There is an old problem, older than Plutarch but attributed to him, about a ship. The Athenians preserved the ship on which Theseus was said to have returned from Crete. As time went by the timbers rotted and were replaced, plank by plank, beam by beam until not a single piece of original wood remained. The ancients wondered if the ship, when it was completely repaired, was still the ship of Theseus, or if at some unmarked moment in the long process of replacement the ship had quietly become an entirely different ship, with the name of the old one. The puzzle has amused philosophers for two thousand years without an answer and for most of that time it was just that, a philosopher’s diversion with no stakes attached to the answer. There are stakes in modern company law, because a company is a Ship of Theseus which can be prosecuted and whether or not it is the same ship is going to answer for the crimes of the ship it used to be. In the language of the law the corporation is an artifici...