Jeremy Sawyer recounts that, after Lev S. Vygotsky's death, Jean Piaget conceded the Russian psychologist correctly understood the social origins, functions, and developmental trajectory of children's egocentric speech (now called private speech) but dismissed this work as irrelevant to children's egocentrism or nondifferentiation of perspectives.…

In the period between sole use of single words and majority use of multiword utterances, children draw from their existing productive capability and conversational input to facilitate the eventual outcome of majority use of multiword utterances. During this period, children use word combinations that are not yet mature multiword utterances, termed…