Spaced Repetition builds on the concept of Active Recall Testing, meaning that instead of reading something twenty times, you test yourself by answering questions you can only answer if you understand and remember the topic. Active Recall builds a sort of “muscle memory” for the brain. Every time you trace a path in your brain to a certain memory, tracing the path again becomes easier.

But blindly repeating recall testing ad nauseam isn’t very useful past a very low threshold. The brain builds memories by allowing them to settle and percolate your long term memory. This takes time. Most long term memories are built during the REM sleep phase.

Building strong memories that are easy to recall requires testing yourself daily, not repeating until you fall over from boredom. Once you’ve accessed a memory path, you are no longer retracing it by asking yourself the same question. The answer is already in your upper mind, and there’s no need to access the memory regions of the brain.

The “sweet spot” can be calculated according to a theory called the “Forgetting Curve”, which dictates that every time we recall something, the memory becomes slightly more permanent. Think of it like walking a path just when it is about to fade. Ideally, you want to find yourself having to stop and think about the answer for a few seconds. If it “pops” into your mind instantly, you’re testing too often. The mental process required to recall a memory that you are about to forget is incredibly powerful at converting short term memory into long term memory.

In order to make sure we’re retracing the same memory path every time we test ourselves, we need to make sure the memory we are trying to bring up is simple, and that the prompt is roughly the same. This way, we strengthen the existing prompt → answer path in our brains, instead of tracing new slight variations of the same path every time.

It would be obvious by now that we require tools to aid our testing. We need to formulate knowledge in a certain way, write it down in a way that allows us to challenge ourselves, and schedule reviews at the appropriate times. It is the latter of these that makes the system somewhat cumbersome to use; but this is a task perfect for a computer program to solve.

You’re mostly on your own when it comes to formulating knowledge, but the storage and scheduling of your notes is best handled by what is known as Spaced Repetition Software. There are a number of options in this field, some free, some not; the one that stands out from the rest is called Anki. Mastering Anki is something that takes time, but is immensely rewarding if you find that spaced repetition works well for you. The program is very flexible, and a read-through of the manual is very much recommended. I made myself an epub version of the manual, for easier reading.

In learning to formulate knowledge the right way for review, this article written by Dr Piotr Wozniak more than 10 years ago is a classic. It assumes the reader is a Supermemo user, but all of the concepts he touches are completely portable to any other system, including Anki.

Deconstructing textbook entries

When presented with the challenge of remembering lengthy definitions, as was I when studying for my driving permit and trying to remember different kinds of road entities, I’ve found that presenting myself with a condensed version of the definition, and asking myself to answer with the defined term, was infinitely more rewarding than being presented with a term and asking myself to recite its definition.

In this regard, I’ve found that recall implies recognition. If you are able to recall a word when prompted with its definition, you should also be able to remember the definition when presented with the word. This concept alone will save you oodles of review time, and make your reviews much more rewarding. Being presented with a word, and being asked to recite its definition is a dictionary case of tedium, especially if the definition is over a few words long.

There are concepts and knowledge fields where two-way prompts are useful and encouraged, but beware of overzealous repetition.

If there are key parts of the definition that I need to remember, I will create separate notes with pertinent questions.

Allow me to illustrate. When presented with the following entry in my textbook:

An automobile is a motorized vehicle designed to transport people and/or freight, with a maximum speed over 45km/h, and a cylinder capacity exceeding 50m³.

I will create the following notes:

Question: Motorized vehicle designed to transport people and/or freight. Answer: Automobile

Question: What is the maximum speed of an automobile? Answer: Over 45km/h.

Question: What is the cylinder capacity of an automobile? Answer: Over 50m³.

Question: What is an automobile designed to do? Answer: Transport people and/or freight.

As you can see, I’ve made sure that each important point is prompted for. I’ve also made sure each has its own note, so a leech doesn’t drag the entire item down. If I have trouble remembering the maximum speed, it should not affect the review scheduling of any of the other notes. That way, I can focus my reviews on the things that I have trouble remembering, instead of being swamped repeating things I remember just fine until I fall over.

Ask the right questions

Avoid yes/no type questions. They require little understanding and reasoning and are pure memorization. “Is Fact A true?” doesn’t teach you anything. Instead, ask “Why is Fact A true?”, and force yourself to recite your reasoning.

This will do two things. First, it forces you to understand the material you’re learning, and allows you to deconstruct it in a way that makes random reassembly easier; i.e.: it allows you to apply concepts to novel problems by rearranging the pieces.

Second, it will reveal to you where you are having trouble. Answering a yes/no question can be as much a matter of understanding as it can be one of luck. If you get lucky and don’t see a card again for 90 days, you’ve wasted a lot of time that you should have spent reviewing something you forgot months ago.

