Why Forgetting English Vocabulary is Actually Part of Learning It

That word you lost? It's coming back stronger. Here's why your brain needs to forget before it can truly remember.

You looked up that word last week. You understood it perfectly at the time. You even used it in a sentence. And now, sitting here today, you cannot remember what it means.

This is one of the most frustrating experiences in language learning. And it happens constantly. You read a word, understand it, feel like you’ve learned it, and then a few days later it’s gone. Vanished. As if you never encountered it at all.

The natural response to this is discouragement. Clearly you’re not learning properly. Clearly something is wrong with your memory. Clearly you need to study harder, drill more, make more flashcards, do something different to make these words stick.

But here is the truth, and it is one of the most liberating things you will ever hear as a language learner: forgetting is not the opposite of learning. Forgetting is part of learning. A necessary, productive, scientifically well-understood part of the process by which your brain turns new information into permanent knowledge.

You are not failing when you forget a word. Your brain is doing exactly what it is supposed to do.

The Forgetting Curve: What Ebbinghaus Discovered

The science of forgetting begins with Hermann Ebbinghaus, the German psychologist who conducted the first systematic studies of memory in the 1880s. His findings were striking and have been replicated countless times since.

Ebbinghaus discovered that after learning new information, we forget it rapidly at first and then more slowly over time. Within twenty minutes, roughly 40 percent of newly learned material is gone. Within a day, around 70 percent has been lost. Within a week, the vast majority has faded.

This sounds catastrophic. And if the story ended there, language learning really would be hopeless.

But Ebbinghaus discovered something else, something far more important: every time you re-encounter that information, the forgetting slows down. The memory becomes stronger and more durable with each cycle of forgetting and remembering. The first encounter might last a day. The second might last a week. The third might last a month. Eventually, after enough cycles, the memory becomes essentially permanent.

This is the forgetting curve, and it has a crucial implication for language learning. Forgetting is not the enemy of memory. It is the mechanism by which memory strengthens itself. Each time you forget a word and then encounter it again, your brain consolidates it more deeply than it was before. The forgetting is literally what makes the eventual remembering possible.

Why Your Brain Forgets on Purpose

This might seem counterintuitive. Why would the brain throw away information it just received? Isn’t that wasteful?

The answer lies in understanding what your brain is actually optimising for. And it is not optimising for remembering everything. It is optimising for remembering the right things.

Robert Bjork, a cognitive psychologist at UCLA whose research on memory and learning has been enormously influential, developed what he calls the New Theory of Disuse. The core idea is elegant and powerful: forgetting is not a failure of memory. It is a feature of memory. The brain uses forgetting as a way of filtering what matters from what doesn’t.

Here is the logic. Your brain is bombarded with an extraordinary amount of information every single day. If it stored all of it permanently and with equal accessibility, the system would become unmanageable. The information you need most frequently would be buried under mountains of irrelevant detail. Retrieval would be slow and unreliable.

So the brain uses a simple but effective heuristic: if a piece of information keeps coming back, it must be important. Store it more deeply. Make it more accessible. If it doesn’t come back, it probably isn’t needed. Let it fade.

This is why forgetting a word after one encounter is not a problem. It is your brain saying: I’m not sure this is important yet. Show it to me again and I’ll take it more seriously. Show it to me several more times and I’ll keep it permanently.

The Two Strengths of Memory

Bjork’s research introduces another concept that is directly relevant to language learning: the distinction between storage strength and retrieval strength.

Storage strength is how deeply embedded a piece of information is in your long-term memory. Once something has been stored with high storage strength, it doesn’t really go away. It is in there, somewhere, even if you can’t consciously access it.

Retrieval strength is how easily you can access that information right now. This is what fluctuates. A word you encountered yesterday has high retrieval strength. The same word a week later, unencountered since, has lower retrieval strength. It feels forgotten. But its storage strength may still be intact. The word is still in there. You just can’t reach it easily at this moment.

This is why you sometimes have the experience of encountering a word you thought you had completely forgotten and suddenly thinking: oh, I know this. I’ve seen this before. The storage was there. The retrieval had faded. The new encounter restores the retrieval strength and, crucially, increases the storage strength at the same time.

