personal identity consists in memory; sameness of episodic memory is metaphysically necessary and sufficient for sameness of persons. In other words, on the Memory Theory, what makes a person identical with herself over time is her remembering or being able to remember the events to which she was witness or agent. If she cannot episodically remember an event, then she is not identical with any of the persons who was witness or agent to the event. In such a case, she would bear the same relation to that event as any other person for whom a memory of the event could rise at best to the level of a semantic memory. If she can episodically remember an event, then her recollection or ability to recall that event makes her identical with the person represented in that memory as agent or witness to the event.Suppose, for the sake of argument, that the Memory Theory is true, i.e., that personal identity consists in memory.
Suppose further that we extract the memories of one person, A, and make exact copies of A's memories. Then, using Rekall's machine, we implant these exact copies of A's memories in B, C, and D. Now, since A, B, C, and D all remember the same things, e.g., they all remember watching the horrible 2012 remake of Total Recall last weekend, does it follow that they are all the same person? If not, does that mean that personal identity does not consist in memory? More explicitly:
- Suppose that personal identity consists in memory.
- If personal identity consists in memory, then A, B, C, and D are all the same person.
- But A, B, C, and D, cannot all be the same person.
- Therefore, it is not the case that personal identity consists in memory.