If every part is replaced, is it still the same thing?
A 2,000-year-old puzzle about ships that turns out to be about you, your company and everything that changes over time.
1The puzzle
The hero Theseus sailed home to Athens, and the Athenians kept his ship as a monument. As its planks rotted, they replaced them one at a time with new timber. Replace the planks yourself and see if you can say when it stops being his ship.
The Ship of TheseusRebuilt from the original planks
Every plank is original. This is clearly Theseus’s ship.
Original timber New timber
2Take a stand
Every single plank has now been replaced. Is it still the Ship of Theseus?
There’s no right answer here. Pick the one closest to what you actually think. We’ll test it next.
3The push-back
A few situations designed to test your answer. After each one, you can hold your ground or shift. Watch where you end up.
4The map of answers
You’re not the first to wrestle with this. Tap a thinker to see their answer and the strongest case for it. Open at least two.
5Turn it on yourself
This question isn’t only about ships. Anything that changes gradually raises it: a company, a friendship, a country, a codebase, you. Take one of these.
Your answers stay in this browser. Nobody else sees them.
6Your question card
The Ship of Theseus
If every part is replaced, is it still the same thing?
When every part changes gradually, what keeps a thing the same thing: its material, its pattern, its history, or just its name?
The main answers
Roderick Chisholm: Strictly speaking, a thing can’t survive losing any of its parts.
Thomas Hobbes: Added the second-ship twist and argued the answer depends on which sense of “same” you mean.
Nāgasena: A “chariot” is just a convenient name for parts arranged together. So is a ship, and so is a self.
Derek Parfit: Identity isn’t what matters. What matters is the degree of connection and continuity.
Aristotle: A thing is defined by its form and function more than by its material.
John Locke: Living things stay the same through a continuous shared organisation, even as matter changes.
Where you stand
Your note
Notice this week
Notice something you call “the same” that has quietly been replaced: a team, an app, a habit, a street. Ask what you actually mean by “same”.