Utterance-final -canha grew from Korean long form negative question construction. The growth of -canha derives from the rivalry between two negation forms in Korean (the short form vs. the long form). The function of -canha changed from transferring negation to transferring what the speaker thinks to be shared knowledge. Its gradual functional/formal change is shown via the usage-based assay of conversational data. Recurrent (inter)subjectification served as potent motive of functional shift.