The words you lose are not the long ones. They are the short common ones with several meanings each, met inside a sentence you had already understood without them, and never written down.
That last step is the one that decides everything, and it is the only step in the whole business that nobody puts in a schedule. Reviewing is scheduled. Reading is scheduled. Writing a word down in the twenty seconds after you met it is left to whether you happen to feel like it, which is why it does not happen.
Eight rules for making a word stay
- a word needs about seven encounters spread over time before it is usable, which is why a single study session never works.
- review just before you forget. Reviewing while it is still fresh is wasted effort; the struggle to recall is what fixes it.
- the first review is the same day, and the intervals then stretch: a day, three days, a week, a month.
- test yourself, do not reread. Rereading produces a strong feeling of knowing and almost no retention.
- learn phrases, not single words. A word stored with its partners comes back with them attached and is usable immediately.
- make the example yours. A sentence about a real person you know is remembered several times better than one from a book.
- write the word in a sentence about your own week, which is the practical form of that rule and takes ten seconds.
- recognition is not production. Being able to choose the right meaning from four options is a much weaker state than being able to say the word.
English loses half of its vocabulary faster than the other half
English carries two layers and they behave completely differently in memory. The Latin and Greek layer is long, spelled the way it is pronounced, and usually carries one meaning: constitute, derive, subsequent. The form itself is a hook, and for anyone whose first language shares those roots it is half learned before it is met.
The old Germanic core is the opposite. Spare, cope, afford, spot, reach, plain: short, unremarkable, and each carrying a fistful of unrelated senses. There is nothing in the shape of the word to attach anything to, and the meaning you looked up was one of eight. A month later the word is not half remembered, it is completely gone, and it feels new when you meet it again.
So the ones that fall out are the ones that looked easiest at the moment you met them. That is the asymmetry worth carrying away from this page, because it decides what you should be writing down.
Where it stops: the third time you look up the same word
Almost every learner has a set of words they have looked up three or four times across a year without ever noticing. Each lookup feels like a first encounter, because there is no memory of the previous one to contradict it, and the dictionary is fast enough that the cost of one lookup is too small to register. Add the lookups up and it is hours, spent on the same forty words.
Nothing detects this from the inside, which is what makes it a stall rather than an error. You are working, the sessions feel productive, and the same words keep arriving. It ends only when something outside your head keeps the record, and the record is the point rather than the reviewing that comes after it.
The one device that captures without asking you to
Vocabulary Builder on a Kindle is the only tool in ordinary use that closes this by default. Every word you tap while reading goes into a list, with the sentence it came from, whether or not you meant to keep it. It replaced writing words in the back of a notebook, which everybody starts and which fails because the interruption costs more than the lookup did.
Be exact about the price. It is free only in the sense that it is already on a device you may or may not own, it works on what you read on that device and nowhere else, and it is worth saying plainly that there is no equivalent for paper. What it gives you is the sentence alongside the word, and that context is most of what makes the entry survivable later.
Whatever collects them, the first review has to be the same day. The forgetting is steepest in the first hours, so a word captured on Tuesday and first reviewed on Saturday is being learned from scratch. After that first day the gaps can open quickly, and the schedule for it is reviewing a word exactly as you are about to lose it.
What it looks like when it goes wrong
The recognisable failure is a note that reads spare: extra, additional. It is accurate, it was the sense in the sentence you met, and it will not survive, because it has recorded a translation rather than a use. Can you spare ten minutes survives, and it survives because it is a thing you might have to say.
The second failure is copying all eight senses of a word at once in the belief that you are being thorough. Learning a set of closely related things together makes each of them harder, and you end with a word you can recognise and cannot deploy in any of its eight jobs. One sense, the one you actually met, is the whole entry.
Words whose form is the hook are covered in one root, and the nouns, verbs and adjectives around it, and the short Germanic verbs above are the raw material of get up, put off, run into: verbs a preposition rewrites, both under building the word count you need to say what you mean.
What this leaves open is what a captured word is worth on its own. An entry that holds a word and its meaning still says nothing about which words English will let it stand beside, and being wrong about that is audible in a way that a missing word is not: which words English puts together, and which it never does.