What is comprehensible input? Here's what language learners need to know

Comprehensible input is anything in your target language hat you can mostly understand. And research shows it's the key to language acquisition.

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The way we learn languages in school is wrong.

Decades of research show that becoming fluent in a new language requires comprehensible input, not the rote memorization and drills you’ll find in most textbooks.

The good news is that learning a language via comprehensible input is far more fun and far less boring than using traditional methods. And better yet — learning via input works great for busy or chaotic people who can’t make dedicated time to study.

I’m a huge fan of comprehensible input and it’s the core of how I learn languages today. I would never have been able to teach myself German to C1 level without it.

But what exactly is comprehensible input?

I talk a lot about input on this blog and on Twitter without ever fully explaining what it is. I wanted to finally change that.

In this post I explain the definition of comprehensible input and give some helpful tips on how to use it for language learning.

This post contains affiliate links. If you click on one of my links and make a purchase, I get a small commission at no extra cost to you. If you like what I do, using my links is a great way to say thanks!

Comprehensible input definition

Comprehensible input (CI) is anything in your target language that you can understand despite not getting every little detail.

There’s no universal consensus on how much you need to understand for input to be considered “comprehensible.” I often see numbers between 80% and 95% thrown around.

Personally, I define comprehensible input as any language that I can understand well enough to stay interested and engaged, even if I don’t understand everything. In my experience, “comprehensible” for me can mean anywhere from 20-100% understanding depending on what I’m watching, reading, or listening to.

Being able to stay engaged is critical — and although it’s often overlooked, it’s actually been part of the theory around comprehensible input and language learning from the beginning.

Comprehensible input (CI) is anything in your target language that you can understand despite not getting every little detail.

Optimal input

All input is not created equal. To work best, input needs to be:

  • Comprehensible — input is best when you understand it. But you don’t need to get all of it, smatterings of “noise” you don’t understand are ok.
  • Compelling — good input holds your interest. It needs to be something you enjoy enough to want to pay attention to.
  • Rich — good input contributes to the meaning or flow of a story or text. Stand-alone sentences are not rich input. Song texts are meh. A sentence within a book or story is great.
  • Abundant — good input is easy to get ahold of so you can encounter it over and over without much effort.

These four criteria come from The Optimal Input Hypothesis: Not All Comprehensible Input is of Equal Value" by Benito Mason and Stephen Krashen. But they also square with my own experience learning German.

The input that worked best for me was always something I could understand, something I enjoyed, something with lots of rich context, and something easy to get my hands on. For me, podcasts nearly always fit the bill. Succeeding with input will mean finding what feels most “optimal” for you.

Comprehensible input examples

One great thing about learning with input is that it doesn’t have to be expensive or complicated. Anything in your target language that you understand well enough to stay engaged in is comprehensible input. And that means you can find it pretty much everywhere online.

There are three types of input: audio, audio-visual, and text:

  • Audio: podcasts, audiobooks, telephone conversations
  • Audio-visual: TV series, movies, YouTube, in-person conversations, video calls
  • Text: books, articles, graded readers, social media, text conversations

Both content intended for native speakers and resources designed for learners can be comprehensible input, but don’t get too cozy with beginner content. It is intimidating to make the jump to the real stuff, but it’s an important. It will greatly deepen your connection to and interest in the culture(s) associated with the language you’re learning and expand the landscape of (interesting! compelling!) input you can consume immensely.

If you want to get started with input but need a bit of guidance, I put together a free cheat sheet with 11 tips to help beginners start learning a language via comprehensible input. This is the advice I gave my mom when she started learning German!

Unfortunately, a lot of foreign-language content online is geographically restricted. This can make finding comprehensible input hard. Using a VPN (Virtual Private Network) is an easy way to securely access foreign language content for input if you don’t live in the “right” country.

You can get 81% off Surfshark VPN using my link. Surfshark is my pick for language learners because it is great for streaming, works seamlessly across multiple devices, and stands out for its international focus — you can use it in 16 languages and there are servers in 100 countries, including multiple options in Africa and South America.

