The Second Language Acquisition Theory of Stephen Krashen

Stephen Krashen’s theories of second language acquisition throw many of the old language-learning theories on their head. 

Even though his hypotheses are widely used in American schools and have become an “educational standard” for learning second languages there, many approaches to language acquisition (including so-called “modern” approaches using language learning apps) still apply the older, grammar-translation methods.

Krashen said that language acquisition “does not require extensive use of conscious grammatical rules, and does not require tedious drill.” 

So, in a purely Krashen-inspired language learning environment, you won’t find flashcards or many grammar books. There may not even be a teacher. Instead, the focus is on creating an immersive learning environment.

Let’s find out more about Krashen, his theories, and a Krashen-inspired tool that can help you learn a foreign language from YouTube videos…

Who is Stephen Krashen?

Born in 1942, U.S. linguist Stephen Krashen is considered an expert in the fields of bilingual education, neurolinguistics, second language acquisition, and literacy.

He received a Ph.D. in Linguistics in 1972 and worked largely as a linguistics professor at the University of Southern California.

His book, Second Language Acquisition and Second Language Learning, published in 1988 was highly influential and won awards. 

Krashen’s theory of second language acquisition consists of five main hypotheses and these soon became the focus of his work.

A summary of Krashen’s five main hypotheses

If you summed up Krashen’s approach to second language acquisition, it would go something like this: language acquisition is driven by comprehensible language input that learners can understand, delivered in low-anxiety environments, and containing messages that students are interested in.

However, the insights go far beyond this. The five main pillars of Krashen’s hypothesis are the acquisition-learning hypothesis, the monitor hypothesis, the input hypothesis, the affective filter hypothesis, and the natural order hypothesis. 

Let’s take a closer look at each one.

1. The Acquisition-Learning Hypothesis

This hypothesis underpins Krashen’s second language acquisition theories and is well-established among linguists and language teachers. The theory states that there are two independent systems of second language performance: 

• The acquired system: the product of a subconscious process, similar to that which children undergo when they acquire their first language.
• The learned system: this requires instruction or meaningful interaction in the target language leading to natural communication in which speakers focus on communicating rather than the form of their communications.

Conscious learning and subconscious acquisition cannot exist at the same time. They are mutually exclusive. Krashen considers the acquired system as the most important whereas most traditional approaches treat the learned system as the priority.

2. The Monitor Hypothesis

The Monitor hypothesis explains the relationship between the acquisition and learning systems.

We already know that Krashen believes the former is far more important than the latter when acquiring a language.

The monitor hypothesis defines the influence of learning on the acquired language. The acquisition system initiates communications and provides fluency while the learning system acts in the “minor” role of monitor or editor of the communications, correcting mistakes and making it more polished and precise. 

It’s worth noting that the latter only comes into play when the learner has sufficient time available to think about correctness.

3. The Input Hypothesis

Krashen’s Input hypothesis is central to his theory of language acquisition. It states that second language learners must receive language input that is one step beyond their proficiency level so that it remains both comprehensible and challenging. 

He believes that speech emerges once the acquirer has built up enough comprehensible input.

The Input Hypothesis is only concerned with the more passive acquisition method of developing proficiency in a language—not active learning.

4. The Affective Filter Hypothesis

Krashen also notes that several variables play an important role in language acquisition: of these, motivation, self-confidence, self-image, and anxiety are key.

Comprehensible input is best delivered in a low-anxiety environment to motivated and self-confident students. The Affective Filter hypothesis states that a mental block or imaginary “filter” in learners’ minds can prevent input from having the desired learning effect.

Low-anxiety environments are best for learners as these tend to lower the affective filter rather than raise it. Conversely, low motivation, low self-esteem, and anxiety raise the affective filter and impede comprehensible input from achieving its target.

5. The Natural Order Hypothesis

The Natural Order hypothesis states that learners acquire the rules of language in a predictable order. It is probably the least-cited of all Krashen’s theories and is based on research from several studies from the 1970s.

For any given language, some grammatical structures tend to be acquired before others regardless of the age or background of the learner. Despite the findings from the 1970s studies, Krashen rejects grammatical sequencing for developing a language program syllabus.

Krashen’s approach to learning grammar

Krashen believes that the study of the structure of the language can have general educational benefits and recognizes that most language program syllabuses will include some elements of grammar.

However, he believes the benefits of learning grammar are greatly overplayed—and only come into play when the learner is already somewhat familiar with the language.

Krashen believes that the teaching of grammar can result in language acquisition (and proficiency) only if the students are interested in the topic and instruction is in the target language (native speaking instruction). The environment must also be conducive to language acquisition. Otherwise, highlighting the rules of grammar is unnecessary when teaching a language and learners should consider alternative ways of acquiring language.

For learners struggling to master the language they’re trying to learn, it could be due to the learning method you’ve adopted.

Apply Krashen’s language theories with video learning

Krashen’s theories of language acquisition do not force early production in the second language. Instead, students are encouraged to produce output only when they are “ready”. 

The focus is on input rather than output. Improvements in language proficiency come from comprehensible input delivered in low-anxiety environments rather than by forcing and correcting output.

Learning a language with video is one of the most effective ways to achieve this — especially for motivated learners who aspire to a high level of proficiency. With video, you’re in control of the topics that you learn from—and as long as the video holds your interest and is in the target language, you can use it to learn.

Our AI-powered language learning app can assist with this: inspired by the work of Krashen, it helps learners master a foreign language by watching subtitled YouTube videos. Learning is immersive, convenient, at your own pace, and motivational.

Learn from native speakers in context on YouTube using our free Chrome extension. Download it now for free!