This paper has four primary objectives. First, we examine two Vietnamese constructions—the locative and existential constructions—in which a locative phrase appears clause-initially, preceding a verb-DP sequence. We demonstrate that, in the locative construction, the locative phrase is an argument of the locative verb, whereas, in the existential construction, it functions as a locative adjunct. Second, we show that this locative adjunct in the existential construction can undergo optional topicalization to the left periphery. More crucially, we argue that the fronting of the locative argument in the locative construction is neither Ā-topicalization to the left periphery nor A-movement targeting Spec,TP, supporting the featural approach to the A/Ā distinction. Third, by comparing the expletive nó with the fronting locative argument in the locative construction, we contend that both compete for the same specifier position of a hybrid A/Ā projection in the high TP domain. Fourth, to detail the movement of the locative argument in the locative construction, we posit a composite probe [D, δ] on the head of the A/ĀP to selectively move the locative argument to Spec,A/ĀP over the structurally higher theme DP.