I really think a VPN is one of the few things you can pay for that can truly make a difference in learning a language via comprehensible input… unlike textbooks!

Note: Using a VPN to get around location restrictions can be against the terms of service of streaming sites. I’m not encouraging you to break the rules!

Is comprehensible input the same thing as immersion?

Though often used interchangeably, comprehensible input is not the same thing as immersion.

Immersion is an activity or a method for language learning. Immersion means living in an environment where you’re constantly surrounded by your target language and learning through your natural exposure to it.

We often think of immersion as living in a country where your target language is spoken. But some language learners also create or take advantage of immersion environments in their home countries, too. This can be as simple as switching over all your devices and media consumption to a new language or as serious as attending an immersion school as a child or signing up for an immersion camp or program. Switching my media diet to German was pretty much all it took to ace the B2 Goethe exam within 2 years of starting to learn German.

Comprehensible input isn’t a technique or learning method. It’s simply material in your target language that you can mostly but not entirely understand.

Of course, when you immerse, you get a lot of comprehensible input. That’s probably why immersion works so well — there are few better ways to rack up hours of comprehensible input consumption in a short amount of time.

But ultimately, immersion is just one of many ways to incorporate comprehensible input into a language learning strategy.

You might be used to different definitions of comprehensible input and immersion. I know, for instance, that Refold.la, which outlines a structured input-based learning method, defines these terms differently.

Settling on a definition is tricky, especially since the term “comprehensible input,” while popular among language learners, isn’t used much by modern second-language acquisition researchers. However, the core concepts associated with comprehensible input live on (and thrive) under other names — focus on meaning vs focus on form, implicit vs explicit learning, etc.

I base my definitions of comprehensible input and immersion on:

  • Stephen Krashen’s writings and research
  • Contemporary scholarly works — especially this paper
  • The usage of these terms “in the wild” in the language learning community

The science of comprehensible input

When I say that comprehensible input is the key to language acquisition, this not something I thought up myself. There’s a huge body of research on input and language learning — my own personal experiences just happen to be consistent with it.

This topic really deserves its own post, so just think of this as a crash-course meant to get you familiar with where the idea of comprehensible input comes from and why we know it works.

Stephen Krashen and Monitor Theory

The idea of “comprehensible input” is often accredited to linguist Stephen Krashen. In the 1970s and 1980s, he developed five hypotheses now collectively known as “Monitor Theory,” which outline how he believed comprehensible input lead to language acquisition.

The five hypotheses are:

  • The Acquisition-Learning hypothesis: Acquisition and learning are distinct. Acquisition is subconscious, learning is conscious. Acquisition is more important for building fluency than learning.
  • The Monitor hypothesis: Acquisition builds our ability to produce and understand language, learning trains the “Monitor” — our ability to notice and correct mistakes, which can only operate in unlimited time settings like essay writing.
  • The Input hypothesis: Language acquisition occurs when learners receive input that they mostly but not entirely understand. If “n” is what the learner has already acquired, comprehensible input is “n+1”
  • The Affective Filter hypothesis: Having a bad attitude or low self esteem gets in the way of language acquisition. This bad attitude is the “affective filter.”
  • The Natural Order hypothesis: Grammatical features of a language are acquired in a natural order that can’t be overwritten by learning and is independent of the learner’s L1.

Although Monitor Theory was widely criticized by second-language acquisition researchers for not being scientific enough, most of Krashen’s core ideas — especially the acquisition-learning hypothesis, input hypothesis, and natural order hypothesis — have been supported by subsequent research.

Krashen is undoubtedly the person responsible for popularizing the idea of input and crystallizing many of the most important ideas about it, but others were thinking about input before him too. Bialystock made a distinction between implicit and explicit learning in 1972, for instance.

Language acquisition vs language learning

There’s not room in this post to get into every component of Monitor Theory, but the most important one to understand regarding comprehensible input is the difference between language acquisition and language learning.

