,
invisible things can't be
destroyed.
You don't get the more modest
conclusion, "invisible things
can't be destroyed or it's a
whole lot harder to destroy
them."
If we've got one,
two and three,
we're entitled to the bold
conclusion: "invisible things
can't be destroyed,
period."
Full stop.
And then if five is true,
if the soul really is
invisible, we're entitled to
conclude six,
the soul can't be
destroyed--not,
the soul can't be destroyed,
or if it can be destroyed it's
very,
very hard and takes a very,
very long time.
We are, rather,
entitled to the bolder
conclusion, the soul can't be
destroyed, full stop,
period, end of the discussion.
So despite the fact that
Socrates draws this weaker
conclusion, it seems to me that
the argument he's offered us,
if it works at all,
entitles us to draw the bolder
conclusion.
Not that the soul is
indestructible or nearly so,
but that the soul is
indestructible.
Well, maybe Plato realized that;
maybe that's the reason why he
doesn't bother giving an answer
to Cebes.
Maybe it's an invitation to the
reader to recognize that there's
a better argument here than even
the characters in the drama have
noticed--don't know,
don't know what Plato had in
mind.
But at any rate,
our question shouldn't be,
"What was Plato thinking?"
but, "Is the argument any good?"
Do we now have an argument for
the immortality of the soul?
After all, if the soul can't be
destroyed, it's immortal.
Is it a good argument or not?
Simmias raises a different
objection.
Simmias says we can't conclude
that the soul is indestructible,
or nearly so,
or whatever,
because we should not believe
the sub-conclusion four,
invisible things can't be
destroyed.
Simmias says invisible things
can be destroyed.
And if that's true,
then of course we no longer
have an argument for the
indestructibility or near
indestructibility of the soul.
Because even if the soul is
invisible, five,
if nonetheless,
contrary to what Socrates was
claiming,
invisible things can be
destroyed, then maybe the
invisible soul can be destroyed
as well.
Now, Simmias doesn't merely
assert, boldly,
invisible things can be
destroyed.
He offers an example of an
invisible thing that can be
destroyed--harmony.
He starts talking about the
harmony that gets produced by a
stringed instrument;
let's say a harp.
In fact, he says,
this is a very nice example for
us to think about because some
people have suggested--Simmias
says--some people have suggested
that the mind is like harmony.
It's as though the mind is like
harmony of the body.
So to spell out the analogy a
bit more fully,
and I'll say a bit more about
it later, harmony is to the harp
as the mind is to the body.
All right.
He says, there are people who
put forward views like this,
and at any rate harmony can
certainly be destroyed.
You don't see harmony, right?
Harmony is invisible.
But for all that,
you can destroy harmony.
So there's the harp making its
melodious, harmonious sounds,
and then you take an ax to the
harp,
bang, bang, bang,
chop, chop, chop,
or a hammer or whatever;
now the harmony's been
destroyed.
So even though it's invisible,
you can destroy it by
destroying the musical
instrument on which it depends.
And of course,
there's the worry,
right?
If the mind is like the harmony
of the body, then maybe you
could destroy the mind,
the soul, by destroying the
body on which the mind depends.
So the crucial point right now
is that thinking about harmony
is offered as a counterexample
to the generalization that
invisible things can't be
destroyed.
Harmony is invisible.
Harmony can be destroyed.
So invisible things can be
destroyed.
So you're wrong,
Socrates, when you say
invisible things can't be
destroyed.
So even if we grant that the
soul is invisible as well,
maybe the soul also is an
invisible thing that can be
destroyed.
That's a great objection.
It's an objection worth taking
very seriously.
And the oddity is,
Socrates doesn't respond to it
in the way that he should have,
in the way that he needed to.
Socrates instead spends some
time worrying about the
question, "Is the soul really
like harmony or not?"
Is this metaphor--think about
the relationship between the
mind and body as similar to the
relationship between harmony and
a harp--Socrates spends some
time criticizing that analogy.
Now, in a few minutes I'll turn
to the question,
what about Socrates' criticisms
of the analogy?
Are they good criticisms or not?
But even if they are good
criticisms, I want to say,
that's not good enough to help
your argument Socrates.
Even if we were to say,
you know what?
The mind isn't very much like
harmony at all.
That analogy really stinks.
So what?
All that Simmias needs to cause
problems for Socrates' argument
is the claim that harmony is
invisible and harmony can be
destroyed.
