 Externalist theories impose more (and also sometimes less) than the seemings internalist requirement that the agent have the relevant perceptual experience. One obvious candidate factor is reliability. Alvin Goldman (1979, 1986) argues that, so long as perception really is reliable,[6]  the agent need not have reasons for believing perception to be reliable in order to be justified in her perceptual beliefs. What makes perceptual beliefs justified, on such a view, is that they are reliably formed. The simplest reliabilist theory of perceptual belief is one that holds