- Of the possible criteria of personal identity, there were three that I took seriously in book that Judith Thomson discusses (RP, "Parfit (Derek) - Reasons and Persons"). On the Wide Psychological Criterion, for some future person to be me, we must be psychologically continuous. On the Physical Criterion, which I shall here rename the Brain Criterion, we must have the same brain. On the Narrow Psychological Criterion, we must both be psychologically continuous and have the same brain.
- My discussion of these criteria was confused. At one point, I endorsed the Wide Psychological Criterion (RP 208). That was a mistake. As I later claimed, we should not try to decide between these criteria. In the so-called "problem cases," where these criteria conflict, questions about personal identity would be indeterminate, and empty. If we knew the facts about both physical and psychological continuity, there would be nothing further to discover.
- According to some writers, even if there is nothing to discover, we should at least consider how we can best refine our concept of a person, by adopting one of these criteria. But that, I believe, is not worth doing. First, as I shall argue again below, personal identity is not what matters. Nor should we try to find some criterion that would make identity coincide with what matters. Such coincidence could not be complete. Unlike what matters, for example, numerical identity cannot hold to different degrees. And, if we try to preserve the coincidence between identity and what matters, it will be harder fully to shake off the view that identity is what matters.
- Though I believe that we need not choose between my three criteria, we cannot discuss persons without making some assumptions about personal identity. And, in some of my arguments, I assumed
These claims I shall call my view. This view seemed to me uncontroversial, since the shared or common element in my three criteria.
- If there will be a single future person who will have enough of my brain to be psychologically continuous with me, that person will be me.
- If some future person will neither be psychologically continuous with me, nor have enough of my brain, that person will not be me.
- Judith Thomson rejects my view. She accepts a fourth criterion, which I dismissed, too lazily, in a single sentence.
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