Derek Parfit wrote a seminal paper on personal identity (called “Personal Identity”) in which he advocates supplanting the language of identity with the language of psychological continuity. Before I make my brief comment, I want to give some sort of summary of Parfit’s reasoning.
First, however, it’s worthwhile to give a quick description of a case study dramatized by David Wiggins. Imagine I undergo surgery in which my brain is removed from my body, split in half, and successfully transplanted into two other bodies. We know this is at least theoretically possible since there have been documented cases in which people survive with half of a brain. The major question with which both Parfit and Wiggins are concerned is, are those two people both me or do I, in effect, die?
Now onto Parfit.
Parfit argues that people erroneously hold the belief that in every instance there must be an answer to the question “is this individual the same as another?” Parfit thinks there are cases in which this question has no answer. In regards to the Wiggins case, Parfit says that the one individual can survive as two persons. He points out that this comes at the price of changing the concept of a person. As an alternative, Parfit suggests giving up the language of identity. But how can one person survive as two?
Parfit suggests that we use the language of identity to imply psychological continuity; continuity is a ground for identity when it is one-one but when it takes a one-many form (as in the Wiggins case) we must abandon the language of identity but realize continuity is what matters. Continuity depends on Parfit’s notion of q-relationships.
I have a q-memory, for instance, if: 1) I have a belief about a past experience which seems in itself like a memory belief, 2) someone did have such an experience, and 3) my belief is dependent upon this experience in the same way in which a memory of an experience is dependent upon it. The individuals in the Wiggins case would have q-memories of the original individual.
Parfit next shows that survival can have degrees. The inverse of the Wiggins case would be a fusion case. Certainly fusion would not be full survival since some of our traits would be lost but it is not death either since we regularly change our traits without thinking we die. Thus, survival can have degrees. Parfit next distinguishes psychological connectedness from continuity. Connectedness is not a transitive relationship (X q-remembers Z’s life and Z q-remembers Y’s life does not mean X q-remembers Y’s life). The distinction between selves can be made by referring to connectedness where ‘I’ implies the greatest degree of connectedness. What matters in continued existence is a matter of degree.
I find it interesting that all of Parfit’s examples indicate that his sense of connectedness and continuity are dependent upon some sort of biological relationsip. In other words, his paper implies that we can only have past selves and future selves–selves with which we are psychologically continuous–if those selves are biologically connected to us in some manner. Parfit is suggesting that what matters when we survive is the amount of stuff one individual has in common with another and that those individuals are related in the ‘right’ way.
I take issue with this notion of the ‘right’ way. Imagine that there are two people with whom you have some sort of relationship. The first is a present relationship with a spouse. You two share interests, talk about your plans, and have an intimate familiarity with the other’s values, desires, and hopes. The second relationship is not an actual present relationship; it is with a future self with whom you are psychologically continuous. Over time, as Parfit acknowledges, that future self will grow and change as we all do. So by the end of his life he will be less similar to you than at the point at which you had, perhaps, a Wiggins split.
It seems to me that what’s meaningful in the psychological continuity is not the persistence of a biological relationship but that our interests, values, and some characteristics survive and continue to ‘act’ in the world. Which individual is most likely to perpetuate those values, the future self who may change or the spouse who loves you, knows your values deeply, and who also may change over time? In my mind, the question cannot be answered. I can imagine cases in which the future self better perpetuates these values and cases in which the spouse better perpetuates these values. The fact that the question cannot be answered–since the spouse may do better at perpetuating what matters than he who is psychologically connected according to Parfit’s biological requirements–is reason to expand the notion of psychological connectedness outside of a purely biological relationship.