At a first pass, epistemology is the study of the questions: "What is knowledge?" And "Do I have any?"As you'll see, there are close connections between these questions and questions about what we have good evidence or reasons to believe. So epistemology is also the study of questions about evidence and reasons.
There are several philosophical arguments that purport to show that you don't have any knowledge--or at any rate, that you don't have very much knowledge.
One philosophical argument begins with some thoughts about lotteries. Suppose you have a lottery ticket, and the chances of winning are only 1 in 15 thousand. The odds that your ticket will lose are very high. But it doesn't seem like you know that your ticket will lose. After all, if you did know that (e.g., if you knew that the lottery was fixed and that some other ticket was already selected to be the winner), then why would you buy a ticket? Plus, if you did know that your ticket will lose, because the odds of its losing are so high, then by parity of reasoning you should be able to know of every losing ticket that it will lose. But then you should be able to say which ticket would win! And of course you can't do that. So it seems wrong to say that you know your ticket will lose.
Notice that it doesn't really matter how good the odds are that your ticket will lose. Even if the odds that you will lose are 15 billion to 1, we're still not comfortable saying that we know your ticket will lose. As long as there's any chance at all that your ticket will win--no matter how small--then it doesn't seem like you can know you won't win.
Similarly, you think you know where your bike is parked right now. But a certain percentage of bikes are stolen everyday. There's a chance that yours has been stolen since you last saw it, too. This is probably much greater than your chance of winning the lottery. So if the chance you'll win the lottery is high enough to keep you from knowing you'll lose, then the chance that your bike has been stolen should be high enough to keep you from knowing where your bike is right now.
For instance, I think that I have hands, because it looks and feels to me as if I have hands. But there is some chance that I'm making a mistake. Maybe I'm just hallucinating hands. Maybe I'm a handless brain plugged into The Matrix, and none of the things I think I'm perceiving right now are real. I think those things are very unlikely, but I have to admit there's some very small chance that they're true. So according to the reasoning we've been considering, it follows that I can't really know that I have hands.
If I were just dreaming all this, or if I were a brain in a vat, then everything would seem the same. So how can I know that it's not a dream? How can I tell whether the world I see around me is real or just an illusion?
There are two ways of arguing to this conclusion:
A skeptic is someone who doubts whether we have knowledge of a certain sort. For instance, a skeptic about the external world is someone who doubts whether we have knowledge of the external world. That's the kind of skeptical challenge that we'll be focusing on in this class.
Above we described three kinds of skeptical argument: from lotteries, from scenarios like dreaming, from the fact that our evidence falls short of proving or conclusively establishing our beliefs. We will discuss all of these this term, but especially the argument from dreaming.