By making you think about the context and history of a concept (i.e.: how it came to be, why it is the way it is, and considering related facts) you provide your web of knowledge with additional connections. These connections are what make memories accessible.

Connect your notes

When you have ten thousand cards in Anki (and no, that’s not insane), it’s very easy for notes to become isolated islands of knowledge, that are only available to you with the right cue and nothing else. To avoid this, ask connected questions. For example, ask “how is A different from B”, or “what do A and B have in common”.

This relates to the previous section in that it connects your memories with more memories, which makes retrieval easier.

Beware the Easy button

Grading yourself properly in Anki takes a little practice, and is something I’ve thought about extensively. In the end, you have to use what works for you, and Anki allows for extensive customization of its scheduling mechanism, but it’s a subject worth touching briefly.

The way Anki works is that you have to grade yourself, instead of having the program figure out whether you were right or wrong. The program can also not tell whether something was hard or easy for you to remember. It does, however, adjust its scheduling based on difficulty.

When presented with a card, you can either fail yourself, or grade the difficulty “hard”, “good”, or “easy”.

“Hard” implies that while you were able to recall the required answer, it probably took you too long, or perhaps you got a little detail wrong that doesn’t warrant failing the card. Note that some people advocate failing yourself for even the slightest mistake.

“Good” is the default answer, and implies, quite simply, that you were able to recall the answer successfully after a few seconds of consideration. You will use this one most of the time.

“Easy” implies that the review scheduling was too short, because the answer was still in your recent memory, and you were able to recall it without the slightest delay. Anki will reschedule the card with a much greater delay. If you are too trigger happy with the “Easy” button, you may find yourself failing a lot of cards afterwards due to an interval much too long.

Failing or grading a card is a very subjective topic. As mentioned above, some people will advocate failing a card for the slightest of mistakes. Arguably, if your cards are dense enough, any “slightest mistake” will have you miss important information, and failing the card would be a good choice. Beware, however, of cards made up of more than one piece of information. Forgetting one detail but remembering the rest might be a sign you need to split it up into separate cards.

As far as “Hard” vs “Good” goes, I find that I hardly ever use the “Hard” button. My cards are very succinct, and forgetting something generally implies a failure. My memory is very fast, and I know that if I’m not able to recall something within 3-5 seconds, I probably won’t be able to recall it at all, no matter how long I mull over it. As such, the “Hard” button tends to be left unused, except for rare cases.

I know how to grade myself because I know how my mind and my memory work. This is simply due to a lot of practice. You should take your time and find what works for you, and establish a basic set of rules for grading. That way, the grading becomes a habit, and your mind is free to think about the things you’re studying instead of the difference between “Hard” and “Good”.

Do review often

One of the greatest things about Anki is the quick review pace. A single card doesn’t usually take more than 2-3 seconds to review, and most are faster. Whenever I find myself idle, be it waiting for public transportation, or for the fiancée to get dressed, I can pull out my smartphone and dish out a few dozen cards.

I’ve found that I can review hundreds of cards every day without a problem this way. If I had to sit down at the computer only to be faced with 300 cards, I’d probably just walk away annoyed.

Every morning, I’ll make myself some bulletproof coffee, and review while drinking it. It’s like a morning workout, but for the brain. I generally manage 100-120 cards easily during the time it takes me to drink my cup. I will then review here and there during the day, on the phone, and do the rest of my reviews in the evening, right before I add any new material.

My general workflow is to use a filtered deck that pulls any due cards from all other decks. This works very well for me, because I use Anki for a lot of different things, including Japanese, my driving permit material, little bits of computer knowledge, such as vim commands, tar commandline switches, and a lot of general things I want to remember, such as phone numbers and what not; but every single deck might only have half a dozen cards up for review on any given day, and I find that I review best when I get into a rhythm, which is broken by having to switch decks every 10 cards.

Most of the time, I just review “things to remember”, but I keep my decks tidy and organized, and all my cards properly tagged, in a way that allows me to focus my reviews when necessary. It’s definitely worth the time to keep things organized.

Don’t use shared decks.

With a few exceptions, shared decks are pretty useless. This is because Anki is the final step in the learning process. Reviewing cards can not replace proper learning.

Formulating knowledge properly can be hard, especially if you’re just starting out, but having someone else do it for you doesn’t solve the problem, and reviewing someone else’s cards doesn’t really help you learn.

Every note you create is a personal cue to a certain memory, born of your own learning process and your existing memories. When faced with new knowledge you want to remember, you don’t just blindly dump it into Anki. That would be a waste of time.

