Dr Alexandre François
email: francois@vjf.cnrs.fr

Social ecology and language history in the northern Vanuatu linkage: A tale of divergence and convergence

This study describes and explains the paradox of related languages in contact that show signs of both linguistic divergence and convergence.

Seventeen distinct languages are spoken in the northernmost islands of Vanuatu. These closely related Oceanic languages have evolved from an earlier dialect network, by progressive diversification. Innovations affecting word formsmostly sound change and lexical replacement -have usually spread only short distances across the network; their accumulation over time has resulted in linguistic fragmentation, as each spatially-anchored community developed its own distinctive vocabulary. However, while languages follow a strong tendency to diverge in the form of their words, they also exhibit a high degree of isomorphism in their linguistic structures, in the organisation of their grammars and lexicons. This structural homogeneity, typically manifested by the perfect translatability of constructions across languages, reflects the traditions of mutual contact and multilingualism which these small communities have followed throughout their history. While word forms are perceived as emblematic of place and diffuse to smaller social circles, linguistic structures are left free to diffuse across much broader networks. Ultimately, the effects of divergence and convergence are the end result, over time, of these two distinct forms of horizontal diffusion.

Admittedly, this perspective offers the most spectacular view on convergence phenomena, as languages can be seen narrowing the gap that used to separate them. However, contact phenomena are not limited to that particular configuration; and it is equally legitimate to observe contact among languages which are closely related. This configuration underlies a number of studies dealing with various parts of the world: see, inter alia, the papers in Braunmüller & House (2009); and also Trudgill (1986) and [START_REF] Labov | The three Dialects of English. Quantitative Analyses of Sound Change[END_REF] for English dialects; [START_REF] Chappell | Language Contact and Areal Diffusion in Sinitic Languages: Problems for Typology and Genetic Affiliation[END_REF] for Sinitic languages; [START_REF] Enfield | On Genetic and Areal Linguistics in Mainland Southeast Asia: Parallel Polyfunctionality of "acquire[END_REF] for Eastern Mon Khmer; Toulmin (2009) for a subgroup of Indo-Aryan; [START_REF] Donohue | Which Sounds Change: Descent and Borrowing in the Skou Family[END_REF] for Skou languages; within the Oceanic subgroup, see in particular [START_REF] Geraghty | The History of the Fijian languages[END_REF] for Fijian dialects, and [START_REF] Ross | Proto-Oceanic and the Austronesian languages of Western Melanesia[END_REF]in prep.) for Western Oceanic.

The reason why this case -related languages in contact -is special lies therefore not in its rarity, but rather in the potential contradiction it entails. For a group of languages to be genetically related means that they have diverged from a common ancestor, so as to become distinct languages over time. But processes of language contact between them typically entail the diffusion of linguistic traits, and would be expected to result in some form of linguistic convergence. This raises the question of how these two contradictory tendencies interact, and what outcome results from their interference.

Divergence of forms, convergence of structures

This study proposes to observe a group of 17 languages spoken by the 9400 inhabitants of the Banks and Torres Islands, in the northernmost parts of Vanuatu. These languages are all related: first, they all belong to the Oceanic subgroup of the Austronesian family; second, they form a "linkage" [START_REF] Ross | Proto-Oceanic and the Austronesian languages of Western Melanesia[END_REF], insofar as they descend from an earlier dialect network (see Section 3). Yet despite their common origin, three millennia of linguistic change have made these languages mutually unintelligible.

While both processes of divergence and convergence are at play in the history of these languages, they have affected different dimensions of their systems. In a nutshell, processes of divergence have been particularly intense with respect to linguistic FORMS, whether this concerns sound change or lexical replacement. By contrast, languages show much more areal homogeneity as far as their STRUCTURES are concerned -whether in the syntactic and combinatorial properties of words, the semantic organisation of the lexicon, or phraseological strategies. (The contrast I draw between the forms of words and their structures, or structural properties, will be presented in more detail in §5.1.) This particular alchemy has brought about an intricate situation, where languages show relative diversity in the forms of their words, but also a strong isomorphism in the structural organisation of meaning. Table 1 illustrates the configuration that typically obtains, by showing the 17 translations of a sentence chosen randomly (meaning "They don't know our language very well yet"). The typical situation is that a single line of interlinear glossing corresponds to a variety of different word forms. These northern Vanuatu languages illustrate in a somewhat extreme way a tendency which has already been observed in other parts of Melanesia [START_REF] Haudricourt | Richesse en Phonèmes et Richesse en Locuteurs[END_REF], Thurston 1987, 1989[START_REF] Dutton | Language Contact and Change in Melanesia[END_REF][START_REF] Ross | Contact-induced Change in Oceanic Languages in North-West Melanesia[END_REF], François 2009b). Pawley (2006:216) describes in which respects the most innovative (or "aberrant", [START_REF] Grace | The "Aberrant" (vs. "Exemplary") Melanesian Languages. Linguistic change and reconstruction methodology[END_REF]) among Oceanic languages typically differ from their more conservative sisters: "In these areas, most of the aberrant languages (…) are atypical in lexicon and phonology, but are not markedly atypical in respect of (…) morphology and syntax."

Other parts of the world show similar configurations -that is, cases where languages in contact show almost perfect intertranslatability, in spite of the difference between their forms. Consider, for example, the way [START_REF] Gumperz | Convergence and Creolization: A Case From the Indo-Aryan/ Dravidian Border in India. Pidginization and Creolization of Languages[END_REF] describe the relation between Kannada, Marathi and Urdu as spoken in the Indian village of Kupwar: "[S]entence-by-sentence comparison of natural conversation texts in all three main local varieties reveals an extraordinary degree of translatability from one local utterance to the other. (…) The sentences (…) are lexically distinct in almost every respect, yet they have identical grammatical categories and identical constituent structures." (Gumperz & Wilson 1971:154) However, the Indian situation there described involves languages which are genetically diverse (Dravidian vs Indo-Aryan), in such a way that lexical forms were historically different to begin with; the spectacular process in the languages of Kupwar is the amount of structural convergence which they have gone through. But in the northern Vanuatu case which I propose to describe here, the languages share a common ancestor, and have maintained contact ever since their geographical dispersal. In other terms, what needs to be explained here is a paradox, whereby a cluster of languages have gone simultaneously through processes of divergence and of convergence.

The present study

Until recently, northern Vanuatu languages had been only known through grammar sketches by early missionaries [START_REF] Codrington | The Melanesian Languages[END_REF], and wordlists (Tryon 1976). The present study, based on data collected by the author since 1997, proposes to describe this region in some detail. The complex situation that prevails here, and which was illustrated in Table 1, will be explained in light of the social and anthropological conditions of these languages" historical development -that is, their language ecology [START_REF] Haugen | The Ecology of Language. The Ecology of Language: Essays by[END_REF][START_REF] Mühlhäusler | Linguistic Ecology: Language change and linguistic imperialism in the Pacific region[END_REF]). I will argue that the syntactic and semantic isomorphism observable across the northern Vanuatu area results from sustained relations of language contact and multilingualism. On the other hand, the heterogeneity of word forms will be shown to correlate with social perceptions of what normally constitutes a distinct community. I will suggest that this interplay of centrifugal and centripetal forces in the social ecology of these groups -distinct village communities in constant interactionprovides the key to the complex linguistic situation observable today, in which languages show both divergence and convergence.

The present article will unfold as follows. Section 2 will present the 17 language communities of northern Vanuatu in their social setting, showing how it involves both some degree of separation and various forms of contact. Section 3 will situate these languages genetically, and establish that they share a single ancestor.

Section 4 and 5 will present in some detail the facts which constitute the paradox under discussion. Section 4 will discuss the various processes leading to linguistic diversification in northern Vanuatu -especially, sound change and lexical replacement. Section 5, in turn, will cite a number of cases where languages show parallel syntactic or semantic structures despite the diversity of their word forms.

The final discussion, in section 6, will attempt to explain the social underpinnings that may account for this paradox, whereby languages can simultaneously show signs of divergence and convergence. Eventually, I will suggest that these two apparently contradictory tendencies observed on the macro scale are really the superficial result of deeper processes that combine social biases and cognitive factors. Both divergence and convergence are rooted in a single, universal process of micro-diffusion across individuals -or "linguistic epidemiology" [START_REF] Enfield | Linguistic Epidemiology: Semantics and Grammar of Language Contact in Mainland Southeast Asia[END_REF]) -as linguistic innovations emerge locally and spread, by imitation, across individuals in contact. However, at least in this part of the world, this process of micro-diffusion does not target the same social circles, depending on the nature of the innovations that spread. Those changes affecting the form of words (sound change, lexical replacement), take up an emblematic role as markers of place, and tend to diffuse through smaller social circles, typically targeting the village or local community to which each speaker relates more or less consciously. Conversely, those innovations that affect the structural organisation of meaning (morphosyntax, semantic categorisations, phraseology) escape this biased anchoring to any particular social group, and are left free to diffuse across entire social networks. Eventually, as the two types of change accumulate over time, the end result is an epiphenomenon whereby these related languages in contact appear to have simultaneously "diverged" in their word forms and "converged" in their structures.

The social ecology of northern Vanuatu languages: Distinct communities in constant interaction

2.1 A fragmented linguistic landscape

SITUATION OF THE BANKS AND TORRES LANGUAGES

The modern country of Vanuatu -known as the New Hebrides until its independence in 1980 -hosts the world's highest density of languages per capita [START_REF] Crowley | The Language Situation in Vanuatu[END_REF]. A total of 106 vernacular languages have been recorded there (Tryon 1976;[START_REF] Lynch | Languages of Vanuatu: A new survey and bibliography: Pacific Linguistics[END_REF] for a current population of 234,000 inhabitants -which makes for an average number of about 2200 speakers per language. All languages of Vanuatu belong to the Oceanic subgroup of Austronesian (see Section 3).

The present study will focus on the northernmost area of Vanuatu, namely the groups of islands known as the Torres Islands and the Banks Islands. Throughout this paper, the label "northern Vanuatu", or the word "archipelago", will consistently refer to the Torres and Banks groups. This relatively small archipelago includes ten inhabited islands, and has a total land surface of 882 km² -most of which is uninhabited. Its population of about 9400, 1 distributed across approximately 50 villages, nowadays speaks 17 different languages. Figure 2 provides a map of the area, together with an approximate number of speakers for each language. Among these 17 speech traditions or "communalects" [START_REF] Pawley | Fijian Dialect Divisions: Eastern and Western Fijian[END_REF][START_REF] Geraghty | The History of the Fijian languages[END_REF], some show enough similarity that they might be considered, under some definitions, as dialects of a single language (Mwesen and Vurës; Mwotlap and Volow; Koro and Olrat). However, they present enough differences, in their phonologies and/or their lexicons, for speakers to consider them as different languages, with limited mutual intelligibility. Because the present study focuses precisely on linguistic 1 The 2009 census carried out by the Vanuatu National Statistics Office (VNSO 2009) gives a figure of 9359 inhabitants for the province "TorBa" (Torres-Banks). This reveals a +20.7 percent increase from the figure of 7757 inhabitants observed in 1999.

diversification, I will mirror the social representation of these speech traditions, and treat them as separate languages. Conversely, when the difference between two varieties is tenuous and of little (linguistic and social) significance, I group them as dialects of a single language. Thus Lo and Toga are subsumed under "Lo-Toga"; Vurē and Qätärew under "Lakon"; Viar and Olrat under "Olrat"; Merig and Mwerlap under "Mwerlap".

DEMOGRAPHY AND VITALITY

As the figures on the map suggest, these 17 languages nowadays enjoy varying degrees of vitality.

Four of them are clearly moribund, no longer transmitted to younger generations, and only remembered by a handful of elderly individuals. Mwesen, with about 10 speakers, is giving way to the locally dominant language Vurës. The three speakers of Olrat are shifting to Lakon, the major language on the west coast of Gaua. Lemerig had five speakers in 2003, and has now gone down to just two individuals, who live in an area settled by Mwotlap speakers.

Volow can be considered extinct now, since its last fluent speaker Wanhan died in 1986. The reason why I still include it here among the 17 languages of the area, is because it is still remembered today -at least passively -by its "last hearer" (Evans 2010:209), Wanhan's son Wolman. A valuable recording of the late Wanhan, which the anthropologist Bernard Vienne carried out in 1969 and later handed over to me, has been extremely useful in the task of reconstructing, with Wolman's help, what spoken Volow used to be like.

These four vestigial tongues (Mwesen, Olrat, Lemerig, Volow) are remnants of languages which seem to have always been spoken by small inland communities, probably never more than one or two hundred speakers each in their heyday.

The other Torres and Banks languages tend to number in the hundreds -from 200 for Lehali, to 2000 for Vurës. At the upper end of the spectrum, Mwotlap is currently thriving, with as many as 2100 speakers of all ages -of whom 1650 live on the island of Motalava. All these languages -except the four moribund ones -are still transmitted to children. In this regard, despite figures which may seem low by world standards, they are safe from immediate endangerment (see [START_REF] Crowley | Melanesian Languages: Do they have a Future?[END_REF][START_REF] Crowley | The Language Situation in Vanuatu[END_REF].

In this part of island Melanesia, it appears that just a few hundred speakers may form a viable speech community. The average number of speakers per language is 550 -or 720 if one removes the four vestigial languages from the count. These figures are much lower than Vanuatu's national average of 2200 speakers per language, which is already a world record in terms of language density per capita ( §2.1.1). This alone shows the extreme linguistic fragmentation which is characteristic of the northern Vanuatu area.

While 17 languages may seem a high number, historical evidence shows that it used to be even higher a few generations ago. François (f/c), compiling accounts both from missionary documents [START_REF] Codrington | The Melanesian Languages[END_REF][START_REF] Codrington | The Melanesians: Studies in their anthropology and folklore[END_REF] and from the oral tradition, lists a total of 35 distinct communalects (languages or dialects) for the Banks and Torres islands, which were alive around the middle of the 19 th century. Various social processes took place in the decades around 1900 -including epidemics, labour trade, and island-internal migrations -which resulted in a drastic demographic downturn (Vienne 1984: 400), as well as in the reshaping of communities and social groups. In just a couple of generations, the consequence was the dramatic erosion of linguistic diversity in the area (François f/c), which went from 35 communalects to 17 today -and down to 13 in the near future.

In terms of social setting, the languages which have survived until today are often spoken by just a single village or two. The maximum for one language is six villages, and the average is three (50 villages for 17 languages). The only way to reach another village on the same island is by walking. These villages and hamlets are scattered across the archipelago. Although some hamlets were occasionally built on higher parts of mountainous islands -especially on Vanua Lava or Gaua -many of them have now been abandoned in favour of coastal villages, where fishing and inland resources are more easily combined. Today, island-internal migrations and the accretion of smaller hamlets have occasionally led to the formation of larger and more densely-populated villages, with up to 1500 people living together in one contiguous area, in the west of Motalava.

Some places in the archipelago show particularly high linguistic density. For example, the village of Jōlap (500 inhabitants) on the west coast of Gaua counts as many as three distinct languages, which are all heard in public every day: Lakon (itself a composite of two dialects Vurē and Qätärew), Olrat (and its variety Viar) and Dorig. These three languages have been spoken and transmitted by families in this village for more than three generations. To these one may add Koro, Mwerlap and Nume: these are the languages of immigrants -spouses, new settlers -and are spoken within certain households. There is enough multilingualism ( §2.2.1) among the small population of this village for everybody to understand, and occasionally speak, each other's language(s).

A homogeneous social network

Despite their relative social separation, the populations of the Torres and Banks Islands have always formed a coherent network. All along their history, the communities of this small archipelago have practised various forms of social interactions and linguistic contact, whether in their traditional way of life ( §2.2.1) or in modern times ( §2.2.2). These constant interactions are an essential component in the social ecology of languages in the region.

SUSTAINED RELATIONS OF CONTACT

The cultural and linguistic similarities found today across the Torres and Banks area are partly due to the common origin of its population ( §3.1), but also to the constant relations of contact which local communities have always entertained with each other. Even though contact took place regularly with islands further south as well, the Torres and Banks Islands evidently form together a particularly cohesive social network.

The distances between the two ends of the archipelago -say, between the Torres Islands and Merelava -were too great to allow for any sustained contact between all pairs of islands of the group. However, it is generally easy for people to travel from their own language community to the closest ones. The distance between two language communities on the same island is, on average, about two or three hours of strenuous walking. It didn't take much longer to cross the sea to the next island when sailing canoes were still in use. In sum, while contact was minimal between distant islands, it has always been possible for a given community to keep contact with the few communities that surrounded them.

