Since the onset of Parkinson’s I have become qualitatively different to the symptom-free person I was in the past (indeed, we are all different compared to the people we were in the past). However, I still describe that past person as me because of the numerical sameness he shares with me; there has only been one of me in the past and now in the present. In other words, my personal identity has remained non-branched and continuous despite, for example, growing into an adult.
My numerical sameness can be described as either “spatiotemporally continuous” or “psychologically continuous”. Spatiotemporal continuity means during my life I have carried out a single, continuous series of actions in space and time that can be traced back to my conception. Psychological continuity states I have the same identity as my past self because I share memories and character traits etc with him.
This raises a question: how much continuity is needed to maintain my identity? Spatiotemporally I can lose significant parts of my body and still be myself but if all the atoms that make up my body were separated I would cease to be me. Psychologically, I can gain new memories and experience new mental states (e.g. depression) but I can still identify with my past self and maintain my identity. There is significant flexibility within personal identity to remain who you are.
Therefore, Parkinson’s may restrict my body and affect my emotions but it won’t be sufficient to change who I am.
This essay was inspired by “Riddles of Existence” by Earl Conee and Theodore Sider.