There have been many attempts of late to formulate a satisfactory theory of knowledge with which to replace the traditional justified true belief analysis. Almost all agree that it must be the case that in order for S to know that p; i.) p be true, and ii.) S believe that p. Although many argue that there must be a condition stating that S has adequate evidence for p, requirements other than i.) and ii.) are controversial. The most popular approach (...) taken, however, is the addition of a requirement to the effect that for S to know that p there must be no other evidence against p strong enough to undermine S's belief that p, should this evidence come to S's attention. I shall call such a requirement a “defeasibility condition” and any theory containing such a requirement a defeasibility theory.Defeasibility theories are quite effective in handling a certain kind of difficulty to which theories of knowledge are subject, namely problems dealing with what Harman has termed the social aspect of knowledge. (shrink)

In the ongoing attempt to provide a satisfactory analysis of knowledge numerous conditions have been proposed as necessary and sufficient — the most noteworthy being justification, truth, and belief. In addition, various epistemic principles are frequently employed. In this paper I intend to show how the seemingly innocuous justification condition, along with two relatively uncontroversial epistemic principles, can give rise to a paradoxical situation.