Language variation and change, and DL in particular, tends to correlate with location, whether it is geographical or social. This takes place when language forms with a wider socio-spatial popularity spread at the expense of more locally specific forms (Britain, 2009: 1). DL in this sense has been a good motivation for a series of sociolinguistic studies across the world
languages, such as English (Cheshire et al., 1999; Kerswill and Williams, 2000b; Milroy, 2002; Kerswill, 2003; Britain, 2009), French (Hornsby, 2007), Norwegian (Hilton, 2010), and Arabic (Versteegh, 1993; Al-Rojaie, 2013; Manfredi, 2013). For example, Milroy (2002) focuses on the role of the contact framework in revealing instances of DL, such as the treatment of the low front vowel /a/ in Belfast. While back-to-front vowel distinction is correlated with status, high status speakers in Belfast eliminate the extreme back and front vowels. Therefore, their orientation is more accurately described as ‘modified vernaculars than as modified standards’ (Milroy, 2002: 8). As Kerswill and Williams (2000b: 2) argue, the new linguistic forms spread more rapidly in socially and geographically mobile groups, such as migrants, than in groups with a strong local base and close-knit networks. They view levelling as an outcome of individuals having open networks to people outside of their community. In contrast, close-knit networks act as powerful maintenance mechanisms of local dialects (Milroy, 1980).
Britain (2009) presents the process of DL as an outcome of the increase in people’s mobility, long-term contact and routine day-to-day movement (Britain 2009:7). Britain views the notion of regions as a complex and unlimited network of realisation rather than sharply predefined restricted entities. He focuses on the role of attitudes and identities in the spread of linguistic forms. He also pays attention to physical and social space and refers to them as special practices. Spatial identities, which are drawn from daily social practices that people are engaged in, and the ways these practices are connected to those of others, are important in affecting the social networks. One of the special practices that could increase the spread of linguistic forms is increased migration. Hilton (2010: 87) pointed out that special practices are as significant as other social factors in decreasing or increasing dialect variation, and should be given further attention in the research on RDL.
Williams and Kerswill’s (1999) study is a good example of the empirical studies of linguistic diffusion in the UK. They investigated the spread of t-glottaling and th-fronting in
three cities in the UK: Hull, Reading, and Milton Keynes. They found that adolescents in these three cities follow similar rates in the use of the two features (Williams and Kerswill, 1999: 161). However, the social promise of adolescents played an effective role in the spread rate. For example, adolescents in Hull use the new features less than those in Reading and Milton Keynes do, and they retain local features (Williams and Kerswill, 1999: 162). This conservative performance is due to close-knit social networks and less exposure to education where RP-like features are available. More importantly, adolescents in Hull use local features as a symbol of a sense of identity.
Neil (2011) presents diffusion models that explain RDL in the UK, focusing on the increase in social and geographical mobility. Neil found that not all forms of linguistic features diffuse by the same pattern, i.e. one feature may spread from one region to another by a wave-like pattern, while another feature may spread more quickly by populations characterised by weak social networks, regardless of how distant they are from the central urban area. In his replication of Williams and Kerswill’s (1999) study of migrants into Reading, Hull, and Milton Keynes, Neil (2011:1) explores DL in relation to internal migration, and concentrates on the fact that linguistic change results from complex factors derived from both diffusion and Levelling. His model accounts for DL depending on one of three mechanisms. The first mechanism is ‘Wave-model diffusion’, which depends on spatial contact between local regions. In this model, innovations spread from a central area to more remote locations, passing through closer areas. An example of this model is the diffusion of the non-salient feature /ʌ/ from London to East Anglia (Trudgill, 1986: 51-53). The second mechanism is the ‘Urban Hierarchy model’, where the spread of innovations is not an outcome of spatial mobility only, but of population density as well. In this model, innovative features spread and are acquired more quickly by populations characterised with weak social ties, regardless of being distant from the central urban area. For example, London tends to have a greater influence on Milton Keynes’s than on Reading’s adoption of new variants of [au] despite the
fact that, geographically speaking, the former city is more distant from London than Reading. The key reason is that, due to exposure to contact that is more special with Londoners, Milton Keynes’ population has less close-knit networks in contrast to Reading (see also Kerswill, 2003). Opposite of this mechanism is the third one, the ‘Contra-Urban model’, which according to Neil is the rarest. Neil (2011: 12) exceeds the traditional research, which concentrates on the ‘role of identities in face-to-face contact’. Although he agrees with Milroy’s (2002) notion about the existence of the relationship between social class and mobility, Neil argues as to how exactly their interrelationships affect innovations, ascribing that to the direct relation between rate of change and social framing and the social- psychological factors resulting from contact. The arguments in Williams and Kerswill (1999), Britain (2009) and Neil (2011) concern the link between spatial practices and diffusion of linguistic forms and the role of individuals’ structure in spreading and adopting such forms. Supralocalisation in Arabic follows one of two mechanisms, neither of which gives a clear account for the factors underlying it. Although it has been claimed that migration does not play an effective role in the evolution of urban dialects and does not contribute in situations of DL and that the development of new vernaculars is determined by the impact of fuṣḥā (Miller, 2003: 193), a war-induced migration urban-urban diffusion model, where dialects spoken in the big cities, usually capital cities, spread out to surrounding regions, usually represents the first mechanism in several Arabic dialects (e.g., Abd-el-Jawad, 1986; Al- Rojaie, 2013). In the second mechanism, more prestigious dialects that are spoken by politically or socially dominant groups spread out to other local dialects regardless of the geographical distance (e.g., Holes, 1983, 1986; Abd-el-Jawad, 1987; Abu-Haidar, 1991). An example of this pattern is Versteegh’s (1993) study on DL in the south of Sudan. He reports a case from Egypt and states that when Egyptians meet informants from Cairo, many of them tend to modify their speech by using the Cairene dialect more frequently than their local dialects (Versteegh, 1993: 70). DL in Arabic may follow a trend similar to that found
elsewhere, as in English (Neil, 2011). Owens (2003) follows the notion that linguistic features seem to disappear in one place and re-emerge in new areas and therefore immigrating groups transmit new linguistic features (2003: 718). His model is one of migration-induced dialect contact (Owens, 2003: 730). For example, the development of the first person singular and plural imperfect in North African Arabic dialects i.e. n-iktib for s., and n-iktibu for p. into Egyptian dialects at the expense of the one originally used in Egypt i.e. b-ə-ktob for s., and m-n-əktob for p. is interpreted by Owens as an outcome of three possibilities. The first possibility is the spread of this feature within local regions inside Egypt. The second possibility is the spread from North Africa into Egypt. The third possibility is likely to be a result of migration from Egypt to North Africa (Owens, 2003: 730). He focuses on one of the main questions arising in the Arabic dialectological studies: that is, whether reconstruction should be seen in terms of the whole dialect or as just a single linguistic feature. Owens (2003: 738) concludes that one can reconstruct the history of individual features in order to reconstruct the history of a whole dialect. It can be concluded from this section that the social structure of individuals and their spatial mobility must be taken into consideration in explaining the spread of new linguistic features.