In this study 1 we set out to discover what is learned by children exposed to English morphology. To test for knowledge of morphological rules, we use nonsense materials. We know that if the subject can supply the correct plural ending, for instance, to a noun we have made up, he has internalized a working system of the plural allomorphs in English, and is able to generalize to new cases and select the right form. If a child knows that the plural of witch is witches, he may simply have

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... the plural form. If, however, he tells us that the plural of * gutch is * gutches, we have evidence that he actually knows, albeit unconsciously, one of those rules which the descriptive linguist, too, would set forth in his grammar. And if children do have knowledge of morphological rules, how does this knowledge evolve? Is there a progression from simple, regular rules to the more irregular and qualified rules that are adequate fully to describe English? In very general terms, we undertake to discover the psychological status of a certain kind of linguistic description. It is evident that the acquisition of language is more than the storing up of rehearsed utterances, since we are all able to say what we have not practiced and what we have never before heard. In bringing descriptive linguistics to the study of language acquisition, we hope to gain knowledge of the systems and patterns used by the speaker. In order to test for children's knowledge of this sort, it was necessary to begin with an examination of their actual vocabulary. Accordingly, the 1000 most frequent words in the first-grader's vocabulary were selected from Rinsland's listing. 2 This listing