thumb|upright=1.3|The station board of [[Hapur Junction railway station in North India demonstrating digraphia of two formal registers, Hindi and Urdu, of a common vernacular, Hindustani, an example of triglossia. The H variety may have no native speakers within the community. In cases of three dialects, the term triglossia is used. When referring to two writing systems coexisting for a single language, the term digraphia is used.
The high variety may be an older stage of the same language (as in medieval Europe, where Latin (H) remained in formal use even as colloquial speech (L) diverged), an unrelated language, or a distinct yet closely related present-day dialect (as in northern India and Pakistan, where Hindustani (L) is used alongside the standard registers of Hindi (H) and Urdu (H); the German-speaking countries, where Standard German (H) is used alongside German dialects (L); the Arab world, where Modern Standard Arabic (H) is used alongside other varieties of Arabic (L); and China, where Standard Chinese (H) is used as the official, literary standard and local varieties of Chinese (L) are used in everyday communication); Tamil, a Dravidian language has one of the largest diglossia with Literary Tamil (H) used in formal settings and colloquial spoken Tamil (L) used in daily life. Other examples include literary Katharevousa (H) versus spoken Demotic Greek (L); Indonesian, with its bahasa baku (H) and bahasa gaul (L) forms; Standard American English (H) versus African-American Vernacular English or Hawaiian Pidgin (L); and literary (H) versus spoken (L) Welsh.
Etymology
The Greek word (), from (', ) and (', ), meant bilingualism; it was given its specialized meaning "two forms of the same language" by Emmanuel Rhoides in the prologue of his Parerga in 1885. The term was quickly adapted into French as by the Greek linguist and demoticist Ioannis Psycharis, with credit to Rhoides.
The Arabist William Marçais used the term in 1930 to describe the linguistic situation in Arabic-speaking countries. The sociolinguist Charles A. Ferguson, building on his research regarding Moroccan Arabic and Bengali, introduced the English equivalent diglossia in 1959 in the title of an article. His conceptualization of diglossia describes a society with more than one prevalent language or the high variety, which pertains to the language used in literature, newspapers, and other social institutions. The article has been cited over 9,000 times. The term is particularly embraced among sociolinguists and a number of these proposed different interpretations or varieties of the concept.
Language registers and types of diglossia
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In his 1959 article, Charles A. Ferguson defines diglossia as follows: