Are You Sleeping?

Descartes doubts everything he sees because he says that everything in life can occur realistically in dreams. We can have the most life-like dreams of being somewhere or doing something and not realize that it’s untrue until we wake up. Our dreams themselves prove that we can be deceived into believing a simulated reality. So how can we ever know that life itself is not a dream?

Well, John Locke has a very well-known argument against this. You probably know it too. Have you ever been so shocked that you pinched your hand to see if you were in a dream? Then you’ve heard of it. He says that the fact that we feel pain means we’re not living in a dream, because you can’t feel pain in dreams the way you feel pain in life. Of course, science has already put this argument to test. It would be nice to say they proved we’re not living in a dream but actually they proved that there have been rare cases where people could feel sharp local pain while dreaming. So you can actually feel pain in dreams! Still, we don’t know if we can feel “agonizing and ongoing pain” in dreams, so Locke might still have a point. But so far we have no way to tell.

Also, naturally there are many other (much less sophisticated and non-philosophical) ways people have suggested to tell dreams apart from reality. Personally I found this one little method very interesting: in the TV show Doctor Who when the characters are locked in a dream, they make up a “dream or reality” test: they each take a copy of the same book, open the same page and read the first word aloud. When they all read a different word, bingo! It means they're dreaming.