Inferring and Explaining

13 emotions; your wishes, hopes, and fears; all of it—is a computer-driven illusion. Dr. Mal- genius’s hypothesis was that a healthy human brain could be attached to his supercomputer and that a “virtual life” program could be sim- ulated on the brain-computer system. You are “living” proof of his theory. All of us involved with this project are sorry. We now see how wrong it was. Just tell us what to do; wewill respect your wishes. Dr. Malgenius is dead and gone. No one here in the lab plays jokes anymore—making you think you see with intuitive clarity that 2 + 3 = 5 or that there are no even primes greater than two and the like. We can simply let your life program continue, or we can wipe the memory banks clean. It’s your call. Te so-called brain-in-a-vat hypothesis is what we might call the ultimate confdence- undermining possibility. It is an updated version of a possibility frst considered by Descartes. He worried about a godlike “evil genius.” I will suppose therefore that not God, who is supremely good and the source of truth, but rather some mali- cious demon of the utmost power and cunning has employed all of his energies in order to deceive me. I shall think that the sky, the air, the earth, colours, shapes, sounds and all external things are merely the delusions of dreams which he has devised to ensnare my judgment. 5 Whether it is stated in a contemporary, science- fction voice or in that of sixteenth-century aca- demic philosophy, the reasoning here fts the familiar pattern. 1. I can be confdent of anything—science, mathematics, or the existence of the external world because of processes of sense experi- ence and logical reasoning in my mind. 2. If I were a brain in a vat tricked by a team of evil computer scientists, any reasoning or experience would no longer justify my conf- dence in anything. 3. It is possible that I am just a brain in a vat, and I cannot prove that I am not a brain in a vat. 4. Terefore, since I cannot rule out my being a brain in a vat, I can no longer be intellectually confdent of anything. In one sense, there is absolutely no reason for believing that you are a brain in a vat. I would bet few of my readers have ever considered such a possibility. But in another sense, the hypoth- esis is a possible one and one for which there is no way of demonstrating its falsity. How could you ever tell? What tests could you conduct? Dr. Malgenius is so tricky that he might cause you to think you’ve come up with some sound argument to defeat this possibility, but that rea- soningmight itself be one of his tricks. You seem stuck, and so does every other person who has gone through this bit of skeptical reasoning. Can I Know Anything? Te conclusion to the above argument was that “I can no longer be intellectually confdent of anything.” Have we really managed to call everything into doubt? Dr. Malgenius can cause us to have any sense experience hewants; he can cause us to think 2 + 3 = 5 when it really equals 7. He seems to have the power to trick us about virtually anything he chooses. Descartes noticed that virtually all our beliefs about ourselves were open to doubt. skePtICIsm