Des cartes puts a proposition that human mind cannot be certain of reality and falsehood. He begins his proposition by stating that he will accept only that which is absolutely certain. He defines himself as the mind which is thinking. He is absolutely certain of existence of his self. However, he says that he does not know what he is. He makes a suggestion that he could be a thinking mind. He also points out that imagination of human mind is always about corporeal things and shapes. Human mind cannot stop thinking whether in sleep or awake. He proposes that he does not exist if his mind stops thinking(which he suggests to be highly improbable scenario).
He goes on to say that since mind is capable of perception of external things including his own body only through the five senses and the senses being deceptive at times are not absolutely reliable, our experience of the external world is not absolutely certain. He rejects senses since they are not reliable. He also says that since senses are the only way of perceiving the world human mind could as well be dreaming.He explains the difficulty involved in his argument by referring to the fact that it is hard to reject what we see, hear, or feel and accept something like we are thinking human mind.
