Though Descartes makes a powerful case, I believe that his arguments do not actually support skepticism to the degree that he claims. Each of his skeptical arguments will be considered and replied to in turn.
First, while Descartes is correct in his claim that the senses deceive us in some cases, his general skepticism about the senses is not warranted. That this is so is shown by the following argument. In order to make his case, Descartes presents a variety of examples in which he has found that his senses deceived him. To be justified in claiming that the senses deceive, a person would need to be able to recognize when an error has taken place. In other words, the person would need to be able to distinguish between being mistaken and being correct. For example, to know that the ‘heat mirages’ that occur on paved roads are ‘deceptions’, one would need to know that they are optical illusions and hence what is seen is not what is actually there. But, in knowing this, one is able to see through the deception and thus avoid being deceived. Ironically, it must be concluded that in presenting examples of how the senses deceive, one is also presenting examples of how we are able to ‘see through’ deceptions-thus undercutting the very claim that is being argued for. Ironically, in arguing that he has been deceived by his senses, Descartes also argues that we can see through such deceptions.
Of course, I do not claim that we are never deceived-just that we can penetrate such deceptions. Given this fact, we can trust our senses as long as we are suitably cautious. To use an analogy: trusting the senses is like relying on a safety rope while climbing. They do fail occasionally, but as long as we are suitably careful we can be reasonably safe. To doubt our senses because they occasionally fail us would be like refusing to use safety ropes while climbing because they sometimes fail. Thus, Descartes’ argument does not justify the degree of skepticism alleged.
Second, while movies like Total Recall and The Matrix make Descartes’ dream argument seem plausible, his argument can be countered. While Descartes claims that there is no way to be certain that one is not asleep, he is mistaken. Based on my own experience, the state I call “dreaming” differs from the state I regard as being awake in many ways. One main difference is that the ‘dream’ world lacks the continuity of the ‘waking’ world. In the ‘waking’ world things remain mostly the same from day to day. If I go to ‘sleep’ and wake up, the next day my truck will still be a basic Tacoma pickup. But, I might have a ‘dream’ in which I have a Hummer 3 and another in which I have a Porsche. Yet, unlike my trusty Tacoma, the Hummer and Porsche will not be readily available for my drive to work or the supermarket.
A second difference is that the ‘dream’ world and the ‘waking’ world appear to have completely different rules or laws. In the ‘dream’ world, people can fly, the dead can walk, cartoons and TV characters can come to life, politicians can tell the truth, and even stranger things can happen that simply do not occur in the ‘waking’ world. In stark contrast, these things do not happen in the ‘waking’ world.
While there are many other differences, these two standards show that even though I might not be able to know the true natures of these two worlds, I have good grounds for believing that the ‘waking’ world is fundamentally different from the ‘dream’ world. Given this ability to distinguish ‘waking’ from ‘dreaming’, it must be concluded that Descartes’ argument fails to warrant the degree of skepticism he claims. I might not know if there is an external world, but I can discern the difference between the world of dreams and the ‘waking’ world.
Third, while Descartes’ evil demon is a formidable opponent, it can be defused by carefully considering the topic of possibility. Perhaps it is possible there is an evil demon whose sole mission in existence is to deceive me. However, to claim that there is such a being (or even that it is possible that such a being exists) is to make a very ‘heavy’ claim. As with houses, a ‘heavy’ claim requires strong support. Without such support, there seems to be little reason to accept even the possibility of such a being.
While Descartes is clearly considering even the most remote possibilities in his method of doubt, all he offers is the claim that such a being could exist. However, this is hardly a solid basis upon which to build the degree of doubt required by Descartes. Ironically, his skepticism undercuts itself-to the degree that I am in a state of doubt, I will also have doubt about the possibility that there could even be such a deceiver. As such, my doubt about the possibility of such a being serves to undermine the greater doubt that is supposed to be generated by this being. In order for the evil demon to generate such a degree of doubt it must be possible for it to exist. However, Descartes does not provide enough support for his claim of its possibility. This shows that Descartes’ evil demon argument fails to warrant the degree of doubt he claims.
Given the above arguments, it seems most reasonable to conclude that while Descartes’ arguments are powerful and well reasoned, they are not powerful enough to create the desired degree of doubt.