5 20TH-CENTURY THEORIES OF PERSONAL IDENTITY Jens Johansson 1. Introduction Three questions have dominated 20th- and early 21st-century thinking about personal identity: (a) What does it take for us to persist? More precisely, by virtue of what is someone existing at a certain time numerically identical to a certain individual existing at an earlier or later time? Tomorrow I am going to be in the dentist’s chair; what makes it the case that that patient is me rather than someone else? Is it because he stands in some mental relation to me, or because he has my soul, or because he has my body, or because some other relation holds between him and me? (b) What matters in survival? Each person seems to have a reason to care about his own future in a special way For instance, I am bound to feel intense pain during tomorrow’s visit to the dentist Like everyone else, perhaps, I have a reason to dislike these future experiences; but unlike everyone else, I also seem to have a reason to have prudential concern about it – to anticipate the experiences “from the inside” with unease and fear Is this because these experiences are experiences of mine – that is, is it because I am numerically identical with the future experiencer – or is it because of something else? Or I not have such a reason after all? (c) What are we? This question concerns what kind of thing a human person is The dentist is going to find a human organism in her chair tomorrow Am I identical to this organism? If not, how am I related to it: am I a part of it (e.g a brain), or is it a part of me, or am I a soul associated with it, or am I “constituted” by it (so that we are composed of the same particles without being identical), or are we related in some other way? Our primary focus in this chapter will be on one particular answer to question (a): personal identity over time holds by virtue of psychological continuity (e.g Lewis 1976; Noonan 2003; Nozick 1981; Parfit 1971, 1984; Perry 1972; Shoemaker 1970; 1984; Unger 1990) This focus is motivated in part by the fact that 126