How do children acquire their native language? This question has prompted a lively theoretical debate and a great deal of empirical research, much of which explicitly tests the predictions of the various competing accounts. In our view, it is therefore unfortunate that most previous child language textbooks and monographs barely cover this debate at all. Instead, most authors, whether implicitly or explicitly, adopt a particular theoretical position and largely discuss only research conducted within the relevant paradigm. If proposals that derive from an opposing theoretical viewpoint are discussed at all, it is generally only to dismiss them, with no serious consideration of their strengths and weaknesses.

We want to change all that with this textbook. Our goal is to identify the key debates in each of what we consider to be the ‘core’ domains in language acquisition (by monolingual, typically-developing speakers) and to outline the empirical evidence for and against each theoretical proposal, in an even-handed, systematic and (as far as space permits) comprehensive manner. We aim to hold every proposal to an equally high standard of proof – making no prior assumptions with regard to parsimony or psychological plausibility – and, in so doing, to provide detailed challenges to all researchers, of all theoretical standpoints.

This focus on theoretical debates has three important consequences. The first is that, although we seek to be comprehensive in covering all the major domains of acquisition (speech perception/segmentation and production, word learning, inflectional morphology and syntax), this textbook does not constitute a descriptive account of what children's language looks like at each age (there are many other textbooks that fulfil this function).