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I can imagine splitting my brain in two and placing the individual hemispheres in individual bodies. This affects the psychological continuity view of personal identity because then I would not be numerically identifiable to either of the individual bodies.

There is a distinction between what is physically possible and what is logically possible. I appreciate the significance of the thought experiment if it is physically possible for me to split my brain in two. And I appreciate that when some people say that brain splitting is logically possible, they may just mean we have not ruled it out as a physical possibility. Therefore, it is logically possible that sometime in the future we may have discovered that it is physically possible.

However, if we discovered (somehow) that it was not physically possible to split the brain, then would the thought experiment would still be relevant? It seems implied that the mere logical possibility of brain splitting is enough for it to be relevant. If this is the case can you explain why it is relevant to me?

Thanks.

IsaiahM3337
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Banana in a vat
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  • The idea is that we can not, strictly speaking, discover that something is physically impossible: physical laws are inductive generalizations, and always fallible. Hence we have to allow for breaking our current approximation of physical possibility. But my sense is that something stronger than logical possibility is usually used in such thought experiments, although not as strong as physical possibility, often called "metaphysical" possibility (see e.g. Kripke's argument). It is argued that conceivability or imaginability imply it. – Conifold Apr 23 '19 at 18:31
  • I appreciate that allowing for "breaking our current approximation of physical possibility" inasmuch that it makes for interesting philosophical debate. For instance, positing the brain splitting scenario as in some sense possible has consequences on the psychological continuity view of person identity. However, if it is only metaphysically possible, i.e. I can imagine it, then I fail to appreciate the significance of these thought experiments. – Banana in a vat Apr 24 '19 at 13:14
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    Are you aware that split brain is a real thing? – curiousdannii Apr 24 '19 at 14:07
  • @curiousdannii Sorry. I should have been more clear. I meant the thought experiment where a brain is split in two and each hemisphere is placed in new bodies. This hasn't been done. – Banana in a vat Apr 24 '19 at 14:20
  • No, the question is clear about that. But split brain is already a real condition with many perplexing issues of its own. – curiousdannii Apr 24 '19 at 14:24
  • That imagining is enough for metaphysical possibility is controversial. But I think the idea is that our imagination implicitly takes into account things that may not be established scientifically yet, so the imaginable is more likely to turn out to be physically possible than merely coherent. I also think that part of the point of the thought experiments is in exploring a range of potential physical theories, after all, we never know what is or is not physically possible beyond practical confidence. It makes sense to consider the bounds, above and below. – Conifold Apr 24 '19 at 17:55
  • @Conifold I appreciate the response you've given and agree metaphysical possibilities may be possible in our world. To be clear, I am not saying that metaphysical possibilities are not physically possible; I am worried, however, that the metaphysical possibility of brain splitting may not be possible in our physical world. I still feel that many philosophers are inclined to think of metaphysical possibility as relevant to personal identity regardless of whether the thought experiments they postulate are possible in our world. – Banana in a vat Apr 24 '19 at 20:05
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    Another option is that thought experiments explore the meaning of the concept of personal identity as such, which does not depend only on its extension in the actual physical world. It also matters what happens under scenarios that are physically counterfactual. This is relevant in theological contexts, for example (since God is not bound by physical laws), where the problem of personal identity arises in the context of the resurrection of the dead: why are those resurrected "the" persons in question, rather than just their copies. – Conifold Apr 24 '19 at 20:31

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