Red rats eater exposes recursion in children's word formation.

The present study examines noun-noun compounds where the internal noun is pluralized (e.g., new books shelf), contrary to normal constraints that prohibit such constructions. It is proposed that these apparent violations are licensed by a recursive mechanism where world formation passes into Syntax and back into Morphology. Thirty-six 3- to 5-year-olds were tested on their interpretations of compounds fronted by an adjective. When asked to point to a picture of a red rats eater, children preferred a picture where the rats were red over one in which the eater was red. The opposite preference was found when children were asked to point to a red rat eater. These response patterns reflect a recursive-syntactic interpretation when the noun is plural, but a non-recursive interpretation when the noun is singular. The results suggest that children's word formation processes allow complex interactions between grammatical systems from early in acquisition.