本文從比較句法的角度切入，來研究越南語中乾坤挪移句的動詞提升及隱性模態詞。我們發現動詞移位跟此類結構的模態性有密切的關連，主句、從句皆然。此外，證據顯示某些乾句的變體其實是由雙層句構組成，而動詞到模態詞的移位則屬右向加接。最後在實證層次上，我們也從泰語找到了平行現象來支持本文的句法分析。

This paper pursues the issues surrounding Vietnamese flip-flop sentences in terms of verb raising and covert modals from a comparative point of view. We show that verb movement in flip-flop constructions is found in both matrix and embedded environments where the presence of modality is attested. Evidence is presented to show the bi-clausal nature of the so-called "flip alternative" construction, as well as the rightward nature of V-to-M adjunction. We also draw cross-linguistic support from Thai data to substantiate our syntactic analyses on empirical grounds.