Shantila's Inside Logic #16
Arguments
| You are still at the
airport. Things have quieted down. The man who
was going to confess is sleeping on a seat beside
you. He got shot but was not killed. What is
death? you ask yourself.
Suppose the man had
died. He
certainly looked dead. If he
had died is it even possible that somehow he
could still have continued to exist? Suppose
he has, or is, a soul. Lots of people believe
something like that.
If
people are or have souls, would that mean we can
still exist somehow even after we have died?
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
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 simply are not relevant to
our existence as people-- at least not if we have
knowledge of our own or others' identities as time
passes. 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 if
personal identity is due to identity of a
soul, then we
must 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.
If personal identity through time is due to
identity of a soul, then we must have
knowledge of soul identity through time.
[This just follows logically from premises 2
and 1 by modus ponens;
-- 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 must be able to correlate a souls
with physical or psychological features.
[Premise]
(Explanation. Suppose we
have knowledge that the same soul exists
at both time 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]
7.
Conclusion: Personal identity through time is
not due to identity of a soul. [From 6 and 3
by modus tollens]
|
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>(P>S), S>C, ~C } ~P
| |
1 |
1. |
K |
A |
|
|
| |
2 |
2. |
K>(P>S) |
A |
|
|
| |
1,2 |
3. |
P>S |
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 MT |
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| |
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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 now 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 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 I can imagine existing without a body
only if it is possible for me to exist without a body. It
isn't possible for me to exist without a body unless some
essential part of me is nonphysical. 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 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, ~E>~I, ~N>~E, N>P }
P
Is this argument valid? Yes, I
think it is, because look, we can use the Rules to prove
that the argument is valid, as follows.
| |
1 |
1. |
I |
A |
|
|
| |
2 |
2. |
~E>~I |
A |
|
|
| |
3 |
3. |
~N>~E |
A |
|
|
| |
4 |
4. |
N>P |
A |
|
|
| |
1 |
5. |
~~I |
1, DN |
|
|
| |
1,2 |
6. |
~~E |
2,5 MT |
|
|
| |
1,2,3 |
7. |
~~N |
3,6 MT |
|
|
| |
1,2,3 |
8. |
N |
7, DN |
|
|
|
| |
1,2,3,4 |
9. |
P |
4,8 MP |
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|
Scully:
Ok.
Mulder: So it
looks like your 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. "Do either of you know who
owns this notebook?" she asks you and Joe.
It is a black notebook.
"Maybe it belongs
to that guy. We'll give it him when he wakes
up," Joe says.
Right. You are still
stuck at the airport with Joe. Great.
"Do you want the
bullet?" she asks Joe.
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 here). Sometimes when people are having
an argument, they will try
to use arguments --but
often they simply begin yelling or sulking and so
forth.
Arguments may be valid
or invalid; and some valid arguments also are
sound. Recall that we define validity and
soundness as follows.
Validity.
We say that in valid
reasoning, the conclusion
must be true if all the premises are true.
Soundness.
And we say that reasoning
is sound
if both (a) it is valid, and (b) all the premises
are in
fact true. Notice that it follows that the
conclusion of a sound argument must
be true.
The
following simple argument is an example of a
valid argument that is not sound.
If
Al Gore is the U.S. President, then the U.S.
President recently won a Nobel Peace prize. Al
Gore is the U.S. President. So the U.S. President
recently won a Nobel Peace prize.
This
argument is valid (as we easily can show using
our valid rule MP). But it is not sound because
one of its premises is false.
*
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. 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 both P and ~P cannot be
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 certainly
do want to understand the difference between
validity and soundness, it is not our
purpose in this logic class to go far into the
specific details about personal identity and
souls so as to determine the soundness of one
argument or the other. (We would do that in other
philosophy courses, such as philosophy of mind or
metaphysics.)
*
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,
apparently) as it is to be found in the
transcript of the recording of the conversation
in John Perry's book, Personal
Identity and Immortality,
with further discussion at http://personal.bgsu.edu/~mbelzer/indexdialogue.html. You will see
that Mulder 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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