The Branch Line Case Notes for November 23

Main points

We started with a problem for Locke: he seems to be committed to intransitive answers. The we provided an answer that seemed to preserve Locke’s central idea while solving the problem. Then we showed that that would encounter a similar problem.

Then things got weird. We talked about whether survival into the future requires being identical with any person in the future. One surprising answer is: no. What the teletransporter example seems to show is that there could be a process that makes it so that there is no one in the future who is identical with you now but that you would survive. Parfit calls being duplicated by the teletransporter a “double success” rather than death.

Is it a success?

I balk. I think that if I’m going to be around tomorrow morning, there will have to be something that it is like for me tomorrow morning. In other words, I’m going to have to see and experience what some person alive sees and experiences.

If I were duplicated, what would I see and experience on the day after duplication? If it’s what the guy on Earth sees and experiences, then I’m the guy on Earth and the guy on Mars is someone else. If it’s what the guy on Mars sees and experiences, then I’m the guy on Mars and the guy on Earth is someone else. So far, so good. It’s weird, but I understand the options.

If you tell me I’ll experience what both of them experience, then I don’t understand. No one alive tomorrow will simultaneously experience what the guy on Earth experiences and what the guy on Mars experiences. So I can’t either.

If you tell me I’ll experience what neither do, then I’m just not there at all.

“So where’s the double success?,” I ask.

Eliminating the alternatives

Parfit pushes back against that line of argument by eliminating the alternatives. An indivisible, immaterial soul might solve the problem. But we didn’t have much enthusiasm for that answer. Perhaps I go with my brain? We’ll talk more about this next week, but for the time being, we noted that you can split a brain too. So you could have a similar situation: two people in the future have the same physical connection with me. So which one am I?

In the end, Parfit thinks, we’ll come back to psychological connections and continuity. Information, in other words. But with information, there is no distinction between qualitative identity and numerical identity. As it happens, the continued stream of information in our lives has met the conditions of identity: there hasn’t been any branching or copying.

But, Parfit says, this is an inessential fact about us. If there were branching, the quality of our lives wouldn’t have changed. Why should the appearance of another person who is a copy of me determine whether I live or die?

It’s a good question. It’s a disconcerting, puzzling, and perplexing question. But it’s a good question nonetheless.

This page was written by Michael Green for Problems of Philosophy, Philosophy 1, Fall 2009. It was posted November 23, 2009.
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