Gettier

Gettier refers to a cluster of puzzles in epistemology introduced by the American philosopher Edmund L. Gettier in 1963 that challenge the view that knowledge is simply justified true belief. In his paper, Gettier showed that there can be situations where a person has a belief that is justified and true, yet intuitively does not count as knowledge because the truth of the belief results from luck or a coincidence rather than solid justification.

The core idea of Gettier problems is that justified true belief may not suffice for knowledge when the truth of the belief depends on factors unrelated to the justification for holding it. In classic examples, a person forms a belief based on strong evidence about related propositions, and the belief happens to be true for coincidental reasons, making it seem justified but not genuinely known.

Gettier problems have had a lasting impact on epistemology by provoking extensive debate about how to define knowledge. Respondents have proposed a range of refinements and alternatives, including adding conditions to exclude false lemmas, adopting reliabilist approaches that emphasize reliable processes, and exploring externalist or virtue-theoretic accounts that separate knowledge from merely justified belief. The Gettier challenge remains a central reference point in discussions of what constitutes knowledge and how to assess epistemic reliability.