Ship of Theseus

The ship of Theseus, also known as Theseus's paradox, or various variants, notably grandfather's axe and (in the UK) Trigger's Broom (based upon the BBC sitcom Only Fools and Horses) is a paradox that raises the question of whether an object which has had all its component parts replaced remains fundamentally the same object.

The paradox is most notably recorded by Plutarch in Life of Theseus from the late 1st century. Plutarch asked whether a ship which was restored by replacing all its wooden parts remained the same ship. The paradox had been discussed by more ancient philosophers such as Heraclitus, Socrates, and Plato prior to Plutarch's writings; and more recently by Thomas Hobbes and John Locke. This problem is "a model for the philosophers"; some say "it remained the same, some saying it did not remain the same".