This paper describes three constraints that together govern the distribution of the exhaustive focus marker
shì in Mandarin Chinese. First, I argue that shì is a sentential focus particle that is
subject to a requirement to adjoin as low as possible within its clause or phase. Second, I show that shì
requires a congruent Question Under Discussion (QUD). Third and finally, I show that there are certain reduced clauses where
shì is completely disallowed, although other focus particles such as ‘only’ may appear. To explain this
last restriction, I propose that reference to a QUD is mediated by a functional head in the clause periphery.
Shì is thus unavailable in reduced clauses which do not project this high functional layer.