(Previous post in this series: The Natural Order of Acquisition)

The next post in this series, The Affective Filter Hypothesis (#6/9) is found here.

Focus like a MANIAC

I: The Input Hypothesis

This is the big one

“Comprehensible input is the cause of language acquisition.”


This is the most influential of Krashen’s hypotheses—the one that has changed the way world languages are taught. It asserts that we develop language ability when we understand messages in the target language. Languages are not acquired by studying, by traditional practice, or by listening and repeating. Languages are acquired as we hear or read messages that we can understand in the language. In How Languages Are Learned (2013), Lightbown and Spada say that, “comprehensible input remains the foundation of all language acquisition.”

The term ‘comprehensible input’ (C.I.) means messages in the target language that the learner can understand. C.I. is the “Goldilocks” level of input—not too hard, not too easy. It is input at the student’s current level of acquisition and just slightly above it, what Krashen calls the “i + 1” level, where “i” is the level of acquisition of the student and “+1” is a wee bit above it. Input that is too simple (already acquired) or too complex (out of reach at the moment) is not useful for second language acquisition.

Even input that is perceived by the student as very simple can have value, as the brain needs time to sort out the complex rules of grammar. Rules that are imperceptible to the  conscious mind can be refined with seemingly simple input.

Comprehensible Input Can Be:

• Understanding messages in the language at your level, and just a bit above it. Krashen calls this i + 1. The “i” in this formula is the student’s current level of acquisition, plus just a little bit more.

The i + 2/3/4… levels would be language that is not understandable to the student for some reason, be it unknown vocabulary, grammar the student has not heard before, unfamiliar topics, or subjects that are familiar but too deep for the current language level of the student.

• Independent reading in the TL at the 95% or better comprehension level.

• Listening to and understanding almost everything said in the TL. This understanding can be with the aid of gestures, body language, context and pictures.

But, there is a problem… The idea of comprehensible input has become widespread in the last few years, which is a double-edged sword. It is being used so often in educational circles that the original meaning has become diluted by so many pouring their own meanings into it. Many seem to think it means teachers are using language that they (the teachers) understand, or that students get the general gist of. An alternate term that keeps the original meaning fresh is one coined by Terry Waltz: comprehended input. The input must be comprehended by the student. If what you say is not understood it is virtually worthless for acquisition.


• Discard listen and repeat. Remember that for acquisition there is little-to-no place for the traditional “Listen and Repeat” strategy. Listening with understanding is often enough. Students sometimes do enjoy “practicing” sounds, but this does not help them to acquire the language or help them to hear it.

• Limit forced output. Since language is acquired by input, there is little role for forced output above the level of acquisition. Give students tools to respond in the form of rejoinders. Allow students to respond but, in general, do not force them to speak until they are ready.

• Allow and encourage output–but do not force it. There is a balance. Students feel like they are part of the club when they can speak. They want to express themselves. So provide them with tools and set up situations where they can express themselves simply and often, just do not force spontaneous discourse when they are neither ready nor able. Rejoinders are one way to encourage output, awareness of levels of questioning is another.

• Be sure it is “Comprehended Input”  This is a genius term originated by Terry Waltz and it makes the meaning of what is valuable input clearer. The teacher speaking in the TL alone is not enough. Sometimes teachers think that if they are speaking the language slowly, clearly and accurately, it MUST be comprehensible input to the students. But students need to understand what is being said. Even if the teacher is speaking the target language perfectly, it does not count if students do not understand. Language only counts as helpful for acquisition when it is comprehended by the students.

Lack of understanding = It is not Comprehensible Input.

Only input that is comprehended by students counts for acquisition.

• Use clear language with interesting topics. Teacher and students have an equal part in the dance of acquisition: the teacher’s job is to speak clearly in the target language about interesting topics. The students’ job is to show you when you are not using language they can understand. If students do not demonstrate when they are understanding, you may not be doing your job and not even know it.

• Check often to be sure it is actually comprehensible. The language we speak in class must be comprehensible to all students, not just the top students that are responding all the time. The above average students may well be giving you a false reading on your degree of clarity.

Tell your students this often:

“My job is to give you clear, interesting language.

Your job is to let me know when I am not doing my job.”

They need to let me know when I am not being clear (speaking TL that they understand). If we are not checking in with students to be sure they understand, we may be busy, but not actually doing our jobs.

• Make sure all students understand. Discard the traditional practice of asking questions and plaintively waiting for the occasional hand to go up by the the boldest and brainiest. The Ferris Bueller model (‘Anyone? Anyone?’) was out of date and mocked in the movie 30 years ago. Don’t revive it.

Ask a variety of questions, and ask often.

Assign a student the task of counting how many questions you ask during the class period. Asking one question per minute of class is not too much.

• Use differentiated comprehension checks questions to be sure individual students understand at different levels. Know who your slower language processors are, who your medium language processors are, and who your faster processors are (this week). Ask them questions that are appropriate for their level. Throw each student the right pitch, the right level of question, for their level.

• Create a classroom culture where NOT understanding is OK. Avoid putting students in situations in class where they have only limited comprehension of the language—this can be extremely frustrating. Reward those that let you know when they do NOT understand. This is the opposite of a traditional classroom where students raise their hands to give an answer and show they know the answer.

The next post in this series, The Affective Filter Hypothesis (#6/9) is found here.


NOTE: This is a series on Stephen Krashen’s main hypotheses of language acquisition presented in a simple form. I teach these ideas in this same way to my high school students. We even have quizzes on each of the hypotheses. It helps students to know something about linguistics so that they understand WHY certain methods are being used in class—that the teacher is not just making up activities, that what is being done in the classroom has a basis in theory, research, and successful practice. I also want to prepare them to be able to identify best practices in language courses they may take later.
We use the acronym MANIAC to remember the hypotheses because a teacher needs to focus like a maniac in order not to be swayed by inertia in education and tradition in schools. And don’t worry about the “maniac” moniker, you’ll get maniacal energy from engaged and acquiring students once you learn how to put these hypotheses into action.