ABSTRACT
Potential challenges and threats to knowledge and rationality have indeed been a focus of traditional epistemology. This chapter addresses threats that stem from the potential inadequacy of some of our cognitive faculties and processes. It explores the prospects for vision-based knowledge by considering the way the visual system classifies objects by reference to their shape. The geon theory postulates that when a viewer perceives an object, the visual system interprets the retinal stimulation in terms of geon components and their relations. Any detailed principle of rationality must recognize that human belief formation operates under the constraints of memory and must take the psychology of memory into account. The pessimistic conclusion that our prospects for rationality are not that good assumes that consistency is indeed a sine qua non of rationality. Perhaps a human being who fails to notice an inconsistency in his belief-set is not ipso facto irrational.