Cultural contact among groups was not only possible, it was socially encouraged. Until today, the relationship prevailing between communities was always one of mutual balance of power, with little socio-economic dominance of one group over others (Vienne 1972). While the oral traditions of the Torres Islands still recall warfare and conflict between villages, this is hardly the case across the various islands of the Banks group. Even if they also occasionally allude to past conflicts, their stories rather tend to revolve around alliances between villages and chiefs, and also around the trade of valuable items, including women. The deity Qat, who lived on Vanua Lava, sailed northwest as far as Vava, the ancient name of the Torres Islands; by giving one of his pigs, he bought the Night, as well as a rooster, and a piece of obsidian (François 2003b:2). Another myth tells how a variety of yam was first discovered in the Torres Islands, and disseminated to populations further south. As for the prestigious white yam, it is claimed by Motalava people to have been first cultivated in their island before a child took it to Mota. Another story tells how the chief of Ureparapara appeased a conflict with the chief of Maewo, to the south of Merelava, by offering him his daughter (François 2003b:26). Finally, the Merelava people who have colonised the eastern coast of Gaua (Figure 2) like to narrate how their ancestors once taught the native people of this island how to marry and beget offspring.

All these stories, among many others, portray an archipelago where communities have constantly exchanged goods and women. A similar picture is drawn by archaeologists and anthropologists. [START_REF] Huffman | Trading, Cultural Exchange and Copyright: Important Aspects of Vanuatu Arts[END_REF] shows how the economy of the Torres and Banks communities -as well as much of the Vanuatu archipelago further south -was dependent on the trade of goods. In particular, the grade-taking ceremonies involved the consumption and exchange of vast amounts of shell-money, which used to be essentially produced on the now deserted atoll of Roua (Figure 2), in northern Banks (Vienne 1972;Bedford & Spriggs 2008:96). These trade contacts had important implications in terms of traditional multilingualism, especially among men: the men of a given community used to know and practise the languages of the neighbouring groups with whom they had contact. Crucially, this form of multilingualism was always egalitarian (Haudricourt 1961:9), in the sense that no group or language was considered dominant or more prestigious than others. Instead, neighbouring groups typically entertained relations of mutual bilingualism. This egalitarian multilingualism is still observed today -with the caveat that much of interisland communication nowadays tends to be carried out in Bislama (François f/c), the English-lexifier pidgin used as a lingua franca throughout modern Vanuatu (Tryon & Charpentier 2004).

Major public events -such as grade-taking ceremonies for new initiates -regularly took the form of large gatherings during which people of remote communities would meet and communicate together. These intercommunity events were also an opportunity for unions to form. Vienne (1984: 232-240) documents in detail the patterns of interisland marriages in the northern islands of the Banks group (Vanua Lava, Ureparapara, Motalava, Mota -see Figure 1). What he shows is a strong habit of exogamy, with more than 20 percent of unions being interisland marriages. Figure 3 is borrowed from Vienne (1984:240). The outer circle identifies the islands; the dots in the inner circle correspond to individual villages. His data, collected in the 1960's and 1970's, documented 455 individual marriages. Each line on the figure symbolises the marriage of at least one woman from the source village with a man from the target village. These unions resulted in the relocation of the wife in 61 percent of cases, of the husband in 39 percent. <Figure 3 about here> Due to this exogamous tendency, it is very common for anyone to have relatives in various neighbouring communities of the archipelago, and occasionally visit them. Because residence tends to be patrilocal, every village will count a number of immigrant women originating from various parts of the archipelago, who have established their residence in their spouse's village. Incidentally, Vienne's observations regarding northern Banks Islands can be safely extrapolated to the whole Torres-Banks archipelago. For example, the small population of Lo Island (Torres) currently includes immigrants from Hiw, Tegua, Toga, Motalava, Mota, Vanua Lava and Gaua.

These social conditions have important consequences in terms of language contact. Each of these adult women quickly becomes bilingual, being able to switch between her own mother tongue and the language of her new village. The linguistic environment of her children will be shaped by this form of language contact, whether directly or indirectly. Should each parent speak their own language at home, then the children are raised bilingually. Even when the mother speaks at home the language of the father, the variety her children will hear will often be tainted by her own linguistic background. Together with other causes for language contact, interisland marriage plays an important role in the development of linguistic convergence (see §6.1).

LANGUAGE CONTACT IN THE MODERN WORLD

Traditional patterns of social exchange, whether through trade or interisland marriages, have been extended in the modern era. The christianisation of the archipelago by Anglican missionaries has put an end to any remaining hostilities that may have existed. Missionaries also encouraged the merger of inland hamlets into larger coastal villages, thereby fostering de facto language contact. Major religious gatherings -such as Christmas celebrations -have replaced earlier traditional ceremonies, yet still play a similar role in sustaining inter-island exchanges and marriages.

Akin to the effects of christianisation are the consequences of modern education as it is organised among these low-density communities (François f/c). Because some small islands lack schools beyond primary level, parents send their children to boarding schools on another island. Relations of power between the vernaculars are not so much affected by the school language itself (French or English) as by the demographic imbalance between students of various linguistic backgrounds. For example, when young speakers of smaller languages are schooled in the Arep secondary school of east Vanua Lava, they tend to learn Mwotlap: even though this language is not indigenous to this island, it is increasingly becoming dominant in the region. This present organisation of schools favours, at best, multilingualism at a young age; and in the long term, endangerment of the weakest language varieties. Finally, the modern era has brought in some technical progress made in the domains of transportation (engine boats, interisland flights) and communication (satellite phones have quickly spread since the end of 2008). The combined effect of all these modern conditions is to considerably increase the frequency of contact between linguistic communities, even beyond what was already the case under traditional circumstances.

Shared ancestry and in situ diversification

In many parts of the world, modern linguistic diversity within a given area results from population movements, whereby genetically diverse languages have come in contact during their history. This, however, is not the case in northern Vanuatu. Both archaeological and linguistic evidence show that the local populations share a common ancestry, and have formed a relatively unified network for about three millennia, until today ( §2.2).

Until European discovery, there is little evidence that the islands of northern Vanuatu had any sustained contact with any exogenous group. While occasional encounters may have happened with Temotu people in the north, or with Polynesian voyagers [START_REF] Clark | The Polynesian Outliers as a Locus of Language Contact. Language contact and change in the Austronesian world[END_REF], they were so scarce that they left virtually no linguistic trace other than a handful of lexical loanwords. The only sustained contact that can be established for northern Vanuatu remained internal to the Torres and Banks Islands. Contact with islands further south -via a Merelava-Maewo connection -also existed [START_REF] Bonnemaison | Arts of Vanuatu[END_REF][START_REF] François | Where *R they all? The Geography and History of *R-loss in Southern Oceanic Languages[END_REF]), but still involved closely related languages. This is an important point for our discussion, as this entails that the present-day linguistic diversity does not result from external causes (historical migrations or contact between genetically diverse languages), but from a historical process of in situ diversification from what was initially a linguistically unified social network.

A common ancestor

Unlike the Solomon Islands to its northwest [Figure 1], the Vanuatu archipelago shows no archaeological trace of any human settlement prior to 3200 BP. Non-Austronesian ("Papuan") populations had settled much earlier -more than 40,000 years ago -in New Guinea and part of the Solomons chain, a region labelled "Near Oceania" by [START_REF] Pawley | Dating the Dispersal of the Oceanic Languages[END_REF]. As for the rest of the Pacific islands -known as "Remote Oceania" -its colonisation only began after a population of navigators, speakers of Austronesian languages, migrated from Island Southeast Asia into Melanesia, between 4,000 and 3,000 BP. This is when populations living off the coast of New Guinea, in the Bismarck archipelago close to New Britain I. [Figure 1], developed a civilisation known as "Lapita" (Spriggs 1995, 1997[START_REF] Kirch | The Lapita Peoples: Ancestors of the Oceanic World[END_REF], 2010). The attributes of this culture complex included a certain style of pottery artifacts ("Lapita pottery") as well as elaborate seafaring techniques (Pawley & Ross 1995:48). Between 3200 and 2900 BP, Lapita navigators managed to cross large ocean gaps, and rapidly settled the then unpopulated archipelagoes of Remote Oceania: the Santa Cruz islands (east of the Solomon chain), Vanuatu, New Caledonia, Fiji and West Polynesia. Although the detail of their itinerary and settlement patterns remains to be fully understood, it is a clear fact that the modern populations of northern Vanuatu descend from these early Lapita settlers [START_REF] Shing | Ripot long saed blong stadi long akioloji long not blong Vanuatu (2005-2007)[END_REF][START_REF] Bedford | Northern Vanuatu as a Pacific Crossroads: The Archaeology of Discovery, Interaction, and the Emergence of the "Ethnographic Present[END_REF].

As far as languages are concerned, all indicators suggest that the language spoken by the bearers of the Lapita civilisation who left the Bismarck archipelago essentially corresponded to what is reconstructed as "Proto Oceanic", the common ancestor of all indigenous languages of Remote Oceania [START_REF] Ross | Proto-Oceanic and the Austronesian languages of Western Melanesia[END_REF][START_REF] Pawley | The Prehistory of Oceanic Languages: a Current View[END_REF][START_REF] Pawley | Locating Proto Oceanic. The Lexicon of Proto-Oceanic : The Physical Environment[END_REF], 2007b[START_REF] Lynch | The Oceanic languages[END_REF]. The language spoken by Lapita navigators had little time to evolve significantly during the swift migrations that led them to settle across island Melanesia: "The rapid spread of Lapita from the Bismarcks to West Polynesia between 3200 and 2900 BP had a linguistic correlate. The speech of the Lapita colonists in the different island groups must have been relatively homogeneous, little differentiated from Proto Oceanic." (Pawley 2007a:11) This observation has important consequences for the linguistic history of the Oceanic family, whose tree must largely be reconstructed as a "rake" rather than a series of neatly nested subgroups [START_REF] Pawley | Chasing Rainbows: Implications of the Rapid Dispersal of Austronesian Languages for Subgrouping and Reconstruction[END_REF]) -see Figure 4 below. In other terms, under the Proto Oceanic node of the family tree, no significantly different intermediate stage was able to form between the time when the populations left the Bismarck archipelago, and the time when they reached the islands of Vanuatu. The only common ancestor which is shared by northern Vanuatu languages, strictly speaking, is thus Proto Oceanic itself.

Pre-dispersal ancestry vs post-dispersal linkages

There are in fact two different ways in which the languages of northern Vanuatu can be said to share a common "ancestry". For one thing, they all descend from Proto Oceanic, the language spoken by the initial settlers prior to their demographic dispersal. But another form of shared development corresponds to the linguistic network in which the populations continued to participate even after their dispersal.

After the initial settlement of northern Vanuatu, archaeological evidence (Pawley 2007a;[START_REF] Bedford | Northern Vanuatu as a Pacific Crossroads: The Archaeology of Discovery, Interaction, and the Emergence of the "Ethnographic Present[END_REF] shows that the newly settled populations maintained a unified social network across vast archipelagoes, for several generations. Such social links are evidenced, for example, by the early presence of obsidian from the Banks Islands in Fiji [START_REF] Ambrose | Obsidian and its Distribution in Melanesia. Ancient Chinese Bronzes and South East Asian Metal and Other Archaeological Artifacts[END_REF][START_REF] Best | Long-distance Obsidian Travel and Possible Implications for the Settlement of Fiji[END_REF], in Bedford & Spriggs 2008:98) and, later, on Efate (Bedford & Spriggs 2008:112). The observation of ceramic evidence allows archaeologists to identify some post-Lapita features which are shared across certain clusters of islands within Vanuatu: "[T]here is regional diversification in ceramic traditions right across Vanuatu soon after Lapita (…) these traditions can be divided into a number of regions: southern, central, northern, and far northern Vanuatu (Banks and Torres Islands)." (Bedford & Spriggs 2008:107; my emphasis)

The linguistic correlates of this ancient social unity are a number of post-dispersal innovations, which historically diffused across a geographically spreadout network of then mutually intelligible dialects. Because some of these innovations did not always spread to all members of the dialect network, they do not define proper subgroups, but linkages [START_REF] Ross | Proto-Oceanic and the Austronesian languages of Western Melanesia[END_REF][START_REF] Ross | Social Networks and Kinds of Speech-community Event[END_REF][START_REF] Pawley | Chasing Rainbows: Implications of the Rapid Dispersal of Austronesian Languages for Subgrouping and Reconstruction[END_REF]. A linkage designates "a group of communalects which have arisen by dialect differentiation" (Ross 1988:8).

Some isoglosses encompass the whole of Vanuatu and New Caledonia, and define the Southern Oceanic linkage [START_REF] Lynch | Linguistic Subgrouping in Vanuatu and New Caledonia[END_REF]. These include certain morphological innovations [START_REF] Lynch | Linguistic Subgrouping in Vanuatu and New Caledonia[END_REF][START_REF] Lynch | Some Shared Developments in Pronouns in Languages of Southern Oceania[END_REF], as well as the irregular loss of the phoneme *R in a vast number of lexical items [START_REF] Geraghty | Proto-Eastern Oceanic *R and its reflexes. Pacific Island languages: Essays in honour of[END_REF]). The detailed history of *R loss in Vanuatu [START_REF] François | Where *R they all? The Geography and History of *R-loss in Southern Oceanic Languages[END_REF] provides crucial evidence for showing that Vanuatu populations participated in dense communication networks even after the dispersal of the first settlers.

Several innovations also spread across the northern two thirds of Vanuatu, from Hiw to Efate. These formed the basis for what [START_REF] Clark | Languages of North and Central Vanuatu: Groups, chains, clusters and waves[END_REF][START_REF] Clark | Leo Tuai: A Comparative Lexical Study of North and Central Vanuatu Languages: Pacific Linguistics[END_REF] has identified as the North and Central Vanuatu linkage, to which he assigned 95 of Vanuatu's 106 languagesincluding the 17 Torres-Banks languages of the present study. The putative "protolanguage" for this linkage is referred to as PNCV "Proto North Central Vanuatu" [START_REF] Clark | Leo Tuai: A Comparative Lexical Study of North and Central Vanuatu Languages: Pacific Linguistics[END_REF]. Finally, those linguistic innovations which spread across the Torres-Banks linkage may be conveniently subsumed under the label PTB "Proto Torres-Banks". The tree-like diagram in Figure 4 summarises the mutual relations between these linkages; I here adopt the convention in [START_REF] Ross | Proto-Oceanic and the Austronesian languages of Western Melanesia[END_REF] There are thus two ways in which a group of closely related languages may share a "common ancestor", as conceived in a family-tree model. First, they fully inherit the features of their pre-dispersal shared ancestor, i.e. the language which was spoken by the initial settlers as they dispersed across territory -in this case, Proto Oceanic. But should the dispersed communities keep sustaining a social and linguistic network for some time, then they will also witness a number of innovations which will diffuse to part or whole of the network. Over time, the accumulation of such innovations defines a linkage, i.e. a cluster of adjacent dialects sharing a common post-dispersal history. Such a linkage will partly have the properties of a subgroup (e.g. some innovations shared throughout the network), but also properties that make it necessary to assign it a distinct status (e.g. uneven distribution of innovations that allow for conservative pockets; intersecting isoglosses; one language may belong simultaneously to several overlapping linkages). One property of the evolution of dialect networks is that those innovations which are exclusively shared across several dialects do not reflect vertical inheritance from an earlier (pre-dispersal) ancestor, but rather post-dispersal events of horizontal diffusion across dialects in contact [START_REF] Geraghty | The History of the Fijian languages[END_REF][START_REF] Pawley | Chasing Rainbows: Implications of the Rapid Dispersal of Austronesian Languages for Subgrouping and Reconstruction[END_REF][START_REF] Garrett | Convergence in the Formation of Indo-European Subgroups: Phylogeny and Chronology. Phylogenetic methods and the prehistory of languages[END_REF][START_REF] Bossong | Divergence, Convergence, Contact. Challenges for the Genealogical Classification of Languages[END_REF][START_REF] Heggarty | Splits or Waves? Trees or Webs? How Divergence Measures and Network Analysis can Unravel Language Histories[END_REF]Babel et al. f/c).

To sum up, from the strict point of view of phylogenetics, the only single ancestor uncontroversially shared by the modern languages of northern Vanuatu is Proto Oceanic. All other lower-level clusterings are linkages, i.e. post-dispersal dialect networks which formed areas of diffusion. This dialect-network model explains how linguistic innovations managed to spread across social groups of varying scope, during the historical development of northern Vanuatu languages.

The changing scope of linguistic innovations

An important point for our discussion is that the spread of the various linguistic innovations differed in geographical scope. Some covered a broad territory, such as the ones which are shared across the North Central Vanuatu linkage. By definition, these innovations did not trigger language fragmentation on the local scale, because they were adopted equally by all (or nearly all) adjacent members of the relevant dialect network. Other innovations, however, only spread across very limited territory -for example, a single island. Such local innovations result in more linguistic diversity.

