Comprehensible Input: Krashen's Idea in Practice
Comprehensible input is language you can understand, in speech or writing, that is slightly above your current level. The linguist Stephen Krashen argued that this kind of input, not grammar drills, is what drives language acquisition. Reading books you enjoy, which he called free voluntary reading, is one of the easiest ways to get a lot of it.
What is comprehensible input?
Krashen developed his ideas from the late 1970s onward, most fully in Principles and Practice in Second Language Acquisition (1982) and The Input Hypothesis (1985). At the center is the Input Hypothesis: we acquire a language when we understand messages in it. In his view, studying rules helps us check and correct what we say, but the deeper knowledge that lets us speak and read naturally comes from understanding meaning.
He described the ideal input as i+1. "I" is what you already know; "+1" is a little more. If a text is entirely familiar, you learn nothing new. If it is far above you, you understand nothing and learn nothing either. The useful zone is in between.
He also described an affective filter: anxiety, boredom or low confidence can block input even when it is understandable. Relaxed, interested learners take in more.
Try it yourself: The Wonderful Wizard of Oz, with a translation of every phrase one tap away
What did Krashen say about free voluntary reading?
In The Power of Reading, first published in 1993, Krashen made a strong case for free voluntary reading (FVR): reading because you want to, with no book reports, no comprehension questions and no obligation to finish.
His argument was that a large share of vocabulary, spelling and grammar knowledge, in both first and second languages, comes from this kind of pleasure reading. Reading supplies far more words in context than any class can teach directly. It also keeps the affective filter low, because nobody is testing you.
What do critics say?
Krashen's ideas are influential but debated. A balanced view helps you use them well.
- i+1 is hard to measure. Nobody can say exactly what "+1" is for a given learner, so the hypothesis is difficult to test directly.
- Output matters too. Merrill Swain's output hypothesis argues that speaking and writing push learners to notice gaps they would miss when only listening or reading.
- Attention helps. Richard Schmidt's noticing hypothesis suggests that learners acquire more when they consciously notice forms in the input.
Many researchers today agree that large amounts of comprehensible input are essential, while also seeing a role for output, feedback and some focused study.
How do you get comprehensible input from reading?
Here is how Krashen's terms translate into practical choices:
| Krashen's idea | What it means in plain words | What to do |
|---|---|---|
| Comprehensible input | You understand the message | Pick texts where most words are familiar |
| i+1 | Slightly above your level | A few new words per page, not per line |
| Free voluntary reading | Reading for pleasure, by choice | Choose your own books and drop dull ones |
| Affective filter | Stress blocks learning | No tests, no pressure, short daily sessions |
Vocabulary research gives a useful number for "comprehensible." A study by Marcela Hu and Paul Nation (2000) found that comfortable reading without help needs about 98% of the running words to be familiar, and Batia Laufer's work treats about 95% as the minimum for adequate understanding.
A practical routine:
- Choose a book on a topic you care about and test a page from the middle.
- Read for 15–30 minutes a day, focused on the story rather than on every word.
- When a sentence blocks you, get just enough help to understand it and keep going.
- Listen to the text as well, so the same input also reaches you through your ears.
- Every few weeks, reread an early chapter. If it now feels easy, you have made real progress.
How to get comprehensible input in Lolang
What makes a text comprehensible is not only the text but also the support around it. A hard sentence becomes comprehensible input once you know what it means.
Lolang is a web app for reading English books phrase by phrase in the browser on a phone or computer, and it is free to read. You see the original one phrase at a time, a sentence or a short part of one. "Show translation" opens an AI translation into your language, "What does it mean?" uses AI to explain the phrase in context, and a synthesized voice can read the phrase aloud. Tap a word to open its dictionary card and save it to "My words" for spaced review. Lolang is not affiliated with Stephen Krashen or any of the other researchers mentioned here.
Books that suit many intermediate readers include The Wonderful Wizard of Oz, The Invisible Man and The War of the Worlds. You can start as a guest.
FAQ
What is an example of comprehensible input?
A short novel you can follow with only a few unknown words per page, or a podcast at your level where you understand the main points. Both give you meaningful language just above what you already know.
What does i+1 mean?
It is Krashen's shorthand for input slightly beyond your current level, where "i" is your present knowledge. In practice it means a text that is mostly familiar, with a few new words and structures.
Is comprehensible input enough to become fluent?
Input builds understanding and a feel for the language, but most learners also need speaking and writing practice. Many teachers treat input as the foundation rather than the whole method.
Is free voluntary reading the same as extensive reading?
They are very close. Extensive reading usually adds guidelines on level and quantity, while free voluntary reading stresses choice and pleasure above all.
Your own books work too
You can also upload your own EPUB, FB2 or TXT file. Lolang splits it into phrases with translation and a synthesized voice, just like the catalog books, and only you can see it. Meanwhile, the free catalog of classics keeps growing.