Inferring and Explaining

12 InferrIng and exPlaInIng is just a dream, your dream experiences tell you nothing about what your term paper looks like. Concrete examples can bemultiplied endlessly. It seems imperative that we fnd a way of circum- venting the dream hypothesis. Folk wisdom, of course, provides tests for distinguishing waking from dreaming. You can check your conscious state by pinching yourself or seeing if your visual experiences are in color. Unfortunately, these tests are psychologically inaccurate. Surely you have enough imagination to pinch yourself within a dream. I have ofen had dreams where something bad or embarrass- ing was happening, and in the dream, I would say to myself, “I wish this was just a dream.” If there are no sure methods for distinguish- ing waking states from dreaming, as many philosophers have claimed, then the following argument is both seductive and worrisome. 1. I can be confdent that there is an external world outside of my mind because of what my senses tell me. 2. If I were dreaming, however, my sense expe- riences would no longer justify my conf- dence in the external world. 3. It is possible that I am dreaming now, and I cannot prove that I am not dreaming. 4. Terefore, since all this being a dreamcannot be ruled out, I can no longer be confdent that there is an external world. As bad as all this seems, there’s worse to come. The Evil Computer Scientist We know that you think you are reading a book about epistemology, considering weird possibilities such as life’s being a dream, and worrying about how you are going to get tested on this stuf. We apologize for the ruse. We sim- ply couldn’t think of any other way to tell you. Tis has gone on too long; you need to know the truth. Tree years ago last summer, you were a pas- senger on a motorcycle and there was a terrible crash.Te driverwas killed and youwere brought to the hospital alive but just barely. Te doctors quickly determined that you didn’t have much of a chance, but you were put on life support while relatives were notifed and decisions could be made. We need to tell you now about Dr. Malgenius. He was an eccentric polymath with expertise in medicine, neurophysiology, and computer sci- ence. He happened to be spending a year on a fellowship at the hospital to which they brought your mangled body. Afer it was determined that you would not survive—the injuries were simply too severe—your familywas approached about the possibility of harvesting some of your organs for transplants and medical research. At this point, Dr. Malgenius came forward with a most unusual request. It turned out that your brain had survived the crash unscathed, and Malgenius wanted to use it to test his new hypothesis. Just before the life support was shut down, your brain was surgically removed and placed in an artifcial environment. It sits in a vat of circulating nutrient liquid to this day! We won’t go into the details of your for- mer life, the promising poetry or the joy in mountain climbing; it’s all too sad. What you need to understand is your current situation. Everything—your memories of your child- hood or yesterday; your thoughts, feelings, and