As long as that is true,
we can't continue to believe
that invisible things can't be
destroyed.
So what Socrates needs to do is
to say either harmony can't be
destroyed, but pretty obviously
it can,
the melodious sounds coming out
of an instrument can be
destroyed.
So he would need to argue then,
perhaps, that harmony is not
really invisible.
If he could show us,
if he could convince us,
that harmony is not really
invisible,
then we would no longer have a
counterexample to the claim that
the invisible can't be
destroyed,
and the argument could still
then proceed as it was before.
So that's what Socrates should
have done.
He should have said,
"You know what?
Harmony is not really
invisible," or "It can't be
destroyed."
But there's not a whiff of
that, at least in the dialogue
as we've got it,
not a whiff of that as far as I
can see.
Socrates never says,
"Simmias, here is where your
objection goes wrong.
Harmony is not really
invisible, can't really be
destroyed, whatever it is.
So we don't really have a
counterexample."
Instead, he gets hung up on
this question,
"Is it a good analogy?
Is it a good way for thinking
about the mind or not?"
But even if it isn't,
that wouldn't save the
argument.
Now, I am going to take some
time to think about whether or
not harmony is a good analogy,
because I actually think it is
a good analogy.
I think what's going on in the
harmony--the suggestion that we
should think about the mind like
harmony,
as though it was the harmony of
the body--is an early attempt to
state the physicalist view.
Talk about the mind,
says the physicalist,
is just a way of talking about
the body.
Or, more carefully,
it's a way of talking about
certain things the body can do
when it's functioning properly,
when it's well tuned,
as we might put it.
Just like, talk about the
harmony or the melodious sounds
or what have you of the harp,
is a way--these things are a
way of talking about what things
the harp can do.
It can produce melodious,
harmonious sounds when it's
functioning properly,
when it's well tuned.
So the harmony analogy is,
I think, an attempt,
and not a bad attempt,
at gesturing towards the
question, how do physicalists
think about the mind?
Now, when I tried to get you to
grasp how physicalists think
about the mind,
I used examples about computers
and robots and the like.
Well, it's not remotely
surprising that Plato doesn't
use those kinds of analogies.
He doesn't have computers;
he doesn't have robots.
Still, he has physical objects
that can do things.
And the ability to do things
depends on the proper
functioning of the physical
object.
And so, I think he can see that
there's this alternative to his
dualism.
He can see you could be a
physicalist and say that the
mind is dependent on the body;
the mind is just a way of
talking about what the body can
do when it's working properly.
It's dependent just the same
way that, well,
for example,
harmony is dependent upon the
physical instrument.
So I think it's a very nice
attempt to discuss the
physicalist alternative to
Plato's dualism.
And that's why it will be worth
taking some time to ask
ourselves, well,
what about Plato's objections
then?
If he can convince us that the
soul is not like harmony of the
body, maybe that will be some
sort of problem for the
physicalists.
So I'll come back to that in a
few more minutes.
But first, let's worry about
the point that I was emphasizing
earlier, namely,
even if the soul's not very
much like harmony,
so what?
If harmony really is invisible
and harmony really can be
destroyed, then invisible things
can be destroyed.
Even if the soul's nothing
like--that's not a good analogy
for thinking about the
physicalist position or what
have you--so what?
If some invisible things can be
destroyed and harmony is an
example of that,
then, by golly,
it's going to follow that we
can't conclude from the
invisibility of the soul that
the soul cannot be destroyed.
So even though Socrates doesn't
respond to that objection,
we need to ask on Socrates'
behalf, is there a possible
answer to this objection?
And I think there are at least
the beginnings of one.
We have to ask:
when we say,
"invisible things can't be
destroyed," what did we mean by
"invisible?"
And I want to distinguish three
different possible
interpretations,
three different claims.
So invisible means,
one, there's one possibility,
can't be seen.
Two, different possibility,
can't be observed.
I've got in mind the broader
notion of all five senses.
Three, different possible
interpretation of invisible,
can't be detected.
What we have to ask ourselves
is, when Socrates puts his
argument forward,
which of these did he have in
mind?
First, let's be clear on how
these things are different.
Some things can't be seen but
can be sensed some other way.
So colors can be seen;
smells cannot be seen,
but of course smells--the smell
of coffee--can be sensed through
the five senses.
