In disputes between supernaturalists and naturalists, one of the minor themes has to do with uniqueness and identity. Naturalists inclined toward functionalism usually think that the mind, for example, is what the brain does, while religious people tend to believe in souls and spirits. But functionalists then also have to think that copies of minds might also be made, since another physical system that realizes the same functions would be equivalent. A soul, on the other hand, conveys a kind of uniqueness on us: we can’t be copied.

As is so often, most ordinary intuition recoils at the more naturalistic views, I think. We think we must be unique. If we make a copy of a person, only one of them must be real. And not a few more secular philosophers favor uniqueness when dealing with personal identity. If we make a functionally equivalent copy of a person, it still does not share the causal history that belongs to the original. Its memories and so forth seem fake, in some sense. Some would argue that if you kept the copy and destroyed the original, there would be something fake here, even if the functional aspects of a personal history proceed seamlessly, with barely a blip. The causal continuity has been disrupted, and somehow this matters.

I wonder if it would help to move out of the swamp of disputes about personal identity for a moment. Let’s look at a different, personality-free example. Say we want a spy to recognize a contact, by presenting a unique artifact. An easy way would be to rip a cardboard box in two, in a jagged fashion, and give the two halves to the spy and the contact. The rip would be very complex in a certain sense. Another ripped piece of cardboard perfectly matching the other half is extremely unlikely. If the pieces match, the spy and contact can be confident they’ve found each other. (Unless it’s been intercepted by enemy agents. But ignore that. It’s just a story.)

Now, technically, it may be possible, though extremely difficult, to make an exact copy of one of the cardboard halves. Say this was doable, and the spy was some day presented with two practically identical copies of what is supposed to be the other half of his cardboard box.

If this happened, the spy should be very concerned. This is because for his purposes, ensuring uniqueness is functionally—vitally—important. Seeing another copy not only makes this alleged contact, but the whole process of identifying contacts useless. The matching complexity of the rip-pattern, a functional characteristic, no longer indicates a unique causal history, which is what it supposed to accomplish.

I wonder if the secular unease produced by person-copying fantasies has similar roots. That is, it’s not really about souls or functionalism so much as caring for uniqueness and personal idiosyncrasies being accurate reflections of a unique causal history that makes us what we are.

But then, perhaps in the science-fiction scenario that we get the sort of technology to make back-up copies of individuals, we wouldn’t care about that sort of thing so much. It might, for example, be a good thing to make a back-up copy of yourself before engaging in dangerous sports. If you kill yourself skydiving, a backup can be activated, missing nothing but a recent thrill. Uniqueness would be preserved, but only because we might socially still want that. And the decoupling of functional properties from causal history would not, after all, be complete, since the backup would not have its particular insanely complex pattern if it not for the causal history behind its original. There is an indirect kind of causal continuity that remains. Whether this indirection matters depends, I think, entirely on what we care about. And I also think that having only a “pure,” direct causal continuity is an odd thing to care about.

In any case, I don’t see what souls would contribute to these sorts of discussions, except perhaps as a way of enforcing caring about the original. But it would do this quite artificially, and I think we’re best rid of that particular sort of confusion.

About Taner Edis

Professor of physics at Truman State University