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Personal Identity

Fission

(Text as at 26/11/2007 23:25:26)

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

The paradigm case of Fission is of two half-brain¹ transplants². It is difficult to consider these cases without slipping into the “psychological view³”. Each hemisphere seems to preserve what matters⁴ to the fissioned individual, and a perdurance⁵ account can maintain identity⁶ after fission. An alternative account is to claim that the two half-brains always were separate persons (and Puccetti has maintained that they are separate persons, in all of us, even prior to the commissurotomy⁷ in this thought-experiment⁸), in a way slightly different from the usual Lewis⁹ view of non-identical spatially-coincident¹⁰ individuals¹¹ (because the hemispheres aren’t spatially coincident, though the shared body¹² is).

We need to consider how the original person¹³ was unified¹⁴. We can press the realism of the thought-experiment by asking how important are the spinal chord and PNS generally to the psychological integrity of the human organism¹⁵? The case of dicephalus¹⁶ twins may be relevant – where the functions of walking and even typing seem to be carried out perfectly adequately despite the coordinated limbs being controlled by different brains.

We also need to consider whether the two half-brains continue to constitute a single scattered¹⁷ person, just parked in separate bodies. A single embodiment is important because it ensures synchronisation of experience, and external communication between the hemispheres (in the absence of the usual internal communication across the corpus callosum). Presumably, this could be achieved in other ways. We can imagine a BIV¹⁸ linked by radio transmitters/receivers to a remote body – the brain is part of the body – so a single physical thing can be spatially discontinuous. Why, if A fissions into B and C, can’t we consider B & C to be parts of the same person? They could fight / argue … but so can someone in two minds about things. What if one killed the other? They would have different perceptual experiences, but so (presumably) does a chameleon, with its eyes pointing in different directions (and sheep and other herbivores, and fish, with eyes on the sides of their heads). I need to consider in detail what is supposed to be going on in fission – ie. press the thought experiment: there needs to be segregation / redundancy prior to separation – this can happen over time (or we would have plain duplication¹⁹). At some point the person will split, with incommunicable consciousnesses²⁰ (cf. Locke²¹’s day-person and night-person).