Kant’s interest in the metaphysical philosophy was nothing new itself or cannot be considered something unique. It was a general characteristic shown in the German philosophers in mid 18th century. The problem of “the possibility of metaphysics” was the core issue of the German philosophy since the late seventeenth century. However, Kant’s philosophy, in its developmental stage, is divided as the former and the latter with his professor thesis as the turning point. Therefore, this paper deals with the “developmental process of the former ideology” which forms the background establishing his ideology in Kant’s maturity. By doing so, the paper will examine what process Kant’s ideology went through to reach its maturity and will provide a way for better understanding of his essential spirit and “moral philosophy” Key Words : Immanuel Kant, rationalist epistemology, skepticism, the possibility of metaphysics