Comprehensible Output

Stephen Krashen
System 26: 175-182, 1998

The comprehensible output (CO) hypothesis states that we acquire language when we attempt to transmit a message but fail and have to try again. Eventually, we arrive at the correct form of our utterance, our conversational partner finally understands, and we acquire the new form we have produced.

The originator of the comprehensible output hypothesis, Merrill Swain (Swain, 1985), does not claim that CO is responsible for all or even most of our language competence. Rather, the claim is that "sometimes, under some conditions, output facilitates second language learning in ways that are different form, or enhance, those of input" (Swain and Lapkin, 1995, p. 371). A look at the data, however, shows that even this weak claim is hard to support.

THE SCARCITY ARGUMENT

A problem all output hypotheses have is that output is surprisingly rare (Krashen, 1994). In the case of CO, the problem is especially severe.

A recent confirmation of the scarcity of output is Ellis, Tanaka, and Yamazaki (1994), who examined vocabulary acquisition under three conditions, tasks in which EFL students heard (1) "premodified" input (input recorded from a task performed with a native speaker and non-native speaker who could request clarification), (2) interactionally modified input (the non-native students could interact with the native speaker), or (3) unmodified input (input recorded from a native speaker doing the task with another native speaker). Of interest to us here is the finding that "of the 42 learners in the IM (interactionally modified) group, only seven engaged in meaning negotiation. The others simply listened" (p. 211).

Even when acquirers do talk, they do not often make the kind of adjustments the CO hypothesis claims are useful in acquiring new forms.

Pica (1988) concluded that instances of comprehensible output were "relatively infrequent" (p. 45). In her study of ten one-hour interactions between low level ESL acquirers and native speakers (teachers), only 87 potential instances of comprehensible output were found, that is, interactions in which the native speaker requested "confirmation, clarification, or repetition of the NNS utterance" (p. 93). These 87 interactions contained only 44 cases in which the non-native speaker modified his or her output (about four per hour), and of these 44, only 13 modifications involved grammatical form, about one per hour.