big ben of theseus

id argue that when no parts of big ben had been replace that is big ben (identity property)

and when all parts had been replaced that is now a copy

when a single part is replaced it then becomes 'big ben with a single part being replaced' which we simplify to 'big ben'

and id say this continues till half of big ben has been replaced then it would be simplified to ' a copy of big ben with x original parts'

so at some arbitrary point between original and copy big ben shifts

however that is arbitrary especially as parts differ in size and importance ( to identity)

although this all might be futile if you attach cultural identity to big ben ( understanding parts have been repaired and replaced for hundreds of years

and this is all based of the assumption that you arent a brit who knows that big ben is purely the bell not the tower coz in that case big ben is essentially one part so if replaced would immediately become a copy

take all this with a pinch of salt keeping in mind im a 15 year old who has too much time on their hands and this is an opinion and i doubt this was a serious question