The Monkey Wrench

Edmund Gettier saw a flaw in this argument of justified true belief. In his paper he presented two counterexamples to the traditional theory of knowledge. He demonstrated that the three conditions were satisfied, but person A really did not know X!

Gettier presented two examples in that: it is possible for a person to be justified in believing a proposition that is in fact false; and that a deduction from believing something which is flawed also allows the conditions to be satisfied yet, them not really knowing.