It was cited together with the lack of reconstructable shared morphology, and evidence that much shared lexical material has been borrowed from Chinese into Tibeto-Burman, by Christopher Beckwith, one of the few scholars still arguing that Chinese is not related to Tibeto-Burman. Benedict also reconstructed, at least for Tibeto-Burman, prefixes such as the causative s-, the intransitive m-, and r-, b- g- and d- of uncertain function, as well as suffixes -s, -t and -n. Study of literary languages Old Chinese is by far the oldest recorded Sino-Tibetan language, with inscriptions dating from around 1250 BC and a huge body of literature from the first millennium BC, but the Chinese script is not alphabetic. Scholars have sought to reconstruct the phonology of Old Chinese by comparing the obscure descriptions of the sounds of Middle Chinese in medieval dictionaries with phonetic elements in Chinese characters and the rhyming patterns of early poetry. The first complete reconstruction, the Grammata Serica Recensa of Bernard Karlgren, was used by Benedict and Shafer. Karlgren's reconstruction was somewhat unwieldy, with many sounds having a highly non-uniform distribution. Later scholars have revised it by drawing on a range of other sources. Some proposals were based on cognates in other Sino-Tibetan languages, though workers have also found solely Chinese evidence for them. For example, recent reconstructions of Old Chinese have reduced Karlgren's 15 vowels to a six-vowel system originally suggested by Nicholas Bodman. Similarly, Karlgren's *l has been recast as *r, with a different initial interpreted as *l, matching Tibeto-Burman cognates, but also supported by Chinese transcriptions of foreign names. A growing number of scholars believe that Old Chinese did not use tones, and that the tones of Middle Chinese developed from final consonants. One of these, *-s, is believed to be a suffix, with cognates in other Sino-Tibetan languages. Tibetic has extensive written records from the adoption of writing by the Tibetan Empire in the mid-7th century. The earliest records of Burmese (such as the 12th-century Myazedi inscription) are more limited, but later an extensive literature developed. Both languages are recorded in alphabetic scripts ultimately derived from the Brahmi script of Ancient India. Most comparative work has used the conservative written forms of these languages, following the dictionaries of Jäschke (Tibetan) and Judson (Burmese), though both contain entries from a wide range of periods. There are also extensive records in Tangut, the language of the Western Xia