Spaced repetition (SRS/FSRS): remember Chinese vocabulary for good

In the late 19th century, German psychologist Hermann Ebbinghaus measured, on himself, how fast we forget new information. His finding, confirmed by many studies since: forgetting is fast at first, then slows down. Without review, much of what you've just learned vanishes within days.

That's exactly what every Chinese learner experiences: you learn 20 words on Monday, know them perfectly that evening… and by Thursday half of them are gone. It's not a memory problem: it's how the brain normally works, filtering out what seems unimportant.

The good news is the second finding: each successful review slows forgetting. After one review, the memory lasts longer; after the second, longer still, and so on. After a few well-timed reviews, a word can stay with you for months or even years.

Chinese is particularly affected: for every word you have to remember the character, the sound, the tone and the meaning. Without a method, it's a Sisyphean task. With spaced repetition, it's manageable.

Spaced repetition (SRS, spaced repetition system) rests on a simple idea: review each item just before you'd forget it.

• Reviewing too early = wasted time (you still knew it well, so your brain learns almost nothing).

• Reviewing too late = you've forgotten and must relearn.

• Reviewing at the right time, when the memory is starting to fade but you can still retrieve it with a little effort = maximum effect.

In practice, intervals get longer with each success. For example: 1 day, then 3 days, then 1 week, 3 weeks, 2 months, 6 months… If you fail, the interval shrinks and the word comes back sooner.

Result: your review time goes where it's useful, on fragile words, and none is wasted on words you've mastered. With 15-20 minutes a day, you can maintain several thousand words.

The second ingredient is active recall: instead of passively rereading a card, you try to retrieve the answer before seeing it. That retrieval effort is what strengthens memory most. Rereading your vocab list gives an illusion of mastery; testing yourself builds real mastery.

For decades, most flashcard software used variants of the SM-2 algorithm (created in the 1980s for SuperMemo): fixed rules that multiply the interval by a factor after each success.

FSRS (Free Spaced Repetition Scheduler) is a more recent open-source algorithm, adopted notably by Anki in 2023. Instead of fixed rules, it relies on a model of memory that estimates three quantities for each card:

• difficulty (D): how hard this item is for you;

• stability (S): how long the memory lasts before dropping below a given threshold;

• retrievability (R): the probability you'll remember the card today.

The algorithm schedules the next review for when your probability of recall drops to a target retention rate (often around 90%). Its parameters can be fitted to your review history.

Advantages over SM-2:

• fewer reviews for the same retention;

• better handling of delays (if you miss a few days, cards are rescheduled sensibly);

• intervals tailored to your memory.

Hanlu uses an FSRS-style scheduler for your reviews: you never have to wonder what to review, or when.

After each card, you rate how well you remembered it. FSRS-style systems usually use four buttons:

• Again: you didn't get it, or got it wrong. The card comes back very soon.

• Hard: you got it, but with a lot of effort or hesitation.

• Good: you got it after a moment's thought. This is the normal button, the one you should use most.

• Easy: instant answer, no effort at all.

Be honest. It's tempting to click "Good" when you "almost" got it. But the algorithm can only help you if your ratings reflect reality. Cheat now and in a month you'll have words you thought you knew.

What counts as "getting it"? For Chinese, set your criterion and stick to it. For example, for a "character → meaning and pronunciation" card: if you have the meaning but not the tone, that's "Hard" or "Again". The tone is part of the word!

Don't press "Easy" by reflex. It spaces the card out a lot. Keep it for truly obvious words.

Not all cards are equal. A few principles from research and learners' experience:

1. One card = one thing to remember. Don't put 5 different meanings on one card. If a word has two very different meanings, make two cards.

2. Work in both directions, but not at the same time.

• Recognition (character → meaning + sound): what you need for reading. Start here.

• Production (meaning → character/pinyin): what you need for speaking and writing. Harder, but essential.

3. Always with an example sentence. The word 意思 on its own is abstract; "这个字是什么意思?" (What does this character mean?) is memorable and useful.

4. Always with audio. Listen at every review and repeat aloud. You train your auditory memory and pronunciation at the same time.

5. Add mnemonics for stubborn words: breaking into radicals, a mental image, a funny story.

6. Don't add too many new cards. Each new card generates reviews for weeks. 10-20 new words a day is a sustainable pace for most people. Beyond that, the review pile explodes.

Here's a 30-45 minute routine that works for the vast majority of learners:

1. Reviews first (10-20 min). Open the Review section and clear all of today's due cards. This is the top priority: it protects everything you've already learned. Ideally do them in the morning or at a fixed time.

2. One new lesson (15-20 min). Read the dialogue, listen to it, study the grammar points, do the exercises. The lesson's new words automatically join your review pile.

3. Listening or reading (5-10 min). Replay a dialogue you've already studied, do some shadowing (repeating along with the audio), or read a text at your level.

Busy days: do at least your reviews, even 5 minutes. Keeping the chain unbroken matters more than duration.

If you've fallen behind (holiday, illness): don't panic and don't add new words until the pile is back to normal. Spread the catch-up over several days. An algorithm like FSRS handles delays well.

Track your progress: words mastered, daily streak, success rate. A success rate around 85-90% is ideal; if it's much lower, slow down on new cards.

SRS is the most effective tool for retaining. But on its own, it won't make you speak Chinese.

• It doesn't replace exposure to the language. Knowing 2,000 words on cards doesn't mean recognising them in fast conversation. You also need to listen and read a lot.

• It doesn't replace speaking practice. Cards train memory, not fluency. Speak, even alone, even with mistakes: describe your day aloud, repeat dialogues, find a language-exchange partner.

• It doesn't replace understanding. Memorising a structure without understanding it leads to wonky sentences. That's why Hanlu pairs reviews with grammar explanations and dialogues.

The winning formula: understand (lessons, explanations) → memorise (spaced repetition) → use (listening, reading, speaking). Spaced repetition is the engine in the middle, the one that makes what you learn stick.