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whatever corrections they can to raise the accuracy of their output (see, for example, Krashen and Pon, 1975).
Optimal Monitor users can therefore use their learned competence as a supplement to their acquired competence. Some optimal users who have not completely acquired their second language, who make small and occasional errors in speech, can use their conscious grammar so successfully that they can often produce the illusion of being native in their writing. (This does not imply that conscious learning can entirely make up for incomplete acquisition. Some unacquired rules will be learnable and others not. The optimal user is able to fill part of the gap with conscious learning, but not all of it.
We will take much more time with this hypothesis than we did with the others for two reasons. First, much of this material is relatively new, while the other hypotheses have been described and discussed already in several published books and articles. The second reason is its importance, both theoretical and practical. The input hypothesis attempts to answer what is perhaps the most important question in our field, and gives an answer that has a potential impact on all areas of language teaching.
The important question is: How do we acquire language? If the Monitor hypothesis is correct, that acquisition is central and learning more peripheral, then the goal of our pedagogy should be to encourage acquisition. The question of how we acquire then becomes crucial.
This section is organized as follows: I will first present the input hypothesis before giving any supporting evidence. Following this is a description of the evidence from research in first and second language acquisition. We will then briefly cover evidence from applied linguistics research, which is discussed in more detail in Chapter V.
(a) Statement of the hypothesis
Let us first restate the question of how we acquire: given the correctness of the natural order hypothesis, how do we move from one stage to another? If an acquirer is at "stage 4", how can he progress to "stage 5"? More generally, how do we move from stage i, where i represents
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