Kilwardby argues that only human beings proffer meaningful utterances because, as Priscian points out, the articulate vocal sound (uox articulata) uttered by humans is tied together (copulata) with a sensus mentis or intellectus in the mind of the speaker; thus only beings that have minds can produce significative utterances.[26] Moreover, the production of the vox litterata requires the control of the modulation of sounds—what Kilwardby calls the figure in the air (through which the utterance