Shantila's Inside Logic #13
Arguments
| You are still at the
airport. Things have quieted down. The man who
was going to confess but then pulled out the gun
and then got shot is lying on the floor. Perhaps
he is dead. EMT personnel burst onto the scene
and begin working on the poor man. You sit down
and catch your breath. What is
death? you ask yourself.
Suppose the man is
dead. He
looks dead. Is it even
possible that somehow he could still exist? Suppose
he has, or is, a soul. Lots of people believe
something like that. Would that mean he could
still exist somehow even if he is dead?
You
remember looking up something on the internet
last week. You had seen Fox Mulder being
interviewed on CNN about something he wrote as
part of an investigation of an alien named Joe
Carson. A website address had flashed on the tv
screen, and having had nothing better to do, you
had written down the website address. http://personal.bgsu.edu/~mbelzer/indexdialogue.html
To
distract yourself from looking at the poor guy
lying on the floor, perhaps dead, you decide to
use your wireless laptop to get online and see
what it was.
|
***
Mulder: Ok,
Scully, now what was I going to explain to you?
Scully: I
believe you were going to explain Gretchen Weirob's
argument that we do not exist by virtue of being
essentially unchanging, substantial souls.
Mulder: Right.
She rejected that idea. Gretchen was a friend of mine. I
was there when she died a few days after the motorcycle
crash.
Scully: So what
was the argument?
Mulder: One
night before she died, she tried to explain that even if
souls happen to exist, they cannot be all that relevant
to our existence as people-- at least not if we have
knowledge of our own or others' identities from one day
to the next. And obviously we do
have that sort of knowledge.
Scully: Ok. How
did she argue for it?
Mulder:
Actually, the philosopher John Perry tape-recorded the
conversations with Gretchen, and he published them in the
great little book, Personal Identity
and Immortality.
Scully: Great.
What was her argument?
Mulder: By the
way, in his transcript he refers to me as
“Miller” rather than “Mulder”--
Scully: Yes, I
know.
Mulder: Perry
apparently was a bit hard of hearing.
Scully: Ok.
What's the argument?
Mulder: Scully,
I am going to give you my reconstruction of Gretchen's argument
that personal identity through time is not due to
identity of a soul.
Scully: Great!
Mulder: I was
there when she made this argument, but Perry thought my
name was Miller. But my name is Mulder.
Scully: Good
Lord, Mulder! I know what your name
is!
Mulder: Yes,
but in the book Perry calls me Miller,
not Mulder.
Scully: Mulder,
I know that too since you have already told me six
times.--So what is the goddam argument?
Mulder: Ok. Relax, Scully..
Here is my interpretation of Weirob's argument, as
follows. There are four premises, or assumptions, for the
argument. I will spell out the whole thing.
1.
We have knowledge of personal identity
through time. [Premise]
(Explanation.
This first premise just says we have
knowledge of our own identity through
time, and we also have knowledge of the
identities of other people through time.
Scully, this point is not complicated.
All it means is that you can know that
you existed at earlier times just as you
know that you exist right now; and about
other people, for example, you can know
that you are having breakfast with your
lover --whoever that might be--and that
he is the same person with whom you went
to the movies the night before.)
2.
If we have knowledge of personal identity
through time, then either personal identity
is not due to identity of a soul or we have
knowledge of soul identity through time as
well. [Premise]
(Explanation.
Scully, this means, for example, when you
know that you are eating breakfast with
the same person with whom you went to the
movies, you must know that you are
interacting with one and the same
soul. --At least,
that has to be true if personal identity
just is soul identity.)
3.
Either personal identity through time is not
due to identity of a soul or we have
knowledge of soul identity through time.
[This just follows logically from premises 2
and 1 by modus ponens MP.
I am spelling this out step by step, Scully,
just to make sure you get it.]
4.
If we have knowledge of soul identity through
time, we are able to correlate souls with
physical or psychological features. [Premise]
(Explanation. Suppose we
have knowledge that the same soul exists
at two different times t and t*. This
what it means to have knowledge of soul
identity through time. What this premise
says is that if we have that sort of
knowledge, then we have to be able to
correlate souls with some physical or
psychological features so as to be able
to determine that there is one and the
same soul present at the two times t and
t*. That is, we would have to be able to
correlate a soul at various times t and
t* with physical or psychological
features at the times t and t*--
otherwise, what right would we have to
assume that the same
soul is present?)
5.
