This book approaches the topic of indefinite pronouns with the goals and methods of language typology as founded by Wilhelm von Humboldt (e.g. 1827), revived by Joseph Greenberg ( 1963), and summarized most recently in Croft ( 1990). A few general remarks on the typological approach are thus in order before we turn to a definition of indefinite pronouns in the next section. Language typology, as understood here, is the scientific study of variation and the limits to variation in the structure of languages. There are several reasons why typological research is of central importance to our understanding of human language.
Despite the bewildering diversity of their structure, different languages have always been regarded as roughly equivalent instantiations of the more abstract notion of 'human language', a unique and universal endowment of human beings. However, the question arises how language could be universal and at the same time be manifested in forms that show seemingly unlimited variation. Systematic cross- linguistic investigations of language structure, as conducted by typologists at least since Humboldt (1827), have made possible significant advances toward a resolution of the apparent contradiction between universality and diversity. Above all, typological studies have demonstrated that cross-linguistic variation is by no means random. On the contrary, the grammatical systems of languages around the world show such striking similarities that it seems not inconceivable to extract a common core, a 'universal grammar', out of the individual grammars.
On another level, linguistic typology is indispensable for our goal of explaining particular grammatical phenomena and of detecting significant generalizations. The fundamental problem is to state generalizations at the right level of generality. Linguists often fall into the trap of explaining a language-particular phenomenon by a high-level generalization (making reference e.g. to innate language structure or to general cognitive capacities), thus wrongly predicting that the phenomenon in question should be universal. Conversely, linguists also often explain a very general phenomenon by a low-level explanation (making reference e.g. to historical or other accidents in a particular language), thus wrongly predicting that the phenomenon in question should be restricted to the particular language they are dealing with. Cross-linguistic studies can help steer us through the Scylla of over- generalization and the Charybdis of undergeneralization. If in a cross-linguistic study a phenomenon turns out to be universal, we know that it must be explained