Most philosophers writing about personal identity in recent years claim that what it takes for us to persist through time is a matter of psychology. In this groundbreaking new book, Eric Olson argues that such approaches face daunting problems, and he defends in their place a radically non-psychological account of personal identity. He defines human beings as biological organisms, and claims that no psychological relation is either sufficient or necessary for an organism to persist. Rejecting several famous thought experiments dealing with personal identity, he instead argues that one could...