The three-page paper that broke the definition of knowledge

Knowing something seemed to mean having a true belief with good reasons. In 1963 Edmund Gettier showed, with two short stories, that this isn't enough.

What is the difference between knowing something and just believing it? A tidy answer had long been the standard one: you know a thing when you believe it, it is true, and you are justified in believing it. Philosophers call this the justified true belief account.

In 1963 Edmund Gettier published a paper of about three pages in the journal Analysis, titled Is Justified True Belief Knowledge? His answer was no, and he made the case with two short examples.

In the first, Smith and Jones have applied for the same job. Smith has strong evidence that Jones will get it, and good reason to think Jones has ten coins in his pocket. So Smith concludes that the man who gets the job has ten coins in his pocket. As it turns out, Smith gets the job himself, and, without knowing it, he also has ten coins in his own pocket.

Smith's belief is true. It is justified, because he reasoned well from good evidence. Yet it seems plain that he didn't know it. He was right by accident, and about the wrong man.

Luck that looks like knowledge

Cases like this are now called Gettier cases, though the pattern wasn't entirely new. Around 770 CE the philosopher Dharmottara described a traveller in a desert who sees what looks like water. It is a mirage, but water happens to be hidden under a rock at that spot. Bertrand Russell wrote of someone who reads the time from a clock that has stopped, at a moment when it happens to be right.

Gettier's paper made the problem impossible to ignore, and philosophers tried to add a fourth condition. One proposal was that the belief must not be inferred from anything false. That handles Smith, whose reasoning ran through a false belief about Jones. But some cases have no false step at all. Someone who looks at the one real barn in a district full of fake barn fronts reasons from nothing false, and still seems to be right only by luck.

Decades later, there is still no repair that everyone accepts. That is the lasting surprise: know, one of the most ordinary words we use, turned out to be very hard to define, and a few pages were enough to show it.