Descartes notices that over the course of his life, he has from time to time accepted false beliefs, and their falsity has infected other beliefs that he based upon them. So what he what like to do is to sort through his beliefs, set aside all the questionable ones, until he's found a perfectly secure basis: some beliefs whose truth is beyond doubt. Once he's done that, then he can consider all the questionable beliefs he set aside, and decide which of them to accept and which to reject.
Many of Descartes' beliefs are based on his senses. So he begins by asking whether he should trust his sensory beliefs. Or is it possible to doubt whether these beliefs are true?
Descartes begins by noting that his senses occasionally mislead him. This gives him reason to distrust some of his sensory beliefs. However, it does not obviously give him a reason to distrust all of his sensory beliefs. It shows that he should doubt those sensory beliefs he forms when the conditions for observation are poor (the lighting is low, the object he's looking at is far away, and so on). But perhaps his other sensory beliefs are OK and can be trusted. Perhaps when he's in good perceptual conditions, he can know how things are on the basis of his senses. Maybe the mistakes only occur in poor perceptual conditions. At least, nothing so far has proven that his beliefs in good perceptual conditions are untrustworthy. (This line of reasoning also comes up in the Rosenberg dialogue: see p. 4.)
But then Descartes remembers that sometimes when he is dreaming, he falsely believes that he's awake. And, reflecting on this, Descartes thinks he can't ever tell whether or not he's dreaming: How can he know that he is really perceiving his hands right now? Maybe it's all just a dream. If it were a dream, everything would seem just the same. (This comes up in the Rosenberg dialogue on pp. 5 and following.)
This is clearly a lot like the predicament Neo is in with respect to The Matrix. Recall when Morpheus says:
Have you ever had a dream, Neo, that you were so sure was real? What if you were unable to wake from that dream? How would you know the difference between the dream world and the real world?
We will come back to this dreaming argument in a moment and pick it apart, piece by piece. For the moment, let's just try to get an overview of how the whole Meditation goes.
Descartes thinks that his considerations about dreaming do give him reason to doubt all of his sensory beliefs, even ones where there seems to be ample lighting, where the objects seem to be close by, and so on. However, he also thinks that there are a number of beliefs that the dreaming argument leaves unchallenged. When we dream, although the particular beliefs we form ("There's a fire-breathing crocodile chasing me") are often false, the materials for our dream (fire, crocodiles, physical objects) derive from things we experience when waking, and Descartes thinks we can still be confident that some things of those kinds exist. So he thinks the dreaming argument leaves unchallenged our belief in general truths about the world (the belief that there are physical objects, that they move in such-and-such ways, etc.) Also, the dreaming argument does not give Descartes reason to doubt his beliefs about mathematics and the like.
So Descartes goes on looking for yet a further ground for doubt. He goes on to ask: What if God created him in such a way that he is always deceived, even about beliefs like the ones we just mentioned? Descartes thinks that God would be powerful enough to do this.
Now, as Descartes conceives of God, God is a supremely good being. Wouldn't that be incompatible with God's letting us be deceived in this way? Descartes considers this idea. He writes:
But perhaps God would not have allowed me to be deceived in this way, since he is said to be supremely good.
However, at the moment Descartes does not think this line of reasoning can succeed. He says:
But if it were inconsistent with [God's] goodness to have created me such that I am deceived all the time, it would seem equally foreign to his goodness to allow me to be deceived even occasionally; yet this last assertion cannot be made.
In other words, God clearly does let us be deceived some of the time. Some of the time our senses do mislead us. If that's compatible with God's goodness, why shouldn't it also be compatible with God's goodness to let us always be deceived? So for now, Descartes concludes that it would be possible for God to have created him in such a way that he is deceived all the time.
This argument assumes that there is no relevant difference between occasional deception and systematic deception, so that if God could permit the one (as he does), he could also permit the other. Later in the Meditations, Descartes will come back to this assumption and he will eventually decide that it's wrong. In the end, Descartes will argue that although God does let us be deceived some of the time, it is incompatible with God's goodness to let us always be deceived. But we're not going to look at those parts of the Meditations; we're just focusing on the First Meditation.
