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 arguments! I am 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

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: Miller, look, why couldn't we do it at least in our own case?

Mulder: Gretchen talked about that. --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.