Rich Comprehensible Input™: The Science of Language Learning

By Dr. Jeff McQuillan, Ph.D. in Applied Linguistics and Education, University of Southern California

Adults learn a second language in only one way: by listening to and reading things they can mostly understand. Researchers call this "comprehensible input." More than 40 years of studies have shown that we learn languages by getting large amounts of comprehensible input (Krashen, 1982).

What is comprehensible input?

Comprehensible input is language you hear or read and mostly understand. "Mostly" means enough to understand the message comfortably while still hearing or reading something you have not yet learned (Krashen, 1985).

Language gets into your brain through listening and reading, both of which are input. When you understand a message in English, your brain unconsciously picks up the words, the grammar, and the sounds of that message (the input). Your brain does this without any conscious, deliberate study.

Speaking and writing are output. Output is the result of the learning you get through input. This means that speaking and writing themselves do not cause language learning (Krashen, 1998). We learn languages only through input.

What is the difference between studying English and learning English?

Your brain has two kinds of language knowledge.

The first kind of language knowledge is knowing ABOUT a language. It includes what you may know about the rules of grammar, spelling, pronunciation, or other "facts" about a language. Knowledge about a language comes from conscious, deliberate studying. This "studied" language is by definition slow, because to use it you need time to think about those rules and how to apply them.

The second kind of knowledge comes from learning the language itself. This "learned" knowledge is an unconscious, fast, automatic system you use to actually understand and speak.

When you listen to a friend tell a story, you are not stopping to ask yourself, "Was that the past tense?" You just understand. That is your unconscious learning of the language being used.

The two types of knowledge are completely separate systems. Studied, conscious, "slow" knowledge does not become automatic, unconscious, "fast" knowledge (Krashen, 1982). You can know the rule for the third-person "s" perfectly and still not say it correctly when you speak.

When you use language in real life, your unconscious system does 95 to 99 percent of the work (Krashen, 1985). The real question for a learner is how to add to that unconscious system. The answer is to get comprehensible input.

Why do most learners stop at the intermediate level?

Fewer than one out of every four students who reach the intermediate level of a second language are able to become advanced speakers (McQuillan, 2019, using data from Nielson, 2011). Some learners call this the "intermediate plateau."

This plateau is not determined by a learner's age or by language learning ability. It is caused by not getting enough comprehensible input in English, by not listening to and reading language the learner can understand and that contains something new. Intermediate learners have heard enough English to understand a slow, careful speaker, but not enough to understand fast speech or to speak fluently.

Why can you understand English but not speak it?

Learners recognize many more words than they can actually use. Stuart Webb (2008) found the difference between recognizing words and using them becomes larger as words become less common.

Many of the words you think you "know," then, are really only half-learned. You can understand them when someone speaks slowly, but you cannot yet use them easily in speaking or understand them when English is spoken quickly.

How much input do you need?

You need to encounter a new word about 10 to 15 times in your listening and reading before you know it well enough to understand it reliably (Pellicer-Sánchez & Schmitt, 2010). Using the word in your own speech, however, often takes even many more encounters than that.

This is why the amount of comprehensible input you get in English matters more than any study technique. When you see a word once or twice, you will learn something about that word, but perhaps not enough to use it. When you see a word several times in different sentences, you are more likely to remember it and be able to use it later on.

Why is the intermediate plateau an input problem?

Not being able to understand fast speech and having trouble speaking are both a result of your brain not yet getting enough comprehensible input in English.

Research from the past 10 years shows that your productive vocabulary, the words you can actually use, strongly predicts your speaking fluency (Uchihara & Saito, 2019, and Tong, Hasim, & Abdul Halim, 2022). The way to increase productive vocabulary is to get more encounters with words in input you understand. Speaking "practice" will not help you, because speaking is output, and you need input (Krashen, 1998).

How does Rich Comprehensible Input™ work?

Rich Comprehensible Input™ is comprehensible input that is presented to you at the right level, what we call "i + 1 Leveling," and in the right amount.

First, the level is right. Lessons contain new language for you but are still understandable, using primarily the first 2,000 to 4,000 most common English word families, the exact words of daily conversation (Krashen, 1985).

Second, the explanations stay in English. Difficult words are explained with easy English words, in real sentences, with no translation (Krashen, 1982).

Third, the amount of input is large and the repetition is designed into the method. The most important conversational vocabulary is repeated across more than 1,800 lessons, which is how you get those multiple encounters (Pellicer-Sánchez & Schmitt, 2010).

The ESLPod Method explains the science behind the design of each lesson.

What should you stop doing?

Stop memorizing word lists, stop making grammar drills your main activity, and stop listening to English you cannot understand. The research says that all three waste time, which could be better spent on something that works: getting comprehensible input.

The data on commercial courses show just how bad most language training is. In one study of 150 adults using a popular language software program, only one person finished the 200-hour course (Nielson, 2011).

Where can you read the deeper science?

Each of these pages covers one part of the research in full, with the studies and the charts.

• Why do most English learners stop at the intermediate level? explains the plateau and how to get past it.
• Why can you understand English but not speak it? covers the receptive-productive gap.
• How many times do you need to hear a word to learn it? covers how vocabulary is actually learned.
• Why don't language apps and tutors make you fluent? reviews the popular methods against the evidence.
• The ESLPod Method explains what the science means for each lesson.

See every research article, grouped by topic.

~ Dr. Jeff McQuillan, Center for Educational Development, Los Angeles, California