本文以台灣話的「是」為目標，特別是在結構上高於言者中心狀語（speaker-oriented adverb(ial)），且於疑問詞問句當中無需鄰接輕動詞詞組（vP）的用法；基於其位置，此 一用法實有別於其他非繫詞用法（non-copular homonyms）（Lee, 2005）。文中提議可由 「FOR-SURE really」的語意做為基礎來進行分析，根據Romero與Han（2004）的主張， 「FOR-SURE really」的語意為「我們應該把p命題加入共知背景（Common Ground）裡」。 本文的分析不僅可解釋該用法與其他非繫詞「是」的用法在語言現象上的差異，同時也 明確指出漢語當中語用標記的存在，而這也佐證了「是」的高度語法化，其同源成分在 今日的其他漢語裡頭，也於功能及句法分布上有了相當分歧的演化。

This paper intends to investigate a usage of sī “be” in Taiwanese, which occurs higher than speaker-oriented adverb(ial)s and need not adjoin to vP in a wh-question, contrary to its non-copular homonyms (Lee, 2005). I suggest that it can be analyzed based on the denotation of FOR-SURE really, which conveys the meaning: “it is for sure that we should add to Common Ground that p,” proposed in Romero and Han (2004). The analysis not only explains all the empirical disparity observed between this sī and other non-copular usages of sī but also reveals the existence of a pragmatic marker in Sinitic languages, which indicates a result of high degree of grammaticalization of sī, an item whose cognates have also evolved into a wide spectrum of functions / distribution in today’s Sinitic languages.