 Thus, the representational theory of sensory qualities cannot be purely representational, but must appeal to some further factor, to distinguish visual representations from other sorts of representations of redness. Dretske (1995) cites only the fact that visual representation is sensory and what he calls “systemic.” Tye (1995) requires that the representation be nonconceptual and “poised,” though he also argues that visual representations of color would differ from other sorts of representations in being accompanied by further representational differences. Lycan (1996) appeals to functional role.