The paper introduces a type of joint utterance construction in Japanese, in which
two independent sentential-level units are amalgamated, which has hitherto received
little attention in the literature. Unlike traditional joint utterance construction
where one speaker maintains authority over the syntactic structure of the forthcoming
continuation and the other accedes to this, thereby constituting a single TCU (turn
constructional unit), our examples demonstrate that both speakers can have authority
over the syntactic design of joint utterances. We call such collaborative utterances
‘co-authored joint utterances’ in this paper.The uniqueness of co-authored joint
utterances lies in their syntactic architecture. While syntactic and semantic continuity
are successfully achieved in constructing co-authored joint utterances, they represent a
co-joined structure in which two sentential-level units are involved with their shared
part constituting a point of amalgamation, and because of this, the structure of a
co-authored joint utterance can no longer be parsed with extant grammar.In analysing
co-authored joint utterances, we examine how they can be treated in relation to the
distinction between TCU (Turn Constructional Unit) continuation and new TCUs. Due to the
particularities of the syntactic architecture of co-authored joint utterances, their
existence raises questions about the way in which this distinction is currently
operationalised, because despite being syntactically an incremental continuation, and so
seemingly a TCU continuation, the co-authored joint utterance implements an action
beyond what was initially instantiated by the antecedent of that joint utterance, and so
arguably constitutes a new TCU.