Is My Past Self Really Me? The Ship of Theseus and Doraemon

I recently wrote a blog post about the Ship of Theseus, inspired by the Japanese practice of keeping a sauce going by repeatedly topping it up.

The Ship of Theseus is a famous thought experiment: if every part of an old ship is gradually replaced until none of the original parts remain, can it still be called the same ship?

A sauce replenished for a hundred years raises a similar question. Even if almost none of the ingredients from the day it was first made remain, we still think of it as “a hundred-year-old sauce.”

Then a thought occurred to me.

Are human beings any different?

Our bodies are constantly metabolizing. Cells and molecules are replaced. Compared with ten years ago, our ideas, jobs, and relationships may all be different.

Yet we regard the person we were ten years ago, the person we are today, and the person we will be ten years from now as a single “self.”

Are those selves really as unified as we assume?

Doraemon Has a Terrifying Story About This

While thinking about this question, I remembered an episode of Doraemon, the classic Japanese children’s manga about a robot cat from the future who lives with a schoolboy named Nobita.

Nobita dumps an enormous pile of homework on Doraemon, who comes up with a brilliant idea.

He will bring his future self back to help.

Doraemon uses the time machine to fetch a future version of himself and puts him to work on the homework. One is not enough, so he brings back more Doraemons from even further into the future.

Eventually, the homework is finished.

What a relief. At last, he can sleep.

But this is where the nightmare begins.

Just as Doraemon is about to fall asleep, a past version of himself arrives and wakes him up.

“Come help me with the homework.”

He goes back, helps, and returns.

He tries to sleep.

Another Doraemon from the recent past appears.

He has to help with the homework again.

The cycle repeats until Doraemon becomes severely sleep-deprived and gradually loses his mind.

The work he pushed onto his future self has returned, after a delay, for him to do.

For a children’s manga, it is remarkably merciless.

Your Future Self Is Almost a Stranger

What makes the story so interesting is that Doraemon treats his future self almost as if he were someone else.

Why not make him work? He is only my future self.

I get to relax now.

But as time passes, Doraemon himself becomes that “someone else.”

We do exactly the same thing.

We leave an unpleasant task until tomorrow. We promise to start exercising next month. We tell ourselves we will think about retirement someday.

In other words:

“Future me, you take care of it.”

I do not know what I will think ten years from now. My values and circumstances will probably have changed.

Even so, I bundle that person together with my present self because we are supposedly the same person.

The Same Is True of Your Past Self

The past works the same way.

Sometimes I read something I wrote years ago and wonder:

“Why did I write this?”

I look back at an old decision and think:

“Why did I not handle it differently?”

That is rather strange.

If the person who made those choices were completely identical to the person I am now, would their behavior feel so alien to me?

My body has changed. I know more. My values have changed, and so have my circumstances.

My past self resembles my present self very closely.

But we are not completely identical.

My future self is even harder to know.

Perhaps the Self Is Not a Single Unbroken Line

We usually imagine our lives as one continuous person:

past self → present self → future self

But perhaps these are substantially different beings.

From yesterday’s self to today’s, memories, a body, and social responsibilities are gradually passed forward.

The changes are so continuous that we feel as though the same self has existed all along.

The Ship of Theseus and the continuously replenished sauce work the same way.

Replace everything at once, and the result looks like something different.

Replace it piece by piece, and it appears to remain the same.

Perhaps human beings are no different.

Place the person I was ten years ago beside the person I am now, and the difference would be considerable.

But between us stand 3,650 days of selves, each changing only a little. That continuity makes them feel like one person.

Perhaps the feeling that “I have always been me” is an illusion created by the continuity of change.

My past self no longer exists.

My future self does not yet exist.

The only self that certainly exists is the one here now.

And yet the debts, mistakes, and extra weight created by my past self are transferred flawlessly to my present one.

Whether we are truly the same person may be philosophically questionable, but the bill never has any trouble verifying our identity.