Knowledge, defeasibility theory of

Based upon an analogy with the legal and ethical concept of a defeasible, or prima facie, obligation, epistemic defeasibility was introduced into epistemology as an ingredient in one of the main strategies for dealing with Gettier cases. In these cases, an individual’s justified true belief fails to count as knowledge because the justification is defective as a source of knowledge. According to the defeasibility theory of knowledge, the defect involved can be characterized in terms of evidence that the subject does not possess which overrides, or defeats, the subject’s prima facie justification for belief. This account holds that knowledge is indefeasibly justified true belief. It has significant advantages over other attempts to modify the traditional analysis of knowledge in response to the Gettier examples. Care must be taken, however, in the definition of defeasibility.