The Gettier problem, in the field of epistemology, is a landmark philosophical problem concerning the understanding of descriptive knowledge. Attributed to American philosopher Edmund Gettier, Gettier-type counterexamples (called "Gettier-cases") challenge the long-held justified true belief (JTB) account of knowledge. The JTB account holds that knowledge is equivalent to justified true belief; if all three conditions (justification, truth, and belief) are met of a given claim, then there is knowledge of that claim. In his 1963 three-page paper titled "Is Justified True Belief Knowledge?", Gettier attempts to illustrate by means of two counterexamples that there are cases where individuals can have a justified true belief regarding a claim but still fail to know it because the reasons for the belief, while justified, turn out to be false. Thus, Gettier claims to have shown that the JTB account is inadequate because it does not account for all of the necessary and sufficient conditions for knowledge.
The terms "Gettier problem", "Gettier case", or even the adjective "Gettiered", are sometimes used to describe any case in the field of epistemology that purports to repudiate the JTB account of knowledge.
Responses to Gettier's paper have been numerous. Some reject Gettier's examples as inadequate justification, while others seek to adjust the JTB account of knowledge and blunt the force of these counterexamples. Gettier problems have even found their way into sociological experiments in which researchers have studied intuitive responses to Gettier cases from people of varying demographics.
History
The question of what constitutes "knowledge" is as old as philosophy itself. Early instances are found in Plato's dialogues, notably Meno (97a–98b) and Theaetetus. Gettier himself was not actually the first to raise the problem named after him; its existence was acknowledged by both Alexius Meinong and Bertrand Russell, the latter of whom discussed the problem in his book Human Knowledge: Its scope and limits. In fact, the problem has been known since the Middle Ages, and both Indian philosopher Dharmottara and scholastic logician Peter of Mantua presented examples of it.
Dharmottara, in his commentary on Dharmakirti's Ascertainment of Knowledge,<!-- Pramāṇa-viniścaya-ṭīkā, commentary on Pramāṇa-viniścaya = Ascertainment of Knowledge or Ascertainment of Valid Cognition--> gives the following two examples: