When philosopher and mathematician Rene Descartes reached his mid-30s, he decided it was time to clear his mind. He decided to go through all his beliefs and list the ones he was sure of. For this he used the 'method of doubt'. By this he ment he would throw out any belief that he could doubt -- even if the doubt was only the smallest, most unlikely possibility.

This ment that he could not trust the past, as his memories, even of the recent past, could be wrong.

He could not trust the future, as even the most predictable things could conceivably not happen.

He could not be sure of his physical environment, because dreams and hallucinations can be mistaken for reality.

Maybe even such basic truths as 2+2=4 could be false -- if the universe were ruled by an Evil Demon, it could be placing this misinformation directly into your mind! He couldn't even trust basic thought processes.

But the one thing that the method of doubt could not attack was the fact that he was thinking. Even the questioning of the actuality of his thinking was a thought.

And if he could think... He must exist!

This is where we get one of the most famous Latin phrases to ever enter into the English language: Cogito Ergo Sum.

It was a start. He wrote up his reasoning process in his book Meditations of a first philosophy. But he didn't stop there.

I think, therefore I am... But what am I? A thing which thinks.

He believed that starting with this one unarguable statement he could deduce certain other things about the universe. (Here's where we give up on logic.) He believed that some things needed to exist before you could think -- namely, God. And God (being all-good and all-knowing) wouldn't let a demon mess with your head... So he decided that you could be sure of the basic laws of math and logic. But what about your senses? They aren't part of your mind, they're part of your body. So, onto the The mind/body problem.

A little more needs to be said. Descartes' original intention was to build a new system of philosophy, without incorporating any, potentially flawed, ideas from his previous beliefs. So he began his method of systematic doubt. A process he actually borrowed from ancient philosophers who's names escape me right now. This method had three levels:

  • Sense Illusions: the possibility that any sense-data one might see, hear, etc does not accurately reflect reality.
  • Dream Argument: the possibility that all our experiences are fact a dream and that we have no experience or knowledge of the real world.
  • Great Deceiver: the possibility that some malicious and powerful being puts incorrect thoughts and experiences directly into our minds, for the sole purpose of deceiving us.

Eventually, Descartes decided that the only thing he could be certain of was his own existance. His logic goes: "If I think that I exist I must be either correct or deceived. If I am correct, I exist. If I am deceived, I must exist in order to be deceived; therefore, I exist.

He then went on to prove all sorts of other things, all based on his presupposition of the perfection of god. But that's another node...

A defence of Descartes' method of doubt:

In his first meditation, Descartes uses his “method of doubt” to try and reject all his old opinions. He feels that this is a necessary procedure in order for him to obtain some, if any, first principles of knowledge, which are indubitable, and could maybe provide a foundation from which to seek further truths. It is important to understand Descartes’ objectives, before we can assess his arguments.

Descartes’ method of doubt is a fairly simple idea. All it is concerned with is eliminating everything that could possibly be doubted until something is found that is indubitable. This procedure, and the arguments to show that such a practice is possible, is all that the first meditation is about. Descartes’ work is very much like a discourse with himself. He proposes an argument, identifies counter-arguments, and then proposes another stronger argument.

Descartes reasons that the systematic demolition of all his opinions and beliefs one by one is impractical. Instead, he decides to go straight for those beliefs that are the foundation for all the others. Descartes believed that once this foundation was removed, like a tower of cards, his entire belief system would collapse. To begin with, Descartes calls into doubt the senses themselves. Since he believed that the senses provided us with all the information we use to form our opinions and beliefs, this seems a sensible place to start. If the testimony of the senses is doubtful, then beliefs based on that testimony must be doubtful too. Descartes makes the point that he knows very well that his senses have been incorrect in the past. For instance, he says that a distant tower may appear round, but up close, it is clear that it is in fact square. Descartes says; “From time to time I have found that the senses deceive, and it is prudent never to trust completely those who have deceived us even once”. This is, albeit impractical in life, a reasonable decision for Descartes to make at this point.

However, there are things which the senses tell us that seem so evident that they must surely be true. It is all very well to question them over distant or very tiny objects, but what about the things in our immediate environment. Descartes recognises this point, and says that he must surely be mad to doubt that he is sitting by his fire and holding his piece of paper and so forth.

Not so, he reasons. Here Descartes brings in the “dream argument”. “How often asleep at night, am I convinced of just such familiar events…when I am in fact lying undressed in bed”, Descartes writes. Descartes suggests that he cannot be certain that he is not dreaming at any point in his experiences. This again seems a reasonable conclusion to make. Of course, it is important to bear in mind that we are not dealing with the probable here, but the logically possible.

