فصل 11

chapter 11

Could You Be Dreaming?

René Descartes

You hear the alarm, turn it off, crawl out of bed, get dressed, have breakfast, get ready for the day. But then something unexpected happens: you wake up and realize that it was all just a dream. In your dream you were awake and getting on with life, but in reality you were still curled up under the duvet snoring away. If you’ve had one of these experiences you’ll know what I mean. They’re usually called ‘false awakenings’ and they can be very convincing. The French philosopher René Descartes (1596–1650) had one and it set him thinking. How could he be sure that he wasn’t dreaming?

For Descartes philosophy was one among many intellectual interests. He was an outstanding mathematician, perhaps best known now for inventing ‘Cartesian co-ordinates’ – allegedly after watching a fly walking across the ceiling and wondering how he could describe its position at various points. Science fascinated him too, and he was both an astronomer and a biologist. His reputation as a philosopher rests largely on his Meditations and his Discourse on Method: books in which he explored the limits of what he could possibly know.

Like most philosophers, Descartes didn’t like to believe anything without examining why he believed it; he also liked asking awkward questions, questions which other people didn’t get round to asking. Of course Descartes recognized you couldn’t go through life constantly questioning everything. It would be extremely difficult to live if you didn’t take some things on trust most of the time, as Pyrrho no doubt discovered (see Chapter 3). But Descartes thought it would be worth trying once in his life to work out what – if anything – he could know for certain. To do this he developed a method. This is known as the Method of Cartesian Doubt.

The method is quite straightforward: don’t accept anything as true if there is the slightest possibility that it isn’t. Think of a big sack of apples. In the sack you know there are some mouldy apples, but you’re not sure which ones they are. What you want to end up with is a sack containing just good apples and no mouldy ones. How would you go about achieving that result? One way would be to tip all the apples on to the floor and then look at them one at a time, only putting the ones that you were absolutely sure were good back into the bag. You might throw out a few good apples in the process because they looked as if they might possibly be a bit mouldy inside. But the consequence would be that only good apples would make it into your sack. That’s more or less what Descartes’ Method of Doubt is. You take a belief, such as ‘I am awake reading this now’, examine it, and only accept it if you are certain it can’t be wrong or misleading. If there is the tiniest room for doubt, reject it. Descartes went through a number of things he believed, and questioned whether or not he was absolutely certain that they were as they seemed to be. Was the world really the way it looked to him? Was he sure he wasn’t dreaming?

What Descartes wanted to find was one thing that he could be sure about. That would be enough to give him a foothold on reality. But there was a risk that he might sink into a whirlpool of doubt and end up realizing that nothing at all was certain. He used a kind of sceptical move here, but it differed from the scepticism of Pyrrho and his followers. They were intent on showing that nothing could be known for certain; whereas Descartes wanted to show that some beliefs are immune from even the strongest forms of scepticism.

Descartes sets out in his quest for certainty by thinking first about the evidence that comes through the senses: seeing, touching, smelling, tasting and hearing. Can we trust our senses? Not really, he concluded. The senses sometimes trick us. We make mistakes. Think about what you see. Is your sight reliable about everything? Should you always believe your eyes?

A straight stick put in water seems bent if you look at it from the side. A square tower in the distance might look round. We all occasionally make mistakes about what we see. And, Descartes points out, it would be unwise to trust something that has tricked you in the past. So he rejects the senses as a possible source of certainty. He can never be sure that his senses aren’t tricking him. They probably aren’t most of the time, but the faint possibility that they might be means he can’t completely rely on them. But where does that leave him?

The belief ‘I am awake reading this now’ probably seems fairly certain to you. You are awake, I hope, and you are reading. How could you possibly doubt it? But we’ve already mentioned that you can think you are awake in dreams. How do you know you aren’t dreaming now? Perhaps you think the experiences you are having are too realistic, too detailed to be dreams; but plenty of people have very realistic dreams. Are you sure you aren’t having one now? How do you know that? Perhaps you’ve just pinched yourself to see if you are asleep. If you haven’t, try it. What did that prove? Nothing. You could have dreamt that you pinched yourself. So you might be dreaming. I know it doesn’t feel like it, and it is very unlikely, but there must be room for a small doubt about whether you are awake or not. So, applying Descartes’ Method of Doubt, you have to reject the thought ‘I am awake reading this now’ as not completely certain.

