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|Region||Khorasan (Central Asia)|
|Era||15th to early 20th century|
Chagatai (جغتای Jaġatāy) is an extinct Turkic language which was once widely spoken in Central Asia, and remained the shared literary language there until the early 20th century. It was also spoken by the early Mughal rulers in the Indian subcontinent, where it influenced the development of Hindustani. Ali-Shir Nava'i was the greatest representative of Chagatai literature. Soviet scholarship termed the language "Old Uzbek".
Early development of the language is sometime known as Middle Turkic, or even simply Turki.
The word Chagatai relates to the Chagatai Khanate, a descendant empire of the Mongol Empire, which was left to Genghis Khan's second son, Chagatai Khan. Many of the Chagatai Turks and Tatars, who were the speakers of this language, claimed descent from Chagatai Khan.
Chagatai belongs to the Karluk branch of the Turkic language family. It is descended from the Old Turkic that served as a lingua franca in Central Asia, with a strong infusion of Arabic and Persian words and turns of phrase. Its literary form was based on two earlier literary languages, Karakhanid and Khorezmian. It can be divided into three periods:
- Pre-classical Chagatai (1400–1465)
- Classical Chagatai (1465–1600)
- Post-classical Chagatai (1600–1921)
The first period is a transitional phase characterized by the retention of archaic forms; the second phase starts with the publication of Mir Alisher Navoi's first Divan and is the highpoint of Chagatai literature, followed by the third phase, which is characterized by two bifurcating developments. One is the preservation of the classical Chagatai language of Navoi, the other trend is the increasing influence of the dialects of the local spoken languages. The Chagatai Turkic language lived its heyday in the Timurid Empire. Chagatai remained the universal literary language of Central Asia until the Soviet reforms of the early 20th century, and had a marked influence on the development of Hindustani (Hindi/Urdu).
Influence on later Turkic languages 
Uzbek and modern Uyghur are the two modern languages most closely related to Chagatai, and Uzbeks regard Chagatai as the origin of their own language and claim Chagatai literature as their own. In Uzbekistan, then a part of the Soviet Union, Chagatai was replaced by a literary language based on the local Uzbek dialect in 1921. The so-called Berendei, a 12th century medieval nomadic Turkic people possibly related to the Cumans, seem also to have spoken a language which ultimately was identified as Chagatai.
Ethnologue records the use of the word "Chagatai" in Afghanistan to describe the "Tekke" dialect of Turkmen. Up to and including the eighteenth century Chagatai was the main literary language in Turkmenistan as elsewhere in Central Asia, and had some influence on Turkmen, but in fundamentals the two languages belong to different branches of the Turkic family.
The most famous of the Chagatai poets is Mir Ali-Shir Nava'i, who among his other works wrote Muhakamat al-Lughatayn, a detailed comparison of the Chagatai and Persian languages, in which he argued for the superiority of the former. His fame is attested by the fact that Chagatai is sometimes called "Nava'i's language". Among prose works, Timur's biography is written in Chagatai Turkic as is also the famous Baburnama (or Tuska Babure) of Babur, the Timurid founding the Mughal Empire.
Important works continued to be written in the Chagatai language into the early twentieth century. Among them are Musa Sayrami's Tārīkh-i amniyya (completed 1903) and its revised version Tārīkh-i ḥamīdi (completed 1908), representing the best sources on the Dungan Rebellion in Xinjiang.
Chagatai literature is still studied in modern Turkey and regarded as part of the Turkish heritage.
- Uzbek: چەغەتاي Chag'atoy; Mongolian: ᠲᠰᠠᠭᠠᠳᠠᠢ Chagadai; Uyghur: چاغاتاي Chāghātāy; Turkish: Çağatayca
- Robert McHenry, ed. (1993). "Navā’ī, (Mir) ‘Alī Shīr". Encyclopædia Britannica (in English) 8 (15th ed.). Chicago: Encyclopædia Britannica, Inc. p. 563.
- C. E. Bosworth, E. Van Donzel, W. P. Heinrichs, Ch. Pellat, ed. (1993). "Mīr ‘Alī Shīr Nawā’ī". The Encyclopedia of Islam (in English) VII. Leiden—New York: E. J. Brill. p. 91.
- МОЛЛА МУСА САЙРАМИ: ТА'РИХ-И АМНИЙА (Mulla Musa Sayrami's Tarikh-i amniyya: Preface)], in: "Материалы по истории казахских ханств XV–XVIII веков (Извлечения из персидских и тюркских сочинений)" (Materials for the history of the Kazakh Khanates of the 15–18th cc. (Extracts from Persian and Turkic literary works)), Alma Ata, Nauka Publishers, 1969. (Russian)
- Kim, Ho-dong (2004). Holy war in China: the Muslim rebellion and state in Chinese Central Asia, 1864–1877. Stanford University Press. p. xvi. ISBN 0-8047-4884-5.
- Eckmann, János, Chagatay Manual. (Indiana University publications: Uralic and Altaic series ; 60). Bloomington, Ind.: Indiana University, 1966. Reprinted edition, Richmond: Curzon Press, 1997, ISBN 0-7007-0860-X, or ISBN 978-0-7007-0860-4.
- Bodrogligeti, András J. E., A Grammar of Chagatay. (Languages of the World: Materials ; 155). München: LINCOM Europa, 2001. (Repr. 2007), ISBN 3-89586-563-X.
- Pavet de Courteille, Abel, Dictionnaire Turk-Oriental: Destinée principalement à faciliter la lecture des ouvrages de Bâber, d'Aboul-Gâzi, de Mir Ali-Chir Nevâï, et d'autres ouvrages en langues touraniennes (Eastern Turkish Dictionary: Intended Primarily to Facilitate the Reading of the Works of Babur, Abu'l Ghazi, Mir ʿAli Shir Navaʾi, and Other Works in Turanian Languages). Paris, 1870. Reprinted edition, Amsterdam: Philo Press, 1972, ISBN 90-6022-113-3.
- Erkinov, Aftandil. “Persian-Chaghatay Bilingualism in the Intellectual Circles of Central Asia during the 15th-18th Centuries (the case of poetical anthologies, bayāz)”. International Journal of Central Asian Studies. C.H.Woo (ed.). vol.12, 2008, pp. 57–82 .