The meanings of preverbal scalar particles in Mandarin, such as dou and jiu, have been widely discussed in the formal linguistics literature. This talk aims to demonstrate a Question-under-Discussion (QUD) based semantic-pragmatic theory for certain uses of dou and jiu and discuss how this new analysis differs from previous accounts. It will be proposed that dou signals a particular discourse structure in which (i) the "associate" of dou that appears to its left is akin to a contrastive topic which introduces the subquestions (in the form of a set of polar questions) of a common QUD, and (ii) dou further requires that each subquestion be positively answered. This new lexical entry of dou in terms of (sub)questions and a question-based entailment relation explains some otherwise puzzling interactions between dou and necessity modals or focus adverbs such as shenzhi 'even'. This model also provides a new, question-based definition for the even-like particle lian in the so-called lian...dou construction, which explains their optional co-occurrence. Finally, it is shown how a similar approach can be applied to jiu, another scalar particle which sometimes indicates sufficiency but sometimes signals exclusivity.