Passage
In one branch of a well-documented language family, nouns once marked two cases by a final vowel. In the coastal dialects the distinction is gone; in the upland dialects it survives. Coastal speakers were also in daily contact for centuries with a neighbouring language lacking that contrast. Most handbooks infer that contact caused the loss; as an account of the coincidence that is hard to better.
It is also hard to test, for reasons worth stating. Written attestation lags speech by an interval nobody can specify, so the earliest text showing the merged form fixes an upper bound on the date of the change and tells us nothing else. The contact is documented from the same records, unevenly. By this period perhaps a dozen noun classes carried the contrast, so its functional load — the utterances in which it alone separated two readings — was slight. A distinction that does little work is a distinction that can be lost for almost any reason, or none.
An internal explanation is therefore available, and on the face of it a more economical one. Final unstressed vowels throughout the branch were being reduced in these centuries, plainly in verbs and adverbs where no case was at stake. Once the final vowels of the two forms had fallen together, the contrast had no signal left to ride on. On this account contact is not refuted but made unnecessary: the coastal dialects did what their sound system was going to do anyway, and the neighbouring language is a bystander.
The difficulty is that the same reduction is attested in the upland dialects, where the contrast survives, carried by a shift of stress and a consonantal alternation the coastal forms lack. An internal account thus explains what made the loss possible, not why it happened here rather than there; the question has been put the wrong way round. In a system whose distinctions are under constant erosion, innovation needs no special motive; what needs one is survival. The upland dialects did not merely fail to change; they rebuilt a contrast under the same pressure everywhere. Until we can say what made the rebuilding worth its cost, an appeal to contact on the coast explains a difference by naming only one side of it.