According to Krashen (and others), learning about a language is not the same as acquiring one. A language is not just another academic subject like history or chemistry. The brain has a special dedicated “language circuit” thought to be universal to all languages and which — critically — is separate from the areas of the brain involved in the kinds of recall tasks that traditional learning usually involves. Using language is an ability innate to all humans. Memorizing the year that William the Conquerer invaded England is not.

It’s not clear if the explicit knowledge we gain from learning about languages actually translates into the implicit knowledge that we build as we acquire them.

Language acquisition is not like traditional learning. It is the unconscious process by which your brain builds up a working mental map of a new language that can be used flexibly — and unconsciously — to understand and communicate. And the only way to build up that map is to receive lots and lots of comprehensible input.

When you understand material in your new language (i.e., when you receive comprehensible input), your brain uses that input to build or refine its model of the language. You further acquire the language.

And while research has shown that input alone is sufficient for language acquisition, the jury is still out as to whether the kinds of formal studying you’re used to from traditional language classes (i.e., “focus on form”) can actually help the acquisition process along at all.

In other words, it’s not clear if the explicit knowledge we gain from learning about languages actually translates into the implicit knowledge that we build as we acquire them.

So go ahead memorize verb charts all you want, but your brain would probably prefer if you heard that verb in its various forms in context a few thousand times and let it put two-and-two together on its own.

Where to learn more

If you want to dig into the research on comprehensible input, there are a few great places to start:

Pablo from the Dreaming Spanish YouTube channel also does a great job explaining input and some of the research behind it in this video. It’s in Spanish, but there are English subtitles.


Comprehensible input strategies for language learning

There are countless ways to incorporate comprehensible input into whatever language learning routine — or non-routine — works best for you.

This section outlines a few tips for learning with comprehensible input and provides recommendations for resources that can help you learn faster (and less painfully).

If you’re curious how I use input, you can read my story of how I learned German and how I aced the B2 Goethe exam mostly without “studying." I also wrote up a free tips sheet to help you get started with input if you’re feeling stuck.

Switch your media diet to your target language

Your progress with comprehensible input depends on two variables: the quality of the input (see the Optimal Input hypothesis above) and the volume of the input.

So switch over as much of your media diet to your target language as possible. Watch dubs of your favorite shows if necessary. Listen to music in your target language. Read newspapers in your target language. Whatever media you like in your native language, find its counterparts in your target language.

Refold.la offers a very detailed roadmap for learning a language to fluency through immersion in comprehensible media. They’re a great resource — though I think they emphasize video input far too much and downplay the importance of audio. Maybe video is more comprehensible since there’s visual context. But most working adults just do not have time to watch hours of video every day, whereas layering a podcast or audiobook over chores or a commute is entirely within reach.

Video

Traditional streaming services like Netflix and Prime Video (30 day free trial) might be enough for you, but there are also great resources specifically for language learners, too:

Lingopie is essentially Netflix for language learners, with built-in features for making and reviewing flashcards as you watch TV in your target language. Its catalogue consists exclusively of “authentic” (i.e., made originally in the language) content and leans towards shorter films and episodes.

Plugins like Toucan and Language Reactor can also enhance your language-learning experience when consuming media online.

Don’t underestimate YouTube either. There are great channels aimed at learners and tons of authentic content to explore. German science YouTube channels were key to my early fascination with — and progress in — German!

Audio

Do not overlook podcasts and audiobooks! They’re incredibly helpful, and podcasts, at least, are free.

For beginners, there are even “comprehensible” podcasts available in many languages. These podcasts use simplified language but are 100% (or almost 100%) in your target language.

Once you’re more confident, listen to podcasts made for native speakers about topics you enjoy. Unscripted conversational or interview podcasts are a great way to hear natural speech. It might be hard to force your exchange partner to chat with you for hours every day, but you can binge conversational podcasts all you want.

Don’t overlook audiobooks, though. Audible is how I listened to most of the German audiobooks I’ve enjoyed, but libraries also offer them these days. Listening along to Harry Potter as I read was a great help. And for language like German for which the written language is quite different from the spoken language, it’s important to get plenty of exposure to writing. Audiobooks makes it much easier to make time for “reading.”

