This book was actually begun with the publication of the monograph One Word at a Time in 1973. The description of the single-word period in that monograph contained several observations of my daughter Allison's development that departed from traditional accounts in the literature at the time. Since then, the theoretical issues raised by these observations have continued to endure. The case study in One Word at a Time was motivated by two issues in particular. The first was that words in the single-word period have a conceptual basis, not a syntactic basis. Nothing I have read or observed since then has changed my strong conviction that the major developments in this period are conceptual rather than linguistic. The second theoretical issue was the nature of the developments in cognition that contribute to conceptual development, word learning, and the eventual emergence of syntax, at the end of the period. Many studies have since attempted to test the hypotheses I suggested, and the results of these studies have been mixed and at times controversial. One thing, however, is now clear: The second year of life is a time of major cognitive developments that contribute to learning words and the emergence of language.

The emphasis on cognitive development for early word learning in One Word at a Time was one of two factors that led to the chain of events that has culminated in this book.