 In addition to these standard worries, there is a pervasive sense among epistemologists that perceptual experiences must play some important role in the justification of perceptual belief, probably an evidential one. There are two ways to make room for experiences in an externalist epistemology. One is to add an auxiliary thesis to the effect that the requisite external property is essentially mediated in certain cases by experiences. For example, some perceptual processes might only be highly reliable when experiences are among the inputs; or they might be designed (Plantinga 1993) to take experiences as inputs. The other way is to defend a genuinely hybrid account, which posits an internalist (usually evidentialist) constraint that is not taken to reduce to the more general external criteria already in place.