Edmund Gettier in the context of "University of Massachusetts Amherst"

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.

The Theaetetus (/ˌθiːɪˈtiːtəs/; Greek: Θεαίτητος Theaítētos, lat. Theaetetus) is a philosophical work written by Plato in the early-middle 4th century BCE that investigates the nature of knowledge, and is considered one of the founding works of epistemology. Like many of Plato's works, the Theaetetus is written in the form of a dialogue, in this case between Socrates and the young mathematician Theaetetus and his teacher Theodorus of Cyrene. In the dialogue, Socrates and Theaetetus attempt to come up with a definition of episteme, or knowledge, and discuss three definitions of knowledge: knowledge as nothing but perception, knowledge as true judgment, and, finally, knowledge as a true judgment with an account. Each of these definitions is shown to be unsatisfactory as the dialogue ends in aporia as Socrates leaves to face a hearing for his trial for impiety.

As one of the major works of Plato's theory of knowledge, the Theaetetus was influential on Platonism from at least the time of the Skeptical Academy of the 3rd century BCE through the Neoplatonism of the 6th century CE. It has also been the subject of increased attention in modern times as a result of its influence on Edmund Gettier, who challenged the existing definitions of knowledge as a "justified true belief" in a paper that investigated Plato's theory of knowledge as outlined in this work.

Definitions of knowledge aim to identify the essential features of knowledge. Closely related terms are conception of knowledge, theory of knowledge, and analysis of knowledge. Some general features of knowledge are widely accepted among philosophers, for example, that it involves cognitive success and epistemic contact with reality. Despite extensive study, disagreements about the nature of knowledge persist, in part because researchers use diverging methodologies, seek definitions for distinct purposes, and have differing intuitions about the standards of knowledge.

An often-discussed definition asserts that knowledge is justified true belief. Justification means that the belief fulfills certain norms like being based on good reasons or being the product of a reliable cognitive process. This approach seeks to distinguish knowledge from mere true beliefs that arise from superstition, lucky guesses, or flawed reasoning. Critics of the justified-true-belief view, like Edmund Gettier, have proposed counterexamples to show that some justified true beliefs do not amount to knowledge if the justification is not genuinely connected to the truth, a condition termed epistemic luck.