In this and the following chapter, I study the ways in which indefinite pronouns arise and change over time in different languages and the regularities in these changes. There are two main reasons for engaging in such a study of diachronic typology. First is the diachrony itself. Language change is a universal and essential feature of human language, and by studying the general laws of language change, we learn much about human language. But secondly, diachronic typology also helps us understand synchronic language states better. All languages are constantly in a process of change, in a kind of flux, and many features that do not fit neatly into a synchronic system begin to make sense once a diachronic point of view is taken. This applies both to recent innovations and to remnants of earlier regularities that are no longer synchronically motivated. Languages can carry around such synchronic irregularities for many generations, and if our goal is the explanation of linguistic structures, we have to take diachronic explanations into account.
Most importantly for my purposes, there is often a close correspondence between the generalizations obtained from synchronic and from diachronic typological studies, so that the results from such studies reinforce each other. For instance, in Hawkins ( 1983) study of word-order universals, the implicational hierarchies that account for the cross-linguistic distribution of word-order patterns also make correct predictions about possible diachronic changes, as Hawkins shows. If a language acquires new word-order patterns, it acquires them in accordance with the order of the implicational hierarchy. Quite analogously, implicational maps that account for the cross-linguistic distribution of different functions of grammatical categories also constrain the possible diachronic changes: a category can acquire a new function only if that function is adjacent on the semantic map to some function that the category already covers. Semantic change of grammatical categories is 'incremental' (cf. Croft et al. 1987), and grammatical categories gradually extend their uses along the paths allowed by the map.
This correspondence between synchronic and diachronic typology can also be observed in the case of indefinite pronouns. As I will show in this chapter (especially § 6.4), the extension of indefinite series to new functions proceeds along the paths permitted by the implicational map of Chapter 4.
One problem for the diachronic-typological study of indefinite pronouns at this stage is that there are very few specialized studies of diachronic change in