The varying distribution of innovations partially corresponds to successive stages in the history of the region. What started as a far-flung network of small voyaging communities maintaining some form of social and linguistic unity slowly crumbled into smaller social networks on a reduced scale. As local populations grew and developed economic self-sufficiency, they relied less and less upon their distant relationships. This breakup of social networks has linguistic correlates, in bringing about divergence among once unified languages: "After the first phase of colonisation, the archaeological and linguistic record indicates that in the Southern Melanesian archipelagos, a sequence of demographic and cultural changes occurred which led to weakening or loss of communication between distant sister communities. (…) Most linguistic innovations spread only short distances, and the speech traditions of distant communities diverged." (Pawley 2007a:21; my emphasis)

In sum, the diversity found among modern languages of northern Vanuatu -as illustrated in Table 1 ( §1.2) -is neither due to any preexisting genetic diversity, nor to external input, but reflects three millennia of in situ diversification. Section 4 will now illustrate some of the linguistic forms taken by these processes of fragmentation.

Processes of language diversification in northern Vanuatu

Addressing the issue of language diversification

The 17 languages spoken in the Torres and Banks Islands are thus related in two ways. On the one hand, they are all genetically related, being all descendants of the same ancestor. On the other hand, they have always entertained close relations of contact and multilingualism. These two factors could have been expected to result in some form of linguistic homogeneity -or at least maintained mutual intelligibility. But this is not what can be observed today. How did it come about that the languages are so divergent in their phonologies and lexicons? Did their history follow universals of language change? Or do we need to resort to region-specific principles of language change, which would only apply to this part of the world? Are these languages so chaotic that they make it impossible to apply the comparative method?

In fact, far from challenging the validity of the comparative method, the data presented here will strongly confirm its relevance in attempting to reconstruct the history of these languages. The careful identification of regular sound correspondences and structural changes -whether in the phonology, the morphology or the lexiconwill prove methodologically crucial in identifying the precise history of phonemes, morphemes and words in the area. Regular correspondences (cf. François 2005a) form the background against which it will become possible to detect irregular developments that are limited to a few adjacent languages. This will allow us to compare languages in their historical development, and track the path taken by each innovation separately.

Linguistic diversification, as I will show in this section, took here essentially three forms: regular sound change ( §4.2), irregular sound change ( §4.3) and lexical replacement ( §4.4). These processes raise two different questions, of a different nature. One question is whether these changes are typologically unusual, and require explanations specific to this group of languages; my answer to this will be negative: in themselves, these three types of change follow universal trends of language evolution, and do not require any local explanation. This comes in contrast with another question, discussed in the final section of this paper (Section 6): namely, how one can explain the sheer density of these innovations, and their propensity to stabilise to small communities? This density, I will eventually suggest, mirrors the social fabric of the archipelago, and the accepted size of social communities in this particular part of the world.

But before I comment on the issue of their social correlates, I first propose to describe here the innovations themselves, and discuss which linguistic processes can explain them.

Language diversification through regular sound change

The initial linguistic unity that can be reconstructed for the early times of settlement gave way to a network of dialects which diverged more and more over the three millennia of their coexistence. One of the forces of such evolution was sound change. This cover term encompasses two distinct types of change:

• REGULAR sound change: changes occurring in the phonological system, and affecting the whole lexicon of a given communalect. The unit of change is the phoneme.

• IRREGULAR sound change: changes specific to some individual lexical items, independent of regular sound change in the system as a whole. The unit of change is the word.

These two forms of sound change are independent of each other, and are not ordered with respect to one another. In the course of their history, individual lexical items are affected both by regular (phoneme-based) and by irregular (word-based) sound change. The first of these two types is the object of the present section §4.2; the second one will be described in §4.3.

Just like any other innovation, both types of sound change can be described as having emerged locally, in the speech of a few individuals, and diffused gradually to their peers across a network of idiolects -following processes of the kind described by [START_REF] Labov | The Social Motivation of Sound Change[END_REF]Labov ( , 1994[START_REF] Labov | Principles of Linguistic Change: Social factors[END_REF]. As we will see, sound changes in northern Vanuatu often stabilised to a small area, usually smaller than the whole Torres-Banks archipelagoe.g. just one island, sometimes just one village.

LINGUISTIC DIVERSITY AT THE PHONOLOGICAL LEVEL

The linguistic fragmentation due to regular sound change is most conspicuous in the domain of vowels. Proto Oceanic, the common ancestor of these languages, is reconstructed with five vowels /i e a o u/. This simple inventory is still preserved in Mota, a conservative language of the Banks Islands. However, all other languages of the area have increased their inventory of vowel phonemes, via a historical process of metaphony -akin to umlaut -correlated with stress (François 2005a). A former trochaic foot *CV 1 CV 2 regularly yielded a closed syllable CV"C, in which V" is a new vowel quality resulting from the colouring of V 1 (stressed) under the influence of V 2 (unstressed): e.g. PNCV *ⁿdámu "yam" > VRS ⁿdoem.

Crucially, the patterns of vowel change (*CV 1 CV 2 > CV"C) are highly regular within each language; but they show strong diversity from one language to another. Thus in Koro, a stressed *a followed by an unstressed *u is systematically reflected as a diphthong ɛ a/: *ⁿdamu > ⁿd am "yam". The same sequence *a(C)u regularly yielded /a/ in Nume (ⁿdam) or Lakon (ʧam); a long aː in Dorig (ⁿdaːm); /ɒ / in Lehali (ⁿd ŋ); ɔ in Vera'a (ⁿdɔm) or Mwesen (nɔm); ɞ in Mwerlap (ⁿdɞm) ; oe in Lemerig (toem); /ø/ in Löyöp (ⁿdøm); ɛ in Mwotlap and Volow; ɪ in Olrat (ʧɪm). As this pervasive phenomenon of metaphony applied regularly to all possible combinations of vowels, it resulted in the phonemicisation of new vowels, in ways different in each language. Table 2 (revised from François 2005a:445) lists the vowel inventories of the 17 modern languages of the Banks and Torres Islands. The last column indicates the total number of vowel phonemes in each language -including short monophthongs, diphthongs and long vowels. Modern vowel inventories are thus diverse, ranging from a conservative 5-vowel system (Mota) to innovative sets of 12 (Mwerlap) or 13 (Lo-Toga). If short and long vowels are counted as distinct phonemes, then the highest numbers are found in Olrat ( 14) and Lakon ( 16). These systems also vary in their internal logics, some being perfectly symmetrical (e.g. Mwesen, Lemerig), others less so [Figure 5]. Only in very few cases can one group together two adjacent languages (e.g. Mwotlap with Volow, Dorig with Koro), and suggest their vowel system may have followed a single history. But everywhere else, it appears that each local community has modified its vowel system in a way different from its immediate neighbours.

Table 2 -The 17 languages of northern Vanuatu and their vowel inventories

The phonological systems of these modern languages also show some differences in their consonant inventories. Thus, some languages have prenasalised stops ( ᵐb , ⁿd , ᵑg ), others don't. While most languages have rounded labialvelars ( k pʷ or ᵑᵐg bʷ , ŋ mʷ ), four languages have rounded velars (/kʷ , ŋʷ ) instead. Certain segments, such as ʧ , h or /ʔ/, are found in some languages, but not in their immediate neighbours. Some languages have two liquids /r/ and /l/, others just /l/; the only liquid of Hiw is a prestopped velar lateral / g ʟ [g ʟ], unheard elsewhere (François 2010a).

Languages also differ regarding their phonological constraints and phonotactic properties. Some license labialvelar stops syllable-finally (e.g. Vurës / p p "speech" in Table 1), others do not. Some license tautosyllabic consonant clusters, others systematically avoid them. Even though both Hiw and Dorig share the same syllabic template CCVC, it can be shown that constraints of sonority are operational in the clusters of Hiw, but not in Dorig (François 2010a).

Even intonation can differ across languages. Whereas most languages express polar questions with a rising pitch, two sets of languages (the two Torres languages, plus those of Gaua) provide these questions with a falling contour.

LINGUISTIC FRAGMENTATION THROUGH REGULAR SOUND CHANGE

These regular phonological changes have sometimes obscured the relations between word forms in neighbouring languages, even when they were ultimately cognate.

Although this is not the typical case (see §4.4), some lexical items show a high rate of retention, in the sense that (nearly) all languages of the Torres and Banks Islands reflect the same original etymon. This etymon may be a retention from their common ancestor (Proto Oceanic), or the result of post-dispersal lexical innovations which spread across dialects during the early times of linguistic unity (PNCV, PTB).

While all the modern words may be cognate, their surface forms have often become different enough to hamper mutual intelligibility. Table 3 provides a small selection of such cognate sets. Regular phonological correspondences (François 2005a) make it possible to reconstruct a possible protoform for each cognate set (last row of table), at the level of "Proto Torres-Banks" (PTB, see §3.2). <Table 3 about here> A proportion of the divergent forms can be explained simply by the regular changes outlined in §4.2.1. Thus, the variety of modern forms for "song", "stroke", "coconut crab" result from the application of regular patterns of sound change to the three reconstructable etyma -respectively PTB *asi, *saraβi, *ⁿdaeru. Except for a couple of exceptions, the way each language treats the proto-consonants (*s, *r, *ⁿd) or sequences of proto-vowels (e.g. *áCi) is very regular. Most of the changes here illustrated are in line with typologically common trends in sound change -whether it is about individual segments (e.g. *s> h ; *t> ʧ , or *t> ʔ ), or processes like umlaut (e.g. *áCi > ɛC ). Other instances of sound change are perhaps less common (e.g. *r>/j/, *r> ᶢʟ ; *ᵐb> ŋ , *ᵐb> k ; *ⁿd> ʧ , *ⁿd> ʈ/; *áCi > ɔC …), but they are still within the limits of the explicable. Overall, what is more conspicuous here in these data, is not so much the sound changes per se, as their sheer density in such a limited territory.

The impression of fragmentation is even stronger if the data are plotted into a map. Indeed, even those languages which share the same sound change (e.g. *s>/h/, *r>/j/, or *áCi>/aeC/), instead of forming a coherent cluster, are geographically scattered. Figure 6 illustrates this with the reflexes of *asi "song" (or with the article, *na asi). When a change is shared across neighbouring languages, it may result from the spread of a single innovation across adjacent dialects on the chain (e.g. *s>/h/ in Mwotlap and Volow). However, it is often the case that a given change is restricted to just a single dialect, and absent from its immediate neighbours (e.g. *asi > VRS /oes/). When the same change took place in two geographically separate dialects, it probably reflects parallel development. For example, given what is otherwise known of these two languages, it would not make sense to group together the geographically distant Lehali and Lakon on the basis of their shared changes *s>/h/ and *a(C)i>/ae(C)/, as illustrated by *asi > LHI n-aeh, LKN ʔ aeh ʔ aeh (see the boxes in Figure 6). Clearly these are two parallel developments, which occurred independently in both places. Now, in the perspective of the forthcoming discussion, it may be interesting to underline the coincidence that both in Lehali and Lakon, the resulting string /aeh/ turns out to be as different as one can get from the forms of their actual day-to-day neighbours -respectively Löyöp /n-ɪs/ and Olrat /nɪs/. And indeed, in this part of Vanuatu, it is common to find a higher degree of phonological differentiation between languages which are otherwise, both geographically and linguistically, very close to each other. It looks as though sound change were being (sub)consciously exploited by each speech community as a means to distinguish itself from its immediate neighbours ( §6.2).

Language diversification through irregular sound change

THE DIFFUSION OF IRREGULAR FORMS

In addition to regular sound change, some forms have gone through irregular changes, i.e. changes restricted to particular lexical items. The precise dialectological history of each cognate set can often be traced with reasonable accuracy. By observing modern forms in the light of known regular sound correspondences, it is possible to reconstruct intermediate protoforms -some of which show irregular innovations -and observe their distribution in the dialect chain.

For example, in the case of the noun "crayfish" (Table 3), while all the modern forms are probably ultimately cognate (but see below), it is necessary to reconstruct not one, but four distinct protoforms:

- etc. The geographical range of these different protoforms is shown in Figure 7.

<Figure 7 about here>

The four intermediate reconstructions are all ultimately derived from the Proto Oceanic etymon for "crayfish", namely *quraŋ (Ross, Pawley & Osmond f/c). Yet among them, only one -namely *ura -shows the expected form based on regular sound correspondences. Thus, considering that the loss of POc *q in all positions, and the loss of word-final consonants, are both common changes in the North Central Vanuatu linkage (Clark 2009: 10, 17), the protoform *quraŋ regularly yielded a pre-modern form *ura, of which a word like ʊr in Vurës is a perfectly regular reflex (via metaphony and unstressed vowel deletion, see §4.2.1). By contrast, the three other reconstructions involve an extra change which cannot be explained by just regular sound change. Thus *ira entails an irregular vowel change *u  *i, found only in this lexeme. The form *uraŋi illustrates the locally frequent yet unpredictable accretion of a non-etymological *-i, and the subsequent retention of the root-final consonant (*ŋ). As for *raɣu, it is unclear whether it is an irregular reflex of *quraŋ (via **ɣura and metathesis? or **uraŋu >**uraɣu?); or if it is in fact non-cognate with *quraŋ -in which case it would be a case of lexical replacement ( §4.4). This minor question makes little difference for our current discussion, which is about the spread of innovative forms. Intermediate innovations for the noun "crayfish" (<POc *quraŋ)

Because *ura is regular, its reflexes are merely cases of shared retention: the processes of sound change affecting them have to do with regular phonological changes that do not target this particular lexeme. But the case is different for the three other forms, which are clearly innovative. Each of these three forms (*ira, *uraŋi, *raɣu) is unpredictable, and cannot be assigned any simple phonetic motivation. The fact that they are each found in several adjacent languages (Figure 7) is best explained by a diffusional scenario: each form had to emerge in some dialect, and then spread, by imitation, across a portion of the social network.

The complete history of this individual cognate set for "crayfish" can thus be reconstructed as a layering of multiple post-dispersal innovations, each with a different geographic scope. Some spread across vast dialect networks, such as the (regular) change *q>*ʔ>Ø -*quraŋ > *ura(ŋ) -witnessed throughout North Central Vanuatu. Others limited their impact to just a few adjacent dialects, such as the vowel change *(q)ura(ŋ) > *(q)ira(ŋ).

Interestingly, in those cases where a relative chronology of changes is reconstructable, it can be shown that innovations affecting a smaller area sometimes took place before those affecting a larger network. Thus, the accretion of a paragogic vowel *-i (as in *(q)uraŋ > *(q)uraŋi), which happened with various lexemes in southwest Gaua (François 2005a: 479), must necessarily have taken place at a time when POc word-final consonants were still there. The regular loss of word-final consonants (e.g. *(q)uraŋ> *(q)ura#), a sound change found all across the NCV linkage, necessarily took place later. At first sight, this scenario seems at odds with the tree-like form of Figure 4 ( §3.2), as it implies that certain innovations characteristic of higher nodes (large social networks, in this case the NCV linkage) must have taken place after other changes in the lower nodes (small social networks, in this case three dialects of *ira *r ɣu Regular *ura *ur ŋi Gaua). But this is precisely an important difference between the classic interpretation of phylogenetic trees in terms of successive demographic splits, and events of postdispersal horizontal diffusion such as the ones I am describing here. Because the "nodes" of Figure 4 do not define subgroups, but linkages, they are not strictly ordered in time; they merely reflect relations of spatial and social inclusion.

In other cases, the reverse ordering of events (large-scope first, small-scope later) must be reconstructed. It must be borne in mind that such processes of diffusionespecially those regarding sound change -were only possible as long as the dialects in contact maintained enough mutual intelligibility to let innovations spread through. For example, it is highly likely that the replacement of *(q)ura(ŋ), across northern Banks (Figure 7), with an innovative form *(q)ira(ŋ), occurred at a time when the dialects involved still had very similar phonological systems, with five vowels and a trill /r/. It is only later, once the form *ira had settled to that area, that each dialect went through its own idiosyncratic forms of phonological change -e.g. *na íra > n-i ɛj in Löyöp, /n-ɪj in Mwotlap, /naer/ in Lemerig, nirɪ in Vera'a. 3 If the order of sound changes had been the opposite (phonological sound change first, lexically-specific change later), this would have meant that the word "crayfish" would have first evolved into distinct forms such as (*na ura>) **n-ʊj in Löyöp and Mwotlap, **nʊr in Lemerig, **nurʊ in Vera'a. Later, as speakers of, say, Lemerig would have shifted irregularly from **nʊr to /naer/, their Vera'a neighbours would have "borrowed" the irregular change, and altered their own **nurʊ into nirɪ . Such a scenario, whereby languages could have borrowed an irregular sound change after they had become phonologically differentiated, would be highly unlikely. In such a case, it is therefore safer to reconstruct a sequence whereby the change with a larger geographic scope -irregular *(q)ura(ŋ) > *(q)ira(ŋ) -took place first; whereas sound changes limited to smaller communities (e.g. regular *iCa > /aeC/ in Lemerig) are more recent (François 2005a: 456). Occasionally, the recent date of certain phonological changes can be supported by external evidence. For example, the shift *r>j in northern Banks can be shown to have occurred within the last century or so, both on Motalava (François 2001:62) and on Ureparapara;4 the {*r>j} isogloss one observes today here results from a recent process of diffusion.

