本文嘗試以語氣副詞為例，說明語法化可由複句省縮引發。文中以讓轉複句為範圍，探討「反正」類、「畢竟」類、「又」、「也」這四組語氣副詞的形成。前兩組詞本身相當於讓步分句，與所在句構成讓轉關係，並從之發展為語氣副詞；後兩個詞則源自轉折關聯副詞，並經歷複句結構重組而發展為語氣副詞。這兩方面演變均起自複句省縮，或是將複句省縮為單句，或是將套疊或包接複句省縮為單一複句，不但展現單複句間巧妙的轉換特性以及語氣副詞的複雜本質，也說明複句省縮對語法化的推動作用。

Based on the history of four groups of mood adverbs, namely the fanzheng 反正 group, the bijing 畢竟 group, you 又, and ye 也, this paper argues that grammaticalization can be triggered by the ellipsis and compacting of complex sentences. The fanzheng and bijing groups of mood adverbs were originally equal to concessive clauses and constructed concessive relations with the sentences they occurred, while you and ye were adversative adverbs and experienced the ellipsis of the previous sentence. These two types of developments all contain the ellipsis and compacting of complex sentences, either from complex sentences to simple sentences or from partially overlapped complex sentences to general complex sentences. Their histories demonstrate not only the flexible transformation between simple sentences and complex sentences in Mandarin Chinese, but also the complex properties of these mood adverbs.