This is quite an interesting case presented by my Minds and Machines professor.

A man named Theseus owns a relatively old boat and feels he should fix it up. Theseus hires a carpenter to remove one plank from the boat and replace that plank with a new plank immediately afterwards. The carpenter does this for every plank on the boat, removing and replacing each one at a time.

Once the carpenter has replaced every plank of the boat is the boat still Theseus' original boat or is it an entirely new boat? And if the carpenter were to construct another boat out of the planks that had originally been in Theseus' boat, would this second boat be Theseus' original boat or a new one?