This book addresses one of the most fundamental questions that can be asked about language: how can we explain language universals? There are currently many different views of this question. Some argue for the innateness of general linguistic principles within the human species. Others see a more social foundation to language, with linguistic structure reflecting various communicative functions. Yet others appleal to the psychological demands placed upon language-users in producing and comprehending language in real time. Language is also seen as a reflection of our human perceptual and cognitive apparatus. And there are also more grammar-internal explanations, whereby one part of the grammar (such as some aspect of surface form) is explained by another (such as the semantics of that form). This book is a state-of-the-art vollume which brings together all of these different views. The contributors have each benn asked to offer some general explanation for which they see evidence, and to provide illustrative universal data supporting it.