Stephen Krashen is an expert in the linguistic field. He specializes in the theories of language acquisition and development. He has published more than 100 articles since 1980 and has delivered over 300 lectures across many renowned Universities in USA and Canada. According to Krashen, language acquisition requires “meaningful interaction with the target language.” Dr. Krashen theorized that there are 5 hypotheses for second language acquisition. All of these 5 hypotheses have been highly influential in the field of second language research and teaching.

The five hypotheses formulated by Krashen in his theory of language acquisition are as follows.

Acquisition-Learning Hypothesis

This hypothesis states that there is a difference between language learning and language acquisition. The learner acquired language unconsciously in language acquisition whereas, in language learning, the learner picks up the language through conscious discovery and by learning the grammatical rules and structures of the language.

Monitor Hypothesis

According to monitor hypotheses, the learner learns the grammar rules and functions of the language consciously rather than its meaning. It lays more emphasis on the correctness of the language. There are three standards required to use this hypothesis properly.

The acquired must know the language rules.
The acquirer must emphasize the exact form of the language.
The acquirer must review the language and apply its rules in a conversation.

Natural Order Hypothesis

This hypothesis believes that language learners learn grammatical structures universally and fixedly. This kind of learning has a sense of predictability which is akin to learning the first language.

Input Hypothesis

This hypothesis focuses more on the acquisition of the second language. It is concerned more with how the language is acquired instead of how it is learned. It believes that the learner develops the language naturally as they receive fun and interesting information.

Affective Filter Hypothesis

In this hypothesis, emotional factors can affect language acquisition. The learner is less likely to learn the language if the affective filter is higher. Hence, the learning environment must be stress-free and positive so that the learner can learn properly.

Stephen Krashen states

“Language acquisition does not require extensive use of conscious grammatical rules, and does not require tedious drill. Acquisition requires meaningful interaction in the target language – natural communication – in which speakers are concerned not with the form of their utterances but with the messages they are conveying and understanding.”

He further added,

“In the real world, conversations with sympathetic native speakers who are willing to help the acquirer understand are very helpful.”