The Greek hero Theseus asks his crew to rebuild his travel-worn boat, and they replace it plank by plank. When the task is done, he ponders whether his restored boat is really the same boat as before, given that all the parts have been replaced. He further considers that if he were to ask his crew to build a new boat with the planks of the old one, two boats would both have a credible claim to being his old vessel. But which is the true original?
