You meet a new word, look it up, understand it completely, maybe even write it down. A week later you see it again and it means nothing. Or worse, you know you learned it, and in the middle of a sentence it simply will not come.
This is not a sign of a bad memory. It is what memory does with anything it has met once, and it is predictable enough that it can be planned around.
Forgetting is fast, then slow
The first person to measure forgetting was Hermann Ebbinghaus, who in 1885 memorised lists of nonsense syllables and tested how much he could still save when relearning them later. His results became the forgetting curve: most of the loss comes early. About 20 minutes after learning, around 40% was already gone. After a day, about two thirds. After a month, the curve had flattened out, and most of what was left stayed.
Real words are easier than nonsense syllables, because they connect to things you already know. The shape still holds. A word you met once, yesterday, is already mostly gone, and a word you have met several times over several weeks is not going anywhere.
Five reasons a word does not stay
1. You met it once. A word needs several meetings before it sticks. Studies of learners reading put the figure at around ten encounters for a substantial gain (Webb, 2007). One look-up in a dictionary is one encounter.
2. You only ever recognised it. Re-reading a word with its meaning next to it feels like studying and does little. In a well-known experiment, students who tested themselves on word pairs remembered about 80% a week later, and those who re-studied them remembered about 36% (Karpicke and Roediger, 2008). If you forget words while speaking but recognise them when you read, this is usually why: you have practised recognising, not retrieving.
3. The reviews came at the wrong time. Reviewing a word five times in one evening does less than reviewing it five times over a month. Spreading reviews out is one of the most reliable findings about memory; a review of 317 experiments found that the longer you want to keep something, the wider the gaps between reviews should be (Cepeda and colleagues, 2006).
4. You learned it next to its twin. Lists grouped by meaning, like happy, glad, cheerful and content all on one page, feel logical and are harder to learn. Similar new words get confused with each other. Research on this goes back to Tinkham (1993), and it is why a vocabulary list sorted by topic can be slower going than a mixed one.
5. The word was too far above your level. A word used in a sentence you only half understand has nothing to attach to. Words from just above your current level stick far better than rare ones.
A schedule that works
The cure for all five is the same idea: meet the word again, on a widening schedule, and try to recall it each time before checking.
A simple version you can keep by hand:
| Review | When |
|---|---|
| First | The next day |
| Second | Two or three days later |
| Third | A week later |
| Fourth | Two weeks later |
| Fifth | A month later |
At each review, look at the word, try to remember what it means (or look at the meaning and try to remember the word), and only then check. A word you got wrong goes back to the start. A word you remember without effort a month later is yours.
The exact gaps do not matter much. The widening does.
Other things that help
- Learn the sentence, not just the word. Meticulous on its own is a definition. She was meticulous about checking every invoice is something you can picture and reuse.
- Say it aloud. Hearing yourself pronounce a word is another path into memory, and it makes the word easier to recall when you need to speak.
- Use it within a day. Writing a new word into a message, a note or a diary entry is a retrieval, and a demanding one.
- Fewer words, more often. Ten words reviewed properly beat fifty glanced at once.
- Sleep on it. Memories are consolidated during sleep. A short review before bed and another in the morning is a good pairing.
When you forget words while speaking
If the problem is words you know but cannot find mid-sentence, the fix is recall practice. Look at a meaning and produce the word, not the other way round. Describing your day aloud and noticing where you reach for a simpler word shows you exactly which words to practise.
What I am building for this
Keeping a review schedule by hand is the part most people drop after a week. I am building an iPhone app, VocabPeek, that keeps it for you on the Lock Screen and Home Screen. It shows one English word at a time and brings words you have met back after one, two, four, eight, 16 and 32 days, mixed in with new ones. A review widget asks you to pick a word’s meaning from three, so the widget asks as well as shows. Words you mark as known leave for good.
It is not on the App Store yet, and it has no release date.
Short answers
Why do I forget new words so quickly? Most forgetting happens in the first day after you meet something new. A word met once is mostly gone within a day; one reviewed several times over weeks stays.
How many times do you need to see a word to remember it? Around ten encounters, spread out over time, is a common estimate from research on learners.
What is the best way to memorise vocabulary? Review on widening gaps (a day, a few days, a week, two weeks, a month) and try to recall each word before checking its meaning.
Why can I understand a word but not use it? Recognising a word and recalling it are different skills. Practise going from the meaning to the word, and use new words in your own sentences.