The Causal Potency of Qualia: Its Nature and Its Source

Abstract

There is an argument (Medlin, 1967; Place, 1988) whichshows conclusively that if qualia are causallyimpotent we could have no possible grounds forbelieving that they exist. But if, as this argumentshows, qualia are causally potent with respect to thedescriptions we give of them, it is tolerably certainthat they are causally potent in other morebiologically significant respects. The empiricalevidence, from studies of the effect of lesions of thestriate cortex (Humphrey, 1974; Weiskrantz, 1986;Cowey and Stoerig, 1995) shows that what is missing inthe absence of visual qualia is the ability tocategorize sensory inputs in the visual modality. This would suggest that the function of privateexperience is to supply what Broadbent (1971) callsthe “evidence” on which the categorization ofproblematic sensory inputs are based. At the sametime analysis of the causal relation shows that whatdifferentiates a causal relation from an accidentalspatio-temporal conjunction is the existence ofreciprocally related dispositional properties of theentities involved which combine to make it true thatif one member of the conjunction, the cause, had notexisted, the other, the effect, would not haveexisted. The possibility that qualia might bedispositional properties of experiences which, as itwere, supply the invisible “glue” that sticks cause toeffect in this case is examined, but finallyrejected.