- the widespread existence within a society of sharply divergent formal and informal varieties of a language each used in different social contexts or for performing different functions, as the existence of Katharevusa and Demotic in modern Greece.
- the presence of two tongues or of a single tongue divided into two parts by a cleft.
- the existence in a language of a high, or socially prestigious, and a low, or everyday, form, as German and Swiss German in Switzerland
