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Personal Identity

Brain Criterion

(Text as at 06/07/2023 00:43:12)

*** THIS IS NOT THE LATEST VERSION OF THIS NOTE ***

Plug Note¹

• Thesis Text:
  1. The question is whether the brain is the be-all and end-all of the matter of personal identity for human persons².
  2. This view seems to be presupposed by those ethicists who espouse the (whole or part) brain death³ criterion for death⁴. There will be some overlap between this discussion and that below on brain death.
  3. It is acknowledged by most that – conceptually at least – there can be persons⁵ that are not humans (ie. not members of the species homo sapiens) – whether these persons be non-human animals, computers, God, angels, aliens or whatever. Non-animals presumably have no brains, though aliens presumably have a brain-analogue, so brains cannot be identity-criteria for personhood as such (indeed, we might argue that there are no criteria for persons as such₆). But for animal-persons (human or otherwise), the brain seems to occupy a central place, both as the seat of psychology (in the absence of an immaterial soul⁷) and as the regulator of the body.
  4. So, the story would go, X is the same person as Y iff₈ X has the same brain as Y.
  5. The trouble is – even if this claim is along the right lines – we can press matters further, and ask whether the whole brain is strictly necessary. If what impresses us is a brain-based psychological view⁹, when what we imagine is “really the minimal me” is the pair of psychology-bearing cerebral hemispheres, then we might imagine (as some philosophers have) a case of fission¹⁰, where – after equalising the hemispheres in psychological potency, we transplant¹¹ one into another body lacking both hemispheres. Or, without needing anything so radical, we sever the corpus callosum in a commissurotomy¹², thereby (on this view) creating two persons in one body.
  6. However, if we are animalists¹³,¹⁴ wondering what the “minimal animal” is, and it’s the command-and-control functions of the brain that impress us, then the paring-down process might₁₅ be able to do without the cerebral hemispheres (or at least the psychology-bearing parts) altogether. So, brain-based views from different perspectives might come to different conclusions about the importance of the cerebral hemispheres – one view might make them essential, the other irrelevant to questions of identity (if not to “what matters¹⁶”). It is an empirical question whether the brain-stem can be divided, and hence whether a brain-based animalist approach is also subject to worries₁₇ about fission.
  7. Anyway, the appropriateness of the Brain criterion of personal identity depends on what we are¹⁸– in particular whether we are (most fundamentally, or in the sense of numerical identity¹⁹, which is not the same thing) human animals or persons constituted by²⁰ them (or various other things).
  8. Only if we believe that we are (identical to) brains²¹ will we adopt the brain criterion (though see Mark Johnston on Human Beings²²).

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  Further Remarks
  1. There will naturally be some overlap on this topic with the topics of
     • Brains²³ and
     • Criteria of Identity²⁴