Personal identity is a field of philosophy that studies the definition of persons and under what conditions persons persist. There are three main accounts of personal identity. The psychological approach claims that a person at a time t1 persists to be the same person at another time t2 if and only if the person at t2 is psychologically continuous with the person at t1. The biological accounts say that bodily or physical continuity is a necessary and sufficient condition for personal identity. The soul theorists maintain that personal identity is defined by soul. There is a large amount of literature about the psychological and biological accounts of personal identity. I will not discuss them in detail here.
But both psychological and biological approach face various objections. I have always had a hard time deciding which of these two theories are more plausible to me since I first learned about these theories. I have also been thinking about a possibility to combine these two views. If we combine the two views brutally and require both psychological and biological continuity for personal identity, we are going to face the objections for both theories. However, maybe the problem exists in our attempt to find necessary and sufficient conditions for personal identity. If we consider Alston’s examples of defining “poem” and “religion”, we may be able to use a similar approach to define personal identity. Personal identity is not defined by the strict criterion of psychological or biological continuity. Personal identity requires a certain combination of psychological and biological continuities each to a certain degree. A large amount of psychological continuity may be able to compensate a small amount of biological continuity, and vice versa. There may be many possible variants of this view. One can say that each component needs to reach a substantial degree in order for personal identity to persist. I can also anticipate many disputes about the weight of each component and/or what counts as substantial for each component. However, instead of adopting a singular account of personal identity, this pluralist account may help us define and understand personal identity better.