Vietnamese has a group of semantically amorphous indefinite words and phrases whose meanings appear to be refined according to the particular syntactic or pragmatic context in which they are embedded. In appropriate environments, they are the functional equivalents of the English "who, someone, anyone, whoever, everyone." Analysis of the occurrence of these words and phrases in Vietnamese suggests four basic contexts that welcome most or all of these indefinites and refine or elaborate their somewhat vague semantics. These include: (1) content questions; (2) situations in which the indefinite functions as an unidentified constant referent; (3) a broad category defined as "irrealis," which subsumes traditional polarity contexts and environments created by both desideratives and root and epistemic modals; and (4) the nomatterative, a semantic structure associated with a type of conditional construction. In each case, attention must be paid to whether the indefinite represents a constant or variable. The syntactic cues associated with each of these contexts are often not sufficiently reliable to prevent ambiguity about the indefinite's function, so both linguistic and extralinguistic information should be used to define these interpretive contexts. This account of indefinites highlights the range of indefinite functions made possible by their apparent lexical underspecification. (MSE)