René Descartes (1596–) was a , mathematician and part-time mercenary. He is equally notable for both his groundbreaking work in philosophy as well as mathematics. As the inventor of the , he formulated the basis of modern geometry, which in turn influenced the development of . In his attempt to refute scepticism, he himself employed methological scepticism, which is a method of using doubt to work further towards the truth. He decides to treat anything that it is possible to doubt as false. He is not concerned with what is likely, but what is possible. When Descartes runs his belief system through the fine comb of scepticism, he realises that he has lost confidence in most of his normal beliefs. He even goes as far to say that it is possible that God does not exist if his belief system were to undergo this kind of rigourous screening, a very risky statement in the times in which he was writing where inquisition was conducted at the slightest hint of anything contradictory to church teachings.
The first of Descartes six meditation reveals four situations which have the potential to distort our perceptions enough to invalidate a series of knowledge claims. He addresses situations in which senses are tricked, such as when a square tower looks round from a distance, or a pain is felt by an amputee in a leg that is no longer there. He gives the example of : in a dream, one's senses perceive things that seem real, but do not actually exist. (This idea is similar to what writes after dreaming that he is a butterfly.) Thus, one cannot rely on the data of the senses as necessarily true. This leads him, using his ‘if you can doubt, chuck it out’ attitude to beliefs, to accept that much of what he would previously have claimed to ‘know’ was in fact a set of naïve assumptions. The most knowledge invalidating argument Descartes presents is that of a mind so powerful that it could decieve us, casting doubt on all we can know of the world and the properties it contains. However, even though the deceiver can falsify our perceptions, it does not have the power to falsify what we "seem" to perceive. Descartes also concludes that the powers to think and exist are untouchable by the deceiver. From this, Descartes tries to arrive at something indubitable so he might be able to rebuild a new system of beliefs, free of errors. This knowledge would be ‘a priori’, which means ‘knowable just by thinking’, without any previous experience. Initially, Descartes arrives at only a single principle: if I am being deceived, then surely "I" must exist. Most famously, this is known as cogito ergo sum. From this Descartes thinks he has defeated scepticism, and feels he knows one thing for certain – my mind exists. He thought he had achieved a priori synthetic knowledge.
This, when it is stood alone, seems to support solipsism: the belief that there is no physical world, just one mind, your own, which is creating these sensations. Whilst this does not seem a very encouraging piece of information – the only thing you can know for certain is that you exist – it does at least confirm that something you do at least, physically exist. Or does it? It could be commented on that Descartes has only established the existance of some thoughts or concious experience. There is little evidence that these experience must belong to any self or ‘I’. Perhaps thoughts can exist by themselves, independent of thinkers. Moreover, Descartes assumes that the evil demon has no power to affect his reasoning. This seems a rash claim, seeing as he has just admitted the possibility of an evil demon that could distort and affect all his senses at will. Why would reasoning be imune to the attack? Thus we can see, scepticism, both global and ordinary seems more and more unlikely to be proved false.
It appears we cannot know whether the world we perceive is an accurate representation of the world as it really is. If we were in fact dreaming, it would imply that there must be some basis of our dreams in reality. How closely our dream resembles reality would depend on how imaginative we are in this dream. Is our experience of drinking chocolate in this dream simply a combination of drinking and chocolate? And is our experience of drinking simply a combination of eating and liquids? The real world could be radically different from the way it appears to us and, because we may never penetrate the veil of either perception, or the dream which we seem to be experiencing so vividly. A seemingly shrewd observation is that if the world we perceive did not, at least roughly, match the world as it really is, then we would have died out long ago as a race, because we would be unable to hunt in order to feed ourselves. Or is it simply that we have evolved so as our senses give us a helpful perception of reality so as to aid us in survival, even though we may be observing a highly distorted picture. Moreover, whilst the notion of a demon or virtual reality machine causing our sensations seems far-fetched, we have no way of verifying that this is in fact the real world. Such doubts will remain so long as there is a gap between the world we perceive and the world as it is. If we could verify the accuracy of our sensations by comparing them with the actual physical objects themselves, then such scepticism could be refuted instantly. Unfortunately, our brains and perception limit us, so even if we try to infer the existence of a material world by the fact that we are alive and thinking as Descartes did, such an inference can always be called into question; for we would still be making such an inference if there were no such world. Is all hope lost for a proof to substantiate scepticism? Whilst it may be impossible for all scepticism to be proved incorrect, global scepticism has several flaws
Recall that Descartes began his enterprise by raising doubts about all his previous beliefs. To doubt all of your beliefs is to claim a global scepticism. It is often argued that such global scepticism is not as easy as Descartes made it appear. So what difficulties does it face?
First, it is important to note that to claim to doubt all beliefs quickly leads into problems. To consistently doubt all beliefs involves doubting the statement of global scepticism itself. To claim that ‘all beliefs are doubtful’ implies that the very belief ‘all beliefs are doubtful’ is itself doubtful. Consequently global scepticism cannot be stated coherently without also bringing itself into question. Thus we can see, not everything can be doubted at once and if we are to doubt one set of beliefs we are also going to have to take certain beliefs for granted. This could in itself be seen as a proof that global scepticism is wrong.
Regular scepticism may be tougher to counter. The claim that ‘because our senses deceive us some of the time, they might always deceive us’, seems its most vulnerable assertion. We notice that senses sometimes deceive, precisely because we can identify and correct errors. The fact that we are aware that senses deception takes place from time to time actually presupposes that for the rest of the time our senses do not deceive us. A similar argument can be made against the sceptical claim that we may always be dreaming since when dreaming, we can’t tell if we are awake or not. It makes no sense to presuppose that someone could be dreaming all the time since the concept of dreaming is in part determined by that of being awake.
