What changed where?

In the field of generative diachronic syntax, it has often been disregarded at which level of the language (dialect or Standard) syntactic change has occurred. However, just as in the case of phonological developments, the syntax often (though not always) turns out to be more conservative at the dialectal level. In this article we will present four cases studies on the syntax of German: the diachrony of pro drop (null subjects), of negative concord, of possessive constructions and of word-order changes in the verbal cluster. Our plea for taking into account dialect data in historical linguistics converges with the growing significance dialects and dialectal data have gained within theoretical linguistics.