4.1 Scepticism of the External World

So last time, we looked at skepticism about induction. This time, we're moving on to skepticism about the external world, which is most famously exemplified in Descartes, particularly the First Meditation, and is closely bound up with related claims about the mind and body. So we're going to be looking at those two topics. Next time, we'll be moving on to more modern responses to skepticism and, in that connection, discussing the topic of knowledge. Well, one can distinguish between two different types of skepticism. This is a very rough and crude distinction. Vertical skepticism, as it's sometimes called, is when you infer from one kind of thing to a different kind of thing. For example, I have perceptions of the world around me. I see colors, lights, I hear things, etc., and I infer that there is something out there -- objects, other people -- distinct from my perceptions. So it's called vertical because I'm, as it were, moving down a level or up a level, depending on how you look at it, from one kind of thing to another. Now, distinguish that from horizontal skepticism, where you're inferring more of the same. So skepticism about induction is an example of horizontal skepticism. I've experienced billiard balls bashing into each other, making each other move or apparently making each other move. I've experienced that in the past, and I infer more of the same in the future. Now, you might naturally think that vertical skepticism, such as skepticism about the external world, is far more worrying than horizontal skepticism because it seems to put a whole category of things into doubt. With external world skepticism, I'm doubtful that there is anything beyond my perceptions. Maybe I am all there is -- me and my perceptions -- and all the rest is an illusion. So that can seem quite worrying. Descartes fleshes out this worry with various hypotheses, in particular, the hypothesis that maybe he's dreaming everything, and then he strengthens that even more — maybe there's an evil demon causing me to have all these illusions, carefully orchestrating everything I perceive in such a way that it seems that there's an external world when really it's all an illusion. And a modern variant of that is brain-in-a-vat skepticism, the idea that I might have been taken by some evil scientist or I may indeed have been created by this evil scientist. Really, there's just a brain somewhere in a vat, and this wicked scientist is manipulating the inputs to my brain in such a way that I seem to perceive all this array of stuff, and in fact, none of it exists at all. Now, very quickly, Descartes' way of dealing with skepticism is quite an extreme one. He says, to start with, we shouldn't assent to anything that is less than completely certain. So he sets a very, very high threshold for knowledge. He's only going to count something as known or even legitimately believed, in a sense, if it is completely certain. And he casts around for where he can find this certainty, and famously, he finds it in his own existence. "I think, therefore I am" (cogito, ergo sum in Latin). Very famous, one of the perhaps one of the most famous quotations in any philosophical works. Here, it's impossible for me to be mistaken because even if I'm dreaming, I must exist. If an evil demon is implanting illusions into my mind, I must exist. If I'm a brain-in-a-vat, I must exist. So all of these skeptical hypotheses actually imply my thinking and my existence. So therefore, I can at least be certain of those. Then, very controversially, Descartes says, "OK, I've got one bit of certainty here, that I'm thinking, that I exist. Can't I look at that instance of certainty and draw a general rule from it? What is it that makes me certain of my own existence? What is it? Well, I just clearly and distinctly perceive it to be true." OK, well, in that case, if clearly and distinctly perceiving it to be true is enough to make me certain in this case, then I can apply that as a general rule. Anything that I clearly and distinctly perceive to be true is true or, at least, so it seems for now. I don't notice that that move is a very, very dubious one. First of all, Descartes trumpets the cogito, "I think, therefore I am," as this special, unique truth that has this wonderful feature that all of the skeptical hypotheses imply its truth. If I'm dreaming, I must exist. If I'm being deceived, I must exist. So it looks like the cogito is really special. But then he tries to draw a general rule from it, a rule that can be applied to other propositions. Anyway, he moves on with this general rule that anything I clearly and distinctly perceive is true. He then says, "I see that I have within me an idea of a perfect being, an idea of God, and I clearly and distinctly perceive that any perfection in that idea must come from a really perfect cause." And after various moves, he concludes predictably that God exists because only God provides an adequate cause of that idea, and a perfect God cannot deceive. Deceit is an imperfection. So, having proved that God exists, I can be quite sure that my faculties are essentially reliable, that indeed anything I clearly and distinctly perceive when I use my faculties properly is true. Now, there's a very famous problem with this procedure known as the Cartesian Circle, and I want to draw your attention to the fact that it's not only a problem for Descartes. The interest in the Cartesian Circle, the reason why it's discussed so much by scholars, is not just some antiquarian interest in Descartes' arguments. It's a much more general point. In Descartes' case, he tries to prove the existence of God by relying on his clear and distinct perception, his mental faculties. He then appeals to the existence of a perfect, non-deceiving God to justify reliance on his mental faculties, and that just looks viciously circular. If he can trust his faculties to start with, then it seems that he doesn't need God to validate them. And if he can't trust his faculties to start with, then how can he justify the argument by which he reaches the conclusion that God exists and that his faculties are reliable? So either way, it looks like he's stuck. How can any anti-skeptical argument even get off the ground? So, as I say, notice that this is a general problem for skepticism, or for attempting to produce an answer to skepticism. If you start by doubting your faculties, how on earth can you dig yourself out of that skeptical pit? Because it looks as though you've thrown away the tools that you might use for the job. If you can't rely on your faculties, then you've got nothing with which to construct any sort of argument against the skeptic.