<P> Vocabulary development is a process by which people acquire words . Babbling shifts towards meaningful speech as infants grow and produce their first words around the age of one year . In early word learning, infants build their vocabulary slowly . By the age of 18 months, infants can typically produce about 50 words and begin to make word combinations . </P> <P> In order to build their vocabularies, infants must learn about the meanings that words carry . The mapping problem asks how infants correctly learn to attach words to referents . Constraints theories, domain - general views, social - pragmatic accounts, and an emergentist coalition model have been proposed to account for the mapping problem...</P>

The usual rate of learning words during the preschool years is 25 to 35 per day