family of languages spoken from northeast India eastward to Taiwan and from China southward to the Malay Peninsula. It is generally divided into two large subfamilies: the Sinitic, comprising Mandarin, Cantonese, and the other languages of China (see CHINESE LANGUAGE,); and the Tibeto-Burman, the best-known members of which are Tibetan and Burmese. The Tibeto-Burman subfamily, although encompassing more languages than the Sinitic, and although spoken by a wider variety of ethnic groups, is more difficult to classify and actually covers a smaller population. Most linguists recognize four main Tibeto-Burman branches, divided into about nine groups. The provenance of the many Tibeto-Burman languages (of which only a portion have been studied by Western linguists) includes Tibet, Nepal, Burma, western China, and Assam State in India.

Sometimes classified either as a third Sino-Tibetan subfamily or as part of a Sinitic-Tai subfamily are the Tai languages, which include Thai or Siamese, Lao, and many lesser-known languages spoken in Burma, Assam, northern Vietnam, and southwestern China. Many modern scholars, however, consider them possibly Austro-Asiatic or of uncertain relation to other language families.

Sino-Tibetan languages are distinguished from Western language families by two main traits: isolating or monosyllabic character and the use of tones. The family was probably at one time agglutinative (joining several grammatically distinct word elements together into complex words translatable by English phrases or sentences). Over the centuries, however, the languages passed into a monosyllabic stage. In monosyllabic languages, case and tense endings and other inflections are not used. Rather, each (usually monosyllabic) word expresses a discrete idea in a sentence. The meaning and syntax of the sentence are determined by word order and by particles (words that indicate grammatical relationship or specify some aspect of meaning). Parts of speech such as nouns, verbs, and adjectives are not so strongly differentiated as in English; some words, for example, can correspond in English either to a verb or to an adjective. The widespread disappearance of meaningful suffixes, prefixes, and infixes from these languages may have led to their other most notable trait, variation in tone or pitch in words that otherwise are pronounced identically to indicate differences in meaning or, sometimes, grammatical function. In extreme cases, as in southeastern China, as many as eight distinct tones may be used.        M.P., MARIO PEI, Ph.D.