The syntactic constraint on English auxiliary contraction

Abstract We offer a new explanation for the difference between cases where an auxiliary verb can and cannot contract, such as Kim is coming versus Kim is. Rather than a banning constraint, we argue that there is a positive syntactic licensing constraint. We consider, and reject, both the familiar Gap Restriction and a range of phonological explanations. Our analysis rests on the category of grammatical relations, valent , which includes all non-adjuncts (i.e. all subjects and complements); the analysis consists of a single claim, the F ollowing V alent C onstraint : that a contracted auxiliary has an overt following valent. We show how this analysis explains the full range of data that has been discussed in the literature and how a minor variant of the constraint captures the data of the Scots locative discovery expressions . We also propose a sociolinguistic explanation for the inability of auxiliaries to contract in certain environments, such as after a preposed negative. Finally, we suggest a functional explanation for the proposed constraint: It allows the hearer to predict the presence of a following valent and thereby to manage the burden of processing.