Overall, events of diffusion sometimes spread across large chunks of the network, and sometimes across reduced areas, with no principled way to order these in time. Both orders are attested:

• innovation spread to a smaller area first [*(q)uraŋ>*(q)uraŋi in southwest Gaua],

3 Various morphological changes also affected each language in ways different from its neighbours. This is the case, for example, with the accretion of a former NP article, whether *na or *wo [START_REF] François | Noun Articles in Torres and Banks Languages: Conservation and Innovation. Language Description, History and Development: Linguistic Indulgence in Memory of Terry Crowley[END_REF], to the noun stem: e.g. *na íra > *n-irɪ > VRA nirɪ; *na uráŋi > *n-urɪŋ > OLR nurɪŋ; *wo úra > *w-ʊr > NUM wʊr.

followed by an innovation spread to a larger area [loss of *C# in all NCV languages]

• innovation spread to a larger area first [*(q)ura(ŋ)>*(q)ira(ŋ) in northern Banks],

followed by an innovation spread to a smaller area [e.g. *r>/j/; vowel metaphony in each distinct language]

In sum, irregular processes of (word-based) sound change were the reason why a single inherited etymon *quraŋ separated, as it were, into four intermediate forms. In turn, these followed various patterns of phonological and morphological change, both regular and irregular, which eventually brought about the various different forms observable today. A similar demonstration could account for the various modern forms shown in Table 3 for "breathe", which combine layered processes of irregular and regular sound change.

In each case, language fragmentation results from an accumulation of various innovations (in these examples, sound change), each of which diffused to a different portion of the social network. The overlay of multiple intersecting isoglosses ended up providing each local communalect with its own linguistic identity.

PARALLEL INNOVATION IN LEXICALLY-SPECIFIC SOUND CHANGE

Geographically speaking, the distribution of etymological variants for "crayfish" as shown on Figure 7 was orderly enough to group together adjacent languages, and reconstruct a single irregular sound change that diffused by contact. But the situation can sometimes be less tidy, in ways that make it necessary to consider the possibility of drift or parallel innovations -in a way similar to what was proposed in §4.2.2 for phonological change.

Consider, for example, the case of the 1 st person dual inclusive pronoun, given in the last column of Table 3. Its full etymological form can be reconstructed as *ɣiⁿda-ruaitself from Proto-Oceanic *kita "1incl:Pl" + *rua "two". 5 This pronoun *ɣiⁿdarua evidently acquired three irregular reflexes at some points of its history: *ⁿdarua (via apheresis); *ⁿdaru (apheresis + apocope); *ɣiⁿdua (via syncope). For reasons of space, I will not detail here the individual changes for each of the 17 modern forms; but each of them can be regularly derived (François 2005a) from one of these intermediate reconstructions, for example:

• LHI ɣɪnjɔ < *ɣɪⁿdrɔ < *ɣiⁿdarúa • HIW t g ʟ < *ⁿdər < *ⁿdarúa (< *ɣiⁿdarua) • DRG ⁿdaːr < *ⁿdáru (< *ɣiⁿdarua) • LKN wʊʧʊ < *ɣʊʧʊ < *ɣəⁿdʊ < *ɣiⁿdúa (< *ɣiⁿdarua)
The dialectological distribution of these four intermediate protoforms (Figure 8) is geographically more chaotic than the neat isoglosses we saw in Figure 7 above. It is likely that at least some of the innovations shared by distant communities reflect parallel innovation, or drift. For example, the syncope which yielded the protoform *ɣiⁿdúa must probably have taken place separately in the history of Löyöp, Vera'a and Lakon; hypotheses resorting to contact or migration, although not excluded, would not be very convincing here. 2), we have seen that processes of wordspecific sound change sometimes involved diffusion -as in Figure 7 -and sometimes occurred independently in separate languages. In both cases, the change was restricted to a relatively small area, and has resulted in more linguistic fragmentation at the scale of the Torres-Banks archipelago.

Language diversification through lexical replacement

In the course of three millennia, the combined effects of regular and irregular sound change thus managed to create enough diversity to make these languages mutually unintelligible, even in those cases where the modern forms were ultimately cognate with each other. But in addition to this widespread tendency towards sound change, another process has proven even more powerful in bringing about linguistic divergence over time. This is lexical replacement -when an inherited form was replaced by another word, historically unrelated, for a given meaning.

LEXICOSTATISTICS AND THE RATE OF LEXICAL REPLACEMENT

In his lexicostatistical study of the New Hebrides, Tryon (1976) calculated percentages of lexical cognacy between pairs of languages, based on a list of about 250 "basic" vocabulary items. In his tables of Torres and Banks Islands (1976:95), the highest figure *ɣiⁿd ru *ɣiⁿdu *ⁿd ru *ⁿd ru of lexical closeness between any two languages -Mwesen and Vurës -is 88.4 percent of shared basic vocabulary. 6 But more significant is the lowest figure of his chart, which shows that the two lexically most distant languages of these islands -Hiw and Lakonshare no more than 44.5 percent of their basic lexicon. All other numbers, for the Torres and Banks Islands, range between 45 and 88 percent of shared vocabulary.

By definition, these figures tell us nothing about linguistic differentiation among cognate forms through sound change ( §4.2, 4.3). Yet they are quite instructive when it comes to weighing the degree of lexical replacement in this area of northern Vanuatu. By way of comparison, lexicostatistical figures calculated with the same method for better-known subgroups of Indo-European [START_REF] Dyen | An Indoeuropean Classification: A Lexicostatistical Experiment[END_REF] show that the rates of shared vocabulary range between 91.4 and 61.0 percent in the Slavic subgroup; between 97.0 and 53.6 in Germanic; and between 89.9 and 51.1 percent within Romance. 7 None of these three groups goes down any closer to the rate of 44.5 which is found within Banks-Torres alone.

One could debate how statistically significant the difference is between the figures of 44.5 percent and the lower rates (e.g. 51.1) found for Indo-European subgroups. The time depth involved in these different cases of linguistic diversification is essentially similar: the "protolanguage" ancestral to the Torres-Banks area ("Proto-Torres-Banks") began its existence about 3,200 years ago, but must have only broken up several centuries later, after a period of shared development during which it formed a homogeneous dialect chain (a "single language"). Such dates (between three and two millennia of age) are thus comparable to those generally accepted for the three subgroups of Indo-European mentioned here. In this perspective, the chronological pace of lexical diversification in the Torres-Banks linkage may be said to be essentially similar with each of the three Indo-European subgroups mentioned here.

While lexical replacement does not seem to be significantly faster than elsewhere, what is extreme here is rather its geographical and human density. Indo-European high-order subgroups such as Romance, Germanic or Slavic, all involve immense language communities whose demographies count hundreds of millions of speakers, dispersed across vast territories. By contrast, the Torres-Banks archipelago represents a land surface about 10 percent the size of Corsica, and has a population of just a few thousand individuals (nowadays 9,400). The fact that this very low-order subgroup of Austronesian, with such a small population, has reached such a degree of lexical diversity, begs for an explanation.

Koro (or to Lakon) and Volow very close to Mwotlap, it is possible that the inclusion of these two languages might have yielded slightly higher figures for maximal lexical cognacy. Conversely, Tryon distinguishes between "Merig" and "Merlav" (94.5 percent of cognacy), which I consider to be just two varieties of Mwerlap ( §2.1.1). 7 Excluding creoles, the lexically most remote languages in each group are: for Slavic, Slovenian and Byelorussian (61.0); for Germanic, Faroese and English (53.6); for Romance as a whole, French and Vlach (51.1).

SEMANTIC CHANGE, MARKEDNESS SHIFT, AND LEXICAL REPLACEMENT

Combined with the various patterns of sound change we saw earlier, lexical replacement largely accounts for the high level of divergence found between the word forms of northern Vanuatu languages. See, for example, the variety of words for "properly" or "speech" in Table 1 ( §1.2).

One question arises from this observation, namely, what motivates lexical replacement. Is this a conscious process? Is it primarily driven by social factors? In the final section of this study, I will indeed argue that sociolinguistic factors in this area of Melanesia play an important role in the diffusion and spread of lexical innovations. However, I will also propose ( §6.3) that these factors only account for the diffusion of innovations once these have already emerged. As for the question of how lexical innovations themselves arise in the first place, I will claim here that this is best explained by universal tendencies of semantic change and lexical replacement, which are not specific to this region.

Languages replace lexical items for a variety of reasons. They may renew items of their vocabulary, for example, to avoid homophony [START_REF] Gilliéron | Études de Géographie Linguistique d'après l'Atlas Linguistique de la France[END_REF][START_REF] Keller | Invisible-hand Theory and Language Evolution[END_REF]Campbell 2004a: 322). Another motivation may be related to the social practice of linguistic taboo [START_REF] Blust | Linguistic Evidence for Some Early Austronesian Taboos[END_REF]. Indeed, Simons (1982: 183) considers linguistic taboo to have played a key role in lexical replacement in the Austronesian family. However, this explanation is not entirely convincing for northern Vanuatu. The only form of taboo reported for this area (Codrington 1891:43), and still in use today, forbids individuals from uttering the names of their in-laws; should they need to use a word phonetically similar to a forbidden name, they will have to replace it with a synonym. Obviously, this form of word taboo differs from person to person depending on their position in the kinship network, in such a way that it never affects a whole community. Such a cultural explanation is therefore not the final word to account for lexical replacement.

Most often, the replacement of a word by another simply results, I believe, from universal processes of semantic shift [START_REF] Blust | Lexical Reconstruction and Semantic Reconstruction: the Case of Austronesian "house[END_REF][START_REF] Blust | Five Patterns of Semantic Change in Austronesian languages. A journey through Austronesian and Papuan linguistic and cultural space: Papers in honour of[END_REF]Wilkins 1996;Blank & Koch 1999b;Vanhove 2008). In typical cases of lexical replacement, the starting point is a language which, at a given point in time, has a number of close synonyms for a given meaning. These may initially differ in their semantic nuances, their connotations, or their stylistic register. As speakers manage their way through the manifold adjustments of daily communication, some semantic or pragmatic extension of one lexeme may gain ground over its lexical neighbour, and tend to replace it in certain situations. Should the new usage take root and spread through the speech community, eventually the old term becomes obsolete and ends up being replaced by the new termfollowing a process called markedness shift (Dik 1989:44). This is how, for example, Late Latin progressively replaced its old term caput "head" with another noun testa, originally "earthen pot" (cf. Blank & Koch 1999a). I propose to illustrate the four stages taken by this case of lexical replacement, in Table 4. The brackets symbolise when a term is marked, as opposed to being the default term for a given meaning (in bold). The first innovation [STAGE 1] was to use the noun "pot" as a figurative, slang word for "head", in competition with the inherited form caput -in a way similar to French slang carafe "jug" for "head". Eventually, testa lost its jocular connotations, and ended up as the standard term for this body part [STAGE 2] -as witnessed by Italian testa, and French tête. The older term caput (> Italian capo, O.Fr. chief) resisted for some time, but had become the marked term among the pair; in 17 th century French, chef was still used as an archaic, highly marked synonym of teste, until it disappeared with this sense. In modern French, chef survives only with another meaning (historically secondary) of caput, namely "leader, chief" [STAGE 3]. The whole process can be summarised by stating that Latin/Romance "replaced" its original noun caput [STAGE 0] with an innovative form testa [STAGE 3]; but it must be borne in mind that this formulation is just a shortcut for what is really a gradual, four-stage sequence involving lexical competition and markedness shift among polysemous terms (see Sweetser 1990:9; Evans & Wilkins 2000:549). Rather than a direct shift from Stage 0 to Stage 3, the key turning point in this evolution is really the shift from Stage 1 to Stage 2, and the inversion of markedness. Most histories of lexical replacement in northern Vanuatu are likely to be explained by a four-stage sequence similar to this caput  testa example. Sometimes, the source of an innovative form can be identified, giving a clue to the semantic path which was followed. One such example can be found in Table 3 ( §4.2.2). While most languages reflect PTB *ⁿdaeru for "coconut crab (Birgus latro)", Löyöp has a non-cognate form n-ⁿd ɣi ɛj. Literally, this noun parses as "pandanus leaves" (i.e. ⁿd -< *ⁿrau-< POc *raun "leaf" + ɣi ɛj < *ɣire < POc *kiRe "Pandanus tectorius"): this is due to an analogy between the prickles of those leaves and the spines on the crab's carapace. In a way similar to the Latin example above, one can imagine that n-ⁿd ɣi ɛj "pandanus leaves" started its life as a colourful metaphor for the animal alongside the inherited form, which was presumably a reflex of *ⁿdaeru. In spontaneous speech, the old form was to be replaced more and more often by its marked synonym, which eventually became the unmarked name for the crustacean. Similarly, Mwerlap has replaced *ⁿdaeru with another compound form: n -ɣ t -tɛ ak, literally "the spearing hermitcrab", by reference to the crustacean"s dangerous limbs. These are cases of lexical replacement via compounding and markedness shift.

LEXICAL COMPETITION IN PROGRESS

Quite often, the process of lexical replacement has not taken any definite shape yet, but already lurks around in the ongoing competition between two semantically very close words. By observing the patterns of variation between speakers, it is possible to literally spot lexical replacement in progress. Thus, to take a last example from Table 3 above, the Hiw noun for "song" used indeed to be ɔs (<*asi); yet this is now a marked, archaic term which is reserved for "sacred song" or "Christian psalm". The unmarked word for "song" nowadays -often the only one known to younger speakers -is təntənɔ, derived from the verb tənɔ "learn".

Instead of showing lexical competition as a completed process [Stage 3], what these cases illustrate is precisely the phase of lexical competition between two words [Stage 1~2], as a forerunner of lexical replacement. Modern languages of northern Vanuatu teem with pairs of synonyms, and it is likely that this was also the case in earlier stages of their history. Some synonyms are just free variants, and indeed are used freely by the same speakers in the same contexts -e.g. na-mtɛ and nɛ-m bɛɣ, two perfect synonyms used for the breadfruit tree in Mwotlap. But in many cases, the two words differ either semantically or stylistically, in terms of register. For example, Mwotlap has a verb jɔŋtɛɣ "hear, listen". All speakers would agree that this form is a "casual word" (hɔhɔlɛ βasapsawjɛɣ), and that in certain social contexts -e.g. in order to adorn one's story-telling with a colourful style, or show respect to one's in-laws by carefully choosing a more delicate wording -it would be more appropriate to use haltiŋk pʷɔj, a "heavy word" (hɔhɔlɛ map) with the same meaning.

Similarly, young Hiw speakers are taught to use "respectful speech" (məŋa t mmaβə) or "avoidance speech" (maŋə βisəβisə) as a token of respect when addressing important interlocutors. In such a situation, rather than using dull and direct everyday words such as (1), it is more appropriate to resort to some sophisticated paraphrasis such as (1"):

(1) HIW nɔ ə ɣənɣɔn 1sg eat "I'm going to eat."

(1') HIW nɔ ə g ʟ -a g ʟ-ɣe ti nɔ ə 1sg seize-seek-thing DAT 1sg

"I shall seize something for myself."

[respectful equivalent of "I'm going to eat"] Insofar as the morphological sequence /ᶢʟak-aᶢʟ-ɣe/ has already become conventionalised, in the respectful register, as a synonym for "eat" (Stage 1), it is not difficult to imagine a potential scenario whereby this expression, after progressively losing its stylistic markedness, might end up becoming the new standard way to say "eat" in Hiw (Stage 2), and eventually replace ɣənɣɔn in the lexicon (Stage 3).

The dynamic lexicons of northern Vanuatu languages display all possible degrees on the scale of stylistic markedness -from the familiar variant to the fading-out, literary archaism. Crucially, what appear to be stylistic differences from the synchronic point of view are often correlated with historical processes of lexical change. Whether the new expression reflects a slangish shortcut or an elevated metaphor, it will start a lexical competition with the word previously in use, for the position of being the default form for a given meaning. While this arm-wrestling may continue for a long time, it will often end up with the victory of one form over the other.

THE DIFFUSION OF LEXICAL INNOVATIONS

These processes of lexical replacement have resulted in a high degree of linguistic divergence among northern Vanuatu languages.

