Modern Chinese confirmative shi

Abstract Modern Chinese confirmative shi (as in mei cuo, wo shi yao dusi ni (沒錯，我是要毒死你) ‘that’s right. I really wanted to poison you to death’) is not an auxiliary but an adverb. It derives from the adjective shi ‘true, real’ in Old Chinese (Yan zhi yan shi ye (偃之言是也) ‘what Yan said was true’). The grammaticalization pathway of the Modern Chinese confirmative shi is different from that of the copula shi (Laozhang shi huoche siji (老張是貨車司機) ‘Laozhang is a truck driver’) or the auxiliary shi (Laozhang shi kai huoche, wo shi kai keche (老張是開貨車，我是開客車) ‘Laozhang drives a truck and I drive a coach car’). Modern Chinese confirmative shi, copula shi, and auxiliary shi have the same morphological form because they all appear to derive from the adjective shi or demonstrative ( shi ke ren, shu bu ke ren ( 是可忍，孰不可忍) ‘if this could be endured, is there anything else that could not be endured’) in Old Chinese. Such a pattern of morphological sameness seems to be cross-linguistically rare, if not unique.