(a) Descartes' first meditation, on what can be called into doubt, is an attempt to discard everything that he has come to be known as true and existing. One might wonder what point there is to adopting such a sceptical way of thinking as, surely, it would only bring about much confusion and a kind of awkwardness which, I think, is unnecessary. However, it is only fair to fully consider an argument before criticising it. I will therefore discuss, in detail, Descartes' "Evil Demon" thought experiment; as to what type of information is it designed to undercut, and how it accomplishes the task of dismissing all his knowledge, opinions and beliefs as false.
In his pursuit of certainty, Descartes applies a special method that he has devised, known as "methodical doubt." As applied, methodical doubt has two steps; the first of which is to doubt everything that can be doubted, and secondly, never to accept anything as known unless it can be established with absolute certainty. Descartes does not analyze each and every one of his beliefs in an attempt to prove that all are fallacious. Instead he chooses to start with the principles upon which all his, now former, beliefs rested. He says that all that he has accepted as truth, until now, has come to him through his senses and further goes on to say that these senses are not trustworthy in the sense as they have deceived him before and, for this reason, are not to be trusted.
He asserts that our senses deceive us by referring to dreams. This is because, in our dreams, senses are still our most trusted source of judging truth, yet none of it really exists, questioning reality to the extent of thinking hat he might actually be dreaming instead of sitting by the fireplace. Dreams, he says, are like paintings; they are but a mere manifestation of what is real; they themselves can never represent anything that is truly unique to our imagination because they based on our imagination. Descartes' suggestion is, who is to say that our senses aren't deceiving us while we are awake, or are we even awake? There's no way of being sure of the truth because in both forms (awake, or dreaming) we base our perception on our senses. For this reason, we can never accept things that come to our knowledge through our senses as truth.
He then goes to mention God's role in all the deception that is taking place. He is confused because is convinced that God is supremely good and would not allow him to be deceived like that yet, he allows him (Descartes) to be deceived. Those who do not believe in an almighty and supreme Lord, he continues, should be even more convinced that they've been deceived ("the less powerful they make my original cause, the more likely it is that I am so imperfect as to be deceived all the time - because deceptions and error to be imperfections" ). This is where the idea of an `evil demon' comes into play. He wonders if the God he has always believed in might actually be a malevolent...