Bidirectionality between modal and conditional constructions in Mandarin Chinese

This paper proposes that modal constructions can develop into conditional constructions in Mandarin Chinese and vice versa. Therefore, bidirectionality exists between these kinds of constructions diachronically. While bidirectionality is an apparent violation of unidirectionality, both directions of change are shown to be regular cases of procedural constructionalization, enabled by the fact that modal and conditional constructions can perform identical indirect speech acts (i.e., they are performatively equivalent) and instances of one may be morphosyntactically categorized as the other in Chinese (i.e., they are morphosyntactically vague). A crosslinguistically generalizable prediction is then proposed: bidirectionality is possible if instances of two constructions are performatively equivalent and morphosyntactically vague with respect to each other in certain contexts.