Red bluebirds and black greenflies: preschoolers' understanding of the semantics of adjectives and count nouns.

Three experiments explored preschoolers' and adults' understanding of the distinctive semantic functions of adjectives (i.e., to name properties) and count nouns (i.e., to name object kinds). In Experiment 1, we modeled a familiar adjective (e.g., "blue") syntactically as either an adjective (e.g., "This is a blue one") or a count noun (e.g., "This is a blue") and applied it to a target object (e.g., a blue creature). In Experiments 2 and 3, we marked the adjective phonologically as either an adjective (e.g., "This is a blue bird") or a part of a count noun (e.g., "This is a bluebird") and applied it to a target object (e.g., a blue bluebird). In all experiments, participants then had to extend the expression they heard to either an object of a different kind with the same property as the target (e.g., a different creature or bird colored blue) or an object of the same kind with a different property (e.g., the same creature or bird colored red). Four-year-olds and adults, but not 3-year-olds, who heard the adjective version were more likely than those who heard the count noun version to choose the object with the same property. Thus, by the age of four years, children treated a word's lexical category, cued syntactically or phonologically, as a powerful cue to its meaning.