Table 5 -Language differentiation through lexical replacement:

a few lexical sets from northern Vanuatu "person" "woman" "true" "Complementiser" "(be) like"

Hiw tajɵ [1] jəkʷen [1] βəwjə [1] tɔm [1] ŋʷe [1]
Lo-Toga

telə [1] ləkʷɛβinə [1] βəwiə [1] tɛ [1] wɛ [1] Lehali n-at [2] n-lɔkβɛn [1] tŋʷas [2] ⁿdɛ [2] nan [2] Löyöp n-at [2] n-lik pʷi ɛn [1] taŋ mʷas [2] sɛ [3] mɛnɛ [3] Volow n-at [2] n-lɛ ŋ g bʷɛβɪn [1] hɛjwɪ [3] ŋ gɔ [4] βɪh [4] Mwotlap n-ɛt [2] na-lk pʷʊβɪn [1] hɪjwɪ [3] sɔ [3] k pʷɛlɛ [5] Lemerig n-ʔɒŋsɒr [3] n-rɛŋɛ [2] ʔirɣi [4] woe [5] maekae [6]
Vera'a In some cases, the comparison of lexical isoglosses, combined with knowledge of regular sound correspondences, make it possible to group together forms that are cognate. Each column of Table 5 has subscript numbers labelling together those forms which derive from the same protoform, i.e. whose modern differences are only due to regular or irregular sound change; the last row shows the number of distinct cognate sets that need to be posited for each meaning.

For example, the 17 modern forms for "person", in the first column of Table 5, can be reduced to four cognate subsets, reflecting respectively *talua, *ata, *tamʷasara and *taⁿdunu. Of these, *ata is PNCV *ʔata "spirit, soul; person" (Clark 2009:76), itself from POc *qata "shadow, reflection; soul". The *ta-element in other forms are either truncated forms of the same noun, or reflexes of POc *tau "person". These longer forms are compounds, literally PTB *ta-ⁿdunu "real person" (cf. column "true") and *ta-mʷasara "ordinary person" (cf. *mʷasara "poor, needy"). The etymology of *talua is unknown.

The dialectological distribution of these four etyma defines four geographically coherent clusters of languages. In line with maps given earlier for sound change, lexical isoglosses for the noun "person" are charted in Figure 9. In the absence of compelling evidence, Figure 9 remains agnostic as to which of the four forms are to be considered conservative vs innovative.

Figure 9 -Language differentiation through lexical replacement:

Intermediate protoforms for the noun "person"

Just like we saw earlier for sound change, linguistic divergence here followed a multilayered process. First, the early dialect chain witnessed the emergence of new forms for the same meaning, each of which spread to a portion of the dialect network. At some point, the initial unity had broken up into four isoglosses for this particular word. Later on, each of the four etyma underwent local patterns of sound change, which increased the degree of differentiation within each dialect set: e.g. *tamʷasara > MSN taŋ mʷsar, LMG n-ʔɒŋsɒr; *taⁿdunu > MTA tanun, OLR ʧuʧuŋ, etc.

Notice, incidentally, that the distribution of lexical isoglosses for this word "person" does not match the one observed earlier for the noun "crayfish" (Figure 7) -let alone the random scattering found with the 1incl:Dual pronoun (Figure 8). The more examples of individual lexical items would be brought in, the more inconsistent the picture would become. This shows how the spreading of innovations differed from one individual item to another. Should the historical linguist attempt to map together various kinds of isoglosses with the hope to identify coherent clusters of shared innovations, this would turn out to be a vain endeavour. Even though some dialects may have evolved together with respect to certain innovations (cf. the four languages of Vanua Lava I. in Figure 9), they are always separated by a large number of other innovations (cf. the same four Vanua Lava languages in Figure 7 and Figure 8). This pervasive intersecting of isoglosses, which is typical of linkage phenomena ( §3.2), jeopardises any hope of ever coming up with any neat phylogenetic tree for the region.

The noun "person" is the simplest case of Table 5. The other examples show even more intricate histories, which I will not detail here. This is true not only of lexemese.g. "woman", "true" -but also of grammatical morphemes, like the complementiser. In *talua *ata *tam w asara *ta n dunu these cases, the combination of lexical innovations with morphological or phonological change appear to have defined small areas of diffusion, sometimes restricted to just one or two adjacent dialects.

Summary: On linguistic diversification in northern Vanuatu

Overall, three major kinds of change have contributed to the diversification of northern Vanuatu vocabularies: regular phonological change at the system's level, irregular sound change and morphological innovations in specific words, and lexical replacement.

Beyond their differences, these three types of change share a few properties. Each innovation must have arisen in the speech of some individuals in the archipelago, and then diffused from speaker to speaker, by imitation, until it settled to a certain portion of the social network. Sometimes, innovations were confined to just a single communalect, or a set of adjacent villages. In other cases, the isogloss covered a larger, contiguous area, involving dialect contact across islands. Some changes found in widely separate places may be due to drift or parallel innovations. As more innovations added up over time, each member of the dialect chain further differentiated itself even from its closest neighbours: this is what brought about the linguistic fragmentation we observe today.

Considered individually, most of the innovations which have occurred in the history of northern Vanuatu languages are unproblematic, and can be explained by typologically common processes of language change. Two points, however, are characteristic of this group of languages, and are still in need of an explanation.

One point is the high density of these innovations. For example, we saw ( §4.4.1) that rates of lexical diversity in basic vocabulary among northern Vanuatu languages are similar, and even higher, to those found within certain high-order subgroups of Indo-European -for a much smaller population. I will propose, in §6.2 below, that this high degree of linguistic diversification can be explained by the language ecology of the area, and with social attitudes that prevail among the local population.

The second paradox is that the high degree of linguistic divergence observed among these 17 languages goes along with a reverse trend, one which could be described as a form of regional convergence. However, this convergence does not show up in the same linguistic domains as the diverging tendency we just observed. Fundamentally, the domains in which northern Vanuatu languages show most intense differentiation are those that affect the FORM of words -whether this involves sound change or lexical replacement. By contrast, the same languages show much more homogeneity with respect to the STRUCTURAL COMPONENT of these words -whether in terms of their morphosyntactic properties or their semantic makeup. This structural homogeneity is the subject of the next section.

Structural isomorphism in northern Vanuatu

Structures vs forms

A sign may be described as the association of a specific phonological string or FORM with properties of STRUCTURE -the latter referring to the organisation of meaning into language-specific categories and constructions.

This contrast structure vs form corresponds more or less closely to what Ross (2001:148) called lemma vs form; or to the contrast drawn by Grace (1981:24) between, respectively, content form vs lexification (see the citation in §6.4). The reason why I am not using Grace's term content form -a term originally from Hjelmslev (1961:52) -is its relative opacity, especially as it is supposed to contrast with what I (following Ross, and others) call form.

As for the term lexification, it is too restrictive, if it is taken to apply exclusively to the form of lexemes. My use of the pair of terms structure vs form is really orthogonal to the traditional divide between grammar and lexicon. The "form" refers to the phonological substance of the linguistic sign, whether it is a lexeme, a grammatical morpheme or a construction. As for the term "structures", it refers to those relational properties between signs -whether relations of contrast or of combination between signs. This includes those structural relations on the syntagmatic axis (morphosyntax, combinatorics, phraseology), as well as those on the paradigmatic axis (lexical and grammatical semantics). Under this structuralist model, semantic properties of lexemes and morphemes (their "meaning") are subsumed under their structural properties, insofar as they are defined by their contrasts, and by their various combinations within the language's repertoire of constructions.

Two languages can be said to be ISOMORPHIC in a particular domain of their system, if the signs they use in a given speech situation share the same structural (or constructional) properties. For example, the two sentences in (2) are perfectly isomorphic, because they express the same functional content by resorting to identical structures:

(2) ENG You can take your time. FR Tu peux prendre ton temps.

2sg POT.AUX take POSS:2sg time "You don't need to hurry."

The isomorphism between English and French concerns here not only the parallel order of words, but also the inherent properties of each component in the sentence. Thus, both languages have parallel constructions in which the abstract notion "time" is modified by a possessor, and the object of an active verb "take". The two languages provide that construction with the same meaning ("act as slowly as necessary or desired"), and with the same array of pragmatic implications ("no need to hurry, you can relax", etc.). Structural isomorphism can be perfect as in ( 2), or quasi perfect as in (3):8

( Even though the two sentences in (3) show one syntactic difference (presence vs absence of NP article on the object), they are otherwise structurally parallel. Thus in English and French, have and avoir are both lexical verbs whose meanings include "possess", and which can both be used as auxiliaries to encode perfect aspect. Cold and froid are both temperature adjectives which can be used as nouns. Finally, catch (a) cold and attraper froid are two parallel constructions that share the same semantic properties, considered as a whole ("become sick due to cold weather") as well as in their internal make-up (identical metaphor involving a "catching" event).

Crucially, structural isomorphism across languages is independent of the relationship between the phonological forms of words. In example (3), the two pronouns I and je, while ultimately cognate, have evolved in such a way to lose any form of similarity. All other words in ( 2) and ( 3) are not cognate between French and English.

Diversification of forms, isomorphism of structures in northern Vanuatu

As §1.2 (Table 1) already suggested, the languages of northern Vanuatu exhibit countless patterns of structural isomorphism, regardless of the diversity of their forms. This parallelism among languages was already witnessed by the missionary-linguist Codrington at the end of the 19 th century: "an examination of their languages discovers a very considerable underlying sameness" (Codrington 1891: 20). Because these languages are all closely related, it can often be ambiguous whether a particular case of isomorphism simply reflects shared inheritance from their common ancestor (Proto Oceanic), or a post-dispersal innovation which diffused across a linguistic network ( §3.2). Only in the latter case is it appropriate to speak of convergence strictly speaking. Usually, external evidence will make it possible to identify what is shared among Oceanic languages and may potentially be reconstructed for their common ancestor. In this section, I will focus on examples which appear to be more specific to northern Vanuatu, as they presumably reflect events of convergence restricted to this area, as opposed to shared retentions from their Proto Oceanic ancestor. 9 Sometimes, structural homogeneity goes along with a set of forms that happen to be all cognate. For example, the verbs meaning "breathe" in Table 3 ( §4.2.2) all colexify the two meanings "breathe" and "take rest" (cf. François 2008:183). Because most of the modern forms are cognate, Occam's razor simply suggests to assign this polysemy to their ancestral etymon -*maᵐbusaɣi, a shared lexical innovation of the Torres-Banks linkage (cf. François 2005a:482, Clark 2009:132) -and conclude that the meaning diffused together with the form. 10 In some way, this is also a case of structural diffusion, in the sense that some structural property (in this case, an apparently innovative case of polysemy) was spread across the whole area; but this is not a spectacular nor a 9 I will come back to the issue of structural convergence vs retention in §6.1.2. 10 The polysemy "breathe; take rest" is not mentioned in Ross's reconstruction for POc *mañawa (Ross 1988:461), yet it is found in the Hiw reflex mənawə. This could reflect areal influence from *maᵐbusaɣi.

problematic case, because it most likely diffused together with the form.

More revealing are those cases which involve both isomorphism of structures and diversity of forms. Indeed, these cases entail that the very same words have gone, so to speak, in two opposite directions. On the one hand, their forms have gone through processes of divergence, either through phonological diversification or lexical replacement; on the other hand, their structural properties have maintained -or created -cross-linguistic homogeneity.

The following pages will concentrate on the latter cases, as they clearly make it necessary to discriminate between the divergence of forms on one side, and the stability or convergence of structures, on the other side. For reasons of space, I will confine the discussion to five sets of words, listed in Table 6. Whether they belong to the lexicon or to the grammar, these words are structurally isomorphic, insofar as they display the same properties across languages: the same semantic range (polysemy, polyfunctionality), the same combinatorics, and parallel usage in phraseology. An obvious manifestation of these languages' isomorphism is the fact that most of their sentences are amenable to a single line of interlinear translation -just like in Table 1 above. In the following pages, even when a given construction is attested in most or all of the archipelago, I will gain space by keeping the examples down to just a small sample of up to five languages. The selection will be arbitrary, but will attempt to cover as wide an area as possible, following the same north-to-south order as in previous tables.

Structural isomorphism in the lexicon

ADJECTIVE "RANDOM"

All northern Vanuatu languages have an adjective (often found in verb-modifying position) showing a broad polysemy, around a meaning which may be glossed "random". Its typical spatial sense describes a motion as random or aimless: Outside the spatial domain, a common semantic extension is "messily, casually, following no specific principle or rule". This may have negative connotations, as in situations where some social rule should be followed:

(4) MTP ɪ ni-
( The combination of this adjective with the verb "do, make" will form a compound verb meaning "mess up, spoil, damage": In all cases, languages show structural isomorphism, regardless of whether their forms are cognate or not.

POSTVERB "FIND"

Northern Vanuatu languages lack any verb "find". What they have is a "postverb" -or verb modifier -which they use to create compound verbs with the sense "find". For want of a better translation, I will gloss this postverb as "find" -even though this is usually not synchronically a proper verb. A rough parallel would be Eng. come across X, where the sense "find" results from the combination of come and across.

The verb V 1 that precedes the postverb describes the action which led to the finding event, i.e. looking (10), listening, groping, searching, walking (11), and so on: "I've found some money (as I was walking)."

(
In all these languages, the same postverb is also used in combination with the verb "think", to construct the meaning "remember":

(12) VLW nɛ m-ⁿdɔn sas ɪɣɪn! LMG noe m-toet ʔɛsɣøʔ β ʔ nɪ! MTA na me nom suar n p ! LKN na n- ʧɪːʧɪm ɣɪn ɣɪnɛ ! 1sg PRF think (find) now "I remember now!"
The map in Figure 10 shows two layers of isoglosses for this postverb "find". The dotted lines show the distribution of cognate sets across the archipelago, and are thus concerned with the dialectological distribution of word forms -in line with Figure 9 ( §4.4.4). The solid line, on the other hand, shows that all modern words, despite events of lexical replacement and sound change, share the same structural features. The case of the postverb "find"

Recently collected data [START_REF] Henri | Éléments de Description d'une Langue Mélanésienne du Vanuatu[END_REF] show that the next language further south (Sungwadia, the northernmost language of Maewo Island), despite occasional contact with the Banks Islands, does not have any word which would share all the structural properties of the postverb "find" found in Torres-Banks languages. In other terms, the solid line in Figure 10 outlines exactly the maximal extent of the structural isogloss for this postverb "find".

THE RESTRICTIVE POSTVERB

All northern Vanuatu languages have a functionally similar restrictive word which may be glossed "just, only". Everywhere, it fits in the same slot of postverb, and thus occurs at the end of the predicative phrase. This restrictive postverb indicates that the predicate is restricted to a low value, as in English only three, or just you. This use was illustrated in (9) above.

Combined with a verb, the restrictive commonly means "do nothing else than": Languages will idiomatically use this restrictive in combination with stative predicates that semantically imply a limited quantity or quality -e.g. "small", "light", "easy", "close", "identical"…: Another idiomatic use is to combine the Restrictive with the predicate "[be] good". Because the meaning of the latter is semantically downgraded by the restrictive, what results is a phrase meaning "it's just fine; no worries" -see ( 21) below. Finally, example (24) will illustrate how the same restrictive postverb is a typical component of the Immediate Perfect construction (Eng. "have just done"). share the semantic and phraseological uses of the Restrictive postverb, as described in this section. As for the smaller circles, they delineate the maximal area of diffusion of each cognate set. Some of these are identified by reconstructions (e.g. *ɣaᵐbu, the regular source of the modern forms ɣɔp, ɣɛm, ɣap, am, ɣɔm); but when a cognate set is restricted to one language, I indicate the form itself.

(
<Figure 11 about here>

Structural isomorphism in the grammar

The isomorphism found in the lexical domain is also present, to a large extent, in the functional properties of most grammatical morphemes. I will take only two examples here: the Negative Existential; and the Time Focus aspect.

THE NEGATIVE EXISTENTIAL

All northern Vanuatu languages possess a word with similar semantics and grammatical properties, which I will gloss "Negative Existential" (NEG:EXIST). First, this word shows everywhere the same grammatical features. It is a member of a closed class of "directly predicative words", which is distinct from verbs. Like other major parts of speech -e.g. verbs, adjectives and nouns -they can form the head of a predicate phrase; yet unlike them, these predicative words can do so directly, without any inflectional morphology. This small class of uninflected words patterns with other non-verbal predicates (François 2005b,c), such as locatives and demonstratives.