Text

There’s a ton of research showing that reading is good for you, so try to read. Reading helped me immensely while learning German and is the main thrust to my efforts to creep towards properly effortless fluency.

Graded readers are also a fantastic resource, especially for beginners. I personally benefitted a lot from Olly Richard’s graded readers. His Short Stories in German for Beginners was my very first book in German, and the Italian version was my first book in Italian, too!

But don’t stick to graded readers forever! Start reading real books, and try before you “feel ready.” I started with the translations of Harry Potter since I knew the story well and could enjoy bumbling along without getting every last word thanks to that context.

Magazines, newspapers, blogs, and social media — and basically the entire internet — are also great places to find things to read in your target language. Read what you enjoy reading!

I write a free newsletter for German learners recommending great new German media for comprehensible input learning every week.

Want in? You can sign up here:

Use audio to fill “dead time” with input

This is my single best tip for learning with input: use audio to fill dead time.

You can’t cook, commute, or do chores while doing flashcards or slumped over a textbook. But you can listen to a podcast or audiobook.

If you want to rack up enough hours of input to make good progress, you need audio. This is doubly true if you live with other people who don’t want to watch TV in a foreign language all the time. There’s a reason I consider my bluetooth headphones to be my single most important piece of language learning “equipment.”

It’s a joke but it’s also not really a joke. I’m really hopeless without audio.

Re-watch, re-read, and re-listen to your favorites

If you’re a beginner, this tip will make a world of difference.

Media you’re already familiar with is more comprehensible. So use language learning as a good excuse to return to all your old favorites — translated into your target language, of course.

There’s a reason I’ve watched The Dragon Prince on Netflix in English, German, Danish, Spanish, and Italian at this point. There’s a reason my first real novel in German was _Harry Potter und der Stein der Weisen. _Familiarity boosts comprehensibility and often also makes input more compelling. We humans are creatures of habit. We like our favorite things.

Especially at the beginning, you can get away with consuming input that’s far beyond your “real” level by re-watching, re-reading, and re-listening to things you know well. So go watch Avatar: The Last Airbender in German or Portuguese or whatever.

Be choosy about language apps

Some language learning apps are built around comprehensible input to one degree or another. Especially as a beginner — that is, before you can really enjoy consuming media in your target language — apps like this can be a useful boost.

What you’re looking for in a language app is language in context. Instead of memorizing words in isolation, apps built with CI in mind show you new words in sentences (at the very least) or full stories (which is better).

Here are some recommendations:

Get input from tutors and crosstalk

Finally, tutors and exchange partners can also be great sources of comprehensible input — if they’re conscious about it.

Remember, for input to work it needs to be comprehensible, compelling, and expose you to new things (n+1). Talking to someone is pretty compelling, so speech works well as input. But make sure your conversation partner keeps their speech comprehensible and that you make sure to talk about new things once and a while.

I found my German and Italian tutors through iTalki, which makes it easy to find affordable online tutors for pretty much any language. I’ve also used Tandem and the (admittedly old-school) MyLanguageExchange.com for exchange.

If you do exchange, consider doing crosstalk. Crosstalk is when you speak your native language and your partner speaks theirs. It works surprisingly well and doubles the amount of time you get input during exchange. I really can’t praise crosstalk enough, it works great. I’ve done it for Italian and Spanish now and it has been super helpful.

Conclusion

Long story short, comprehensible input is material in your target language that you mostly but not necessarily entirely, understand. It feeds your brain’s language acquisition system which is necessary (and probably sufficient on its own) to learn a language well. And you do not need fancy tools to learn via comprehensible input — TV, podcasts, and books will get you far, though there are great resources out there for learners, too.

All you need to do to learn with input is to find media in your target language that you like enough to spend hundreds of hours listening to, watching, and reading.

And I mean hundreds, if not thousands of hours.

For me, that way was my mom’s Netflix account, Spotify, YouTube, Audible, a library card, Duolingo (and then Speakly, and then Glossika), and a few graded readers.

What was — or will be — yours?