But in fact we are not able to correlate
souls with physical or psychological
features. [Premise]
(Souls are
supposed to be nonphysical entities; they
cannot be seen or touched or detected by
the senses. We never observe our own soul
or those of our friends, and so we can
never correlate physical or psychological
features with souls.)
6.
So we never do
have knowledge of soul identity through time.
[From 4 and 5 by modus
tollens MT]
7.
Conclusion: Personal identity through time is
not due to identity of a soul. [From 6 and 3
by disjunctive syllogism
DS]
|
Scully:
Wow. Nice job, Mulder. I didn't know you could make up
arguments! I am actually very impressed.
Mulder: Scully,
what this means is that even if souls do exist, they
cannot account for our identity through time as people.
Scully: Hmm.
Mulder: So
Weirob's point was that whether or not souls exist
is a question completely
independent of how we should think
of ourselves as people -- at least,
given the obvious everyday knowledge of our own identity
and the identities of our friends.. I hope this is clear.
Scully: Ok, I
see it, I think. The knowledge of personal identity is
simply that we know who our friends are--
Mulder: Right.
Scully: When we
are with them, we know that they are really our friends
and not some sort of fakes?
Mulder: Yes,
that simple sort of knowledge. Or just the simple
awareness that you existed yesterday and that you still
exist today. That is knowledge of your own identity
through time.
Scully: So the
argument is about something as simple as knowing that I
am having breakfast with the same person with whom I went
to bed?
Mulder: Yes.
That simple sort of knowledge.
Scully: Hmm.
Mulder: By the
way, who is
he?
Scully: None of
your business, actually. So the argument's conclusion is
that we exist through time, but this cannot be understood
as being due to the existence of a soul?
Mulder: Right.
Of course, the conclusion depends on four assumptions --
those are the premises listed in lines 1,2,4, and 5.
Scully: Hmm.
Mulder: The
argument definitely is valid. And each of the premises
seems true -- so the argument seems sound as well.
Scully: Wait a
minute. Why should I believe that the argument is valid?
Mulder: Because
each line is either a premise or it is derived using a
valid Rule of inference. Here --let me spell it out for
you using Shantila's system-- the one we used in FBI
school.
Scully: Sorry,
I really don't think I paid much attention to all that.
Mulder: I will
use these abbreviations.
| K: We
have knowledge of personal identity through time.
P:
Personal identity is due to identity of a soul.
S: We
have knowledge of soul identity through time.
C: We
are able to correlate souls with physical or
psychological features.
|
Here is the
argument spelled out.
K, K>(~PvS),
S>C, ~C } ~P
| |
1 |
1. |
K |
A |
|
|
| |
2 |
2. |
K>(~PvS) |
A |
|
|
| |
1,2 |
3. |
~PvS |
1,2 MP |
|
|
| |
4 |
4. |
S>C |
A |
|
|
| |
5 |
5. |
~C |
A |
|
|
| |
4,5 |
6. |
~S |
4,5 MT |
|
|
| |
1,2,4,5 |
7. |
~P |
3,6 DS |
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|
Scully:
Ok. Suppose the argument is valid.
Mulder: Well,
it is valid.
You don't have to just suppose
it. I just proved it.
Scully. Ok,
fine. But are all four premises true?
Mulder: Well,
good question. So you are asking, is the argument sound?
Scully: Yah.
Mulder: We have
to examine that. When we spell out the premises, then we
can examine them and raise questions about them and test
them to see if they are true. But in this argument, all
the premises look pretty good to me.
Scully: I
wonder about premise 5. Is that one really true? Why are
you so sure we cannot correlate souls with physical or
psychological features?
Mulder: Well--
Scully: But why
couldn't we do it at least in our own case?
Mulder:
Gretchen talked about that.
Scully: Well,
listen. I remember reading about this sort of thing in a
philosophy class. Descartes had an argument something
like yours, except with exactly the opposite conclusion.
Mulder: Oh,
really?
Scully: Yes, it went something
like this. I can imagine existing
without a body. Yet if I can imagine existing without a
body then it is possible for me to exist without a body.
Now either some essential part of me is nonphysical or it
wouldn't be possible for me to exist without a body. And
if some essential part of my is nonphysical, then
personal identity is due to identity of a soul.
Therefore, personal identity is due to identity of a
soul.
Mulder: Well.. uh... can you
spell that out for me?
Scully: Nah, I don't really
want to bother. I want to polish my nails. Besides, I
can't remember Shantila's system. Why don't you do it?
