Many theories have been proposed to account for the fact that wh- phrases across languages can obtain various quantificational interpretations depending on the syntactic contexts where they occur. For example, Nishigauchi (1990) and Cheng (1991) hypothesize that wh-phrases are variables, and their quantificational forces derive from the binders that bind them. Their theories, however, do not provide a plausible answer to the island effects in wh-questions in Vietnamese given that in their theory there is no need for LF movement. To account for the Vietnamese data, their theories need to be revised. Namely, wh-phrases in Vietnamese are ambiguous between a quantifier interpretation and a variable interpretation. Based on Kratzer and Shimoyama (2002) I provide a unified analysis of wh-phrases, according to which a wh-phrase is a set of individual alternatives bound and assigned an interpretation by an alternative set taking operator. Yet, unlike Kratzer and Shimoyama (2002), I propose that LF movement is still required for scope interpretation and the moved wh-phrase functions as a scope marking operator.