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3. IS THAT REALLY A COMPUTER SCREEN IN FRONT OF YOU?
What reason do you have to believe there's a computer screen in front of you? Presumably that you see it, or seem to. But our senses occasionally mislead us. A straight stick half-submerged in water sometimes look bent; two equally long lines sometimes look different lengths.

But this, you might reply, doesn't show that the senses cannot provide good reasons for beliefs about the world. By analogy, even an imperfect barometer can give you good reason to believe it's about to rain.
Before relying on the barometer, after all, you might independently check it by going outside to see whether it tends to rain when the barometer indicates that it will. You establish that the barometer is right 99% of the time. After that, surely, its readings can be good reasons to believe it will rain.
Perhaps so, but the analogy fails. For you cannot independently check your senses. You cannot jump outside of the experiences they provide to check they're generally reliable. So your senses give you no reason at all to believe that there is a computer screen in front of you.