According to the Soul Theory, a necessary condition for person A to be one and the same as person B is that they have the same soul. This theory is impossible to prove because the soul lacks definition, is physically unproven, and because humans naturally identify one another based on physical characteristics. According to this theory, however, it is possible to survive after physical death.
Arguers against the soul theory note its lack of definition. Some of them propose the Body Theory, which states that A is the same as B only if they have the same body. What exactly is meant by body in this case? The physical form changes regularly and is never “the same” twice, a seeming contradiction. However, the answer may lie with Aristotle, who noted two types of changes an identity can undergo: accidental changes (a river’s changing current) and essential changes (the river dries up or is completely rerouted). So, the body’s natural alterations are accidental, but what constitutes an essential change must be more severe such as death or brain injury.
But what exactly is it about the brain that causes identity? Is identity a result of memory? The Memory Theory supposes that A and B are numerically identical (one and the same thing) only if they are connected through time by stages that genuinely remember prior events. Because this is partially a body theory, survival after death is not possible.
Detractors of the memory theory argue that, if you cannot recall ever being 5, then you were never 5. Supporters called detractors idiots because one needn’t remember being 5 directly as long as B is connected to A indirectly through a prior stage that remembers. This also accounts for the Alzheimer’s critique of memory theory. However, because memory theory uses circular reasoning that presupposes identity and does not allow for a greater complexity to personal identity than memory, it is inherently flawed and incomplete.
In an attempt to complete the memory theory, the Psychological Continuity Theory evolved. In addition to memory, PCT states that A is the same as B as long as there is psychological continuity through the stages – as long as B is the product of A’s psychological growth. So, according to PCT, if subject Sara was duplicated, Sara 1 and Sara 2 would be one and the same person as long as their causal connection had not branched (the Non-branching Theory of PCT).
However, this cannot be the case because No. 1 and No. 2, being of separate bodies, would not experience uniformly and so would immediately diverge psychologically. This is the same argument used against the Closest Continuer Theory, which claims that B is one and the same as A as long as B is the closest psychological continuation of A in the event of multiple copies.
In the end I’m still clueless as to what creates personal identity, but at least I can say that the situation is so much more complex than the 450 words I’ve written about it that there might be an answer somewhere. Until then, I still want to know: Who are you?