The multifunctional Japanese particle *ka* occurs in questions,
indefinites, and disjunctions. This calls for a compositional treatment in
inquisitive semantics, where these three items form a natural class
(Ciardelli, Groenendijk & Roelofsen 2018). Our central insight is that *ka*
in
all its guises can be understood in terms of inquisitive union plus
conditional inquisitive closure.