The isomorphism concerns not only the morphosyntactic behaviour of the Negative Existential, but also its semantic and phraseological properties. When it takes an overt noun phrase as its subject, NEG:EXIST states the absence of the referent at a given place (Eng. "there is no X"): With a human referent as its subject, the same predicate word will often translate as "not be there, be absent": The same word "NEG:EXIST" is also often used absolutely (i.e. with no overt subject), with various meanings. For one thing, it forms the heavy equivalent to Eng. "no" in an answer to a yes/no question. In all northern Vanuatu languages, a negative reply may consist of two parts:

(
• the "light no", consisting of a prosodic gesture of the form [ ] uttered either on a schwa ə ə ə [ ə. ə. ə] or on ɔ ɔ ɔ ɔ [ ɔ. ɔ. ɔ]

• the "heavy no", which is the Negative Existential used absolutely. In sum, even though the form of the Negative Existential differs considerably between languages, its morphosyntactic properties as well as its constructional combinatorics are identical across the whole region.

THE TIME FOCUS ASPECT

Tense-Aspect-Mood (TAM) paradigms show a certain degree of variation across the area. Languages will sometimes differ in the way they cut up the semantic space of TAM reference, some languages making contrasts where others do not. For example, the TAM category called "Aorist" (encompassing sequential, prospective, subjunctive, hortative, etc.) is found only in the northern part of the archipelago; in the southern Banks languages, it is broken down into several categories (François 2009a). However, even this domain shows some areas of cross-linguistic homogeneity, as certain TAM categories are found to be very similar across the whole northern Vanuatu group. Thus, all languages possess a distinct modal category of Apprehensive (cf. [START_REF] Lichtenberk | Apprehensional Epistemics. Modality in Grammar and Discourse[END_REF]; they all distinguish Perfect vs Complete, or Future vs Potential; and so on. One particularly idiosyncratic aspectual category which can be found everywhere in the area despite the variety of its forms, is one I suggest to call "Time Focus" (TMFOC). Its underlying semantic mechanism (François 2003a: 199-216) consists in anchoring an event in time by establishing an explicit contrast with earlier possible time anchorings. In other words, a general gloss for this TAM marker would be "[do] then, and not earlier". 11As often happens in these languages which encode aspect but not tense, the Time Focus is compatible with any time anchoring, whether past, present or future. This accounts for the polyfunctionality of this morpheme. When narrating past events, the Time Focus may be used to anchor an event contrastively in the timeline: This construction combines the aspectual operation of the Time Focus ("then and not earlier") with the semantics of the Perfect, as well as with the pragmatic orientation of the restrictive towards a low quantity ("only"  "just a moment ago"). Finally, when used in an irrealis context, the TMFOC works as a sort of delayed future, thereby drawing a subtle argumentative contrast with the ordinary Future (François 2003a:205). While both markers present an event as bound to happen (e.g. "we will play, I promise you"), the Time Focus is used as a dilatory future. That is, it will place the emphasis on the necessary delay between the moment of utterance and the beginning of that event -in a way consistent with its core semantic mechanism "then, and not earlier". As these examples show, northern Vanuatu languages all share the same idiosyncratic aspect category of "Time Focus", both in the fine-grained detail of its semantic polyfunctionality, and in its various combinatorial abilities.

(
(

Summary: "One grammar, 17 lexicons"

The examples cited in the preceding pages illustrate the various forms of structural isomorphism which can be found across languages of northern Vanuatu: parallel word order, identical polysemies and semantic categorisations, similar phraseological strategies.

Such a survey could potentially be expanded infinitely, considering how a vast proportion of these languages' structures show isomorphism, whether "perfect" or "quasi perfect" ( §5.1). Of course there are always exceptions, and careful observation unveils subtle differences across languages: for example, the fine-grained semantic detail of certain TAM markers, or of possessive classifiers, seldom matches exactly across the archipelago. Also, while some patterns of polyfunctionality encompass the whole Torres and Banks Islands, other isoglosses are restricted to smaller areas. Ideally, the structural distances among northern Vanuatu languages could be measured, in a way similar to the percentages of lexical distance in basic vocabulary ( §4.4.1); but such an endeavour would go beyond the limits of this study. At this stage, I can at least offer an impressionistic figure based on my observations, and estimate that any two languages of the Torres-Banks area would exhibit about 85 percent of structural isomorphism in their utterances. The closer (geographically or socially) the two language communities, the higher this figure would be.

One finds everywhere the same distribution of meaning into functional categories and constructions, even though the boxes are filled with heterogeneous phonological forms. One could almost propose to summarise the situation using a bold formula, and say that these 17 languages represent "one grammar with 17 lexicons" -in a way reminiscent of Friedman"s (1997) paper "One grammar, three lexicons", about language contact in the Balkanic area. Of course, this would be slightly exaggerated, as each of these languages also has its own idiosyncrasies and innovations; but it would capture quite well the paradox under discussion here. Also, such a formula would have to be taken with caution due to its deceptive terminology, as the contrast is really orthogonal to the traditional divide between "grammar" and "lexicon" ( §5.1). What is observed is rather a strong diversification of the phonological forms of words (regardless whether they belong to the "lexicon" or the "grammar") vs a strong isomorphism between the structural properties of these same words (whether syntactic or semantic properties). Now that these empirical facts have been established, it is time to investigate the motivations for such a complex situation. This is the object of the final section.

Divergence and convergence: Two forms of diffusion

Explaining structural isomorphism

Among the two major trends at play in northern Vanuatu, the isomorphism is probably easier to account for. The main force at play here is language contact, and the mutual influence that neighbouring languages exert on each other.

STRUCTURAL CONVERGENCE IN MULTILINGUAL CONTEXTS

We know ( §2.2.1, 3.2) that northern Vanuatu language communities have always been in contact with each other. They have kept relations of multilingualism through their social relations, especially sustained patterns of exogamy. The fact that many children in the archipelago are raised bilingually, or by a mother who is herself bilingual, increases the rate of interference whereby languages tend to constantly reshape each other's structures. This multilingualism is evidently the key to the structural homogeneity observed in the area. Haudricourt (1961:9), in his discussion of the New Caledonian situation, also proposed to correlate patterns of grammatical isomorphism with the social configuration he calls "egalitarian bilingualism".

Many other cases around the world have been described, where distinct languages in contact have developed parallel structures -including, sometimes, perfect morphemeby-morpheme correspondences -despite their words' different origins. To take just a few examples, patterns of structural convergence have been observed between various branches of Indo-European in the Balkans (Weinreich 1953, Thomason & Kaufman 1988), between Indo-Aryan and Dravidian languages in southern India [START_REF] Gumperz | Convergence and Creolization: A Case From the Indo-Aryan/ Dravidian Border in India. Pidginization and Creolization of Languages[END_REF], between various linguistic families in southeast Asia [START_REF] Enfield | On Genetic and Areal Linguistics in Mainland Southeast Asia: Parallel Polyfunctionality of "acquire[END_REF][START_REF] Enfield | Linguistic Epidemiology: Semantics and Grammar of Language Contact in Mainland Southeast Asia[END_REF] or America [START_REF] Campbell | Meso-America as a Linguistic Area[END_REF][START_REF] Bossong | Divergence, Convergence, Contact. Challenges for the Genealogical Classification of Languages[END_REF], or between Austronesian and Papuan languages of New Guinea (Thurston 1987). The latter area of contact also gave rise to Ross" (2001) concept of metatypy, which describes the processes of structural influence which one language can play upon another one in multilingual situations. To these examples, one can add the whole field of pidgin and creole studies, which regularly unearth patterns of structural parallelism between pidgins or creoles and their substrate languages [START_REF] Keesing | Melanesian Pidgin and the Oceanic Substrate[END_REF][START_REF] Keesing | Substrates, Calquing and Grammaticalization in Melanesian Pidgin. Approaches to grammaticalization[END_REF][START_REF] Lefebvre | Creole Genesis and the Acquisition of Grammar: The case of Haitian creole[END_REF][START_REF] Lefebvre | The Contribution of Relexification, Grammaticalisation, and Reanalysis to Creole Genesis and Development[END_REF]Siegel 2000[START_REF] Siegel | The Emergence of Pidgin and Creole languages[END_REF]; or research in second-language acquisition, which consistently shows how the structures of L1 influence the acquisition of a second language L2 [START_REF] Odlin | Language Transfer: Cross-linguistic Influence in Language Learning[END_REF][START_REF] Odlin | Cross-Linguistic Influence[END_REF][START_REF] Doughty | The Handbook of Second Language Acquisition[END_REF]Winford 2003). As different though they may be in their social circumstances, all these contact situations typically follow a similar tendency, which [START_REF] Sasse | Sprachkontakt und Sprachwandel: Die Gräzisierung der albanischen Mundarten Griechenlands [Language Contact and Language Change: The Hellenization of the Albanian Dialects of Greece][END_REF], in Ross 2001:149) summarised in an enlightening formula: "With advanced language contact, there arises the tendency to develop a single language with different vocabularies."

These processes of structural convergence are ultimately rooted in cognitive pressures in multilingual situations. Structural convergence arises when multilingual speakers in contact give in to a "trend towards word-for-word translatable codes" (Gumperz & Wilson 1971:165). Achieving cross-linguistic structural isomorphism makes it cognitively easier for speakers to learn and speak the other language varieties. Also, by limiting the risk of semantic loss in translation, such parallelism increases the chances for successful communication events. Individuals who learn or practise a language distinct from their own are tempted to "transfer" [START_REF] Odlin | Language Transfer: Cross-linguistic Influence in Language Learning[END_REF]) the structures of the language they are most familiar with to the new system they attempt to use. In doing so, they tend to "relabel" [START_REF] Lefebvre | Relabelling: A Major Process in Language Contact[END_REF]) their native categories using forms of the target language. This classic model provides the explanation to the ongoing processes of convergence observed in northern Vanuatu.

CONVERGENCE OR RETENTION?

A particularity of the northern Vanuatu area, though, is that languages share the same ancestor. For this reason, it might be objected that some cases of structural isomorphism, rather than resulting from the areal spread of an innovation, really reflect the retention of an inherited construction or structural configuration; this configuration would have been transmitted over time in spite of lexical replacement in various languages. This is clearly a possibility, which can sometimes be confirmed through external comparisons (François 2010b). For example, each Torres-Banks language has a noun -different in each language -which colexifies "tree stump, tree base" with "beginning", "origin", "source" or "cause". The same polysemy is found in most Austronesian languages (Fox 1995:5); it is reconstructed by [START_REF] Blust | Austronesian Comparative Dictionary (ACD)[END_REF] for Proto Malayo-Polynesian *puna(ŋ), and by Evans (2008: 90) for POc *puqun. This is a case where languages may prove innovative in their forms, yet conservative in their semantic structures. This polysemy found across Torres-Banks languages is likely to be an inherited pattern. Strictly speaking, it could hardly be described as a case of areal convergence, since it simply reflects shared retention; logically, language contact should be irrelevant in this case. However, even in such a case where the structural isomorphism is probably inherited rather than innovative, I believe that language contact does play a role if -and only iflexical replacement has taken place. Consider, for example, the domain of WATER, whose semantic outline is identical in all Vanuatu languages: one noun colexifies "(fresh) water" with "river" or "lake", and is also a generic term for "(drinkable) liquid"; but it cannot refer to "sea" or "(salty) water", which is a separate word. While the noun "(fresh) water" is lexified, in most Torres-Banks languages, with reflexes of a root *ᵐbei, the language Lakon has replaced *ᵐbei with an innovative form tuŋ, etymologically from *tuŋu "sap, juice of a plant or fruit". The most likely "bridging context" [START_REF] Evans | In the Mind's Ear: the Semantic Extensions of Perception Verbs in Australian Languages[END_REF] which can account for the word's semantic shift from "juice" to "drinking water" would be a generic meaning "drinkable liquid". At some point in history, pre-Lakon ended up having two synonyms for "drinking water": the inherited form *ᵐbei, and an innovative synonym *tuŋu -presumably with some stylistically marked connotation, as if "juice" were used as a slang term for "water". In Typical cases of lexical replacement via semantic shift result in a change of semantic categorisation over time. Thus we saw earlier, in Table 4 ( §4.4.2), that Latin initially colexified "head" with "leader" (caput), but eventually, after a process of semantic shift, lost that polysemy and acquired a new one "head" -"pot" (testa). Likewise, the semantic shift affecting *tuŋu in pre-Lakon should logically have resulted in a new semantic organisation corresponding to Stage B, in which "drinkable liquid" (*tuŋu) and "river, lake" (*ᵐbei) would be lexified separately. But this is not what we observe in modern Lakon. Instead, some time after the meaning "water" had been relexified using the innovative form *tuŋu, this form ended up replacing the former *ᵐbei in each and every part of its initial polysemy. Streams and rivers, and even the large sulphuric lake of Gaua, are lexified as tuŋ in Lakon, despite its etymology as "juice". Not only has the new label tuŋ taken up all the senses formerly associated with *ᵐbei, but it has even lost its meaning "juice of plants", which is now lexified with a derived form (tuŋuhwiː); in parallel, Lakon has lost all traces of *ᵐbei. Stage C illustrates how Lakon now assigns to *tuŋu exactly the same semantic outline (shaded area) as that which can be reconstructed for the other root *ᵐbei.

In a way, the structural properties of Lakon tuŋ constitute a form of "retention". But considering how lexical replacement is normally expected to result in some form of semantic restructuring, this unexpected preservation of semantic structures from Stage A to Stage C needs to be explained. This paradox, whereby a language can renew its word forms without renewing their semantic outline, would be difficult to explain if Lakon had evolved in isolation from its neighbours: why should a language, after having gone through semantic change, retrieve polysemies of the past? The most likely explanation is, again, language contact. After Lakon had innovated a new word *tuŋu for the sense "drinking water", its multilingual speakers felt the cognitive pressure to (re)align its semantic properties with the ones found in neighbouring languages. This triggered the shift from Stage B to Stage C, and the generalisation of *tuŋu to all senses (and only those) formerly associated with *ᵐbei.

While the process ends up giving the illusion of structural conservatism, it can only be satisfyingly explained by positing a two-step process whereby languages diverge, and later partially reconverge:

Stage B: a local innovation, affecting both the form and the structural properties of a lexical item, takes place in one language; Stage C: while the new form is maintained, its structural properties are realigned with those of neighbouring languages, due to areal pressure.

The same reasoning could be proposed to account for all cases where structural isomorphism comes along with lexical replacement, whether in the lexicon or the grammar. In sum, language contact does not only account for the spread of innovative structures. Even conservative structures, whenever they survived processes of semantic shift, are best explained by the pressure of language contact in a multilingual setting.

Language as an emblem of place

While contact-induced convergence accounts for the structural homogeneity of northern Vanuatu languages, one still has to define a model capable of integrating it with what seems like a contradictory trend, namely the strong tendency for language divergence. I will suggest that the attested diversity is the effect of an ideological bias widespread in Melanesia, which de facto encourages cultural and linguistic differentiation.

A SOCIAL BIAS FOR CULTURAL DIFFERENTIATION

In these parts of Melanesia, constant reference is made to the precise anchoring of things and people within the social and geographic space [START_REF] Fox | The Poetic Power of Place: Comparative Perspectives on Austronesian Ideas of Locality[END_REF]. Individuals identify themselves, and each other, as belonging in a vast network of kinship relations, but also as tied to specific locations in the archipelago: to their island, their village, or even to a smaller area within their village. This constant awareness of the spatial anchoring of people and things has its corollary -namely, the attention paid to whatever may vary between local communities. People are often heard commenting, with conspicuous pleasure and excitement, on particular manners of cooking, matweaving, dancing or singing, which may differ, sometimes quite subtly, between two social groups. However they arose in real life, those cultural differences are not so much assigned to contrasts in age or gender, or to individual performers, but tend to be formulated and remembered in terms of specific spatially bound communities.

Overall, these two dimensions of cultural life in northern Vanuatu -the constant reference to places, the constant attention to local differences -design an idealised geography, in which the world is conceived as a mosaic of small-sized communities, as diverse in their cultural forms as their landscape can be rugged and variegated.

This magnetic attraction towards cultural diversity has a linguistic manifestation. Should some novel way of saying emerge in the speech of a few villagers, it can quickly spread to a whole village. And given the social bias towards the differentiation between local groups, there is high likelihood that the new usage will become a trademark of this community, in contrast with its neighbours.

The linguistic principles underlying those changes are essentially universal, and the languages of Vanuatu follow the same processes as in other languages. What makes them conspicuous is their high density within such a small human community. The high degree of language divergence observed in this region appears to be indirectly correlated with a prevailing social bias that tends to foster cultural and linguistic differentiation between local communities.

AVOIDING TELEOLOGY

The sociolinguistic explanation I here propose in order to account for the emergence of linguistic diversity in northern Vanuatu may be reminiscent -at least apparently -of previous studies about language differentialism in various parts of the world.

