What makes me the same person today that I was yesterday or will be tomorrow? In Plato's Symposium, Socrates observed that all of us are constantly undergoing change--physical as well as changes in our manners, customs, opinions, desires, pleasures, pains, [and] fears. Aristotle theorized that some underlying substratum remains constant even while we undergo these changes. John Locke rejected Aristotle's view and reformulated the problem of personal...