“La répétition fixe la notion.” — Anonymous

I have been using mnemotechnic techniques for about a dozen years now (they are definitely the one thing I wish I would have known when I was a student with important exams coming up), but I recently became enamored with spaced repetition as an easy way to learn anything you want and remember it forever.

Imagine being able to trust the process and knowing that if you get started today, in six months you will know a complex piece of knowledge. That is the promise of spaced repetition.

Spaced repetition is an elaboration on the idea that practicing at regular intervals works significantly better (giving you better long-term recall for lower effort) than binge working a topic (the common experience of reviewing the night before an exam and having forgotten everything by the next day)¹.

To use it, you break the knowledge you want to remember into cards that are each a simple pass/fail task (i.e., “What is the French for butter?” / “Beurre”), add the cards to your implementation of choice (I will give you various options later in this guide), and it will ask you about them at regular intervals. If you fail, it will test you again soon. If you succeed, it will take a little more time before testing you again so that you don’t waste time reviewing easy cards too often².

So, what can I use it for? Turns out that you can apply it to remember a lot of very different things³:

• school work is the most obvious application; a lot of education (at least up to high school, but also a number of certifications that one might need to get as an adult) is still very much a test of one’s ability to recall given information.
• languages are the killer app of spaced repetition; it makes it trivial to increase your vocabulary and memorize the rules of grammar. It will not be enough to fully grasp a language, but it takes a lot of the work out of the task.
• multi-step processes this could be memorizing a piece of music, a full theater play, a complex hypnotic induction, etc. Anything that has too many steps to fit comfortably in one’s head.
• scripts there are great ways to remember scripts down to the exact word; spaced repetition becomes useful when you want to keep that knowledge in for the long term or if you want to remember a series of ideas rather than specific words (talks would be an example of something where you do not have to be word-exact).
• maintaining motor tasks is more tricky to find uses for⁴ but very much worth it when you can find a use case. Basically, any manual activity that you can practice as a bite-sized thing and classify as pass or fail would fall into this category.
• remembering everything some people just want to remember every movie or book they ever read. Adding a summary of it to your system is an easy way to do that if it is of interest to you (I personally just take notes).
• preserve existing knowledge any knowledge you currently have and fear you will forget with time is, pretty much by definition, perfect for spaced repetition.

I would insist on the fact that it is a system designed for forever learning. If you need to practice for next week’s exam, then binging is actually more likely to get you ready in time (!). But if you care about remembering the information next month or next year, then spaced repetition is the gold standard.

To me, the value in spaced repetition is that it makes time work for me and not against me. Before using it, any knowledge I would learn would be at risk of being lost if I did not practice it often enough⁵. Now, I know that every day gets me closer to having a good recall of the knowledge I placed in the system.

First and foremost, the key behind spaced repetition is regular work. The exact details of how you use it matter less than dedicating time to it every day, every other day, or every week. Someone using hastily written flashcards in a shoebox every day will get better results than someone using state-of-the-art algorithms and impeccable cards every month.

Spaced repetition is fairly easy (and fun!) to implement by yourself if you know some programming. As a corollary, you will find many free implementations of spaced repetition (there is no reason to pay for it⁶).

The classic one is Anki. It is pretty much the reference open source implementation by which all others are measured. You will find front ends for it on computers as well as phones but, I found that their barebone user interface is a big turn-off for me.

I am currently using Space, a free Android app. It is… fine. I like the user interface, and it works; that is all one needs.

If you like analogue solutions, then you can do with 5 boxes (or envelopes) and a bunch of flashcards with the Leitner System. It will be slightly less optimized from an algorithmic perspective, but it works.

Writing cards is a skill and you will get better at it with practice. I have found that a few key things are good to know when you are getting started:

First and foremost, you should write your own cards. The process of writing them is a great way to let your brain know that a piece of information is of interest to you and worth remembering; that alone will boost your recall.

At first, you might be tempted to turn wide topics into single cards; that will make your life significantly harder. Smaller, as easy and bite-sized as you can, cards are a lot easier to learn which compounds nicely: a single card will be a lot harder to learn than five cards covering each a fifth of the topic⁷. Break down your subject as much as you can!⁸

As you break down a topic, you will end up with a lot of easy cards and, naturally, immediately add all of them to the system. That can quickly overwhelm you (when the daily review gives you 30 things to review, it starts feeling like a very real effort). The solution for that is to take your time (after all, time is your friend here) and add one or two cards a day, no more.⁹

Finally, spaced repetition is there to help you remember things forever. I would thus recommend being picky with what you apply it to. Many things are not worth remembering forever and would only clutter your system. Focus on things you have always wanted to know and learn, things you know and don’t want to forget, or things you know for a fact you will need to know in the future.

Resources on the topic abound. If you want to give it a try, I would recommend giving the following a go:

• Nicky Case has a fantastic educational game introducing spaced repetition, it is a great way to understand what it is, how it works, and if it might be a fit for you.
• As usual, Gwern has a very good in depth article on the topic and the science behind it.
• Fernando Borretti has a great article on how to use the method effectively, giving you further tips on card writing.