BUN in Hakka exhibits multiple grammatical functions. The paper maintains that BUN illustrates a good example of polygrammaticalization. Like a prototypical double-object verb, BUN involves dative alternation that brings out two separate functional paths of BUN. From the first frame, BUN is decategorized from a full-fledged verb of giving, through a goal marker, into a clause-linking complementizer. Along the structural development, BUN extends its meaning from denoting a giving activity, through marking the given object, to marking more abstract goal and purpose. From the latter, BUN is developed from a verb-of-giving into a causative verb and then into an agent marker. Due to the parallelism between the conceptual structures embodied in possession and control, the meaning of giving someone something is transferred into giving someone the permission to do something. Along this transfer-of-control argument, the meaning of BUN then develops into agent marking.