The dominant approach in psychology to the explanation of human cognition i
s information-processing theory, which is a version of the representative r
ealist theory of knowledge, according to which knowledge of external states
of affairs is not direct but rather comes about through the immediate awar
eness of representations of such states internal to the knower. An alternat
ive to information-processing theory that to date has received Little atten
tion in the psychological literature is direct realism, which is the view t
hat the external world, not a representation of it, is the immediate object
of awareness. This article addresses a long-standing criticism of direct r
ealist epistemology-namely that it does not enable a plausible analysis of
perceptual error. That objection must be overcome if direct realism is ever
to be entertained seriously as a means by which to account for the phenome
na of human cognition. It is contended here that instances of perceptual er
ror can be accounted for within a direct realist framework by reference to
the notions lack of opportunity to cognize, and lack of ability to cognize.