Roughly speaking, it`s said that Yi I`s ideas were composed of 2 pans. One was the philosophical, and the other was the political idea. Today, more light is shed on his philosophical idea. On the other hand, weak light is shed on his political ideas only through the lens called the Silhak(實學). However. his political idea, that is, the statecraft theory was his lifelong idea, and never forgot even before the Silhak redicovered his political idea. The Queen Munjeoong, who was the king Myeongjong`s mother, was dead in 1565, which meant that the long political dark age was over in the end. For the age, the political role of the Salim(士林) was only to criticise the corrupt power elites. When the new age was begun, their role was dramatically changed. Now, they should proved that their ideas were right, and available. In a word, they got to need the statecraft in order to solve a lot of social problems that had been piled up for the ``dark age``. However, the learning of Yi Hwang, which most Salim firmly had believed in, could not provide the political methodology unlike their expectation. In results, Yi I could use just 2 materials of his learning and the reality in order to make up his own statecraft. With regard to the statecraft theory, Yi I had the double tasks. One was to frame me available statecraft, and the other was to make his friends colleagues figure out his new theory. He succeeded in me first task to a considerable extent, but could not succeeded in the second task at all. Right after his death, officials and intellectuals of Joseon experienced Japanese Invasion of Kore(1592~1598), which was the long, and nation-wide war. For the wartime, they experienced the reality, and built up me statecraft experiences. In the process, they came to understand me Yi I`s assertions, and me theory.