You read/watch/listen to the material once. If you find it useful and worth remembering, you will probably go over it again, but at a slower pace. I like to go over things at least three times before attempting to formulate facts, but that’s just me. If you have trouble understanding the subject, you might try to ask someone for help, look something up in a dictionary or on the internet. Once you fully understand the subject, you separate the interesting from the filler text. You digest this knowledge, and reword it to fit the way you think by connecting it with existing memories.

When you’re done processing the information, and you have points of information that you want to remember, it’s time to dump things into Anki, using your own clues and wording.

That’s why using someone else’s decks is pretty useless: you’re skipping the entire process and using someone else’s clues.

Now, there are times where shared decks are definitely useful. For example, I use a shared deck for kanji, in the RTK format. This is fine because the personalized part of each note is the mnemonic story that goes with a keyword/kanji pair. The keywords and the kanji do not change. By using a shared deck, I can skip typing out over three thousand kanji and all of their keywords, and go straight to figuring out my stories.

In cases like that, a shared deck can save you a lot of time, but you should not get used to finding shared decks for everything, and always prefer making your own.

Don’t skip the obvious

Anki is really good at getting the easy cards out of the way. After a few reviews, the intervals will be so big that you will only see the cards once in a blue moon. You will only be presented with them more often if you end up failing. This means that it’s very easy to make sure your basics are well covered, and allows you to build your notes on them, instead of having to provide a lot of context with each and every one.

An example, pulled from my driving license deck, is that the term “vehicle” has a very specific definition. I have a single note for this, which I haven’t seen in weeks, and isn’t scheduled for at least another month. I can confidently use this term in other notes, knowing that I know what the term means, because Anki will make sure I know it. And if I forget what a vehicle is, Anki will allow me to fail the card, and review it more often until it settles into memory.

Don’t be afraid to throw it all out

Getting things right in Anki can be hard, and takes a lot of practice. Even if you’re a demigod of formulating knowledge in a magical way that makes learning and reviewing so easy your grandma could learn quantum physics in a week, the best way to feed things to Anki isn’t always obvious.

For example, I started my driving license permit studying with a lot of cloze deletion cards. These are cards where you paste some text, and mark regions that will be deleted, one per card. Your task is to be presented with this text, with a missing piece, and fill in the blank. I thought this was the obvious way to study all those road entity definitions. I was wrong, and reviews were beyond tedious. I didn’t remember much. I deleted all of them.

I then made cards that would present to me the term and ask for its definition. As legal definitions tend to be really lengthy, this was just as tedious as the cloze cards, if not more so. Recall rate improved slightly.

I added a card template that flipped term and definition over, and I found that these cards were a lot easier to review, and also improved my performance in the term → definition cards. This was enlightening.

I separated term definitions into their own note type, which generated two cards: one for recall and one for recognition. I made a separate note type for regular questions, that did not generate an inverse card.

After some more time, I realized that the definition recognition cards were really tedious to review, and gnawed at my will to even start reviewing. I found that whenever I was faced with such a card, my concentration would vanish almost instantly. I deleted the recognition template from the note type, and started reviewing only with recall.

I found that my recognition rate did not drop at all. Whenever I encountered a term in some other note, I would immediately recall its definition. This made me feel like I had wasted my time with the recognition drills that were so tedious, and which I forced myself to do anyway, because I thought it was necessary.

During this entire process, I probably deleted all my cards at least 6 times, because I was simply not happy with the way I formulated the knowledge. Circulation law is dense, aseptic, and things that seem irrelevant will often turn out to be important. It took me a few tries to find a good way to formulate things in a way that made reviews pleasant and facts easy to remember. I’m glad I wasn’t afraid to throw things out the window when I wasn’t happy with them, because otherwise I’d be stuck reviewing terrible notes.

Dismiss the leeches

When you fail a card very often, it will be tagged as a “leech” by Anki, and suspended. By default, this threshold is 8 failures, but you can adjust that. When you fail a card that often, it is often a sign that you need to rethink the way you formulated the fact on that card, but it can also mean that it quite simply is not a fact that you find interesting, to the point where you refuse to remember it. I call these facts “natural leeches”.

For example, agricultural vehicle classification was one hell of a natural leech for me. Who the hell cares about the difference between a produce truck and a machinery truck?

Don’t be afraid of skipping these natural leeches, because they will drag your entire review session down, and just make you feel bad about not remembering them, eating away at your motivation. You quite simply do not need to remember everything. Getting 100% on a test is amazing, and you should pat yourself on the shoulder with a big ale, but it’s not necessary. Try hard, never give up, but learn to compromise when something threatens the overall wellbeing of your learning process.