From Nautil.us' "Fakes" issue:
In the 1960s, the American philosopher Edmund Gettier devised a thought experiment that has become known as a “Gettier case.” It shows that something’s “off” about the way we understand knowledge. This ordeal is called the “Gettier problem,” and 50 years later, philosophers are still arguing about it. Jennifer Nagel, a philosopher of mind at the University of Toronto, sums up its appeal. “The resilience of the Gettier problem,” she says, “suggests that it is difficult (if not impossible) to develop any explicit reductive theory of knowledge.”
What is knowledge? Well, thinkers for thousands of years had more or less taken one definition for granted: Knowledge is “justified true belief.” The reasoning seemed solid: Just believing something that happens to be true doesn’t necessarily make it knowledge. If your friend says to you that she knows what you ate last night (say it’s veggie pizza), and happens to be right after guessing, that doesn’t mean she knew. That was just a lucky guess—a mere true belief. Your friend would know, though, if she said veggie pizza because she saw you eat it—that’s the “justification” part. Your friend, in that case, would have good reason to believe you ate it.
The reason the Gettier problem is renowned is because Gettier showed, using little short stories, that this intuitive definition of knowledge was flawed. His 1963 paper, titled “Is Justified True Belief Knowledge?” resembles an undergraduate assignment. It’s just three pages long. But that’s all Gettier needed to revolutionize his field, epistemology, the study of the theory of knowledge.
The “problem” in a Gettier problem emerges in little, unassuming vignettes. Gettier had his, and philosophers have since come up with variations of their own. Try this version, from the University of Birmingham philosopher Scott Sturgeon:
Suppose I burgle your house, find two bottles of Newcastle Brown in the kitchen, drink and replace them. You remember purchasing the ale and come to believe there will be two bottles waiting for you at home. Your belief is justified and true, but you do not know what’s going on.
Does it seem odd to say that you would know that there are two Newcastles in your fridge? Sure, you’re confident they’re there. But the only reason they’re there is because this burglar evidently had a change of heart. You, though, believe two are there because you put them there. You’re right that you’ve got beer in the fridge, and you’ve got good reason to believe they’d be there once you get back—but doesn’t your true and justified belief that you have two Newcastles waiting for you seem lucky somehow? After all, your belief is true only because the burglar replaced the beer. Can lucking into a true and justified belief be considered knowledge?
Consider another case, from the philosopher John Turri:...MORE