Dual (grammatical number)
Dual (abbreviated DU) is a grammatical number that some languages use in addition to singular and plural. When a noun or pronoun appears in dual form, it is interpreted as referring to precisely two of the entities (objects or persons) identified by the noun or pronoun. Verbs can also have dual agreement forms in these languages.The dual number existed in Proto-Indo-European, persisted in many of the now extinct ancient Indo-European languages that descended from it— Ancient Greek and Gothic for example—and can still be found in a few modern Indo-European languages such as Scottish Gaelic, Slovenian, and Sorbian. Among surviving ancient languages, Sanskrit uses dual forms across nouns, verbs, and adjectives. Many more modern Indo-European languages show residual traces of the dual, as in the English distinctions both vs. all, either vs. any, neither vs. none, and so on.Many Semitic languages also have dual number. For instance, in Arabic, ان -ān, is added to the end of any noun to indicate that it is dual (regardless of how the plural is being formed).Dual number is also present in those Khoesan languages that have a rich inflectional morphology, particularly Khoe languages.