Philosophy
Justified True Belief and Gettier Problems
Quick fact
Edmund Gettier's 1963 paper, just three pages long, is one of the most influential in 20th-century philosophy, spawning thousands of responses and entire research programs.
Why this is interesting
You probably think you know what 'knowledge' means. But what if you could have a justified true belief and still not actually know something?
Read the full explanation
Understanding Justified True Belief and Gettier Problems
Imagine you look at a clock that reads 3:00. You form the belief 'It is 3:00.' The clock is accurate. You have a justified true belief: you have justification (the clock reading), the belief is true, and you believe it. Normally, we'd say you know the time. But suppose the clock actually stopped exactly 24 hours ago. It's only by luck that it shows the correct time now. Intuitively, you don't really know the time—your belief is accidentally true. This is the essence of a Gettier problem: a justified true belief that fails to be knowledge due to epistemic luck. Gettier presented two such counterexamples that systematically undermined the 'JTB' definition, which had been widely accepted since Plato.
A deeper explanation
The mechanism behind Gettier problems is the presence of epistemic luck that bridges the gap between justification and truth. In standard JTB, justification must be robustly connected to the truth of the belief. Gettier cases show that justification can be sound (based on good evidence) yet the truth of the belief can arise from a different, coincidental circumstance. This reveals that knowledge requires not only justification, truth, and belief, but also an anti-luck condition—a fourth element that prevents accidental correctness. The problem matters because it forces philosophers to refine what counts as 'adequate justification' and to explore alternative accounts of knowledge, such as causal theories, reliabilism (where the belief must be produced by a reliable process), or virtue epistemology (where the belief must arise from intellectual virtue). The Gettier problem remains unresolved in a universally accepted way, making it a live issue in epistemology.