According to Tibetologist John Powers, Tibetan sources counter this narrative of titles granted by the Chinese to Tibetans with various titles which the Tibetans gave to the Chinese emperors and their officials. Tribute missions from Tibetan monasteries to the Chinese court brought back not only titles, but large, commercially valuable gifts which could subsequently be sold. The Ming emperors sent invitations to ruling lamas, but the lamas sent subordinates rather than coming themselves, and no Tibetan ruler ever explicitly accepted the role of being a vassal of the Ming.