diglossic

Diglossic is an adjective used in sociolinguistics to describe a situation in which a single language exists in two distinct varieties that are used for different social functions. The related noun is diglossia. In a classic diglossic arrangement, the two varieties are labeled High (H) and Low (L). They are not interchangeable in the social contexts for which they are designed and typically carry different prestige.

In a diglossic system, H is usually employed in formal domains such as education, official discourse, media, literature, religion, and formal writing, while L is used in everyday conversation, family settings, and informal interactions. The H variety is generally learned through schooling and standardized instruction, whereas the L variety grows from daily use within the community. The varieties may differ in phonology, vocabulary, syntax, and sometimes orthography, yet they remain varieties of the same language rather than separate languages.

Arabic is the most widely cited example, with Modern Standard Arabic as H and regional vernaculars (such as Egyptian or Moroccan Arabic) as L. Swiss German and Standard German illustrate another well-known diglossic arrangement in the German-speaking world. Greek provides a historical example, with Katharevousa as a high form and Demotic Greek as a low form, until Demotic Greek became the standard for education and public life. Diglossia is distinct from bilingualism and from code-switching, because it is a stable, society-wide pattern with defined domains for each variety, rather than situational switching between two languages.

The concept was introduced by Charles A. Ferguson in 1959 and remains a foundational framework in sociolinguistics, language planning, and education.