Recent studies in written languages have clarified how writing systems (scripts) are invented, evolve, and are adapted to other languages. The origins and the typology of scripts are interrelated, yet partly independent. We distinguish PICTOGRAPHIC scripts, which are not written language, but from which writing systems may arise; LOGOGRAPHIC scripts, like that of Chinese; SYLLABARIES, like Japanese kana; and ALPHABETS. This last category is in turn divided into ABUGIDAS (e.g. Arabic), ALPHASYLLABARIES (e.g. the native scripts of India and SE Asia), and ALPHABETS PROPER (e.g. Greek, Roman, Cyrillic). Alphabetic systems that have been developed for East Asian languages include Korean HANGUL and Chinese BOPOMOFO.
　
Some languages use a mixture of features; thus European languages use logographs like メ2モ and メ+モ along with alphabetic symbols. Japanese combines kanji (Chinese logographs) with kana (syllabary) as well as roman letters. In the Chinese area, Taiwanese and Cantonese are sometimes written with roman letters supplementing Chinese characters.
　
Some languages have had changes in their writing systems in recent centuries. Vietnamese once used an adaptation of Chinese characters (chu$ユn冦), but it now uses the roman alphabet, with numerous added diacritics. Among minority nationalities in mainland China, languages like Uighur (Turkic) and Dehong (Dai) have been sometimes written in the roman alphabet, but they now use adaptations of Arabic script and of a native Dai system. The Yi (Lolo) language, which once used a logographic script inspired by that of Chinese, now uses a very large syllabic script.
　
When writing systems are invented or adapted by missionaries, educators etc., it is important to respect several criteria, related to the facts mentioned above: (a) The value of traditional scripts, where they exist, should be recognized. (b) Nevertheless, scripts should reflect accurate grammatical and phonological analyses. (c) The phonological structures of some languages may be well represented by syllabic, rather than alphabetic scripts. (d) Consideration should be given to whether a script corresponds more to MORPHOPHONEMIC or to purely PHONEMIC structure. (e) Relationships to existing scripts, politically or socially dominant, should be considered. (f) Differences in handwritten and typographic styles should be taken into account. All these criteria are relevant to the writing systems used for the aboriginal Formosan languages of Taiwan, such as Ami and Paiwan.