Topic drop in German: Grammar and usage

German topic drop clauses are a subtype of declarative clauses where the initial position (usually filled by an overt constituent) is left empty. It is often noted that topic drop appears mainly in specific registers (e.g. spoken dialogues), but this claim has neither been previously experimentally validated, nor formally implemented. In this paper, we report the results of a matched-guise study which indicate that the syntactic variation between topic drop and regular V2 declaratives in fact correlates with different social meanings, leading to the register variation postulated in the literature. In order to model German speakers' grammatical and register knowledge about topic drop in HPSG we propose, (i) a unified grammatical constraint that licenses topic drop structures, (ii) a formal theory of register that treats social meanings as a type of use-conditional content subject to compositional rules.