Philosophy
The Gettier Problem and Justified True Belief
Quick fact
Edmund Gettier’s entire 1963 paper was only three pages long, yet it is one of the most discussed and influential works in 20th-century philosophy.
Why this is interesting
You probably think knowledge is just a justified true belief. But what if you could have all three and still not really know something? That’s the Gettier problem.
Read the full explanation
Understanding The Gettier Problem and Justified True Belief
For centuries, many philosophers defined knowledge as 'justified true belief' (JTB). The idea is simple: to know something, you must believe it, that belief must be true, and you must have good reasons (justification) for holding it. But in 1963, Edmund Gettier published a paper showing that even when all three conditions are met, something can still be missing. He gave two clever examples. In one, you see a man named Smith in the office, so you believe 'Smith is in the office.' That’s justified by your perception. But actually, you were looking at a hologram of Smith, while the real Smith is elsewhere—however, another person happens to be in the office. So your belief is true (someone is in the office) and justified, but you don't really know that someone is in the office because your justification was faulty. Your true belief came from luck, not reliable evidence. This shows that JTB is not sufficient for knowledge.
A deeper explanation
The Gettier problem reveals a fundamental flaw in the JTB account: it doesn’t rule out epistemic luck. In Gettier cases, the belief is true by accident relative to the justification. The justification points to a false proposition (e.g., 'Smith is in the office'), but the belief happens to be true for unrelated reasons. This demonstrates that knowledge requires something more—a fourth condition or a different analysis. Philosophers have proposed numerous responses: adding a 'no false lemmas' condition, requiring that the belief be produced by a reliable process (reliabilism), or that the belief manifests cognitive virtues (virtue epistemology). The Gettier problem matters because it forces us to refine our understanding of what knowledge really is, moving beyond simple definitions to consider the connection between truth and the reasons for belief. It remains a central challenge in epistemology, driving research into the nature of justification, the role of luck, and the criteria for genuine knowledge.