Abstract

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.