Fifty years ago, in June 1963, Edmund Gettier published a very short paper in Analysis called “Is Justified True Belief Knowledge?”. Philosophical folklore has it that, before Gettier published this paper, most people were with Plato in thinking that justified true belief is both necessary and sufficient for knowledge. If you know something, it has to be true, you have to believe it, and you have to have a justification for your belief. In the original paper, Gettier gave some slightly complicated examples which appear to show that the conditions are not sufficient, not enough for knowledge: a person might have a justified true belief in a proposition but still not know it. Since then, a very large number of more straightforward counterexamples to what’s now called the JTB conception of knowledge have been given.
Here’s an easy one (I think owed to Bertrand Russell). Every day you walk past a church on your way to work and check the time. You look up and see that it’s exactly 8 am. You believe it’s exactly 8 am. In fact, it is exactly 8 am. You’ve got a justified true belief that it’s exactly 8 am. But suppose the clock actually stopped twelve hours ago. Many believe this is an instance of justified true belief, but not knowledge. The JTB bit is in place, but that’s not enough, not sufficient for knowledge.
Some argue that there are examples that pull against necessity too, and it might be possible to imagine cases of knowledge even where one or another of the JTB components are missing. Imagine a college student who’s been up all night cramming for a history exam. She’s wired on caffeine, totally frazzled, and when asked “When was the Battle of Hastings?” she thinks she has no idea. 1066 comes to mind, but she has no confidence in the answer. She writes it down anyway. Knowledge without belief?
For the last 50 years philosophers have tried to find answers to Gettier — by shoring up the definition of knowledge, finding ways to defuse the problem, even formulating new conceptions of knowledge. In honour of this anniversary, The Philosophers’ Magazine asked Fred Dretske to tell us what he thinks we should have learned from 50 years of Gettier. His answer appears in the current issue, and you can read it here: Fred Dretske, “Gettier and Justified True Belef: Fifty Years On”