Numerical Personal Identity Over Time

This honors thesis examines the question of numerical personal identity through time. What are the necessary and sufficient conditions for a human person X that exists at time t* to be numerically identical to a human person Y that exists at time t1? In consideration of this philosophical inquiry, I will explore four of the most prominent accounts of numerical personal identity through time: the Psychological Approach, the Bodily Criterion, the Brain Criterion, and Animalism (the Biological Approach). I will provide the various arguments for and against each approach; however, I will primarily focus on the Psychological Approach and Eric Olson’s Animalism. My thesis will be that Animalism does not provide an adequate answer to the numerical identity question and that a more acceptable answer to the question can be obtained by adopting an alternative somatic approach: part of the brain, the cerebral hemisphere, provides the necessary and sufficient conditions for numerical identity and persistence through time. More specifically, I will introduce a Modified Brain Criterion which states that the necessary and sufficient condition for a person X that exists at time t* to be numerically identical to a person Y that exists at time t1 is that person X has an operative cerebral hemisphere that produces either X’s memories, intentions, and beliefs or X’s rudimentary psychological features at time t* that are both strongly connected to and continuous with either the memories, intentions, and beliefs or the rudimentary psychological features produced in person Y’s operative cerebral hemisphere at time t1. Given Olson’s initial assumptions, I will conclude that the Modified Brain Criterion is the most efensible approach to the question of numerical identity through time