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Dialect continuum

A dialect continuum or dialect chain is a spread of language varieties spoken across some geographical area such that each differs only slightly from its neighbors, but the differences accumulate over distance so that widely separated varieties are not mutually intelligible. That happens, for example, across large parts of India or the Maghreb. Historically, it also happened in various parts of Europe such as between Portugal, southern Belgium and southern Italy, and between Flanders and Austria. Leonard Bloomfield used the name dialect area. It is analogous to a ring species in evolutionary biology.

Dialect continua typically occur in long-settled agrarian populations, as innovations spread from their various points of origin as waves. In this situation, hierarchical classifications of varieties are impractical. Instead, dialectologists map variation of various language features across a dialect continuum, drawing lines called isoglosses between areas that differ with respect to some feature.

Since the early 20th century, the increasing dominance of nation-states and their standard languages has been steadily eliminating the nonstandard dialects that comprise dialect continua, making the boundaries ever more abrupt and well-defined.

Standard varieties may be developed and codified from one or more locations in a continuum, a process known as ausbau, until they have independent cultural status, or autonomy. Speakers of local varieties typically read and write a related standard variety, use it for official purposes, hear it on radio and television, and consider it the standard form of their speech, so that any standardizing changes in their speech are towards that variety. In such cases the local variety is said to be dependent on, or heteronomous with respect to, the standard variety.