Descartes' intent for his meditations is to establish whether or not he can possess any certain knowledge. To do this, he engages in the method of Cartesian doubt, doubting everything he once believed at their foundations. To do this, Descartes reasons that almost everything he has come to believe has been a result of sensory perceptions but senses often are deceptive. If something deceives you at all, Descartes argues that the source cannot be held as a reliable foundation of knowledge. Descartes mentions that he would be insane to doubt certain things understood through the senses, such as his possesion of body parts or his location, but those things could be doubted on the basis that it is not entirely clear whether or not he is in a dream
