|So you think you're having a beer?|
The dude: I guess.
The skeptic: Well, you're wrong, and I can prove it.
The dude: So prove it.
The skeptic: What if we're brains in a vat. We're hooked up to a computer that transmits images of a bar, people, drinks, and so on, and so we think that we're having a beer together, when in fact we are just brains in a vat.
The dude: So what?
The skeptic: So everything we believe about the world could be false. For example, we believe that we're having a beer right now. But we believe that just because the computer is transmitting these images to our brains. In reality, there is no bar, no beer, and no friend.
The dude: I don't get it.
The skeptic: Don't you see? If we can't be sure that we are not brains in a vat, then we can't be sure that we're having a beer right now.
The dude: So, are you saying that we don't know that we're having a beer right now?
The skeptic: Exactly!
The dude: How do you know that?
The skeptic: Know what?
The dude: That we don't know that we're having a beer right now.
The skeptic: Oh, because we don't know that we're not brains in a vat.
The dude: So we do know that we don't know that we're having a beer right now?
The skeptic: Wait,... No. We don't know that, either.
The dude: Well, if you don't know what you're talking about, why should I listen to you?
Is the skeptic's position self-defeating? If so, is there a way to restate the skeptic's position that would avoid this problem?