Comprehensible output hypothesis

In the field of Second Language Acquisition, there are many theories about the most effective way for language learners to acquire new language forms. One theory of language acquisition is the Comprehensible Output Hypothesis.

Developed by Merrill Swain, the comprehensible output (CO) hypothesis states that learning takes place when a learner encounters a gap in his or her linguistic knowledge of the second language (L2). By noticing this gap, the learner becomes aware of it and may be able to modify his output so that he learns something new about the language. Although Swain does not claim that comprehensible output is solely responsible for all or even most language acquisition, she does claim that, under some conditions, CO facilitates second language learning in ways that differ from and enhance input due to the mental processes connected with the production of language. This hypothesis is closely related to the Noticing hypothesis. Swain defines three functions of output: 1. Noticing function: Learners encounter gaps between what they want to say and what they are able to say, and so they notice what they do not know or only know partially in this language. 2. Hypothesis-testing function: When a learner says something, there is always an at least tacit hypothesis underlying his or her utterance, e.g. about grammar. By uttering something, the learner tests this hypothesis and receives feedback from an interlocutor. This feedback enables reprocessing of the hypothesis if necessary. 3. Metalinguistic function: Learners reflect on the language they learn, and thereby the output enables them to control and internalize linguistic knowledge. In addition to second language acquisition context, comprehensible output has been found to be effective in elicitation of modified output in foreign language acquisition. Production of language for communication in a meaningful way is hypothesized to help its acquisition.

Stephen Krashen argues that the basic problem with all output hypotheses is that output is rare, and comprehensible output is even rarer. Even when the language acquirer does speak, they rarely make the types of adjustments that the CO hypothesis claims are useful and necessary to acquire new forms. Another difficulty with CO is that pushing students to speak in a second language may be uncomfortable for them, raising the affective filter and thus hampering acquisition. When asked which aspects of foreign language learning caused them the most anxiety, students placed speaking in the foreign language at the top of the list. Methods that are based on comprehensible output frequently put acquirers in this uncomfortable position.

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