ABSTRACT
Imagine the following scenario: I am supposed to meet my friend Mary for lunch in a crowded restaurant. Arriving twenty minutes late, I wonder if she will still be there. She hates to be kept waiting, and told me that she will leave after waiting ten minutes. With some relief I hear her calling my name from a table across the room. “I should have left like I threatened,” she says, “but I was too hungry.” There is nothing remarkable in this story, least of all the fact that I am able to tell that the person with whom I nally sit down to eat is my friend, Mary. Many of our everyday activities involve re-identifying other people. Without the capacity to make quick and (usually) accurate judgments about when we are dealing with the same person at two different times, we could not do much of what we do. When we stop to ask what it is that actually makes someone the same person at two different times, however, it is surprisingly difcult to nd a satisfying answer. In the story described above various cues indicate that the person with whom I am lunching is the friend with whom I made the plan to lunch. Some of these have to do with evidence that the human being at the table is the same human being with whom I made the plan – her voice sounds like Mary’s and she looks like Mary. Other cues have more to do with evidence that the person in the restaurant is psychologically continuous with my friend – this person obviously remembers making a lunch date with me and threatening to leave if I was late; I will undoubtedly also nd that she remembers a great deal of Mary’s past and in other ways demonstrates a psychological life continuous with the person with whom I made my plans. All of these factors taken together present me with such strong reasons to believe that this is Mary that it is almost misleading to say that I judge this person to be Mary; it will almost certainly never enter my mind that she might not be. But what if we imagine circumstances in which the various features that reveal this person to be Mary diverge? Suppose, for instance, that upon entering the restaurant I hear Mary’s voice, and look over to the table where I see someone I recognize as Mary. When I go over to join her however, she has no idea who I am. Seeing her up-close and getting a good look at the distinctive birthmark on her hand, I am convinced that this human being is the same human being I have known as my friend Mary. But she denies having ever seen me before and acts nothing like Mary.
