Competence and Performance in Child Language *

This paper presents the results of our recent experimental investigations of a central issue in linguistic theory: which properties of human language are innately determined? There are two main sources of information to be tapped to find the answer t9 this question. First, universal properties ofhuman languages are plausibly (even if not necessarily) taken to be innately determined. In addition, properties that emerge in children's language in the absence of decisive evidence in their linguistic input are reasonably held to be innate. Clearly, it would be most satisfactory if these two diagnostics for what is innate agreed with each other. In some cases they do. For example, there is a universal principle favoring transformational movement of phrases rather than oflexical categories e.g., topicalization of noun phrases but not of nouns. To the best of our knowledge children abide by this principle; they may hear sentences such as Candy, you can't have now~ but they don't infer that nouns can be topicalized. If they did, they would say things like *Vegetables, I won't eat the. But this is not an error characteristic of children. Instead, from the moment they produce topicalized constructions at all, they apparently produce correct NPtopicalized forms such as The vegetables, I won't eat. In recent years, this happy convergence of results from research on universals and research