Parfit's View of Personal Identity

Extract

[...] This disregard for the common view that personal identity involves something beyond psychological continuity in a one-one relation would cause a radical change in our belief system. It undermines the deep-seeded belief “that however much we change, there's a profound sense in which the changed us is going to be just as much (“Brain Transplants” 301). Instead, the Derek Parfit that exists tomorrow will be much more closely related to the present Derek Parfit than the Parfit that exists twenty years from now. [...]

[...] A conventional view of personal identity would assert that there must be an answer to the question, “Which one is now However, none of the three possible responses to the question seem to give a reasonable answer. Possibility that I am now both of the resulting people, is contradictory. It violates the one-one relation of identity. In addition, the resulting persons will be different people and live different lives, so they cannot possibly both be me. Possibility that I am going to be one of the two resulting bodies, is also unsatisfactory, as it requires a totally arbitrary selection of one of two exactly similar people. [...]

[...] Bernard Williams attacks this definition of personal identity as violating the one-one relation principle inherent in the concept of identity. For, as Parfit has agreed, psychological continuity need not be one-one. Therefore, according to Williams, it is not a sufficient criterion for identity (“Personal Identity” 175). Therefore, some other criterion for identity is necessary because judgments of personal identity have great importance. Parfit agrees that psychological continuity does not always correspond with identity but maintains that if it occurs in a one-one relation, it constitutes reasonable usage of the term identity. [...]