This is the golden – the fiftieth – anniversary of Edmund Gettier’s remarkable paper on why knowledge isn’t justified true belief. It seems like an appropriate time, therefore, to evaluate what we have learned – or should have learned – from his elegant counterexamples. Gettier’s paper had a tremendous impact on contemporary epistemology. Measured in terms of impact per page his three-page paper (yes, only three pages) rates among the most influential of twentieth-century essays in philosophy. Prior to Gettier it was more or less assumed (without explicit defence) that knowledge, knowing that some proposition P was true (when it was in fact true), was to be distinguished from mere belief (opinion) that it was true, by one’s justification, evidence, or reasons for believing it true. I could believe – truly believe – that my horse would win the third race without knowing it would win. To know it would win I need more – some reason, evidence or justification (the race is fixed?) that would promote my true belief to the status of knowledge. Gettier produced examples to show that this simple equation of knowledge (K) with justified true belief (JTB) was too simplistic. His examples triggered a widespread search for a more satisfactory account of knowledge. Read more at: Gettier and justified true belief: fifty years on | The Philosophers Magazine.
And see this similar video: