If it is a new ship when the parts are all replaced and only then, would that mean that when it only had one part left to replace, it was still the old ship? If so this seems a little strange. If not, then when did it become the new ship? This particular problem is a version of what is known as the sorites paaradox ( from the Greek for "heap"): "How many grains of sand make a heap?"
How do we conceive the self?
Imagine Dara discovers that he was once someone else called Sean. Sean was a bad person who committed all sorts of crimes but an operation was performed on him to remove Sean's memories and to have them replaced with a new set of fictional memories of an entirely different kind of person: those of Dara. Dara is a good, law-abiding citizen.
- Who would you consider this person to be : Dara or Sean?
- And should Dara be held morally responsible for any crimes committed by Sean?