You're crossing the ocean on a wooden ship. One of the boards rots, so you replace it with another that you've stored on your hold. It is still the same ship? Most people will agree that it is. But what if, bit by bit, as you make your journey, your ships sustains more and more damage, so that by the time you reach your destination, you have substituted each piece with its counterpart and not a single piece remains unreplaced. Now is it the same ship? Why or why not? How much of a thing is its pattern and how much its physical material? I was fascinated by the question of wether and how long you could remain the same person after casting off part of your body or, for that matter, after casting part of your history, part of your personality, part of your life.