There are some books that people read for fun. I’m currently rereading Ender’s Shadow, for example, and have no desire to take notes on it, given that it is a book of fiction that I’m reading for entertainment. But many books that people read they do not read for fun; they instead read those books to learn specific things. These are the cases where people should obviously take notes on what they read.

Think about a book that you read a year ago. Try to write a 1,000-word summary of the major points. What happened in chapter 3? It’s almost certain that, unless you’re Von Neumann, you can’t remember the specific points made in chapter 3 and certainly don’t have the ability to write a 1,000-word summary of the points.

This is pretty extraordinary amnesia. You spent maybe 10 hours reading a book, and you can’t write a 1,000-word summary of the major points without intentionally stretching them out. You read 300 pages, and it left a mental imprint of less than 5 pages worth of material. Maybe you spent an hour reading chapter 3, and you can’t remember what it was about—at all. Now, maybe there are some points that will resurface if someone references something related to them in conversation, but still, your retention is probably pretty limited.

About a year ago, I read Shelly Kagan’s book The Limits of Morality, and I took notes on it. Every time he made a point, I would type out a concise statement of that point in my notes). As a result, I can, at any time, rediscover a 5,000 or so word summary of every single major point made in an extremely dense and argument-filled book that I read about a year ago.

I read The Point of View of the Universe while not doing this. Now, I still remember a lot of the points made in The Point of View of the Universe, but I certainly do not have the same ability to instantly find every single point made that I do with The Limits of Morality.

This may seem like a very long and arduous task, but it’s really not. If one writes efficiently, even long books can be decently encapsulated in only a few thousand words. As Hanania has pointed out, books have lots of extra, unnecessary material. I read Desert Collapses recently, which is a very dense book, and my summary was only about 5,000 words. One additionally need not write down all the points, they can just write down only the points they’d like to recall. When I read The Geometry of Desert, for example, I didn’t take notes on various niche points that I didn’t care to remember.

And it’s not just books that one should write down. If one has a good idea, it’s quite useful to write it down. I’ve made enormous amounts of intellectual progress just because I write blog posts when I have ideas. This is helpful not only for recalling ideas if one later forgets about them—for they can just look at their writing—but also for remembering the ideas. When one writes something down and thinks about how to explain it, it’s much easier to retain it. I can recall, with some detail, almost all of the blog posts I’ve ever written, while I have great difficulty recalling various other ideas I’ve thought of that I did not turn into blog posts.

But suppose you don’t want to take notes. Maybe you’re one of the many people missing arms who reads this blog. It turns out that remembering things is sort of like a muscle—if you repeatedly try to remember things and do so successfully, that makes it easier to do so in the future. So if you want to remember things said in books you’ve read, try to remember them. After you read a chapter, think hard and try to remember the points made in the chapter. Then a few days after, see if you can still remember what was said. If you can’t, flit back through the chapter.

This technique works pretty well. Rather than being a passive consumer of information, actually thinking about the information after you learn it makes it easier to learn it. I did this when reading Desert Collapses, and as a result, I can, off the top of my head, give a summary of each of the chapters, as well as a decent summary of the arguments in each of the chapters. If your memory is worse and you think you’ll forget the major points by the end of the chapters, do it every ten pages or so.

The second technique for learning things is to use Anki. I swear I have not been sponsored by Anki; I’m an Anki evangelist because it has made my life dramatically better. It’s an evidence-based flashcard app, sort of like Quizlet. However, unlike Quizlet, it uses spaced repetition—after a person turns over a card, they’ll rank it based on how familiar they are with it. If the information is very unfamiliar, then it will come up again very soon, if they’re very familiar, it won’t come up again for days.

The problem with Quizlet is that when one turns over a card that they don’t remember, it will be a while before they see it, and by then they’ll have forgotten it. But with Anki, when it comes up again, you’ll have it much fresher in your mind, so if you really wrack your brain, you can usually think of what it is. Racking your brain to remember cards that your sort of, kind of remember turns out to be the best way to remember things long-term—it forces you to remember them over and over again. I used to use Quizlet to study for exams—when I started using Anki, the time it took to learn things was cut by around 75% and I learned them more thoroughly. Semester 1 of college, I got a 90% of the first exam, while semester 2 I got 100% on that exam—and I spent far less time studying.

If you don’t want to use Anki then just use regular flashcards. But when a word is unfamiliar, rather than putting it in the back, put it only about 10 cards back. That way, it’s much easier to remember things.

These techniques can be combined. If you want to learn the points made in a book, you can use Anki to make flashcards of the points in a book. I’m trying to learn about the history of philosophy, so I’m using flashcards to remember the pertinent details. Von Neumann apparently could remember everything he ever read, word for word. These techniques won’t allow one to do that, but you can remember all the important points you read in a book, and it only takes about twice as long as it would if you just read the book.

Much of non-fiction reading is not for pleasure, it is instead to try to retain information. And yet just reading books, absent notes, absent flashcards is a uniquely terrible way to retain things. If you just read something once, you won’t effectively retain the information. But it’s actually not hard to retain things; there are techniques to allow one to do so effectively. Most people just don’t do these things for no good reason. So don’t not do them for no good reason. Actually do them! Don’t just allow ideas to float in one ear and out the next—actually take steps to retain them.