A philosophy blog needs a philosophical puzzle or two to discuss. Better puzzles of course are welcome. In the meantime, how about Earl Conee's version of a classic?
The Ship of Theseus
Theseus has just bought himself a brand new wooden ship. He is a maintenance fanatic. Whenever some part of his ship gets a mark on it, he removes the part and replaces it with a new duplicate. Over many years, Theseus has eventually replaced every single original part with new wood. He is proud of how well he has kept up the condition of his ship.
Xanthippe buys used ship parts for refurbishing and resale. Theseus has been a source of high quality material. Xanthippe has bought from him each part of his ship as he replaced them. As it happens, Xanthippe has not sold any of them. She realizes that she now has the parts of a whole wooden ship, and they all have just minor cosmetic flaws. Xanthippe cleans off the marks on the wood and re-assembles the parts into a ship, placing them back in their exact original arrangement.
Does Theseus still own the ship that he purchased? If so, how does the ship that he purchased differ from the ship that Xanthippe now has? If not, when did Theseus stop owning the ship that he purchased?