This book grew out of many years of teaching an interdisciplinary survey course, “Language Development,” at Cornell. Many generations of students and their persistent questions, challenges and insights have built the material on which this book is based.

Like the course it is based on the book is essentially interdisciplinary, on the assumption that only an interdisciplinary approach can begin to advance our understanding of the fundamental mystery we are concerned with, i.e., the nature of the competence of the human species for language. It addresses this mystery by attempting to convert it to issues which allow and support scientific inquiry. Thus it does not simply adopt one point of view; nor does it deny debates in the field. It does not simply adopt a “logical” or “empirical” approach to the study of language acquisition. Rather, in the interest of grounding scientific inquiry in this area, it attempts to represent opposing points of view and to articulate their premises and predictions. It combines both theoretical and empirical inquiries in order to ground scientific inquiry. Hopefully, on the basis of the articulation of theoretical premises and the summary of empirical evidence which is provided in this book, the field now will have strengthened foundation for future research, allowing the continual course of inquiry which will be necessary to resolve fundamental debates which characterize the field.