The Duplication Problem

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This is the 56th post in my Theories of Knowledge and Reality series. The last post began looking at the psychological account of personal identity. This post presents a further objection against the psychological account: the problem of duplication.

The psychological view claims that someone is the same person as an earlier person when there's sufficient continuity between the two in terms of memory, personality, beliefs, desires, and character traits. The duplication problem 

Suppose God creates a person in the afterlife who has memories duplicating mine. Is it me? God's choice of those memories is because they were mine at death, so there's a dependence on my memories. Is that enough, or is this an imposter? Could I look forward to being this person? Or is this is just a duplicate, not me?

To make the problem more vivid, consider the story of William Riker, from the sixth season Star Trek: The Next Generation episode "Second Chances". Lieutenant Riker was attempting to transport off a planet with difficult atmospheric conditions. Because of the risk of not getting through, the transporter technician decided to run two beams from the transporter, in case one didn't get through or in case information needed to be compiled from both beams to reconstruct the full signal. These extra measures were intended to insure Riker's survival. It turned out they did something entirely different, because on beam successfully made it back to the ship, and Riker was rematerialized there (it seems), but the other beam was reflected back to the planet, where Riker was also rematerialized there (it seems).

The Riker who made it back to the ship lived for years, continuing his career in Starfleet and eventually becoming Commander William Riker, first officer on the Enterprise-D. The Riker who ended up back on the station had to wait years before the Enterprise-D showed up in this episode and rescued him, since no one had known he was there. From the moment there were two of them, you could no longer assume that either was the original. After all, nothing makes either seem like a better candidate for being the original. Both originated from beams that was exactly the same, from a process that seems as if it would ensure survival of Riker if only one beam had succeeded in rematerializing him. According to the psychological view, all you need is a resulting person who has all the right psychological characteristics. Either version of Riker would have met that criterion, and thus either Riker (if he were the only one) would have been the same Riker as the original, as long as the other hadn't existed, according to the psychological view.

But with two of them, the psychological view has a problem. We have two thinking things. Each has a different body; each thinks "I'm Riker, the guy who did ... beforehand". But that can't be right, because these guys aren't the same as each other . So is this kind of knowledge of who we are as firm as it seems to be? They can't both be the original. Let's assign them distinguishing names to make it clear what's going on here. We'll call the original guy Riker. Commander Riker returning to the planet is Will. Lieutenant Riker, who had been stuck on the planet all these years, is Tom (based on Riker's middle name, which the planet-version goes on to take to distinguish him from the other one).

So we've got Tom and Will. Can they both be the original? Each has as much right to that claim as the other. However, assume they both are the original. Tom is Riker, and Will is also Riker. But Tom is not Will. How can Tom be the same guy that Will is without Tom being Will? Will and Tom are two separate individuals. If it's true of both of them that they're the same guy as Riker, then they're the same guy as each other, and we already know that's false.

There are a couple crazy things a psychological theorist might say to avoid this contradiction. One proposal would be to say that there were always two people in the Riker case, and they were present in the same body all along, thinking the same thoughts as each other, both doing everything the original body did. Then when the split occurred, each one went his separate way. This does seem crazy, though. What made one of them go one way and the other the other way? Why wouldn't both go to both new bodies, creating the same problem again? Also, if there would only have been one without the accident, then how does the mere existence of a duplicate in the future make there be two beings in the same body earlier? That's a funny causal relationship. The future duplication makes there have been two all along.

Another crazy view that a psychological theorist might hold to avoid the contradiction is that there never ends up being two. Riker still exists as one person. He just has two bodies from that point on. It's not that there are two of him. There's only one of him. But he has two bodies, two brains, four arms, and a bi-located existence. He's just as present in each place where he exists, and he might be running in one body while sitting down in the other body. He might be thinking Captain Picard is a jerk with one brain while thinking Captain Picard is not a jerk with the other brain. He might be thinking with one of his brains that the guy with the other body is a jerk, not realizing that in such an instance he's thinking of himself as a jerk, since the guy that he's thinking about is himself. There's actually no contradiction here. It's a coherent view. It's not as if he'd be both sitting and not sitting when one body is sitting and the other standing. After all, in that situation one body is sitting, so he is sitting. He's not not sitting. He's just standing too while he's sitting. It's not a contradiction unless you can generate something of the form "P and not-P", and you can't do that with this view. But the view is indeed crazy. There obviously seem to be two people after the transporter accident.

