Mind 95 (April):224-9 (
1986)
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Abstract
It has been argued that 'brain bisection' data leads us to abandon our traditional conception of personal identity. Nagel has remarked: The ultimate account of the unity of what we call a single mind consists of an enumeration of the types of functional integration that typify it. We know that these can be eroded in different ways and to different degrees. The belief that even in their complete version they can be explained by the presence of a numerically single subject is an i1lusion.l Parfit has adopted a similar position, contending that patients with 'split brains' become two separate 'streams of consciousness' and thus that our normal sense of personal identity, or at least 'what matters' about personal identity is constituted by psychological relations between connected conscious experiences2 It is claimed that in 'split brain' patients certain of the relations are disrupted and that we thus see clearly that the nature of the unity that is normally present does not reside in a single subject with a given identity, but in the connectedness and continuity that normally obtains. Parfit draws on two sources of support for these contentions: the first is the actual events that transpire after a human being is submitted to the operation of sectioning the corpus callosum (or 'brain bisection'), and the second is the imaginative consideration of various scenarios involving graded mental and physical discontinuity, and the 'fission' and 'fusion' of persons. I shall do little more than argue that the actual data will not sustain the interpretation put on them