In sum, the three languages of Vanikoro can be characterised by two contradictory properties. On the one hand, their fundamental genetic relatedness is blurred by a high degree of dissimilarity in the phonological forms of words, whether in the lexicon or in the morphology. But on the other hand, their grammatical categories and semantic structures show no equivalent to this formal diversity: instead, the three languages reveal perfect isomorphism, in each and every corner of their system. To paraphrase a formula by Sasse (see fn.19 below), they could ultimately be described as “a single language with different vocabularies”.
The question arises of what historical scenario would best explain this paradox, where divergence goes along with convergence. A simple explanation that comes to mind when accounting for the lexical diversification of cognate languages, might focus on the physical separation between language communities. The absence, still today, of any land path relating villages across Vanikoro island, and the stories of ongoing fierce territorial fights between its three tribes, would then be understood as genuine evidence for geographical or social isolation, and thus as a possible key for the high degree of formal divergence between Teanu, Lovono and Tanema. However, several facts seem to contradict this diagnostic. First, the relatively small size of the island is at odds with the notion of a neat separation between the three tribes. And more crucially, their extreme degree of structural isomorphism is likely to reflect not only cases of shared retentions from a common ancestor, but also later linguistic convergence induced by language contact. In other words, the explanation resorting to the mere physical separation between communities does not tell the whole story.
The solution to the puzzle will probably have to be found not in the factual features of geography, but in the more subtle dimension of sociolinguistic behaviour. Indeed, a conspicuous characteristic of cultures in certain parts of Melanesia – in comparison, for example, with the Polynesian world (see Pawley 1981) – seems to be a social preference for small-scale social communities with no marked hierarchy between them, as well as a strong emphasis put on whichever anthropological or linguistic features may differ from one community to the other. Heterogeneity between villages or village groups tends to be socially valued as a way to construct a world of diversity, where each community is endowed with its own identity. In this framework, a local innovation in cultural and linguistic forms will tend to be perceived, and eventually retained, as emblematic of a specific group. Over time, this behaviour favours the emergence of cultural and linguistic divergence between erstwhile homogeneous communities. Interestingly, some language groups can be said to have only gone down this track to the point when the languages began to lose mutual intelligibility; but what is conspicuous in the case of Vanikoro languages, is that they seem to have pushed the process of differentiation far beyond that point, as though they were to keep diverging for ever.
In order to account for similar facts in other parts of Papua New Guinea, Thurston (1989), and later Ross (1996; 2001:155), have used the term “ESOTEROGENY”:
Esoterogeny is a process that adds structural complexity to a language and makes it more efficient as a medium of communication among people of the same social group, while making it more difficult for outsiders to learn to speak well. (Thurston 1989)
Esoterogeny arises through a group’s desire for exclusiveness. (Ross 1996:184)
If the members of a community have few ties with other communities and their emblematic lect is not usually known to outsiders, then they may use it as an ‘in-group’ code, an ‘esoteric’ lect from which outsiders are consciously excluded. Innovations leading to increased complexity and to differences from neighbouring lects will be favoured. (Ross 1997:239)
One could probably discuss the degree to which such sociolinguistic processes are “conscious”, and also how they interfere with motivations of various kinds (semantic, structural, pragmatic) in bringing about change. This being said, one can probably accept the general idea behind Thurston’s concept, that language differentiation in Melanesia, far from being just an accident of geographical isolation, is largely influenced by a certain social attitude whereby each group tends to produce – whether consciously or not – its own distinctive speech tradition.
Now, while this hypothesis may help explain the high amount of lexical innovation and formal divergence that took place between Vanikoro languages, it seems at odds with the remarkable stability that we’ve observed among their structures. I would suggest this mismatch can be explained by the different nature of the linguistic components involved here. For one thing, the phonological form of the words (Saussure’s “signifiant”, Grace’s “lexification”), whether lexical or grammatical, is the component most salient and conspicuous to the speakers’ conscience, and therefore most likely to be preempted by motivations based on social emblematicity. Conversely, the structural and semantic dimension of language (Saussure’s “signifié”, Grace’s “content form”) would fall out of reach of the speakers’ immediate linguistic awareness, in a way that would make it exempt of the sociolinguistic force of esoterogeny. Instead, structures tend to obey a totally contrary force, typical of language-contact situations, that leads them to diffuse and converge: this is when multilingual speakers feel the “pressure towards word-for-word translatable codes” (Gumperz 1971). The structural isomorphism that can be observed today among Vanikoro languages has the considerable advantage, for the bilingual speaker, of reducing any translation loss, thereby increasing the efficiency of cross-linguistic communication, and facilitating the cognitive processing of speech. …
The comparison of Teanu, Lovono and Tanema reveals the intricacies of the island’s local history. The strong isomorphism found between the structures of these languages betrays their remote common ancestry, as much as it points to a history of intense language contact which the three tribes, nolens volens, have lived through over the centuries. On the other hand, the actual word forms found in their vocabularies and morphology have tended to follow a powerful tendency towards diversification, in accordance with the speakers’ tacit perceptions that the three communities, often caught in conflict and territorial hostilities, should sound and feel to be distinct social groups.
Overall, the paradox observed among the three modern languages of Vanikoro – dissimilar forms, similar structures – results from the interplay between these two contradictory forces: a socially driven push to increase language differences vs a functionally grounded tendency to minimise them.