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In this article, we study the representation of phrase structure in early child German through the investigation of extensive longitudinal data from 7 monolingual German-speaking children (ages 1;8 to 2;9) with respect to verb placement, verb inflection, negation, wh-pronouns, and complementizers. In our data, we find clear evidence that children's grammar at Stage I generates at least one functional projection-namely, IP, or rather F(inite)P. There is, however, no empirical support for a second functional projection (CP) in Stage I. We argue that children construct phrase-structure trees in a gradual fashion, on the basis of X-bar' theory and the input they receive.
Clahsen et al. (Fri,) studied this question.