Now what if Descartes were not created by God? In that case, Descartes thinks he would have been produced by some "inferior cause," and he thinks that if he were produced by an "inferior cause," then that inferiority would somehow have gotten into the product (him), making him defective in such a way that of course he could be deceived all of the time.
This is a very puzzling line of reasoning. It is not clear why Descartes thinks that inferior producers can only make defective products. (After all, Microsoft made Internet Explorer, that works pretty good.) But anyway, Descartes does think this, and so he thinks that we have a dilemma here. If God produced him, then it'd be possible for him to always be deceived, even about his very general beliefs about the world and about mathematics, and if something inferior produced him, then again it'd also be possible for him to always be deceived in these ways. So at this point Descartes is pretty pessimistic. He thinks he could be mistaken about pretty much all of his beliefs.
At the end of the First Meditation, he conjures up the image of a malevolent demon or spirit, a creature exceedingly powerful and bent on deceiving him about as much as possible. He wonders whether he can find any beliefs that he could still trust even if there really were such a demon hell-bent on deceiving him. If so, then he could start to pull himself out of his pit of doubt.
In the Second Meditation, Descartes will argue that the beliefs "I think," "I exist," and "I am a thinking thing" have this status. He thinks those beliefs could still be trusted even if there were a demon trying to deceive him in these ways. For after all, if he thought "I think," then his belief would have to be true, wouldn't it? Because he's thinking it, and what the belief says is that he's thinking. So the belief would be true. Descartes then tries to use these beliefs as a starting-point to respond to all the doubts laid out in the First Meditation. But as I said, we're going to focus in this class on the First Meditation, not on the later parts of Descartes' project.
Let's go back and look more closely at the passage where Descartes gives the dreaming argument.
Descartes begins with the observation that:
1. When he's dreaming, he sometimes mistakenly thinks that he's awake. So when he's dreaming, he's not in a good position to tell whether or not he's dreaming.
But as his discussion proceeds, he moves on to the following, further claim:
2. Even if he's awake, he's not in a good position to tell whether or not he's dreaming.
This is an important step. 2 is a stronger claim than 1. It may not look like a very big step, but we should be suspicious about every step in the skeptic's argument, no matter how small it may look. We should examine every step closely, to see whether it really is warranted.
The step from 1 to 2 is a step from a claim of the form:
BAD. When you're in the bad situation, you can't tell that you are.
to a claim of the form:
GOOD. Even if you're in the good situation, you can't tell whether or not you're in the bad situation.
Now, steps of that sort won't always be legitimate. For instance, suppose the bad situation is one in which you're blind. Let's suppose that when you're blind, it's difficult to tell for sure that this is so. After all, maybe it's just dark outside... It does not follow that even if you're sighted, it would be impossible to tell that you are. If you're sighted, you may see the sun streaming in your window at this very moment. It seems like that would let you know that you're not blind. So here we seem to have an example where the people in the bad situation can't know that they are, but the people in the good situation--at least, some of the people in the good situation--can know that they're in the good situation.
For another example, let the bad situation be "I'm drunk" and the good situation be "I'm sober." When you're drunk, you may be very bad at telling that you are drunk. Being drunk tends to make people very confident that they're not drunk. So when you're in that bad situation, you may be unable to tell that you are. It does not follow that even when you're sober, you'd be unable to tell whether or not you're drunk. At the moment, you're (probably) soberly reflecting on Descartes' Dreaming Argument, and this may be perfectly obvious to you. It may be perfectly obvious to you that you are sober. So here we seem to have an example where the people in the bad situation can't know that they are, but the people in the good situation can know that they're in the good situation.
But Descartes thinks that the case of dreaming is special. He thinks that when the bad situation is "I'm dreaming" and the good situation is "I'm awake," then he is entitled to move from claim 1 to claim 2. What does he think makes dreaming special? Let's look at the text.
