Cartesian Doubt and the Search for Foundational Knowledge
We begin our study of epistemology with Rene Descartes’ Meditations. Descartes tells us he wants to rid himself of his false opinions and to “begin again from the first foundations”. Notice how Descartes uses the metaphor of a building or a structure. He thinks of knowledge as having foundations and other knowledge built upon the foundations. Pause a minute here and think about what that might mean. Why would some knowledge be more foundational—what is it about that knowledge that makes it foundational? When some knowledge is built upon some other knowledge, does the former depend on the latter—what does “dependence” mean here? Are there better and worse ways to build an edifice of knowledge?
Descartes thinks foundational knowledge should be certain, and he thinks that the foundational knowledge serves as justification for the rest of what one knows. From this, we can infer that the best-built structures of knowledge are those in which (i) the foundations are completely certain and (ii) the non-foundational knowledge follows from the foundational knowledge deductively. If that is how one’s edifice of knowledge is erected, then one won’t have any false beliefs. One’s ‘structure of knowledge’ will reflect the truth. Descartes wants to have this sort of knowledge, so he’s trying to find beliefs of which he’s absolutely certain to use for his foundation. In order to find the absolutely certain beliefs, he decides to doubt everything he can. His idea is that if there’s a belief he can’t possibly doubt, then he can be certain of that belief.
Rather than go through his beliefs one-by-one trying to doubt them, Descartes all at once throws into doubt all the beliefs he’s come to have on the basis of sensory experience. He supposes that most of what he’s come to believe has come from his senses, but he wonders if his senses are a reliable guide to truth. If his senses have ever misled him, then they can’t be fully trusted as a source of knowledge. And, of course, Descartes’ senses have misled him. We get unreliable information from our senses all the time. If you look at pavement on a hot day, it looks like it’s wet, but it’s not. If you look at a stick that’s half-submerged in water, it’ll look like disjointed or bent at an odd angle (depending on the angle from which you’re looking). These are cases in which what you see is inaccurate, cases in which it looks like your perceptual capacities don’t lead you to truth. So Descartes can doubt the beliefs he’s come to have by virtue of perceptual experience; hence, he won’t use any of these beliefs in his foundations.
But he doesn’t stop there. Descartes considers the possibility that he’s dreaming. Have you ever dreamt something and believed at the time that it was real? I had a dream not long ago that I was sitting beside a lake, when I woke up, it took a minute for me to realize that I hadn’t really just been sitting beside a lake. When you’re having a dream like that, you don’t know at the time you’re dreaming it that it’s just a dream. If someone were to ask you in the dream whether you’re dreaming, you’d say you aren’t. You think you’re beside a lake (or wherever)—not in bed, dreaming. But you’re wrong. Because in those cases, you are in your bed dreaming. Descartes wonders if he can be absolutely sure at any moment that he’s not having a dream like that. Are you absolutely sure that you won’t wake up in a moment and realize you’d been dreaming about reading a lecture for your philosophy class? Keep in mind that if you were having such a dream, you’d be absolutely convinced that you’re not dreaming—just like you probably are now, so your conviction that you’re not dreaming isn’t enough to prove that you’re not really dreaming. You could be. And, if you could be dreaming, then you’re not absolutely sure that you’re not dreaming. And if you’re not absolutely sure that you’re not in your bed dreaming, then there’s a whole lot more that you’re not sure of either: you’re not sure that you’re looking at a computer screen; you’re not sure which day of the week it is; you’re not sure how old you are. If you have to be sure of something to know it, then you don’t know where you are or when.
But that’s not all! The thing is, when you’re having one of those dreams, you don’t really know anything about what the non-dream world is like. You might wake up and be a completely different person than who you think you are in your dream—you might be a different gender, a different race, a different age; you might live 2000 years after the time it seems it is in the dream or 2000 light years away. You might wake up to discover that you’re a slug living on Mars. If you don’t know whether you’re dreaming or not, it could be that having a body at all is part of the dream, when in reality, you’re just a disembodied soul. It may be that Earth is just part of your dream, and there isn’t really any material universe at all. If you can’t be sure of any of it, you don’t know any of it.
So then maybe you don’t know anything. There’s nothing you know for certain, so there’s nothing you can use in the foundation for you ‘edifice of knowledge’. You don’t even know that you don’t know whether you’re really so ignorant—it’s just possible that you are, but it’s also possible that you’re just dreaming that you don’t know anything.
After thus destroying the edifice of knowledge, Descartes rebuilds. He finds something that he thinks is completely indubitable—something that he just cannot doubt. It’s his own existence. It’s not that he can’t doubt it because he’s constitutionally unable to or because it would be too painful for him. It’s that he can’t doubt it without contradicting himself. Recall that he started out by asking what he could doubt. For any belief he came across, he asked whether he could doubt it; if he could, he decided that he must not know it for sure. Can he doubt that he exists? He thinks he can’t.
Why not? Notice that if he doubts that he exists, then he has reason to believe that there’s something doing the doubting—that is, when he doubts, he does something. And in order to do something, one must exist, of course. So he’s got to exist in order to doubt his existence; but if he exists in order to doubt his existence, it must be a contradiction to doubt his existence. So he can’t doubt that he exists without contradiction. So he knows that he exists; he’s certain of it.
In fact, he thinks he knows more than that. Suppose he tries to doubt that he’s doubting. But in order to try that, he’s got to doubt; and, if he doubts, he’s doubting. So, again, he can’t doubt that he’s doubting without contradiction. Moreover, since doubting is a kind (or species or mode) of thinking, and Descartes can’t doubt that he’s doubting, he knows, he’s certain, that he’s thinking.
Descartes uses these ideas to resurrect the edifice of knowledge he’d previously torn down. In our reading, he reasons that he must be a thinking thing and not a body, since he can conceive of existing without a body but not without a mind. That is, he would contradict himself if he were to think that he exists but isn’t thinking, but he wouldn’t do so if he were to think that he exists but has no body. So he concludes that he is, essentially, a thinking thing. “A thing that doubts, understands, affirms, denies, wills, refuses, and which also imagines and knows.” (194)
When you read the excerpt from John Locke, ask yourself how Descartes might respond.
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