This paper is focused on analyzing the characteristics of Lee Ik's historical theory, the implications of his thought for the Silhak that emerged during the latter period of the Joseon dynasty, and the differences between the Silhak and Zhu Xis nee-Confucianism. Moreover, the historical importance of Lee Ik's understanding of history, and the lessons to be acquired by modern history scholars were also delved into. The results can be summarized as follows: First, while Lee Ik can be considered as a realist in that he defined history as being decided by the power of reality (actual power), he also believed that history should be analyzed from a moral standpoint as well. Furthermore, Lee considered democracy to be a moral good but not the ultimate end in itself. Lee Ik believed that the common people could be the main actors in history, and that humans, regardless of their social class, possessed the power to change human society through their own actions. Thus, tersely stated, Lees historical view was one that, while not excluding the possibility of people positively affecting change in the course of history, was based firmly in reality. Lee Ik's main objective was to establish a society in which the social status and landlord systems were abolished, I would like to label his historical theory as a realistic historical theory centering on the Minjung(People). Within Lee's theory, the concepts of Sein and Sollen (existence and ought) are not separable, but rather combined to form a new Minjung-oriented value based on reality, As such, his historical theory can be regarded as the unification of existence with Minjung-oriented ought. Thus, Lee Ik's historical theory should not be regarded as one in which the division of existence and ought occurs. Furthermore, It is also difficult to accept his approach as a transitional type of theory moving towards the division of existence and ought. Second, Let us take a look at the characteristics of the Silhak which emerged in the latter period of Joseon dynasty. The above-mentioned Minjung-oriented nature of Lee Ik's historical theory indicates the Silhak's desire to remove the hierarchical social system. Third, this paper analyzed the differences between the Silhak and Zhu Xi's neo-Confucianism. As both scholars recognized that Sisae (actual conditions) are an essential variable affecting the flow of history, there can be no doubt that both the Silhak and nec-Confucianism were based on reality. However, these two schools of thought are different in the objectives they pursued. For his part, Zhu Xi's theory was one that strived to stabilize peasant society and had the acceptance of the landlord system and the existence of social classes, with the Sadaebu(ruling class) at the apex, as its core features. Accepting the basic structure of the feudal society, Zhu Xi strived to partially improve or reform the contradictions that prevailed in society in order to stabilize the country. As a result, Zhu Xi school was based on a cyclical view of history that did not allow for any fundamental alterations of history to occur as a result of human effort. On the other hand, Silhak philosophy was based on the fundamental dismantlement of the feudal social system. Thus, it can be argued that Zhu Xi's philosophy is more realistic while Lee Ik's is more idealistic. More likely than not, these differences can be explained by the fact that both scholars lived during different eras. Fourth, Lee Ik's historical theory can be evaluated as being the extension of Zhu Xi's in that his theory was based on the acceptance of Sisae (actual conditions) and emphasized the role of morality in history. However, Lee Ik's historical theory used different standards to evaluate morality and was based on the belief that historical change could occur as a result of human efforts, including those of the common class. Nevertheless, it is hard to find any clear definition of the development of history in Lee Iks work. In fact, one has to wait until the emergence of Jeong Yak-Yong, who defined the development of history as being based on technological development, to see a clear definition of this term in Silhak writings. Fifth, this paper discussed the implications of Lee Iks historical theory. Lees historical theory is in harmony with the scientific view of history currently used to evaluate modern history in that it is based on actual conditions (Sisae). The strength of Lee Iks theory can be found in its practical approach, which allows for the possibility that historical reforms can be carried out by human effort, and its avoidance of the elitism that has plagued many a theory. In Lee's view, the unification of existence and the Minjung oriented ought can be carried out in practice through human effort. Moreover, as his theory unifies these two terms with the Minjung at the center, it can be said to be in keeping with modern historical theory. Sixth, Lee Ik's adoption of an open-minded approach toward the countries surrounding China, while preserving his Sino-centric view of the world, is another aspect of his theory with modern ramifications. Seen under this light, Lee Ik's historical theory may be useful in overcoming the nationalism afflicting modern society.