First, Descartes considers the hypothesis that he can know he is not dreaming:
...at the moment my eyes are certainly wide awake when I look at this piece of paper; I shake my head and it is not asleep; as I stretch out and feel my hand I do so deliberately, and I know what I am doing. All this would not happen with such distinctness to someone asleep.
To this Descartes responds:
Indeed! As if I did not remember other occasions when I have been tricked by exactly similar thoughts while asleep! As I think about it more carefully, I see plainly that there are never any sure signs by means of which being awake can be distinguished from being asleep.
Descartes' point here seems to be that for any experience you have, no matter how much it seems to indicate that you are awake, it would also be possible for you to have that experience while dreaming. This is not true in the case of being drunk and being blind. There are certain kinds of clear-headed thoughts and experiences that you can only have when you're sober. But there are no experiences that you can only have when you're awake. Any course of experience whatsoever might be dreamt. So even if you're awake, there is no test you can use to prove that you're not dreaming. No matter what test you appeal to, the possibility will always remain open that you are merely dreaming that you have performed the test, and that it delivered the results it did.
That is why Descartes thinks you can't tell whether or not you're dreaming, even if as a matter of fact you are awake.
Let's make this step explicit. We'll rename the earlier step 2 "step 3," and we'll insert a new step 2, as follows:
1. When you're dreaming, you're not in a good position to tell whether or not you're dreaming.
2. Any course of experiences you can have while awake can also be dreamt. So it'd be possible for you to be dreaming and having all the experiences you're now having. Everything would seem just the same, whether this were a dream or waking reality.
3. So even if you're awake, you're not in a position to tell whether or not you're dreaming. In other words, you can't know you're not dreaming--even if it's true that you're not dreaming.
Now, what is Descartes claiming here? Is he saying:
3a. For each of your experiences, you can't tell whether that experience is a dream or not. (You can't tell which of your experiences are waking experiences and which are dreams.)
Or is he saying:
3b. For all you know, all of your experiences may be dreams. You may be walking around in a total dream, never having any waking experiences.
The second claim 3b is much stronger than 3a. (Compare: Someone might say "For each painting you look at, you can't tell whether it is a forged copy." But we would hesitate to say "For all you know, all the paintings (there ever were) may have been forged copies." If all the paintings were forged copies, what were they copied from?)
It is not clear in the text whether Descartes means to be arguing for the stronger claim 3b or for the weaker claim 3a. Some philosophers think that the Dreaming Argument is powerful enough to support both conclusions. Other philosophers disagree; they think the Dreaming Argument is powerful enough to support 3a but not powerful enough to support 3b. We will look into this issue in a week or two. As I said, it is not clear whether Descartes means to be arguing for the stronger claim or for the weaker claim. And perhaps the weaker claim is enough for his purposes here. Perhaps he does not need the stronger claim. Anyway, let's be on our guard. Let's be alert to the difference between 3a and 3b and make sure that these don't get run together as we proceed.
The last step in Descartes argument says that if he can't tell whether or not he's dreaming, then how can he trust any of the things his senses tell him about his environment? To know anything about the external world on the basis of his sensory experiences, it seems like Descartes would have to know that those experiences aren't all a dream:
4. To know anything about the external world on the basis of your sensory experiences, you have to know you're not dreaming.
To keep things simple, we'll ignore the point we discussed earlier, about how Descartes thinks he could know very general things about his environment--for instance, that there are physical objects--even if he were dreaming. We'll just assume that when we talk about "knowing things about the external world," we mean knowing specific things about the external world, such as that you have hands, that you're sitting in front of a computer, and so on.
Now, if we put all these claims 1-4 together, we get the result that:
5. You can't know anything about the external world on the basis of your sensory experiences.
For 4 says to know that, you'd have to know you're not dreaming. But 3 says that you can't know you're not dreaming. So you're out of luck.
So goes the skeptic's argument.