Gettier problem

Etymology

An eponym from Edmund Gettier, whose brief 1963 paper "Is Justified True Belief Knowledge?" offered counterexamples that upended a definition dating back to Plato. His surname became the standard label for such luck-tainted cases.

noun phrase · /GET-ee-er PROB-lum/
A type of case showing that having a justified true belief is not always enough to count as knowledge.
What it names
A handle for the discovery that knowledge is harder to define than “justified true belief” — reach for it when a belief turns out true by luck despite good reasons.
Example
You correctly believe the clock says noon and it is noon — but the clock stopped exactly twelve hours ago: a textbook Gettier problem.
Related idea
It targets the classical account of epistemic justification, showing that truth and good reasons can coincide by accident without yielding real knowledge.