Mulder: Ok, let's see. I will
try. Let's use the following symbols.
| I: I can imagine
existing without a body. E: It is possible for me to
exist without a body.
N: Some essential part
of me is nonphysical.
P:
Personal identity is due to identity of a soul.
|
| |
The argument
then can be represented by this sequent:
I, I>E, Nv~E, N>P } P
Is this argument valid? Yes, I
think it is, because look, we can use the Rules to spell
it out. We can prove that the argument is valid, as
follows.
| |
1 |
1. |
I |
A |
|
|
| |
2 |
2. |
I>E |
A |
|
|
| |
3 |
3. |
Nv~E |
A |
|
|
| |
4 |
4. |
N>P |
A |
|
|
| |
1,2 |
5. |
E |
1,2 MP |
|
|
| |
1,2 |
6. |
~~E |
5, DN |
|
|
| |
1,2,3 |
7. |
N |
3,6 DS |
|
|
| |
1,2,3,4 |
8. |
P |
4,7 MP |
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|
Scully:
Ok.
Mulder: So it
looks like this argument also is valid.
Scully: Great.
Wonderful. So listen, Miller, why are we on this case?
Why are we wiretapping these girls?
Mulder: What
did you just call me?
Scully: What?
Mulder: Did you
call me Miller?
Scully: Miller?
Why would I call you that? Your name is Mulder.
Mulder: But I
thought you--
Scully: Just
look at your badge.
| You suddenly
realize an EMT person is talking to you. "He had on a bulletproof
vest! --He's going to be ok. Here's the
bullet." You
don't know whether to be happy or sad.
Joe takes the bullet.
|
| ** The word
"argument" can be used in two ways. A
dispute or debate between two people (who
disagree about something) may be called an
argument. But that is not exactly the way in
which Mulder and Scully are using the word.
Rather, they are using it to mean a set of
premises that are presented together with a
conclusion, where the premises are offered as
support for accepting the conclusion (such as in
the arguments that
they give. Sometimes when people are having
an argument, they will try
to use arguments --but
often they simply begin yelling or sulking and so
forth.
Notice that the
conclusion of Scully's argument is just
the opposite of the
conclusion of Mulder's argument! The conclusion
of her valid argument is P. But the conclusion of
Mulder's valid argument is ~P. We can see that
both arguments are valid. But it cannot turn out
that both P and ~P are true!
So now we have an
interesting situation!
What this tells us,
quite simply, is that at least one of the two
arguments must fail to be sound. Recall that a sound
argument is a valid argument that has all true
premises. Both arguments are valid, but at least
one of the arguments must have at least one false
premise, making it unsound.
Of course it may be the case that neither
of the arguments is sound.
The question was
whether personal identity is due to identity of a
soul. Mulder's argument is valid and has the
conclusion ~P. Descartes' argument is valid and
has the conclusion P. We know that both arguments
cannot be sound (because it cannot be that both P
and ~P are true). That is, we know on the basis
of logic alone that at least one of the two
arguments must have a premise that is false.
Otherwise, we would have to say that both P and
~P are true, and that is absurd!
Now recall that, for the purposes of
logic, we are not primarily concerned with the
truth or falsity of premises. While we do want to
understand the difference between validity and
soundness, it isn't our
purpose in this logic class to go very far into
the specific details of this discussion of
personal identity and souls so as to determine
soundness of one argument or the other. We might
try to do that sort of thing in other philosophy
courses. For our purposes here, it is enough that
we have found two good examples of arguments that
are drawn from discussions about an interesting
philosophical topic.
*
If you
are interested in more details about Mulder's
argument, you can examine what Weirob said in her
conversation with Sam Miller (a.k.a. Fox
Mulder??) as it is to be found in the transcript
of the recording of the conversation in John
Perry's book, Personal
Identity and Immortality.
There is further discussion at http://personal.bgsu.edu/~mbelzer/indexdialogue.html. You will see
that Mulder here has given a specific
interpretation of Weirob's argument. Similar
arguments can be found in the writings of the 17th
century philosopher John Locke and and the 18th
century philosopher Immanuel Kant and it has been
developed by contemporary philosopher Sydney
Shoemaker and others.
An argument like
Scully's can be found in the writings of the 17th
century philosopher Rene Descartes and has been
developed by contemporary philosopher Richard
Swinburne (in Personal
Identity) and by others.
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