Susan Curtiss & Bruce Hayes 
Linguistics [PDF ebook] 
An Introduction to Linguistic Theory

Linguistics: An Introduction to Linguistic Theory is a textbook, written for introductory courses in linguistic theory for undergraduate linguistics majors and first-year graduate students, by twelve major figures in the field, each bringing their expertise to one of the core areas of the field — morphology, syntax, semantics, phonetics, phonology, and language acquisition. In each section the book is concerned with discussing the underlying principles common to all languages, showing how these are revealed in language acquisition and in the specific grammars of the world’s languages.