3. The Grand Deception Doubt (Or, the GDD)

Consider this possibility from the philosopher René Descartes (1596-1650):


“Nevertheless, the belief that there is a God who is all powerful, and who created me, such as I am, has, for a long time, obtained steady possession of my mind. How, then, do I know that he has not arranged that there should be neither earth, nor sky, nor any extended thing, nor figure, nor magnitude, nor place, providing at the same time, however, for the rise in me of the perceptions of all these objects, and the persuasion that these do not exist otherwise than as I perceive them? And further, as I sometimes think that others are in error respecting matters of which they believe themselves to possess a perfect knowledge, how do I know that I am not also deceived each time I add together two and three, or number the sides of a square, or form some judgment still more simple, if more simple indeed can be imagined?”[1]


We might reformulate Descartes’s doubt into a set of steps as follows:

  1. Everything I believe about the world is based on what has come to me either through my senses (what I have seen, read, heard, or experienced), or through my own power of thought.
  1. It seems to me there could be a being, like God, who has power over what I sense and even has power over my own power of thought.
  1. If God wanted to, he could make it seem like I am perceiving something when really I’m not, and God could make me think something must be true when really it isn’t.
  1. I cannot know for certain that God isn’t deceiving me in these ways.
  1. So I really cannot be certain about anything I believe about the world.


Call this “the Grand Deception Doubt,” or the GDD, for short. If you prefer not to bring God into arguments like this, consider replacing God with a very powerful demon or some mad scientist who has captured you, removed your brain, and put it into a jar with a bunch of wires connecting it to a supercomputer which gives the scientist complete control over what you think you perceive and what you think you think.


Is there any way to refute the GDD? No, not really. But let’s see why. To refute it, we would need some way to “defuse” it and show that, in fact, we could not be experiencing such a massive and thorough deception. Our first move might be to point out that it would just be too impractical for some god, or some demon, or some mad scientist with a lot of advanced technology, to accomplish such a deception. Who could have the power to do such a thing? Why would they want to do it? What advantage would they have in deceiving us so thoroughly? But the answer to all of these questions is the same: “Who knows?” That is to say, we do not know what motivates gods and demons and mad scientists, and for all we do know, they might have very good reasons for deceiving us. Maybe they are competing in a cosmic contest. Maybe the GDD is cheaper than creating an actual universe. Maybe they are teaching us a lesson. Maybe they are malicious. Maybe, maybe, maybe. For all we know, the skeptic will say, there might be a powerful demon with both means, motivation, and opportunity to deceive us. So long as we cannot rule that out, we cannot be certain of the truth of what we experience.


Next effort. We might point out that this is crazy talk, and normal people don’t go around worrying about the possibility of a GDD. But the skeptic will respond that the fact that “normal people” don’t worry about something does not in any way show that the thing isn’t true. And—by the way—the skeptic will point out that the very existence of these alleged “normal” people is also cast into doubt by the GDD. They could be part of the grand illusion, like non-playable characters in a video game.


OK, let us try a more philosophical approach. We have experiences. The experiences must come from somewhere. We could believe that they come from what they seem to come from—namely, a real world with other people and animals and trees and buildings and so on. Or we could believe they come from some radically different source—a god or demon or mad scientist. It is more rational to adopt the simpler and most straightforward explanation which is that experiences are coming from what they seem to be coming from. Therefore, it is rational to reject the GDD.


This is a much better sort of reply. For one thing, it uses words like “rational” and “therefore,” so it seems very philosophical! But is it enough of a reply? No, it isn’t. It makes two highly questionable assumptions. The first is that our ordinary view, that our experiences come from a real world, is simpler than the view that our experience comes from some other source. But why should the ordinary view count as “simpler”? It’s more common (or seems to be), but “common” does not mean the same as “simpler.” The fact that the view is more common could be entirely accidental. If we were all taught that experience comes directly from an eggplant in the heavens, then that belief would be more common, but we should not on that account take it to be more likely true.


The second questionable assumption is that it is more rational to believe the simpler and most straightforward explanation. But why should we believe this principle is true? Is it because we know the world to follow rational rules and principles? Why must this be true? I might believe that the world would be a more rational place if people shared their surplus wealth with others who needed it, but it does not follow that the world is as I believe it rationally should be. Why should this case be any different?


At this point someone might throw up their arms and insist, “It doesn’t matter! You can raise all the skeptical scenarios you like, but in the end we are all going to keep believing the ordinary view of things!” Most skeptics would agree. People will continue to believe what people will continue to believe. The skeptic’s point is merely that people do not have good reason for believing what they believe, and if people claim they do, they are mistaken.


This puts us in a somewhat awkward position. Is it true that we don’t have good reason for believing what we believe? Is it no more rational to believe the claims of scientists and historians than to believe that all our experience comes from an eggplant in the heavens?

  1. Rene Descartes, “First Meditation,” in Meditations on First Philosophy (translated by John Veitch, 1902).


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