 We can make this epistemic problem more vivid by imagining a three-dimensional duplicating machine. When you step into the “in” box, it reads off your complete physical (and mental) condition and uses this information to assemble a perfect duplicate of you in the “out” box. The process causes temporary unconsciousness but is otherwise harmless. Two beings wake up, one in each box. The boxes are indistinguishable. Because each being will have the same apparent memories and perceive identical surroundings, each will think, for the same reasons, that he or she is you. But only one will be right. If this happened to you, it’s hard to see how you could know, afterwards, whether you were the original or the duplicate. (Suppose the technicians who work the machine are sworn to secrecy and immune to bribes.) You would think, “Who am I? Did I do the things I seem to remember doing? Or did I come into being only a moment ago, complete with false memories of someone else’s life?” And you would have no way of answering these questions. In the same way, psychological-continuity views raise the questions, “What am I? Am I a nonanimal that would go with its transplanted brain, or an animal that would stay behind with an empty head?” And here too there seem to be no grounds on which to answer them.