Every cycle of forgetting and re-encountering is building the storage strength higher while refreshing the retrieval strength. This is the mechanism by which vocabulary moves from fragile short-term knowledge to durable long-term knowledge. And it requires the forgetting step. Without the forgetting, the re-encountering doesn’t produce the same strengthening effect.

The Desirable Difficulty Principle

This leads to one of the most important and counterintuitive findings in memory research, and it comes from Bjork’s work as well.

He calls it the principle of desirable difficulties. The idea is this: learning conditions that make initial encoding feel harder actually produce stronger and more durable long-term retention. Conversely, conditions that make learning feel easy and smooth often produce weaker retention.

Applied to vocabulary: a word that you encounter, forget, encounter again, forget again, and encounter a third time is being learned under conditions of desirable difficulty. Each retrieval attempt, even the failed ones where you cannot quite remember the meaning, is strengthening the memory trace. The struggle to remember is itself a form of learning.

A word that you drill on a flashcard ten times in a row until you can recite the definition perfectly feels like it has been learned thoroughly. But the ease of that retrieval is misleading. Because there was no forgetting between the repetitions, there was no desirable difficulty, and the storage strength built up is surprisingly shallow. A week later, the word may be gone entirely.

This is one of the reasons why extensive reading is such a powerful vocabulary builder, and why flashcard drilling is so deceptively ineffective. When you read extensively, you encounter words at natural intervals, with gaps between encounters, with forgetting happening between each one. Each re-encounter is a retrieval event that benefits from the desirable difficulty of the gap. The learning is slower and less visible, but it is dramatically deeper.

How This Plays Out in Language Learning

Let’s trace a single word through the process to see how forgetting actually builds your vocabulary.

You are reading an article and you encounter the word “compelling.” You don’t know it. You look it up or infer from context that it means something like convincing or powerful. You understand the sentence and move on.

Three days later, the word is gone. You have forgotten it entirely. This feels like a failure but it is not. Your brain registered the word. It created a trace. The trace faded because one encounter was not enough to signal importance. But the trace exists, faintly, in storage.

A week later, you encounter “compelling” again in a different article. Something stirs. You have a vague sense of having seen it before, though you cannot quite remember the meaning. You look it up again or gather it from context. This second encounter strengthens the storage trace significantly, because the act of re-encountering something partially forgotten is exactly the kind of desirable difficulty that produces deep learning.

Two weeks later, you hear it in a podcast. This time you recognise it immediately. The meaning clicks without conscious effort. The storage strength is now high. The retrieval strength has been refreshed by a third encounter in a new context.

A month later, you use it in conversation. It comes out naturally, without planning, because it has moved from passive to active vocabulary through exactly this cycle of encounter, forgetting, re-encounter, and deepening.

At no point in this process did you sit down and deliberately memorise the word. At no point did you drill it. At no point did you beat yourself up for forgetting it. You simply encountered it enough times, across enough different contexts, with enough forgetting in between, that your brain did what brains do: it made the word permanent.

Sleep and Memory Consolidation

There is another dimension to the forgetting and remembering cycle that is worth understanding, because it reveals just how much of the work is happening outside of your conscious awareness.

Matthew Walker’s research on sleep and memory has shown that a significant proportion of memory consolidation happens during sleep. During the deep stages of non-REM sleep, the brain replays and reorganises the information it encountered during the day, strengthening important connections and pruning less important ones.

This means that the forgetting you experience between today and tomorrow is not simply decay. It is, in part, the result of an active consolidation process. Your brain, while you sleep, is deciding what to keep and what to let go. The words that were encountered in meaningful, engaging contexts are more likely to survive this nightly filtering. The words that were crammed without context are more likely to be pruned.

And here is the remarkable part: the words that survive the first night’s sleep and are then re-encountered have been through a genuine consolidation cycle. The storage strength has been tested and reinforced by the brain’s own internal filtering process. They are stronger for having been through the forgetting.

This is why sleeping on new vocabulary, rather than drilling it relentlessly in a single session, produces better long-term retention. The brain needs the cycle. It needs the time. It needs the forgetting in order to do the remembering properly.

What This Means for Your Emotional Relationship with Forgetting

Most of the anxiety that language learners feel about forgetting comes from a misunderstanding of what forgetting is.

