December 2014

I've read Villehardouin's chronicle of the Fourth Crusade at least two times, maybe three.

And yet if I had to write down everything I remember from it, I doubt it would amount to much more than a page.

Multiply this times several hundred, and I get an uneasy feeling when I look at my bookshelves.

What use is it to read all these books if I remember so little from them?

I've read Villehardouin's chronicle of the Fourth Crusade two or three times, yet couldn't fill a page with what I remember. Multiply that across hundreds of books: what use is reading them?

I've reread Villehardouin's chronicle, yet could barely fill a page with what I remember — and that unease multiplies across a whole bookshelf.

A few months ago, as I was reading Constance Reid's excellent biography of Hilbert, I figured out if not the answer to this question, at least something that made me feel better about it.

She writes:

Hilbert had no patience with mathematical lectures which filled the students with facts but did not teach them how to frame a problem and solve it. He often used to tell them that "a perfect formulation of a problem is already half its solution."

That has always seemed to me an important point, and I was even more convinced of it after hearing it confirmed by Hilbert.

Reading Constance Reid's biography of Hilbert, I found something that made me feel better. Hilbert had no patience for lectures that taught facts but not how to frame a problem: "a perfect formulation of a problem is already half its solution."

Reading Constance Reid's biography of Hilbert gave me something that made me feel better about it, if not an answer.

But how had I come to believe in this idea in the first place?

A combination of my own experience and other things I'd read.

None of which I could at that moment remember!

And eventually I'd forget that Hilbert had confirmed it too.

But my increased belief in the importance of this idea would remain something I'd learned from this book, even after I'd forgotten I'd learned it.

Reading and experience train your model of the world.

And even if you forget the experience or what you read, its effect on your model of the world persists.

Your mind is like a compiled program you've lost the source of.

It works, but you don't know why.

But how had I come to believe it? From experience and reading I could no longer recall — yet the belief remained, even after I'd forgotten learning it.

Reading and experience train your model of the world, and even if you forget what you read, the effect on that model persists.

Your mind is like a compiled program you've lost the source of. It works, but you don't know why.

But I couldn't recall how I'd come to believe it. The belief stayed anyway: reading trains your model of the world, and that effect persists after you forget the source.

The place to look for what I learned from Villehardouin's chronicle is not what I remember from it, but my mental models of the crusades, Venice, medieval culture, siege warfare, and so on.

Which doesn't mean I couldn't have read more attentively, but at least the harvest of reading is not so miserably small as it might seem.

This is one of those things that seem obvious in retrospect.

But it was a surprise to me and presumably would be to anyone else who felt uneasy about (apparently) forgetting so much they'd read.

Realizing it does more than make you feel a little better about forgetting, though.

There are specific implications.

What I learned from Villehardouin isn't what I remember but my mental models of the crusades, Venice, siege warfare. The harvest isn't as small as it seems.

Obvious in retrospect, but it surprised me — and it does more than console you. There are implications.

So what reading taught me lives not in what I remember but in my mental models. Obvious in retrospect, but a surprise — and it has specific implications.

For example, reading and experience are usually "compiled" at the time they happen, using the state of your brain at that time.

The same book would get compiled differently at different points in your life.

Which means it is very much worth reading important books multiple times.

I always used to feel some misgivings about rereading books.

I unconsciously lumped reading together with work like carpentry, where having to do something again is a sign you did it wrong the first time.

Whereas now the phrase "already read" seems almost ill-formed.

Reading is "compiled" using your brain's state at the time, so the same book compiles differently at different points in your life. Important books are worth rereading.

I used to lump rereading with carpentry, where doing something twice means you botched it. Now "already read" seems almost ill-formed.

Reading is "compiled" using your brain's state at the time, so the same book compiles differently across your life — which makes important books worth rereading.

Intriguingly, this implication isn't limited to books.

Technology will increasingly make it possible to relive our experiences.

When people do that today it's usually to enjoy them again (e.g. when looking at pictures of a trip) or to find the origin of some bug in their compiled code (e.g. when Stephen Fry succeeded in remembering the childhood trauma that prevented him from singing).

But as technologies for recording and playing back your life improve, it may become common for people to relive experiences without any goal in mind, simply to learn from them again as one might when rereading a book.

Eventually we may be able not just to play back experiences but also to index and even edit them.

So although not knowing how you know things may seem part of being human, it may not be.

This isn't limited to books. Technology will increasingly let us relive experiences — today to enjoy them or to debug our compiled code, as when Stephen Fry recovered the trauma that stopped him singing.

But as replaying life improves, we may relive experiences simply to learn again, eventually indexing and even editing them. So not knowing how you know may not stay part of being human.

This isn't limited to books. As technology lets us replay experiences to learn again, not knowing how you know things may not stay part of being human.

Thanks to Sam Altman, Jessica Livingston, and Robert Morris for reading drafts of this.

Thanks to Sam Altman, Jessica Livingston, and Robert Morris.

Thanks to Sam Altman, Jessica Livingston, and Robert Morris for reading drafts.