A competence grammar of English must account for the English speaker’s ability to predict the shape of the regular past tense morpheme on the basis of the stem-final segment, faced, for example, with a neologistic verb like *rolk or *glag. But whether efficient processing of known words routinely utilizes this creative ability is another matter. Efficient on-line processing may favour selection from a store over computation. To what extent selection and computation are balanced in on-line production may even be different from the balance required in efficient comprehension.
It would appear therefore that not only is behaviour not a criterion for possession of knowledge — it is in fact only one kind of evidence for it — but also that the constructs required in characterizing competence cannot serve as the only criteria for determining the forms of processing. The evidence from both domains can support but not disconfirm the hypotheses of the other. Nevertheless, the grammars being produced within the generative paradigm are beginning to have the requisite richness of detail that must underly the capacity for language use. As such they provide independently motivated and sufficiently elaborate hypotheses regarding the structures and processes underlying production, allowing the production theorist a preliminary distinction between crucial facts and those best considered irrelevant.