Sounds can't be seen,
they're not visible,
but for all that they can be
sensed.
You can hear them through your
ears.
So, without getting hung up on
what does the English word
"invisible" mean,
let's just notice that there's
a difference between saying "it
can't be seen through the eyes"
and "can't be observed through
one sense or the other."
And then three is a different
notion altogether,
a stronger notion altogether.
There might be things that
can't even be detected through
any of the five senses.
The number three--not only
can't I see it,
I can't taste it,
I can't hear it,
I can't smell it,
can't touch it,
right?
The number three is invisible
in this much bolder way.
It can't be detected at all by
the five senses--can't be
detected in terms of its--it
doesn't leave traces behind,
right?
I don't see dinosaurs,
but of course they leave traces
behind in fossils.
There's a way in which you can
talk about it being detected by
its effects.
All right.
So again, don't get hung up on
what does the English word
invisible mean.
Let's just ask ourselves,
what notion of invisibility--if
we'll use the word between these
three ways--what notion did
Socrates' argument turn on?
Well, the most natural way to
start by interpreting him is
with number one.
When he says,
"Invisible things don't
change," what he means is,
things that you can't see don't
change,
and so--continue to interpret
invisible in number four the
same way--invisible things can't
be destroyed.
On the first interpretation
what he'd be saying is,
"If you can't see it with your
eyes, it can't be destroyed."
Now, the trouble is,
harmony shows that that's not
so.
Harmony is indeed invisible in
sense number one.
You cannot see it with your
eyes.
But for all that,
it can be destroyed.
So if what Socrates means by
invisibility is the first
notion, can't been seen with
your eyes, then the argument's
not any good.
Harmony is a pretty compelling
counterexample.
But maybe that's not what
Socrates means by invisible.
Maybe instead of one,
he means two.
When he talks about the soul
being invisible and invisible
things being indestructible,
maybe he means things that
can't be observed through any of
your five senses.
Now, in point of fact,
I think that is what he meant.
Let me just give a quick quote.
In our edition, this is page 29.
Some of you may have noticed
that there are little
standardized paginations in our
edition as well.
So it's in the academy
paginations, number 79;
he's talking about the
difference between the visible
and the invisible things,
chairs versus the forms.
And he says,
"These latter,
chairs, trees,
stones, you could touch and see
and perceive with the other
senses.
But those that always remain
the same, the forms,
can only be grasped by the
reasoning power of the mind.
They are not seen but are
invisible."
So I think it's pretty clear
that when Socrates starts
talking about what's visible
versus invisible,
he doesn't mean to limit
himself to vision;
he means to be talking about
all of the five senses.
So when we say--when he
says--"Invisible things can't be
destroyed," he means the things
that you can't see or touch or
hear or feel--whatever it
is--see,
touch, smell, taste.
Those things can't be destroyed.
Now, notice that if that's the
way we interpret his argument,
harmony no longer works as a
counterexample.
Harmony was invisible when we
meant definition number one,
can't be seen.
But it's not invisible if we
mean definition number two,
can't be sensed,
can't be observed.
Harmony can be sensed through
the ears, in which case it's not
a counterexample.
It's not a counterexample to
four.
Four says, "Invisible things
can't be destroyed."
And what Socrates should have
said is, harmony is not
invisible in the relevant sense
of invisible,
since it can be sensed.
But--and this would be the
crucial point--notice,
Socrates should've continued,
the soul is invisible in
that sense.
You don't see the soul;
you don't taste the soul;
you don't touch the soul;
you don't hear the soul.
So if we understand the
argument in terms of the second
interpretation of invisible,
it looks as though the argument
still goes through.
Simmias' counterexample fails.
Harmony is not invisible in the
relevant sense,
so it could still be true that
invisible things can't be
destroyed.
Since the soul is invisible in
that sense, it would follow that
the soul can't be destroyed.
However, even if Simmias'
objection, his particular
counterexample,
harmony,
fails, that doesn't mean that
we should still accept the
argument because there might be
a different counterexample.
So here's my proposal.
Suppose we think not about
harmony but radio waves.
Radio waves are not sensible.
They are not observable.
You don't see a radio wave.
You can't touch a radio wave;
you can't smell a radio wave,
and interestingly enough,
you can't hear radio waves.
But of course,
for all that,
they can be destroyed.
