artes used evil genius argument to prove that even a priori, beliefs whose truth or falsity can be established independently of experience could be doubtful. Maybe it's evil genius, which is tricking us and making us to believe that 7+5=12. Look at the structure of the reasoning that will help us to understand a little better. (A) It looks to me that it's raining. (B) If I am being deceived by the evil genius then while it looks to me that it's raining however, it's not raining. So, I cannot be certain that it's raining because I could be just deceived by the evil genius. This example confirms that if evil genius exists then we cannot be certain about anything because it could be the evil genius that is tricking us and making us believe in certain ways. Also Descartes used illusion argument which basically tells us how our senses deceive us. For example, I believe that it's raining based on vision. This could be false because vision can be uncertain. "And it is mark of prudence never to trust wholly in those things which have once deceived us." Descartes is telling us never trust your senses which once deceived you because we cannot tell of course if we are being deceived or not. These arguments form doubt on great numerous beliefs we occupy. The only way out of this would be, if we could tell whether we are dreaming or being deceived. For example, if I knew that I was not dreaming nor am I being deceived, then I would know that what is happening to me was in fact the real thing. But the problem is we cannot be sure that we are not dreaming or being deceived. Dreaming, illusion, and evil genius arguments weaken all sort of knowledge from counting as accurate knowledge. However, one thing is certain in these arguments that they involve thinking. For instance, if I am dreaming that it's raining, I still think. Even if I am being deceived that it's raining, I still think. So, no matter if I am dreaming or being deceived I am still thi...