A third crazy view to avoid the contradiction while maintaining the psychological view seems less crazy when you first consider it, but I actually think it's more crazy. What you say is that there would normally have been a continuing Riker if the transporter had worked to materialize one Riker (in either place), but given that there are two of them he ceases to exist, and now there are two people who think they're Riker, but neither really is. This seems less crazy than the above two crazy views. After all, neither Tom nor Will can claim to have a better right to being the original guy, and they can't both be him, so it must be that neither is Riker. Riker is dead. That seems like the right thing to conclude, after looking at the arguments I've already discussed.

However, there's a serious problem remaining. Someone holding a psychological view should want to maintain that with an ordinary use of a transporter the original person does survive. It's only in these weird cases of duplication that you kill the person. But why would the same exact occurrence produce a surviving person most of the time, but then kill the person in these weird cases? The only difference in these weird cases is that some other occurrence, completely outside the causal path of the transporter, occurs. If you just had one transporter beam successful, say Tom's, then Tom would be Riker. If you just had the other successful, then Will would be Riker. But if both success, Riker dies. The exact operation that makes him survive kills him if this additional occurrence takes place in addition to the operation that would otherwise make him survive. If the events within the original transporter beam should make him survive, how can the appearance of an additional transporter beam invalidate that survival? And how can it be that any beam would count as survival if any of the others would invalidate the survival? If you're going to say that more than one beam prevents survival, why should it occur with just one beam? You're better off saying that you don't survive with this kind of transporter to begin with, and thus every time anyone on the show steps into a transporter and gets disintegrated, someone else appears on the other end of the beam. But then the psychological account would be wrong. So it seems the duplication problem is areal difficulty for the psychological account. Anything it has the resources to say to avoid the problem results in a pretty crazy view.

This problem can arise without futuristic technology, also. Go back to Locke's original example. He wanted to say that God could make someone in the afterlife be me just by giving the person my memories. A more robust psychological view would include other psychological properties than just memories, but anyone holding the psychological view could say the same thing. But what if God creates two duplicates of me? They can't both be me, because they begin to have different thoughts and be in different places. But how could you pick one over the other unless one appears first? What if both occur at once? How could facts like the existence of a duplicate or when it was created affect whether the other is me, anyway? Shouldn't it just be facts about the one that determine if it's me? The psychological view, then, fails to determine whether some proposed candidate for being me really is me, unless you're willing to say something that, upon closer examination, seems intolerable.

In the next post, I'll move on to the bodily view, the first biological account of personal identity that I'll be covering.


Reminds me of Dollhouse. All these duplicates going on having the same memories and thinking "I am {X}" with X being whoever and yet, I don't think any of them are really the real {X} (though they talked like that because of remembering being Them). Echo was weird though because she housed all those other memories, tapped into them, and spoke of them as Other while even referring to Caroline as an Other. Paul was another weird one because of his whole becoming a doll for himself.

Dollhouse raises similar questions about the psychological view, but if the original person survives then you'll always give them priority, because there's a continuing person. But then on the psychological view someone is the original if the original has died and you've implanted the memories and personality into a new body. I suppose the problem arises if you can do it so two bodies simultaneously get the same person's memories and personality. But it's much more vivid with Star Trek transporters, because presumably it's more likely you could get both materializing simultaneously.

I wrote the original notes to these long before Dollhouse. The main template I had for that sort of thing was the Babylon 5 death of personality. There's an episode dealing with that that I love to show my classes when I cover this. It's hard to imagine one Dollhouse episode that could do as well, but if you have any suggestions I'd be interested in hearing them.

I can't think of a single episode that is as good as your Riker example and I have yet (hangs head in abject embarrassment)to see Babylon 5.

You do need to watch Babylon 5, from the pilot on, in order and without missing any episodes. Be prepared for the pilot to be boring, but it's more important than it seems. Once they got to the series, it got very good very quickly. I watched it all, well after it had ended, but I saw a bunch of mid-series episodes first, and it would have been better to watch it in order. It's still near the top in my view, with Dollhouse possibly being the sort of series that could compete in terms of quality if it had continued, but its length diminishes that.

Depending on how Lost turns out in the end, it may be a candidate (no pun intended). But I'm suspicious that they're going to pull something stupid at the end with the flash-sideways being a reset that occurs after the finale, and if they do that I'll be very disappointed. The fact that it took so long to get interesting is also an issue.

I can't think of another show that I'd put on the same level.

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