14.Read the text. What philosopher is it dealt about? Write his name. He concluded, if he doubted, then something or someone must be doing the doubting; therefore, the very fact that he doubted proved his existence . "The simple meaning of the phrase is that if one is skeptical of existence, that is in and of itself proof that he does exist. He concludes that he can be certain that he exists because he thinks. But in what form? He perceives his body through the use of the senses; however , these have previously been unreliable. So he determines that the only indubitable knowledge is that he is a thinking thing. In this manner, he proceeds to construct a system of knowledge, discarding perception as unreliable and, instead, admitting only deduction as a method.