Skeptical hypothesis are nice philosophical quandries. Do we have reason to believe the world we perceive is real? Maybe we’re brains in vats or under the spell of an evil demon. (What is this “we”, anyway? How do I know there’s any experiences besides my own?) I spend a fair bit of my thinking time on these problems. Berkeley wrote a substantial amount on why skeptics are wrong, and I also spend a fair bit of time thinking about Berkeley.
But someone might think that these questions don’t really matter. They might say the quandries are fun little puzzles, but don’t ultimately matter. I think that’s entirely wrong, and here’s one argument against it:
Let’s assume there is some value. If there isn’t, then this whole point is rather moot. Moreover, value happens at the level of reality. If anything at an imaginary or virtual level is of value, it’s only in virtue of impact on the real. For example, nothing in a video game matters in itself. But, what happens in a video game can matter for the real players.
For the sake of argument, let’s say petting kittens is good, and kicking kittens is bad. But of course we’re concerned with real kittens. Enter the skeptic. She suggests that there is a demon that inverts our perceptions of these two things. Whenever you appear to pet a kitten, in reality a kitten is kicked. But whenever you appear to kick a kitten, in reality a kitten is petted. If that were the case, then you should act to appear as though you are kicking kittens. When you see someone pet a kitten, you should condemn them.
This could be generalized to nearly any pair of values. You could also remove the pairing and just have a neutral thing correspond with a good or bad thing. Perhaps tapping your fingers on a table in appearance causes a real kitten to be kicked. Then you better not tap your fingers on a table in appearance.
(Of course, I think that hypothesis is wrong, but my point is that its being wrong is important.)