A Study on Cheokjae Lee Seo-gu’s Sangseohak

「Sangseo Kangeui」, a part of 『Cheokjaejip』, is a collection of questions and answers that King Jeongjo and Cheokjae Lee Seo-gu exchanged over 『Sangseo』 in 1784. At the time, Cheokjae was one of civil officials that were selected as Chogyemunsin. Shown in that collection is a much higher acceptance of answers from Cheokjae than the other respondents. This study reviewed his 「Sangseo Kangeui」 by each of 5 themes, turning out that Cheokjae had not only mastery of Chinese classics, but also excellence in Sangseohak. Cheokjae had little interest in debate over authenticity of Gomun Sangseo. He highly appreciated Zhu-zi's theories so that he was in much favor of Cai-shen's 『Seojipjeon』. In this regard, as far as Sangseohak is concerned, Cheokjae stayed away from some tendency of the late Joseon period that sought creation of own theories beyond Zhu-zi and Cai-shen's established interpretations. However, Cheokjae supplemented 『Seojipjeon』 from the perspective of positivism as he embraced for Gu-yanmu's theories. Similarily, he contributed to achieving the goals King Jeongjo pursued when discussing 『Sangseo』, especially clarification of Zhu-zi's original thoughts and ideas. As well, he was so knowledgable of historic facts about the times of Yao-Shun and the Three Dynasties that he approached questions from King Jeongjo in quite a reasonable, practical way, in which Cheokjae occasionally made responses that put emphasis on promotion of public welfare. Thus, Joseon's academic trends that newly emerged in the 18th century was in some respect reflected in Cheokjae's Sangseohak, explaining why he was regarded as a scholar of the Realist School.