No worries! I guess my rule of thumb isn't the greatest - the drama does sometimes follow us back here. Sorry if my lighthearted jab caught you at a time when you were being legitimately hassled!

I'ma have to read up a bit on Gettier, sounds interesting.

I'm a bit of an overenthusiastic (albeit rusty) epistemology geek - as evidenced by my willingness to drop an overly obscure joke at the slightest suggestion that knowledge and belief were identical. So I'll gladly explain what's up with Gettier!

If you were just being polite, stop reading here.

So, Gettier challenged the idea that knowledge is identical to justified true belief (hereafter JTB), by attempting to present cases where someone believed x, the belief was justified, and x was true, but where we would deny that they knew x. If he succeeds in that, then someone can have JTB and not have knowledge, hence we must concede that the two are not identical.

Here's an example. This isn't exactly how he framed it in his famous paper, but it has the same shape. Let's say you're wandering down the street having a night out on the town with a couple of your coworkers, Jones and Smith. You're walking a bit ahead of them, Jones to your left and Smith to your right. You know they're both applying for a promotion to the same position, and your sources in higher management have told you that Smith is going to get the job. You notice a quarter on the ground, a little to your right, but you wander on, not bothering to pick it up. Without looking back, you hear someone pick up the quarter - must have been Smith, since it was directly in his path. You think to yourself, "That's a bit of fortune. The same guy who is getting the promotion is now twenty five cents richer."

That seems like a justified thing to believe.

Here's the twist. The needlessly contrived twist, because we're in an epistemological thought experiment that's designed to challenge our common sense. It turns out that your sources in management have been cut out of the loop on this one, and it's actually Jones who is getting the job. There's a second twist - while walking, Smith was zoning out and didn't see the quarter, but Jones did, and stepped over and snapped it up.

The upshot of all this is that your justified belief was true! The same guy who is getting the promotion is now twenty five cents richer. However, it is sort of true by accident. Most people would say that you didn't know that that was the case, you just happened to get it right. So we have a situation where it looks like you have JTB but not knowledge, and hence the two aren't identical.

He presented some other counterexamples, they tended to take the same sort of form, where you had false (but reasonable) premises and a valid argument from those which led to a conclusion that just happens to be true.

This sort of shook up the whole field of epistemology (extra impressive because he did it with a paper that was only 2.5 pages long). There were two main kinds of response - people either tried to formulate an entirely new definition of knowledge, or tried to defend JTB mostly by defining "justification" in a way that would preclude Gettier cases but include actual examples of knowledge.

My preferred response is the latter kind. I hold that a belief is justified if and only if there are no reasonably likely cases where your experience would be identical and yet the belief would be false. I'm pretty sure this has been argued elsewhere but I'm having trouble digging up the sources because it's been years since I studied this. But I think this model of justification (and hence knowledge) both defeats Gettier cases and closely follows our intuitions about knowledge.

Gettier cases inherently rely on situations where it would be very easy to have the exact same experience/evidence, and yet draw a false conclusion. In the example above, all of the evidence is compatible with Smith getting the job - the counterexample relies on that being considered justified. However, it is also compatible with Jones getting the job - the counterexample relies on that being what turns out to be true. So an affirmative belief in either conclusion would not be justified, because there are reasonably likely cases where either one could be false. The very structure of Gettier cases tends to preclude justification under my model.

I think this is also more or less how people naturally tend to think about knowledge. Gettier himself arguably relies on it - "You don't know that knowledge and JTB are identical, because here's a reasonably likely case where they would not be identical". People just tend to disagree over what counts as "reasonably likely" - Descartes would say it's reasonably likely that there's a malevolent demon deceptively controlling all of our sense perceptions, so we can't know anything unless we prove it from first principles. A less stringent person might think it is not reasonably likely that anyone they trust would lie or be incorrect, so they claim knowledge on anything that comes from their preferred authority figure.

Personally, I try to use the common law definition of "reasonable", which is why I worded it that way. If you stop a man on the street and ask him if x is reasonably likely, would he say yes? If so, and x is compatible with your evidence, and precludes y, then you don't know y. If you ask him whether a trusted source might ever lie or be incorrect, he will say yes. If you ask him whether a malevolent demon might be deceptively controlling all our sense perceptions, he will say no but will also back away anxiously.

Anyway. That's a rough overview of Gettier, and how he shook up epistemology, and how I think a common sense view of knowledge can survive his arguments. Hope it wasn't horribly more boring and pedantic than you expected!