The various codes in a multilingual speech community usually fulfill complementary functions. They are used differentially according to the interlocutor, domain, topic and role, and the choice of one rather than the other involves an act of identity. on the part of the speaker. Diglossia is at hand if different varieties or languages co-occur throughout a speech community, each with a distinct range of social functions in complementary distribution (Hamers and Blanc 1989: 173-174).
Ferguson first introduced the term diglossia in 1959 to refer to a relationship between varieties of the same language, but nowadays the term covers also relationships between different languages used in a society (ibid, 33-35). The variant reserved for informal uses within a speech community, the low variety, enjoys less social prestige: it is the language of informal interactions (such as ones family life). The high variety, in its turn, is used in formal and outgroup situations (Sebastian 1982: 8). The low variety is typically acquired at home as a mother tongue, the high variety, on the other hand, is learned later, normally at school, never at home. It is a language of institutions outside the home (Hamers & Blanc 1982: 34).
Fishman distinguished in 1971 between a high and low language, where the high language corresponds to status, high culture, strong aspirations toward upward social mobility, whereas the low language is more associated with solidarity, comradeship and intimacy by its speakers (Carranza 1982: 64).
Carranza has come to the conclusion that the level of prestige which languages/language varieties enjoy is influenced by two factors: social structure and cultural value systems: the social structure is an important determinant of how a language is regarded by members of the society. Cultural values, on the other hand, are important especially in the case of a less prestigious language for it to be maintained: it must be associated with positive values with which its speakers can identify themselves (ibid).