タングート
Nishida also made studies of the "Flower Garland Sutra" (1975–1977) and Tangut ritual poems (1986). In order to explain the fact that in some ritual poems each line was written twice using different vocabulary and different grammatical structures, Nishida proposed that there were two different Tangut language registers: most Tangut text represented the language of the ordinary Tangut people (the "red-faced people"), but the ritual poems represented the language of the ruling class (the "black-headed people"), the latter preserving a linguistic substratum that had been lost in ordinary Tangut speech.