Keeping it in the family: disentangling contact and inheritance in closely related languages

The striking similarities between Old English (OE) and its neighbour Old Frisian (OFris)—including aspects of phonology, morphology, and alliterative phrases—have long been cause for comment, and often for controversy. The question of whether the resemblance was caused by an immediate common ancestor (Anglo-Frisian) or by neighboring positions in a dialect continuum/Sprachkreis has been hotly disputed using phonological and toponymic evidence, but not in recent years. Consensus in the nineties fell in favour of the dialect continuum, and there the issue has largely rested. However, recent finds in archaeology, history, and genetics argue that the case requires a second look. Developments in grammaticalization theory and contact linguistics give us new tools with which to investigate. Are the similarities between OE and OFris due to an exclusive shared ancestor, or are those languages merely part of a dialect continuum, with no closer relationship than that shared with the other early West Germanic dialects? And are there any reliable criteria to separate out inheritance-based similarities from those that are spread by contact? Shared developments seem, primo facie, to be evidence of shared inheritance, but there are other possible explanations. Parallel drift after separation, convergent development, or coincidence might be the cause of any shared feature. In this paper, I discuss recently proposed methods of distinguishing inheritance from drift and contact, focusing on how morphosyntax can help explore the shared history of OE and OFris. While grammaticalization processes often lead to cross-linguistic similarities, the fact that OE and OFris display a cluster of grammaticalizations not found in other early West Germanic dialects may be significant. The exclusive developments under investigation include aga(n) ‘have’ > ‘have to’ and the present participle as verbal complement. By comparing the forms, meanings, and distribution of these grammaticalized forms in the OFris corpus to that of their cognate forms in OE, I show that the two languages probably diverged from one another substantially later than they diverged from Old Saxon and Old Low Franconian