This article presents some data from Vietnamese that provide significant empirical support for the theoretical claims articulated in Klein (1998, 2006): first, that finiteness should be understood as a composite of tense and assertion, and that assertion may be realized independently of tense marking; second, that the assertion operator so realized has only partial scope over elements of the clause, so that fronted elements may evade this scopal influence. Vietnamese is of special interest because — as claimed here — it expresses assertion independently of Tense or Aspect: in this regard Vietnamese contrasts with most Indo-European languages, as well as with other isolating East Asian languages. The formal analysis of these data involves two further theoretical claims. The first is that assertion is syntactically projected in a comparatively low functional projection, immediately above vP: this claim is thus opposed to recent proposals that would place these type of functional category higher (on the left periphery of the clause). The second claim developed here is that in Vietnamese the displacement of certain underspecified constituents is explained by their requirement to come within — alternatively, to evade — the scope of this assertion operator. That is, syntactic movement may be driven by considerations other than purely formal feature checking.