Outline Descartes’ ‘evil deceiver’ argument and explain what he then says about his knowledge of his own existence.

Descartes suggests, that if we assume that there is an evil power, who's only goal is to deceive us, exists, then we can not be certain about the nature of our reality. He uses many examples. In one of them, he says that he might perceive that he is sitting at the desk, writing, but at the same time, this might be an illusion, which was cast on him by the demon. He doesn't say, that this demon exists, he only says that we should use the idea of such demon to demonstrate how inaccurate our perception of reality might be. In my opinion, there are much simpler examples: after a truly engaging conversation with someone, we might feel that time passed incredibly fast, and at the same time, if we do something which is boring, we might feel time passing slowly. All this suggests, that humans view the world subjectively. We might all have our subjective reality (slow or fast time), but there is only one objective reality (an hour for example). Descartes later argues, that if we cannot trust our senses, how can we be sure if we exist at all? What if the belief that we are alive, is only another illusion which the demon uses to deceive us? Amidst thousands of cases, he finds one, in which he believes existence can be proven. He says, that if we are aware of ourselves thinking, it means we exist, because otherwise we couldn't think. Although this statement was questioned by many other philosophers over time, we still need to understand how he got to this conclusion.