But, that said, is the dream argument enough to make us doubt the properties of the world? Could it not be the case that dreams are composed of elements and objects that do actually exist in the “real world”, whatever that might be? Descartes illustrates this point by analogy to an artist creating a creature on canvas. The artist would use a jumbled up mixture of parts of various animals in existence, or at the very least, the colours he uses would be already existent. Well, this is of course a possibility, but there is still no reason to reject the idea that dreams may conjure up totally original and unreal objects and environments. It remains logically possible, and that is all Descartes is interested in.

But the dream argument only holds so far. It is not enough to deny that there must be something real – it cannot reject simple universal notions, such as extension, shape, size, number, place, and time. Dreaming cannot make Descartes doubt these things. He cannot dream that mathematical principles such as 2 + 3 = 5 and squares have four sides are incorrect since they are based purely on reason, not the empirical knowledge that Descartes has so far called into doubt. To continue in his pursuit, Descartes needs another argument to augment his doubting position.

Descartes ponders the possibility that God Himself is making it so that he goes wrong every time he performs mathematical operations. But this view of God doesn’t sit easily with Descartes. He says that since God is “said to be supremely good” it would be inconsistent to believe that He would allow him to be deceived all the time. It would perhaps be consistent for God to deceive some of the time, hence these things can be doubted from this perspective. It would also be logically possible that there is in fact no God, and Descartes reasons that if this were true then these imperfect origins would mean that his confidence in his judgements would be lessened still further. Descartes then concludes as the sum of all his arguments; “there is not one of my former beliefs about which a doubt cannot properly be raised”.

But Descartes admits that it is very hard to keep his old and habitual opinions from coming back. It is in the final part of the first meditation that Descartes puts forwards a proposition designed to maintain his suspension of all his beliefs. This is the idea of the “malicious demon” who uses all his energies to confound Descartes in everything he does. The implication of this is that we can always have doubts so long as the malicious demon is a logical possibility.

Descartes' arguments are all intended to establish the conclusion that we have reason to doubt all of our beliefs – this is the whole point of the first meditation. He offers a series of arguments, each providing more to doubt than the last. Each is therefore more effective than the last. The final malicious demon argument is the ultimate one as it cannot be rejected as a logical impossibility, and it suffices to call all beliefs into doubt – there is no reasonable objection to the fact that it can call things into doubt, as oppose to the other arguments.

It is important to say that Descartes is not rejecting the senses, he is merely saying that there is reason to doubt them. Thus he doubts his empirical knowledge of the world, he is not saying it should be rejected. He does not say his opinions are false, he says they might be false. Descartes does proceed in rejecting all his previous beliefs, but this is only because the rejection of all that we think we know is the exercise that the first meditation requires us to undergo in preparation for the remaining meditations. The first meditation is just a means to an end. Descartes says that he will only pretend that all his beliefs are false just so he can find an indubitable truth.

A criticism of Descartes’ arguments is that he doesn’t offer any criterion of truth. So how can he decide whether something is true or not? What is he doubting? But, I am not sure if a criterion of truth is really necessary. Surely no matter how you define such a criterion, there will still be things that are true and things that are false. It would follow that the malicious demon could make one think that these false things are real and true in the world. However, I agree with the view that Descartes’ notion of truth is somewhat implied – that truth goes hand in hand with certainty, the coherence of all evidence, and the absence of evidence to the contrary. Besides, the fact that one might not be able to distinguish between truth and falsehood is really the theme underlying the first meditation.

There is another, potentially crippling, problem with Descartes’ method and this is in his reliance on his reason. If he has suspended all beliefs, then how can he have a starting point like this from which to build on? Descartes has to rely on logical truths and valid arguments, but he has nothing to justify using these principles. The problem Descartes faces is that if he rejected his reason then he would lose the tool that allows him to reject anything else. And in any case, he cannot reason away his reason. However, this counter argument to Descartes’ method has been rejected by the idea that reason is in the very nature of his pursuit. Reason can be thought of as being a working hypothesis of sorts. Should his confidence in his reason be well placed, then his task will end up going somewhere. If this confidence is misplaced, then his whole task would be doomed to failure, and this would become apparent during its course.

Descartes’ points in the first meditation, are all somewhat self-evident in a way, and as such one gets the feeling that he feels that he does not need to justify them at length. This may be why they are open to argument. What is clear is that his arguments cannot be denied within the realms of logical possibility, and this is all Descartes requires for us to doubt our empirical knowledge of the world. But this is the key – doubt. Doubt over empirical knowledge does not allow one to reject it. There is just as much reason to believe our senses as there is to doubt them. What Descartes succeeds in doing is highlighting this doubt, and then using it in his later meditations. By renouncing all his beliefs, Descartes is merely pursuing a “worst-case-scenario” to find things that are indubitable. The point of the first meditation is to prepare the reader to do the same, nothing more.

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