If forgetting were permanent loss, permanent erasure of information that will never return, then yes, it would be something to worry about. Every word forgotten would be a word wasted. Every encounter that didn’t stick would be a failed investment of time and attention.

But that is not what forgetting is. Forgetting, in the context of language learning through extensive reading and listening, is temporary inaccessibility of information that your brain has registered but has not yet committed to permanent, easily retrievable storage. The information is not gone. It is just not yet prioritised. And every re-encounter signals to your brain that it should be prioritised more highly.

When you reframe forgetting this way, the entire emotional experience of language learning shifts. You stop feeling like a failure every time a word slips away. You stop feeling the urge to drill and cram and force words into your memory through brute repetition. You start to relax into the process, trusting that the words you need will come back, that each encounter is doing its quiet work, that the forgetting is not the enemy but the ally.

Why Extensive Reading is the Perfect Forgetting Machine

Here is something beautiful about learning vocabulary through extensive reading on a platform like LingQ.

When you read widely and consistently, you encounter the most common and most useful words frequently and the less common ones less frequently. This is not a design flaw. It is a perfectly calibrated natural system, as we have discussed in a previous post on reading as natural spaced repetition.

The common words, the ones you need most, cycle through your reading so often that the forgetting barely has time to take hold before the next encounter arrives. These words move to permanent storage relatively quickly.

The less common words cycle more slowly. You encounter them, forget them, encounter them again weeks later, forget them again, encounter them again months later. Each cycle builds the storage strength a little more. The learning is slower, but it matches the importance of the word. You are learning the most useful words first and the less useful ones later, exactly as it should be.

And at no point are you making this happen consciously. You are just reading things you enjoy. The natural frequency distribution of English vocabulary is handling the spacing for you. The forgetting is handling the strengthening for you. Your brain is handling the consolidation for you.

All you have to do is keep reading. The forgetting takes care of the rest.

LingQ tracks every word you encounter, every word you look up, and every word that moves from unknown to known, giving you a concrete picture of this process in action. Sign up here: lingq.com

Embracing the Cycle

Here is the mindset that the most successful language learners eventually arrive at, and it is worth stating as clearly as possible.

Forgetting is not something that happens to your learning. It is something that happens inside your learning. It is a necessary, productive, scientifically validated part of the process by which your brain converts new information into permanent knowledge. Without forgetting, there is no desirable difficulty. Without desirable difficulty, there is no deep storage. Without deep storage, there is no real vocabulary acquisition.

Every word you forget is a word your brain has registered and will recognise more quickly next time. Every re-encounter after forgetting is a strengthening event that builds the word deeper into your long-term memory. Every cycle of forget and re-encounter moves you closer to genuine, permanent, automatic knowledge.

You do not need to fight the forgetting. You do not need to prevent it. You do not need to feel bad about it.

You just need to keep reading. Keep listening. Keep encountering English in all its richness and variety. The words will come. They will go. And they will come back stronger every time.

Trust the Process. Trust the Forgetting.

Your brain knows what it is doing. It has been building memories this way for your entire life, in every domain, not just language. The cycling of forgetting and remembering is the fundamental mechanism by which all durable learning happens.

Give it the raw material. Give it real English, in meaningful contexts, consumed with genuine interest, across hundreds and thousands of hours. And then trust it to do the sorting, the filtering, the consolidating, and the permanent storing in its own time and in its own way.

The vocabulary will come. Not all at once. Not in a straight line. But inevitably, reliably, and permanently, built on a foundation of forgetting that was never the enemy you thought it was.

Ready to Put Your Vocabulary to Work?

All those words cycling through your memory, building and strengthening with every encounter, are waiting for their moment in conversation. When you are ready to let them out, book a trial lesson here.

And for the best way to keep the encounters coming, keep the forgetting productive, and keep your vocabulary growing through real, enjoyable English content: lingq.com

For learning English through TV shows and films with interactive subtitles, Lingopie turns your screen time into genuine acquisition.

Forget freely. Read widely. The words will find their way home.

✍🏼 Richard

Disclosure: Some links on this blog are affiliate links. I earn a small commission if you sign up, at no cost to you. I recommend these services because I genuinely believe in them.