AbstractAn infrequently attested pattern of isomorphism between markers of valence-affecting constructions involvesoverlap between causatives and applicatives, with a transitivizing function, and middles, which are detransitivizing. Suchsynchronic overlap must be due to some feature of the development of the constructions; however, so far there has been littledetailed argumentation for directionality in such cases. We consider an instance of this pattern in the South CentralTibeto-Burman languages. The representation of multiple stages of the phenomena allows us to posit directionality and motivationsfor the evolutionary pathways involved. Here, the source morphology developed into a comitative applicative; in some languagescausative meanings emerged, and in others, the construction developed an array of middle meanings via a portative applicativebridging context. The study provides new evidence for how patterns may arise in which the same morphology marks both causative orapplicative constructions, on the one hand, and middles, on the other.