Thus several scholars, trying to explain the high linguistic fragmentation of Melanesian languages, have proposed the idea that such form of language change may be deliberate and conscious. For example, here is how [START_REF] Dutton | Language Contact and Change in Melanesia[END_REF] summarises the observations made earlier by [START_REF] Laycock | Linguistic Diversity in Melanesia: A Tentative Explanation. Gava" Studies in Austronesian languages and cultures, dedicated to Hans Kähler[END_REF] on "conscious" linguistic change in Papua New Guinea: "Melanesians thus appear to foster linguistic diversity purposefully because they see linguistic differences as important badges of group identity. It is, as it were, a Melanesian choice to promote diversity." (Dutton 1995:219; my emphasis)

Likewise, [START_REF] Ross | Social Networks and Kinds of Speech-community Event[END_REF]) borrows from Thurston (1987, 1989, 1994) the notion of esoterogeny; he defines it as a process whereby communities increase the complexity of their language, so as to develop "an "esoteric" lect from which outsiders are consciously excluded" (Ross 1997:239; my emphasis). Finally, Thomason (2007:52) describes similar processes which she explicitly characterises as "deliberate change". Can this model apply to the situation in northern Vanuatu? This depends on the way these ideas are to be interpreted. The general notion that linguistic divergence can be explained -at least partly -by sociolinguistic factors, and in particular by the building process of in-group identities, is a point which can safely be granted [START_REF] Labov | The Social Motivation of Sound Change[END_REF][START_REF] Labov | Principles of Linguistic Change: Social factors[END_REF][START_REF] Page | Acts of Identity: Creole-Based Approaches to Language and Ethnicity[END_REF]. However, the use of such words as "deliberately" (Thomason), "purposefully" (Dutton) or "consciously" (Ross) might lead to some misunderstanding.

It is true that the difference between languages or dialects, in this part of the world, is a social phenomenon of which individuals are highly aware, and on which they can even have ideological views. In various part of Vanuatu, I have often heard the same idea that linguistic opacity and fragmentation are valuable assets rather than problems, as they potentially form a protective shield for each social group. This being said, there is a fine line between acknowledging such ideological representations and providing them with the explanatory power to account for the emergence of linguistic change itself (cf. Silverstein 2001).

Indeed, the views by Dutton and Thurston seem to suggest that the push for divergence may form the primary reason why languages change. This runs the risk of representing linguistic change in a teleological fashion, as though the speakers' "conscious" craving for a distinctive identity, or for linguistic isolation, were able to trigger alone the sort of phonological, lexical or morphosyntactic innovations whereby languages diverge from each other. Campbell (2004b:127) rightfully highlights how difficult it would then be to identify exactly, for a given language, which instances of linguistic change would result from such a "separatist motive", as opposed to "changes which just happen with no such motive".

It is thus desirable to design a model of language change which can take into account such factors as speakers' social attitudes, yet manage to avoid the snare of teleology. I'd like to propose that differentialism is never the primary motivation for language change; the fundamental reason why innovations diffuse is rather due to speakers' desire to converge on particular speech habits. The linguistic differentiation between groups is just an indirect and epiphenomenal effect of that fundamental push for in-group homogeneity. This proposal makes it necessary to redefine the contrast between convergence and divergence.

The social group as a focus of convergence

DIVERGENCE AND CONVERGENCE: A SINGLE PROCESS

As a first approximation, the terms divergence and convergence portrayed well the apparent contradiction which emerged from the data -as though the mutual relations between languages followed two opposite directions at once. But while this formulation is a valid metaphor, it may be insufficient to understand the precise mechanism at stake here. Now that I have presented the linguistic facts, I would like to propose here another way of framing the paradox.

We know that languages "converge" with each other due to contact and diffusion ( §6.1). On the other hand, we saw earlier that the various ways in which languages appear to "diverge" from each other really result from an accumulation of linguistic innovations, each of which spread to some portion of the dialect chain. In other words, both cases of convergence and of apparent divergence ultimately involve processes of social diffusion. The difference between them is a matter of geographical scope for these patterns of diffusion -large scope in the case of convergence phenomena vs restricted scope in the case of divergence.

For some innovation to emerge and spread across a certain linguistic territory necessarily means that some new way of speaking -an innovative pronunciation, a new metaphor, a new lexical collocation -was first used by an individual, or a group of individuals, and was then felt worthy to be imitated by other people who heard it. As more and more people came to adopt this new speech habit, the innovation diffused to larger social groups, moving across age classes, across villages, or across entire networks. This process has been dubbed "linguistic epidemiology" by [START_REF] Enfield | Linguistic Epidemiology: Semantics and Grammar of Language Contact in Mainland Southeast Asia[END_REF][START_REF] Enfield | Transmission Biases in Linguistic Epidemiology[END_REF], and "Propagation" by Toulmin (2009:23) down to a certain group, it draws an invisible line between two sets of speakers: one circle within which individuals have converged together in adopting the new form, vs the rest of the population for whom this innovation means more linguistic divergence. In other terms, what may appear to be an effect of divergence on the macro scalebetween different dialects -is first and foremost the result of events of convergence on the micro scale -between individual speakers: see Figure 12. The term "group" used in Figure 12 is intended as a neutral term likely to refer to any social network of any size. It may refer to a family, a village, a group of villages, an island, a whole archipelago; it may be specific in age, gender, or any other dimension of social significance. Each unit is here simply defined as the social group which has adopted a given linguistic innovation; it corresponds to Toulmin's (2009:27) notion of "Propagation Network", whose outline can differ for each propagation event.

Crucially, the same diagram (Figure 12) fits equally with the cases I described earlier as "divergence", and those which were understood as "convergence". Whether one observes the processes of sound change, or the adoption of certain phraseological patterns, ultimately what we observe is that some social network of some size has converged into adopting some new speech habit; and that this shared innovation has incidentally resulted in the differentiation between this group and the others around it, which have not adopted this speech habit.

The way dialects have differentiated from each other was by adopting certain innovations which their neighbours did not adopt. The typical case was that lexical or phonological innovations would encompass only a subset of the archipelago, and stop somewhere between two dialects. Given a chain of adjacent dialects A, B, C, D and E, an innovation in dialect C might spread to B and D, but not go any further. While this particular change did sanction the social bonds between communities B-C-D, it also highlighted the perceived difference between communities A and B, or between D and E. Later, another innovation would arise in dialect B and spread to A but not C, thereby splitting up B-C-D into different groups again. Compare, for example, the maps in Figures 7-11. The more innovations would accumulate over time -each with its own spatial distribution•-the more different each member of the earlier dialect chain would become with respect to its immediate neighbours. Eventually, the distribution of intersecting isoglosses has resulted in language diversity. However, the very process whereby each individual innovation diffused across space was in itself not a process of divergence, but of local convergence between speakers.

THE CRITICAL SIZE OF SOCIAL GROUPS

Rather than portraying northern Vanuatu -or Melanesia as a whole -as a region of "deliberate" differentiation, it might be more accurate to describe it as a cultural area where each stable social group, recognised with its distinctive -and internally homogeneous -identity, can be extremely reduced in dimension. Indeed, a parameter which differs considerably across cultures is the minimal size of the social unit which may constitute a stable focus of linguistic convergence (Nettle 1999:139).

In societies with centralised political structures and immense social networks -as in Polynesian kingdoms [START_REF] Pawley | Melanesian Diversity and Polynesian Homogeneity: a Unified Explanation for Language[END_REF](Pawley , 2007a)), or in modern Europe -an emergent change will only start to really stabilise in mainstream varieties once it has managed to spread to vast groups of speakers. Should an innovation be restricted to just a small local group, it might survive for a while but then eventually fade out, under the wide-scale pressure towards levelling and uniformity.

Conversely, in the islands of northern Vanuatu -as well as in most parts of island Melanesia, and elsewhere -the socially accepted size of an identifiable community can be much smaller (Pawley & Ross 1995:66;[START_REF] Pawley | Explaining the Aberrant Austronesian languages of Southeast Melanesia: 150 Years of Debate[END_REF]Lynch, Ross & Crowley 2002:92;Evans 2010:14). The typically pertinent circle within which individual speakers will tend to imitate each other's linguistic behaviour will coincide with the perceived limits of a local community -a handful of adjacent villages in daily interaction. In this part of Melanesia, social actors are highly aware of their environment's linguistic geography, and the notion of "language" as a discrete notion is meaningful to them (pace Mühlhäusler 1996:5). The social unit encompassing speakers of "the same language" typically forms a focus of convergence for its members (François 2001:16;cf. Enfield 2003:20). It is the primary circle within which individuals, in order to optimise the success of communication with their day-to-day peers, will most likely feel the pressure to imitate each other's ways of saying. Should one innovation emerge as new linguistic usage in their community, chances are great that they might quickly adopt it; it will only take a few hundred speakers to adopt it, before it characterises the speech of a whole community. In principle, nothing should prevent local innovations from spreading further to neighbouring dialects or languages, especially considering the amount of areal contact and multilingualism traditional in the region. But crucially, this expansion to other communities is not a necessary step for the new usage to become socially stable. Should it remain confined to a single village and lack from the speech of its neighbours, then this will not threaten its survival; on the contrary, its emblematic power may precisely facilitate its social stabilisation within a local group. The potential drawback in terms of intervillage communication would anyway be offset by people's willingness to learn the tongues of their neighbours ( §2.2).

Speakers do not deliberately bring about language diversity. In a way reminiscent of Adam Smith's "Invisible Hand" (cf. [START_REF] Keller | Invisible-hand Theory and Language Evolution[END_REF][START_REF] Keller | On Language Change: the Invisible Hand in Language[END_REF], the linguistic kaleidoscope of modern Vanuatu is best understood as the unplanned outcome of multiple micro-events of convergence between individual speakers, within the invisible boundaries of what they spontaneously identify as their most salient social group.

Forms vs structures: A difference in awareness

The paradox raised by northern Vanuatu languages, which was initially formulated in terms of divergence vs convergence, could thus be rephrased in terms of size of social networks. While each propagation event outlines a different social group, the first sections of this study have shown a correlation between the size of the network and the nature of the linguistic innovation (see Figure 11 as an illustration):

• those innovations which have to do with STRUCTURAL PROPERTIES of signs typically diffuse across larger networks [ effect on the macro scale = convergence]

• those innovations which affect the FORM of signs typically diffuse across smaller networks [ effect on the macro scale = divergence] These observations entail the necessity to distinguish between the form of words and their structural properties as two different components of language ( §5.1), ultimately capable of evolving along opposite directions. Arguably, the reason why linguistic forms tend to differ among small-scale communities, is that the phonological form of words is, as it seems, more salient to awareness. In speakers' meta-discourse, the distinctive identity of each particular language is typically defined by the form of its words, rather than by their structural properties, which appear to be less accessible to spontaneous representations.

The asymmetry between these two components explains why they do not respond to social attitudes in the same way. On the one hand, word forms undergo a strong pressure to be preempted for their emblematic function, as they signal the distinctive identity of a specific language community. By contrast, the structural or typological properties of linguistic systems are not invested with this emblematic function. Consequently, this structural component is left free to comply with constraints on easeof-processing, which multilingual speakers tend to resolve through the mutual alignment of their systems.

Impressed by the situation of structural convergence described by [START_REF] Gumperz | Convergence and Creolization: A Case From the Indo-Aryan/ Dravidian Border in India. Pidginization and Creolization of Languages[END_REF] in India, [START_REF] Grace | An essay on language[END_REF] arrived at a similar conclusion when he proposed to distinguish between the structural organisation of languages (his "content form"see §5.1) and the phonological material attached to these structures (his "lexification"): "[T]he two components of language -content form and lexification -can be distinguished. They evolve independently because (…) they are responding to different selective pressures, and those selective pressures are different because the functions of the two components are different. (…) It is the lexification on which the emblematic burden ultimately falls. (…) If the language serves as the emblem of the group, it is the lexification in turn which is the emblem of the language." (Grace 1981: 30-31) The situation Grace was referring to was a case of contact-induced convergence between Dravidian and Indo-European languages in the village of Kupwar. The contrast of word forms between these genetically unrelated languages was present from the start, and had only later taken up a secondary function of social emblematicity as the two communities historically came into contact. What the Vanuatu case shows is that a similar asymmetry between heterogeneity of forms and homogeneity of structures can also arise spontaneously, among communities that once spoke the same language. Where linguistic diversity does not exist, it can be invented.

Issues for further research

The social and linguistic ecology of northern Vanuatu combines a number of specific ingredients: scattered habitat in a landscape of mountainous islands; stateless social organisation; egalitarian multilingualism; economy based on land ownership and horticultural practices; preference for village exogamy; related languages sharing a same ancestor (proto-language), as well as a shared history of contact (linkage); ideological emphasis placed on the value of local identities. But while this region may be extreme in some ways, there are no reasons to believe that the social and linguistic processes at play there should be unique. Even though the present article chose to avoid any universal claim, future debate and research should help assess its broader relevance.

Some aspects of the situation described for the Banks and Torres Islands presumably apply to a wider regional area -say Melanesia as a whole. Other parts of the world are also characterised by strong language fragmentation, and it would be useful to know which factors are shared there with the ones observed in Vanuatu. More broadly again, some processes described here might have universal relevance -such as the proposed correlation between the culturally accepted size of distinct social groups, and the scope of certain forms of linguistic diffusion.

Several questions arise, which go beyond the limits of the present study.

Is the paradox described here (convergence of structures, diversification of word forms) also found in many parts of the world? If so, does it always take the same shape, or are other configurations attested? For instance, while the phonological systems of northern Vanuatu rather stood on the diverging side, other contact areas show the reverse tendency, namely the alignment of their phonologies. Do diffusional areas evolve in island settings differently compared to continents? Is language diversification stronger in situations of demic separation than in contact? How are linguistic convergence and divergence affected by economic dimensions (selfsufficiency vs mutual dependency among communities; hunter-gatherers vs horticulturalists…) or political factors (egalitarian vs stratified societies; polycentric social networks vs centralised states)?

Is the value given to ethnicity or local identities -assuming this can be empirically identified -a key factor in language diversification? What is the exact role played by speakers' awareness of their own linguistic practices (cf. Silverstein 2001), and by conscious ideological discourse on homogeneity vs heterogeneity? What configuration obtains when the most salient dimensions for group identities are not so much the anchoring in space, as in social class, gender or urban communities?

How do processes of post-dispersal diffusion across dialect networks affect the methodology of linguistic subgrouping (cf. [START_REF] Ross | Proto-Oceanic and the Austronesian languages of Western Melanesia[END_REF][START_REF] Pawley | Chasing Rainbows: Implications of the Rapid Dispersal of Austronesian Languages for Subgrouping and Reconstruction[END_REF]Aikhenvald & Dixon eds 2001;[START_REF] Bossong | Divergence, Convergence, Contact. Challenges for the Genealogical Classification of Languages[END_REF]Toulmin 2009;[START_REF] Heggarty | Splits or Waves? Trees or Webs? How Divergence Measures and Network Analysis can Unravel Language Histories[END_REF]? It is desirable to define a mode of representation that can address the shortcomings of the family-tree model, and capture accurately the history of these social networks as it can be reconstructed based on the comparative method.

While many of these issues are already the object of ongoing debates, it is hoped that this study of northern Vanuatu languages can shed a new light on processes of language change and their social underpinnings.

Summary

The paradoxical relations that can be observed among modern languages of northern Vanuatu reflect the intricacies of their social ecology. In particular, the contradiction between their two evolutionary trends reflects the two major concentric social circles to which all individuals belong.

Under traditional circumstances, the day-to-day social unit which is most relevant for an individual -and also the most salient in people's representations and social practices -is the village, or the group of nearby villages which constitute a stable language community. This level of social organisation constitutes a privileged focus of convergence for those linguistic components that are more salient to awareness, namely the form of words. The spatial distribution of these communities is mirrored in the 17 distinct languages which compose the linguistic mosaic of the archipelago, and differ mostly in their phonologies and vocabularies.

But at the same time, whether they realise it or not, individuals are also entangled in a much larger network of social relations that transcends the dimension of their village. This vast web of acquaintances and kinship, tirelessly spun through generations of cross-community contact, intermarriage, and cultural exchange, spreads from village to village, from island to island, and ultimately encompasses the whole Torres and Banks archipelago. While these languages' lexical idiosyncrasies reflect people's fundamental attachment to their local communities, ultimately the strong parallelism found among their structures reveals the profound coherence of their peaceful universe.

  Figure 1 situates northern Vanuatu within Island Melanesia and the Pacific.

