This document discusses different theories of how people acquire language and the stages of language development. It presents three main views: the structural view which focuses on phonological and grammatical units, the functional view which emphasizes the semantic and communicative aspects of language, and the interactional view which sees language as a tool for social relationships. The document also outlines five domains that influence language acquisition: social, perceptual, cognitive processing, and conceptual/linguistic factors. Finally, it describes five stages of language development based on vocabulary size and abilities.