Dialect levelling or leveling (in American English) is the process of an overall reduction in the variation or diversity of features between two or more dialects. Typically, this comes about through assimilation, mixture, and merging of certain dialects, often by language standardization. It has been observed in most languages with large numbers of speakers after industrialisation and modernisation of the areas in which they are spoken.
Definition
Dialect levelling has been defined as the process by which structural variation in dialects is reduced, "the process of eliminating prominent stereotypical features of differences between dialects", "a social process [that] consists in negotiation between speakers of different dialects aimed at setting the properties of, for example, a lexical entry", "the reduction of variation between dialects of the same language in situations where speakers of these dialects are brought together", "the eradication of socially or locally marked variants (both within and between linguistic systems) in conditions of social or geographical mobility and resultant dialect contact", and the "reduction... of structural similarities between languages in contact", of which "interference and convergence are really two manifestations".
Leonard Bloomfield implicitly distinguished between the short-term process of accommodation between speakers and the long-term process of levelling between varieties and between the social and the geographical dimensions. On the geographical dimension, levelling may disrupt the regularity that is the result of the application of sound laws. It operates in waves but may leave behind relic forms. Dialect levelling and Mischung, or dialect mixing, have been suggested as the key mechanisms that destroy regularity and the alleged exceptionlessness of sound laws.
Dialect levelling is triggered by contact between dialects, often because of migration, and it has been observed in most languages with large numbers of speakers after the industrialisation and the modernisation of the area or areas in which they are spoken. It results in unique features of dialects being eliminated and "may occur over several generations until a stable compromise dialect develops". It is separate from the levelling of variation between dialectal or vernacular versions of a language and standard versions.
Motivations
Contact leading to dialect levelling can stem from geographical and social mobility, which brings together speakers from different regions and social levels. Adolescents can drive levelling, as they adapt their speech under the influence of their peers, rather than their parents.
In 20th-century British English, dialect levelling was caused by social upheaval leading to larger social networks. Agricultural advancements caused movement from rural to urban areas, and the construction of suburbs caused city-dwellers to return to former rural areas. The World Wars brought women into the workforce and men into contact with more diverse backgrounds.
Role in creole formation
It has been suggested that dialect levelling plays a role in the formation of creoles. It is responsible for standardising the multiple language variants that are produced by the relexification of substrate languages with words from the lexifier language. Features that are not common to all of the substrata and so are different across the varieties of the emerging creole tend to be eliminated. The process begins "when the speakers of the creole community stop targeting the lexifier language and start targeting the relexified lexicons, that is, the early creole". Dialect levelling in such a situation may not be complete, however. Variation that remains after dialect levelling may result in the "reallocation" of surviving variants to "new functions, such as stylistic or social markers". Also, differences between substrata, including between dialects of a single substratum, may not be levelled at all but instead persist, as differences between dialects of the creole.