This book presents a critical comparison of the two leading theories of linguistic change. After introducing the aims and methods of historical linguistics, Olga Fischer provides an exposition of the main theories used to describe morphosyntactic change and a full account of the causes and mechanisms by which their leading exponents seek to explain it. Professor Fischer emphazises the unity of form and meaning in the linguistic sign and examines the role played by analogy. She looks at how changes in discourse, lexicon, semantics, pragmatics, and sound interact with changes in morphosyntax, and explores the relationship between external and internal causes of change.