I personally agree with Trigger that there's a legitimate sense in which he still has the same broom after 20 years. Though I also accept why somebody would say

I personally agree with Trigger that there's a legitimate sense in which he still has the same broom after 20 years. Though I also accept why somebody would say it's not the same broom. The problem for that person though is: at what point does it become a new broom? What is that fundamental (irreducible) part of the broom, that once changed, makes it a new broom?