Diglossia is a stable language situation where in addition to primary dialects of a language, there is a highly codified superposed variety that is learned formally and used for written/formal communication. This high (H) variety is distinct from the vernacular low (L) variety used in everyday conversation. The H variety has more prestige and is used for literature/education while the L variety is used between family/friends and is acquired naturally rather than taught. Diglossia can last over 1000 years as the varieties are protected by their association with education/writing and stable norms around pronunciation, grammar and vocabulary.