What is necessary for a person to survive over time? Is it the continued existence of the living body? Or is it just the living brain? Or is it one’s psychology, which might persist even without one’s original brain in a computer or in an entirely new brain? How important are questions of personal identity for ethics and rationality? John and Ken are joined by Raymond Martin, Professor of Philosophy at Union College and co-author of The Rise and Fall of Soul and Self: An Intellectual History of Personal Identity.