premise: The Chagatai language was completely extinct by the 1700s.
hypothesis: Chagatai 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 . As part of the preparation for the 1924 establishment of the Soviet Republic of Uzbekistan , Chagatai was officially renamed `` Old Uzbek '' , which Edward A. Allworth argued `` badly distorted the literary history of the region '' and was used to give authors such as the 15th-century author Ali-Shir Nava'i an Uzbek identity .