This shows us that we can’t wholly trust our senses. We can’t be absolutely sure we’re not dreaming. But surely, Descartes says, even in dreams, 2 + 3 = 5. This is where Descartes uses a thought experiment, an imaginary story to make his point. He pushes doubt as far as it will go and comes up with an even tougher test for any belief than the ‘Could I be dreaming?’ test. He says, imagine there is a demon who is incredibly powerful and clever, but also fiendish. This demon, if it existed, could make it seem that 2 + 3 = 5 every time you did the sum even though it really equals six. You wouldn’t know the demon was doing this to you. You’d just be adding numbers up innocently. Everything would seem normal.

There is no easy way of proving that this isn’t happening now. Perhaps this fiendishly clever demon is giving me the illusion of sitting at home typing at my laptop, when in fact I’m lying on a beach in the south of France. Or perhaps I’m just a brain in a jar of liquid on a shelf in the evil demon’s laboratory. He might have put wires into my brain and be sending electronic messages to me that give me the impression that I’m doing one thing, while I am really doing something completely different. Perhaps the demon is making me think that I’m typing words that make sense, when in fact I am just typing the same letter over and over again. There’s no way of knowing. You couldn’t prove that that isn’t happening, however crazy it might sound.

This evil demon thought experiment is Descartes’ way of pushing doubt to its limits. If there was one thing that we could be sure the evil demon couldn’t trick us about, that would be amazing. It would also provide a way of answering those people who claim that we can’t know anything at all for certain.

The next move he made led to one of the best-known lines in philosophy, though many more people know the quotation than understand what it means. Descartes saw that even if the demon existed and was tricking him, there must be something that the demon was tricking. As long as he was having a thought at all, he, Descartes, must exist. The demon couldn’t make him believe that he existed if he didn’t. That’s because something that doesn’t exist can’t have thoughts. ‘I think, therefore I am’ (cogito ergo sum in Latin) was Descartes’ conclusion. I’m thinking, so I must exist. Try it for yourself. As long as you have some thought or sensation, it is impossible to doubt that you exist. What you are is another question – you can doubt whether you have a body, or the body that you can see and touch. But you can’t doubt that you exist as some kind of thinking thing. That thought would be self-refuting. As soon as you start to doubt your own existence, the act of doubting proves that you exist as a thinking thing.

This may not sound like much, but the certainty of his own existence was very important for Descartes. It showed him that those who doubted everything – the Pyrrhonic Sceptics – were wrong. It was also the start of what is known as Cartesian Dualism. This is the idea that your mind is separate from the body and interacts with it. It is a dualism because there are two types of thing: the mind and the body. A twentieth-century philosopher, Gilbert Ryle, mocked this view as the myth of the ghost in the machine: the body was the machine, and the soul the ghost inhabiting it. Descartes believed that the mind was able to produce effects in the body and vice versa because the two interacted at a certain point in the brain – the pineal gland. But his dualism left him with real problems about how to explain a non-physical thing, the soul or mind, producing changes in a physical one, the body.

Descartes was more certain about the existence of his mind than his body. He could imagine not having a body, but he couldn’t imagine not having a mind. If he imagined not having a mind, he’d still be thinking, and so that would prove that he had a mind because he couldn’t have thoughts at all if he didn’t have a mind. This idea that body and mind can be separated, and that the mind or the spirit is non-physical, not made of blood, flesh and bones, is very common amongst religious people. Many believers hope the mind or spirit will live on after the death of the body.

Proving his own existence, just so long as he was thinking, would not have been enough to refute scepticism, though. Descartes needed further certainties to escape from the whirlpool of doubt that he had conjured up with his philosophical meditations. He argued that a good God must exist. Using a version of St Anselm’s Ontological Argument (see Chapter 8), he convinced himself that the idea of God proves God’s existence – God wouldn’t be perfect unless he was good and existed, just as a triangle wouldn’t be a triangle without interior angles adding up to 180 degrees. Another of his arguments, the Trademark Argument, suggested that we know God exists because he has left an idea implanted in our minds – we wouldn’t have an idea of God if God didn’t exist. Once he was certain that God existed, the constructive phase of Descartes’ thought became much easier. A good God wouldn’t deceive humanity about the most basic matters. So, Descartes concluded, the world must be more or less as we experience it. When we have clear and distinct perceptions these are reliable. His conclusion: the world exists, and is more or less as it appears, even though we sometimes make mistakes about what we perceive. Some philosophers, however, believe this was wishful thinking, and that his evil demon might just as easily have deceived him about God’s existence as about the thought that 2 + 3 = 5. Without the certainty of a good God’s existence, Descartes would not have been able to move beyond his knowledge that he was a thinking thing. Descartes believed that he had shown a way out of complete scepticism; but his critics are still sceptical about this.

Descartes, as we’ve seen, used the Ontological and Trademark arguments to prove to his satisfaction that God exists. His fellow countryman Blaise Pascal had a very different approach to the question of what we should believe.