Defectivity and auxiliary syncretism: diachronic aspects

In this article, we argue for the existence of neutralised (i.e. featurally underspecified) auxiliaries, and consequently that the feature content of auxiliaries can change over time in such a way that it interacts with the labelling algorithm. Our core contention is that auxiliaries which are underspecified for being HAVE or BE, such as English ain’t and Southern Italo-Romance seva/sɔva, have an optional LOC(ATIVE) feature. For example, while ’s in a sentence like There’s students in the room is a neutralised auxiliary with an optional LOC feature, which crucially involves LOC agreement between there and (the neutralised) ’s, and a sentence like There are students in the room involves ϕ-agreement between there and are, the non-contracted is in the ungrammatical *There is students in the room is unambiguously a form of be and so lacks a LOC feature. As such, it involves neither LOC agreement between there and neutralised ’s, or ϕ-agreement between there and are, thus leaving the root node unlabelled and leading to ungrammaticality. We argue that non-neutralised HAVE-auxiliaries on the other hand have an obligatory LOC feature. By comparing the development of the two different cases of neutralised auxiliaries, we see that the diachronic convergence of HAVE and BE can arise in different ways (phonologically or morphologically). We also show that our account of the neutralised auxiliaries can readily be integrated into existing approaches to locatives and existentials.