Arabic grammar. The literal meaning of the word nahw is “way” or “manner,” signifying the way language is used by its native speakers. One of the earliest sciences developed by Muslims, its origins are usually traced back to Abul Aswad al-Duali, who is said to have organized the rules of Arabic grammar at the request of Ali. Al-Sibawayh's Kitab fil-nahw, however, is considered to be the first authoritative text of the field. Arabic grammar is usually divided into two major parts: sarf or tasrif, the conjugation of verbs, and nahw or irab, modulations of words and declensions. The Baghdad and Basra schools of grammar are well known for their differences concerning Arabic syntax, semantics, and philosophy of language.