Introduction

Acquisition of form class categories such as nouns, verbs, adjectives, prepositions, etc. is an important step toward mastery of adult language. In particular, nouns and verbs are essential elements of a sentence and how children identify them in input has been a central issue in language acquisition research. Several theorists emphasize the importance of object words as an initial entry point into a language system. For instance, Gentner (1982) proposes the Natural Partitioning hypothesis, which claims that nouns are learned earlier than verbs because they are universally more accessible to children than verbs. Concepts denoted by concrete nouns are already formed as perceptually cohesive packages (e.g. concrete objects, persons, etc.) before word learning begins, while those denoted by verbs (e.g. action, events, and change of states) are crosslinguistically more variable and must be learned through a specific language. Markman (1990) proposes lexical constraints such as whole object and taxonomic constraints that initially guide children to acquire object words over action words. As a result, children show a noun bias in early vocabularies.

Although a prevalence of nouns over verbs in the early productive vocabularies of English-speaking children has been widely reported in the literature (e.g. Goldfield, 2000), the claim of a universal early noun bias has been challenged by recent findings from Korean and Mandarin studies and has become the focus of intense controversy.