Are you the same person you were ten years ago?

An ancient puzzle about what makes a thing itself.

Here is a puzzle that is more than two thousand years old.

A ship sails for years. Over time its planks rot and get replaced, one by one. Eventually not a single original plank remains.

Is it still the same ship?

Most people say yes. It changed gradually, it kept its shape and its name, so it stayed itself.

Now add a twist. Suppose someone gathered all the discarded planks and rebuilt the original ship from them.

Now there are two ships. Which one is the real one?

This is the Ship of Theseus, and people have argued about it since ancient Greece. The reason it will not die is that it is really a question about you.

Because you are doing the same thing the ship did.

Over the years, much of the physical material in your body is replaced. Most of the cells that make you up are not the ones you had a decade ago. You are, in a real sense, rebuilt from new planks.

And it is not only the body. Your beliefs have shifted. Your tastes, your opinions, the things that scare you and the things you want.

The person reading this is not made of the same stuff, or the same ideas, as the person you were at fifteen.

So in what sense are you the same person?

The unsettling answer is that there may be no fixed "you" sitting underneath it all. Just a pattern that holds its shape while everything inside it flows and gets swapped out.

This sounds like bad news. It is actually freeing.

If you are not a fixed thing, you are not stuck. The person you have been is not a sentence you have to keep serving.

The planks are always being replaced anyway. You get some say in what the new ones are made of.

No man ever steps in the same river twice.

Heraclitus.