The fundamental strategy of Descartes' thought was his claim of doubt in everything that is directed at defeating the skepticism on its own ground. Skepticism has always been an outstanding feature of the French mind, as well as the pursuit of knowledge of mathematical precision. The fact that the basis of existence and knowledge is the reason, Descartes proved in his First Meditation. Concretely, in the world, there exist a lot of things and phenomena which are unknown for the human and hence remain to be questioned in various ways. In particular, if these things and phenomena truly exist and what are their basic properties. For example, whether an omnipotent god exists and if so, that deity may devote its complete attention to deceive the