Figure 1 -

 1 Figure 1 -Situation of northern Vanuatu in the Pacific

Figure 2 -

 2 Figure 2 -The 17 languages of northern Vanuatu (Torres and Banks islands)

Figure

  Figure 3 -Interisland marriages in northern Banks Islands (Vienne 1984)

Figure 5 -

 5 Figure 5 -Modern vowel systems are more or less symmetrical Lemerig (11 vowels)

Figure 6 -

 6 Figure 6 -Lexical differentiation through regular sound change: reflexes of the noun *asi "song"

Figure 7 -

 7 Figure 7 -Lexical differentiation through irregular sound change:Intermediate innovations for the noun "crayfish" (<POc *quraŋ)

Figure 8 -

 8 Figure 8 -Irregular morphological change and chaotic distribution: Intermediate protoforms for the 1incl:Dual pronoun

Figure 10 -

 10 Figure 10 -Diversification of forms, isomorphism of structures:The case of the postverb "find"

Figure 11 -

 11 Figure 11 -Diversification of forms, isomorphism of structures:The case of the Restrictive postver "just"

(

Figure 12 -

 12 Figure 12 -Global divergence results from events of local convergence: Individual speakers adopt local innovations within their social network, thereby increasing the gap with neighbouring groups

Febaian

  Din (MTA); Antonet Rovanle (NUM); Mrānga Sales Maklēn (DRG), John Star (DRG, OLR); Derek Bogo, Banabas Womal (KRO); †Maten Womal (OLR); Moses Stiven Wēting, Nelson Vagēl (LKN); Mata Uli Rowon, Nikson Wevalēs (LKN, MRL); Nora Philip (MRL); Mama Brian, Elton Gëgelikwe, Eron Jefri Muglol (LTG); Sipo Ngwoypitvën, Stanley Elfrik Vëniwyōy, Sekōp Elison and Mama Jimmy Tiwyoy (HIW).

Table 1 -

 1 Divergence of forms, convergence of structures in the 17 languages of northern Vanuatu: an example sentence †

	HIW sisə tati	jɵjmə g ʟen wu g ʟɔɣ kʷe	i	nə məŋa	ta
	LTG nihə tat	lolmərɛn ʉrβɛ	kʷɛ	e	nə βəɣəβaɣə məʈə
	LHI	kɛj tɛtnɛ	ɣlal	ɣalsɛ	kʷɒ		n-βap	munɣɛn
	LYP	ki ɛj tɛ	ɣilal	ʧøjmat ʧɛk pʷɛ		n-βaβap	ŋ mʷɔni ɛn
	VLW ŋ gɪj ɛt	ɣilal	ɣalsi	tɛ ŋ g bʷɛ		n-ɣatɣat	njɔnɣɪn
	MTP kɪj ɛt	ɪɣlal	ɣalsi	k pʷɛtɛ		nɔ-hɔhɔlɛ	nɔnɔnɣɪn
	LMG taer ɪ	ɣɒlɒl	ʔørmaʔ ʔae.kiʔis		n-tɛktɛk	mʊɣʊt
	VRA ⁿdir ɪʔ	lamai	ɛntɛɣ	ʔɪn		ɪn tɪktɪk	muⁿdɪ
	VRS nɪr ɣɪtɪ-	ɣilal	warɛɣ	tɛn		ɔ	k pʷak pʷ namøɣynɪn
	MSN nɪr ɛtɛ	lɪlɪ	maŋtɛ βɪs		ɔ	ɣatlɛ	mɔɣɔnin
	MTA nra ɣate	ɣlala	mantaɣ tk pʷe		o βaβae	naŋ mʷunina
	NUM nir βitis	ɣil	liŋliŋi	mi		u luwluw	namɣin
	DRG nɪr sɔwsɛ βrɪɣɪl	taβul	tɛ		na lŋa	-ɣɪn
	KRO nɪr tɪ	rɔŋ	taβul	wʊs.mɛlɛ		ɔ	βalβalaw namɪɣɪn
	OLR nɪj tɪ	rɔŋ	βɪlɪː	wʊs.mɛlɛ			ususraː	mʊʧ
	LKN ɣɪː atɪ	rɔŋ	kɛrɛ	aβʊh.malɛ		ɛlŋa	-nɣɪʧ
	MRL kɛr ti	βalɣɛ ar	mɪnmɪn tɪkʷɪtɛ a		nɞ-liŋɪ	-ɣɛ an
		3pl NOT.YET 1 know	properly NOT.YET 2	[OBL] ART speech

POSS:1incl.pl "They don't know our language very well yet." † All forms are given in IPA transcription. Languages are ranked on a geographical basis, from northwest to southeast. For language abbreviations, see the map in §2.1.1, or the Appendix.

Figure 4 -Proto Oceanic has split into various dialect networks, which have given rise to loosely-bound linkages of various sizes Oceanic

			of representing linkages with a double line, to
	distinguish them from proper subgroups.
	Western Oceanic linkage	(other groups)		(other groups)
			Southern Oceanic linkage
		North Central Vanuatu	Southern Melanesian
		linkage (Clark 2009)	linkage (Lynch 2000)
	Torres-Banks	(other linkages	Southern	New
		linkage	of North &	Vanuatu	Caledonian
			Central Vanuatu)
	(17 modern
	languages)

Table 3 -

 3 Language differentiation through sound change: a few cognate sets from northern Vanuatu †

		"song"	"stroke"	"coconut crab"	"crayfish"	"breathe"	"1incl:Du"
	Hiw	ɔs	sə g ʟɔβ	ɣʉtʉt	g ʟɔɣ	mənawə	tɵ g ʟɵ
	Lo-Toga	ɛh	hərɛβ	ɣəhʉh	rɔɣ	məkʷhɛ	ʈor
	Lehali	n-aeh	hɪjaep	n-ⁿdɪj	n-jɒ	mɔksae	ɣɪnjɔ
	Löyöp	n-ɪs	sɪjɪp	n-ⁿd ɣi ɛj	n-i ɛj	ŋ mʷɔŋsɪ	i ɛⁿdʊ
	Volow	n-ɪh	hɪjɪɸ	n-ⁿdij	n-ɪj	mɔŋhɪɣ	ⁿdʊ(jʊ)
	Mwotlap	n-ɛh	hɛjɛp	na-ⁿdij	n-ɪj	ŋ mʷʊkhɛɣ	ⁿdʊ(jʊ)
	Lemerig	n-ɛs	soeroeɸ	tɪr	n-aer	moepsɪ	ɣaetru
	Vera'a	nɛs	saraβ	ⁿdiɪr	nirɪ	mɔmsɛ	ɣiⁿduʊ
	Vurës	oes	soeroeβ	ⁿdɪr	ʊr	mɛmsɛɣ	ⁿdʊrʊk
	Mwesen	ɛs	sɛrɛɸ	nɪr	ʊr	mɔpsɛ	ninrʊ
	Mota	as	saraɸ	naer	ura	ŋ mʷaɸsaɣ	nara
	Nume	wɛs	saraɸ	ⁿdɪr	wʊr	mamsɛŋ	ⁿduru
	Dorig	aːs	sraːβ	ŋⁿdɪr	ʊr	maː m bsɪɣ	ⁿdaːr
	Koro	ɛ as	sɛrɛ aβ	ⁿdɪr	rɛ aŋ	mɛmsɛ aɣ	ⁿduru
	Olrat	nɪs	?	ʧɪj	nurɪŋ	mɪpsaː	ʧʊrʊ
	Lakon	ʔ aeh ʔ aeh	haeraeβ	ʧɪː	uraeŋ	mahpaeɣ	wʊʧʊ
	Mwerlap	n-ɛs	sɛrɛp	n -ɣ t tɛ ak n-ɵ ʊr	mɔm	ⁿdʊrʊ
	Proto-TB	*asi	*saraβi	*ⁿdaeru	*uraŋ	*maᵐbusaɣi

*ɣiⁿdarua † The prefix /n-/ before nouns is a separable article. Forms in italics are not cognate with the rest of the list.

  MTA ura, VRS ʊr, NUM wʊr, MRL n-ʊr… all point to a pre-modern form *(na) úra -LYP n-i ɛj, VLW/MTP n-ɪj, LMG n-aer, VRA nirɪ all point to *(na) íra -KRO rɛ aŋ, OLR nurɪŋ, LKN uraeŋ all presuppose a form *(na) uráŋi

-HIW ᶢʟɔɣ, LTG rɔɣ, LHI n-jɒ all point to a protoform *(na) ráɣu For reasons of space, I will not detail here the individual changes for each of the 17 forms of this noun; but each of them can be regularly derived 2 from one of these four intermediate protoforms -e.g. LHI n-jɒ < *n-rɒɣ < *na ráɣu; LYP n-i ɛj < *n-i ɛr < *na íra;

Table 4 -

 4 When markedness shift drives lexical replacement: Words for "head" in Late Latin / Romance

		'leader, chief'	'head'	'earthen pot'
	STAGE 0	caput	caput	testa
	STAGE 1	caput	caput ~ (testa)	testa
	STAGE 2	caput	(caput) ~ testa	testa
	STAGE 3	caput	testa	testa

  Table 5 provides a random sample of words of different syntactic categories, showing various degrees of lexical replacement. Other similar cases can be found in Table 1 ( §1.2), and in Table 6 ( §5.2).

Table 6 -

 6 A selection of word sets combining formal diversification and structural parallelism across languages

			LEXICON		GRAMMAR
		Adjective	Postverb	Restrictive	Negative	Time Focus
		"random"	"find"	"just"	Existential	aspect
	Hiw	βitikəje	sɔgʟ	ŋʷutʉjə	təɣɔ	takə
	Lo-Toga kʷure	hɛr	wərəŋɔ	tatəɣɛ	akə
	Lehali	βaelaekjae	sɪɣɪt	ɛwwɛ	tɛtɣɛ	jak
	Löyöp	βɔlɔkjɛ	søɣøt	wi ɛ	mamʧɛɣɛ pɛj
	Volow	ŋgɪlŋgɪl	sas	ɣɛwɪ	tatɪh	ŋg bʷaja
	Mwotlap sɔlɔtɛɣ	sas	ɪwɪ	tatɛh	k pʷɔjɔ
	Lemerig βɒlɒkrɛɣ	ʔɛsɣøʔ	k pʷɔɣɔr	niβ	mak
	Vera'a	βalakra	sɛr	ɣiβa	ɣitaɣ	mak
	Vurës	βalakrɛɣ	sioer	ɣɛm	ɔⁿdiaŋ	kara
	Mwesen pɔlɛtɛ	siɛr	ɣɔp	ɛnɛŋ	kara
	Mota	popolotaɣ	suar	ɣap	taɣai	k pʷara
	Nume	kɪlkɪl	wun	am	mbɛk	k pʷar
	Dorig	kɪlkɪl	wʊn	wɔr	(ɔ)mbɛk	k pʷra
	Koro	kɪlkɪl	wɛs	wɔr	mbɛk	k pʷara
	Olrat	kɪlkɪl	wɛn	wɔj	ɣaiβ	tak
	Lakon	saelɪn	ɣɪn	wɔː	ɣaiβ	lak
	Mwerlap kɪlkɪl	βɔ ɞn	ɣɔm	tɪɣɪ	kʷɛr

  Another common usage of "NEG:EXIST" in discourse is when one's effort is frustrated by a lack of result. In this case, the predicate would translate "in vain, to no avail":

	19) HIW jə en ənɔmə nenə? -ə ə ə , təɣɔ!	u uj	ŋ utʉjə!
	woman your	that	(no) NEG:EXIST friend	just
	MTP	iɣni	nɛn? -ɔ ɔ ɔ , tatɛh!	p ul p ul ɪwɪ!
	MSN ɛ	ɣunu-m nɔ?	-ɔ ɔ ɔ , ɛnɛŋ!	pulsal	ɣɔp!
	MRL	rɔn tɔ-ŋ kan? -ɔ ɔ ɔ , tɪɣɪ!		m bulsal	ɣɔm!
	[ART] wife-2sg	that	(no) NEG:EXIST friend	just
	(20) LHI lɪ	ʊŋ nɒ	nɛ-mjɪs	ⁿdɛ	k-	mutuj, pɔ	tɛtɣɛ!
	VRA lɪn p ʊŋ nɔ	ɣ	mʊrʊs sɔ	k-	miʔir,	m ba ɣitaɣ!
	DRG lɪ	p ʊŋ na	β	mrʊs			ŋɔr,	la	m bɛk!
	LOC night 1sg STAT want	[COMP 1sg] sleep	but NEG:EXIST
	"Last night, I tried to sleep, but no way!"
	Finally, a widespread formulaic pattern employs this word "NEG:EXIST" in greetings. The
	literal meaning must be understood as "[there's] no [problem]", but it is routinely used
	to mean "I'm fine":
	(21) HIW ŋ e.n ?	-təɣɔ,		ne	mə g ʟ wə	ŋ utʉjə
	LMG mae aeβae.nɛ?	-niβ,		ɣɛ	wi		p ɔɣɔr
	VRS timi . βɪ?	-ɔ i aŋ,	ɣʊ-	wɪ		ɣɛm
	MTA t ŋ m .βɛa?	-taɣai,	we	wia		ɣ p
	DRG ⁿd s ?	-m bɛk,		β -	wɪ		wɔr
	how		-NEG:EXIST	STAT	good		just
	"How's things? -No [worries]! Everything's alright."

"Is that your girlfriend? -Oh no, no! She's just a friend."

Table 7 ,

 7 this corresponds to a shift from Stage A to Stage B.

Table 7 -

 7 When lexical replacement perserves semantic structures:

			Words for "water" in Lakon
		"(fruit) sap, juice"	"(drinkable) liquid"	"fresh water"	"river, lake"	"sea water, salt, sea"
	STAGE A	*tuŋu	*ᵐbei	*ᵐbei	*ᵐbei	*nawo
	STAGE B	*tuŋu	*tuŋu	*tuŋu~*ᵐbei	*ᵐbei	*nawo
	STAGE C	tuŋuhwiː	*tuŋu	*tuŋu	*tuŋu	*nawo

  . Once a given innovation has settled

	group
	G 1
	intra-group
	CONVERGENCE
	group
	G 2	group
	inter-group	G 3
	DIVERGENCE

François (2005a) discusses the various regular patterns of sound change attested in the 17 languages. It provides tables of regular correspondences as well as principles for the reconstruction of protoforms in this area, based on the comparative method.

Here is whatCodrington (1885:323) wrote about the languages of "Bligh Island" (Ureparapara):"The practise of pronouncing r as y cannot be limited precisely; it is always followed at Retan, but in the Bay, children and some adults do it; r would at any rate be written".

The prenasalised ⁿd in *ɣiⁿda is an irregular development shared by all NCV languages(Clark 2009:114).

Note that Tryon's statistics include neither Olrat nor Volow. Seeing how Olrat can be often close to

In forthcoming examples -e.g. (3), (5) or (6) -, square brackets in interlinear glossing will indicate morphemes that are found in only some languages of the sample.

Mandarin Chinese has a similar aspect particle cái which can be glossed "[then and] only then"(De Francis 1966:20; Li & Thompson 1989:333).

Acknowledgments

Various aspects of this research were presented at the international workshops Ecology and Language Evolution of LACITO-CNRS (2008, Paris) and Grammatical Constructions in Time and Space (2008, Oslo); at the 7 th conference of the Association of Linguistic Typology (2007, Paris); and the annual meeting of the Australian Linguistics Society (2009, Melbourne). On these occasions, I found of great help the questions and comments from my colleagues. I am also indebted to several people for their useful comments on earlier drafts of this paper: Mark Donohue, Beth Evans, Rob Mailhammer, Martine Mazaudon, Alexis Michaud, Andy Pawley, Malcolm Ross, Claudia Wegener; I also thank Jóhanna Barðdal as well as two anonymous reviewers of JHL. Any remaining flaws and errors remain my own.

The collection of data took place during several trips to the Banks and Torres islands, between 1997 and 2007. This research would not have been possible without the moral support of the Vanuatu Cultural Centre, and the financial support of the Académie Française, of the Centre National de la Recherche Scientifique (LACITO), as well as a scholarship Jeunes Chercheurs granted by the French Ministère de la Recherche.

But more than anyone else, I would like to express my gratitude to the many individuals from Vanuatu who so generously shared their time with me, teaching me their beautiful languages and telling me their countless stories. To name but a few, my warmest thanks go to †William Hagēt, Moses Meywēlgen, Richard Woris Lerig, Edgar Howard (MTP); René Wolman (VLW); Fred William Qasvarong (LYP); Stanley Lengson (LHI); †Wolta Robin, †Taitus Sërortelsöm (LMG); Fedrik Qarngi (VRA); Tevēt Mesigteltōk (MSN); Mama Isikiel Wurvegqiat, Alban Mofet (VRS), Eli Field (VRS, VRA, LMG); Mama

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Abbreviations

Languages

The abbreviations for language names appear on Figure 1, and are repeated below.

BSL