1. Isolating the linguistic and sociolinguistic consequences of

migration Language change may be thought of as having internal (intra-systemic), external (contact-based) and extra-linguistic (socio-political and economic) motivations (Farrar/Jones 2002, 1). It is reasonable to suppose that the migration of people is a leading cause of contact-induced change; in other words, migration is a key extra-linguistic factor leading to externally-motivated change. In every case of migration, except where a homogeneous group of people moves to an isolated location, language or dialect contact ensues (Thomason/Kaufman 1988; Trudgill 1986). Migration also has far-reaching consequences for the social fabric of the three communities affected: the society of origin, the society of destination, and the migrants themselves (Lewis 1982, 25, summarising Mangalam (1968)). It follows that migration has profound sociolinguistic consequences, as the demographic balance of the sending and receiving populations is altered (migrants are typically young and economically active), and as the migrants are uprooted from familiar social and sociolinguistic set-ups, perhaps forming an ethnolinguistic minority which has to relate sociolinguistically to a new, ‘host ’ speech community – which in its turn becomes transformed by their arrival (Kerswill 1994). Until recently, the study of the (socio)linguistic effects of migration has been conceptually separated from that of the spread of linguistic features by means of geographical diffusion, the simplest manifestation of which is the wave-like spread of a linguistic innovation from its point of origin. This is an example of the geographical phenomenon known as expansion diffusion (Britain 2003), and by definition does not implicate population movements. The study of this type of diffusion was central to the concerns of 19th and 20th century dialect geographers, later refined by the application of models from human geography, particularly hierarchical diffusion (Trudgill 1983