The classical version assumes an unlimited supply of planks. Replace one, replace all, argue about it for two thousand years. The problem is stable because the replacements are equivalent.

The modern version: the planks are no longer manufactured. The mill closed. The species of oak is under quarantine. What is available is a laminate that outperforms the original in every measurable respect — stiffness, rot resistance, mass — and looks, at two metres, identical.

The ship is rebuilt from photographs of the ship. The photographs are better than the ship, because photographs are taken in good weather.

The rebuilt vessel is more seaworthy than the one that sailed. It is faster. It is a superior instance of the class. The class, however, was defined by the vessel, and the vessel is gone, so the class is now defined by its best member, which is a laminate copy of a photograph.

This is the ordinary condition of every institution you belong to.

Nobody asks whether it is the same ship. Everyone asks whether it is in spec.