True by luck

The classic definition holds knowledge to be a belief that is both true and justified. Yet one can believe something for good reasons, and have it be true, without thereby knowing it: the stopped clock we glance at just at the hour it still shows, the rock we take from afar for a sheep while a real one grazes behind it. The belief is true and justified, but it hits the mark by accident. Must we then redefine what knowledge is, or tighten what we are entitled to demand of a justification, until it links belief to truth otherwise than by luck?

Anchors: Gettier · Plato · Russell