Over the course of the last three decades, a wealth of data has been published on the origin and development of grammatical forms. The main purpose of the present work is to make this wealth accessible to a wider readership. To this end, over 400 processes relating to the evolution of grammatical categories are discussed, using data from roughly 500 different languages. (See Appendix 3 for a list of languages figuring in this book.)

The readership we have in mind for this book includes first of all linguists. Grammaticalization theory, which is the framework adopted here (see §1.1), is concerned with language use across space and time; hence the findings presented may be of help for diachronic reconstruction, especially in areas where other tools available to the historical linguist, such as the comparative method and internal reconstruction, do not yield appropriate results. The descriptive linguist will find information, for example, on how and why different grammatical meanings can be related to one another in a principled way (i.e., on how to deal with issues like polysemy and heterosemy), on why there are some regular correspondences between grammatical forms and the meanings expressed by them, or on why certain linguistic forms have simultaneously lexical and grammatical functions. Anthropologists, sociologists, and psychologists may discover that the kind of human behavior held responsible for the evolution of grammatical forms is not all that different from the kind of behavior they observe in their own fields of study.