Per Linell 
Written Language Bias in Linguistics [PDF ebook] 
Its Nature, Origins and Transformations

Linguists routinely emphasise the primacy of speech over writing. Yet, most linguists have analysed spoken language, as well as language in general, applying theories and methods that are best suited for written language. Accordingly, there is an extensive ’written language bias’ in traditional and present day linguistics and other language sciences. In this book, this point is argued with rich and convincing evidence from virtually all fields of linguistics.