The English plural is about the number of individuals in a set of like kinds. Two year old children use the plural but do not do so in all obligatory contexts. The present report asks whether the limitations on their production of the plural are related to aspects of meaning. In two Experiments plural productions were elicited from two-year old children for sets of size two and four and for instances of basic level categories that were either similar or identical. Children were much more likely to produce the plural of these well-known nouns when there were four rather than two and when the instances were identical rather than merely similar. The results provide new evidence on children's acquisition of the English plural, showing that children's early productions are not just limited by knowledge of the noun and its plural form but also is limited by properties of the labeled sets in ways that are relevant to the underlying meaning of the plural.Two-year-old children learning English spontaneously produce the plural forms of nouns, using them to label sets containing multiple instances of the same kind. However, they do not use the plural in all required contexts (Cazden, 1968; Mervis & Johnson, 1991;Brown, 1973;Berko, 1958). Past explanations of this limited productivity have focused on morphological rules, exceptions to those rules, and phonological constraints (Marcus et al., 1992;Marchman, Plunkett, & Goodman, 1997;Winitz, Sanders & Kort, 1981). The meaning of the plural, however, has not been studied in relation to its growing productivity. This report presents new evidence that meaning matters.Formally, the English plural partitions sets into those with precisely one individual versus those with more than one. Although this seems natural to mature English speakers, other meaning distinctions are possible. For example, the Russian plural distinguishes sets of one, sets with few members, and sets with many members. Many Indo-European languages have a separate plural form for sets of exactly size two. Sursurunga, an Austrongesian language, has five plural forms that are dependent on the number of instances in the referred to set. Other languages such as Japanese have no plural but quantify sets through the use of quantifiers that depend on the kind of thing in the set. These cross-linguistic differences mean that learners have to figure out the relevant meaning categories for their language. This paper examines two factors that might be relevant to young children's figuring out the meaning of the English plural: the similarity of the instances in the set and the number of things in a set.Address for correspondence: Jennifer A. Zapf, Indiana University, Department of Psychology, 1101 East Tenth Street, Bloomington, IN 47405, E-mail: jenzapf@indiana.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and ...