
13 Aug 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 coordinates’ — 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.
You take a belief, such as ‘I am 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?
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.
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.
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.
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.
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.
A Little History of Philosophy
Nigel Warburton