So even if we grant that what
Socrates meant by invisible was
"cannot be observed,"
we still have to say,
with Simmias,
"You know, four is just not
true.
Some invisible things can be
destroyed."
Radio waves can be destroyed
even though they're invisible in
the relevant sense.
Yeah? Question?
Student:
[inaudible]
Professor Shelly Kagan:
Okay.
So the suggestion was,
radio waves are a bit like the
forms.
Student:
[inaudible]
Professor Shelly Kagan:
They're not forms,
but they're perfect in that
way.
Was that the thought?
Student:
[inaudible]
Professor Shelly Kagan:
Ah!
Okay, I misunderstood.
So the question is rather,
"Look, radio waves are not like
forms," to which the answer is
"Yes, that's exactly the
problem."
They are invisible,
like the forms,
but unlike the forms they're
destructible.
And that's precisely why we've
got to worry about the soul.
Is the soul invisible in the
way the forms are,
being indestructible,
or is it invisible in the way
that radio waves are,
destructible?
Now again, my point here is not
to say, "Oh, you idiot,
Plato!
Why didn't you think of radio
waves?"
Our question is not,
was Plato overlooking something
he should've thought of?
It's, does his argument work or
not?
Is it true that the invisible
things can't be destroyed?
And it seems to me that some
things that are invisible in the
relevant sense,
radio waves being an example of
that, can be destroyed.
So even though the soul is also
invisible in the relevant sense,
maybe it can be destroyed as
well.
Now, the answer,
it seems to me,
the only answer I can imagine
Socrates or Plato giving at this
point,
is to say, "Look,
I need a different definition
of invisible.
Not two, but three.
Don't talk about what we can
sense;
talk about what we can detect."
Radio waves can be detected,
right?
After all, radios do that.
You turn on your radio,
the radio wave's passing by,
boom--properly tuned,
you detect it.
It turns it into these sounds
that we can hear.
We can detect radio waves on
the basis of their effects on
radios, among other things.
So maybe by invisible he
should've moved to this
stronger, bolder definition of
invisible.
Let's call something invisible
not only if it can't seen,
not only if it can't be
observed, but if it can't be
detected at all.
Look, the forms,
after all, can't be detected.
There's no radio for the number
three that will tell--There's no
Geiger counter to tell you the
number three is nearby or
something, right?
So Plato could still insist
things that are invisible,
in the sense of undetectable,
can't be destroyed.
But radio waves,
they're detectable.
So they're not a
counterexample,
now that we interpret the
relevant notion of invisibility
as undetectability.
So couldn't Plato continue to
claim, things that are fully
invisible, meaning undetectable,
those things can't be
destroyed.
Radio waves aren't a
counterexample to that.
I think maybe Plato could say
that.
But, if we give him four,
where we read invisible as
meaning utterly undetectable,
it's no longer so clear to me
that we can give him five.
Is the soul invisible?
Well, it was,
when by invisibility we meant
can't be seen;
it was, when by invisibility we
meant can't be tasted or touched
or heard or smelled.
But is it still invisible if by
invisibility we mean can't be
detected?
Is it true that the soul can't
be detected?
I've got to say,
I think it's no longer right.
Once we interpret invisibility
that way, the soul is detectable
in just the way--not literally
just the way,
but in something similar to the
way--that radio waves are
detectable.
If you hook a radio wave up
with a radio,
you can tell the radio
is--radio wave--was there
because of what the radio's
doing, giving off these sounds.
If you hook a soul up to a
body, you can tell the soul is
there by what the body is doing,
discussing philosophy with you.
You detect the presence of your
friend's soul through its
effects on your friend's body.
But that means the soul isn't
really undetectable.
But if the soul's not really
undetectable,
it's not really invisible in
the relevant sense.
And if it's not really
invisible, then even if there is
a notion of invisible,
such that things that are
invisible in that sense can't be
destroyed, the soul's not
invisible in that sense.
I've gone over this argument at
such length because--I hope it's
clear--I think it's a pretty
interesting argument.
The argument from simplicity is
quite fascinating.
The idea that you couldn't
break the soul if it didn't have
parts, and the way to tell that
it doesn't have parts is because
it's invisible,
because invisible things can't
have parts, that's a quite
difficult argument to pin down,
does it work or does it not
work.
But I think,
as we think it all through,
we have to conclude it doesn't
work.
Okay.
