Publisher Summary This chapter provides a hypothesis of language development and a description of a method for studying language, both based on Kantor's psychological linguistics. According to the hypothesis, language develops in four stages. In the first, spanning the first 9 to 15 months, random movements evolve into body management, manual, and locomotor skills that enable an infant to engage in play activities, among other things, with the mother and others. Simple gestural communication soon follows. During the second stage, coinciding with the child's second year, vocalizations evolve into “idiosyncratic expressions” and rough approximations of heard sound patterns. Language is now holophrastic-one-word utterances-mostly of the mediative variety. During the third stage, extending to about 30 months of age, language skills are described as first-approximation referential interactions: they are longer and more detailed, include some narrative interchanges, and refer to past and future events. In the fourth stage, when the child reaches the age of 52 months or so, second-approximation speech begins. By then the vocal apparatus is sufficiently developed to enable a child to make most of the vowel sounds and the enhanced language skills set the occasion for more frequent linguistic interchanges. He/she also begins to respond to symbols and other representations of objects and events. The method for studying language interactions involves, through the use of TV tapes, a description of the behavior of a speaker and the listener, the referent, and the setting conditions. The behavior of a speaker is analyzed in terms of the frequency with which he/she begins a language interchange, the average length of the initiation, the modality and the accompanying behavior.