This book addresses one of the most fundamental questions that can be asked about human language: how can we explain language universals? There are currently many different views on this question. Some scholars 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 appeal 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 brings together all of these different views. The contributors have each been asked to motivate some general type of explanation for which they see evidence, and to provide illustrative universal data supporting its reality. In the editor's view all of these fundamental considerations are relevant to an understanding of why language is the way it is, because successful systems of human communication and of cognitive representation must regularly satisfy demands of all of these types. And the challenge before us is to make each of them more precise, thereby clarifying their respective domains of applicability, and to understand how they work together to constrain the variation space within which the set of possible human languages can occur. Explaining Language Universals contributes to these issues and draws on expertise from several related disciplines: from linguistics (generative theory, typology, syntax, semantics, morphology, the lexicon, discourse pragmatics, and historical change); psycholinguistics (language acquisition and language processing); and computer science (neural computing and artificial intelligence). The contributors include Michael A.Arbib, Melissa Bowerman, Joan L.Bybee, Bernard Comrie, Anne Cutler, Lyn Frazier, Christopher J.Hall, John A.Hawkins, Jane C.Hill, Teun Hoekstra, Edward L.Keenan, Ekkehard Konig, Jan G.Kooij, Michael Lee, Keith Rayner and Sandra A.Thompson.