Seo Yubon(徐有本) was an important person to understand the scholarship and ideology of Dalsung Seo Family, which began from Seo Myeongeung(徐命膺) and continued by Seo Hosu(徐浩修) and Seo Hyeongsu(徐瀅修) in late Joseon dynasty. Seo Yubon also communicated with the prominent scholars of the contemporary astronomy and calendrical science, Such as Ryu Geum(柳琴), Kim Yeong(金泳), and Ryu Hui(柳僖), which makes his more important in understanding the history of science of late Joseon dynasty.
The first element to emphasize its significance in Seo Yubon’s intellectual backgrounds was his familiar scholarly lineage. Seo Myeongeung’s xingshuxue, Seo Hosu’s zhoubijihexue, astronomy and calendrical science, luluxue, and Seo Hyeongsu’s Jingxue revealed the true achievements of the Seo family. In addition, there showed a strong influence of Western Learning and the Evidential Larning (documental archaeology).
Another element one should take into account when discuss Seo Yubon’s scholarship is ‘beixue(Northern Learning)’. His intellectual friends included many beixue scholars, such as Bak Jega(朴齊家), Ryu Geum(柳琴), Ryu Deukgong(柳得恭), Seong Daejung(成大中), and Yi Huigyeong(李喜經). Also, Seo family had many materials of beixue influence in storage, and some of them were Matteo Ricci’s Jiheyuanben(幾何原本) and Hungaitongxiantushuo(渾蓋通憲圖說), important text books of Western Learning.
Over the foundation of these studies, Seo Yubon paid attention to xingshuxue(象數學) and dushuzhixue(度數之學). His xingshuxue was not zhouyixiangshuxue(周易象數學), but closer to mathematics and astronomy and calendrical science of jiaodubaxian(角度入線). Moreover, his dushuzhixue meant mingwudushuzhixue(名物度數之學), which specified the name, physical shape and nature of all objects.
Seo Yubon thought ‘lishu(曆數)’ important. Lishu was ‘shu’, which documented ‘li(曆)’, the movement of the sun, the moon, and the stars. He argued that all natural phenomena were not out of lishu. Following his grandfather Seo Myeongeung’s arguments, Seo Yubon contended that the basis of recording astronomical ephemeris was to calculate beijigaodu(the altitude of the north celestial pole; 北極高度). He also showed his interest in the then heated question of ‘dongguofenye(allocated fields of Korea : 東國風水).’
Seo Yubon also manufactured ‘xuanjiyuheng(璿璣玉衡)’ by himself. He considered that xuanjiyuheng was a crucial instrument not only to grasp the shape of sky, but also to calculate the movement of celestial objects. He actually did ‘ceyan(測驗)’ using his own xuanjiyuheng, and recorded the factual methods of observation in detail. Seo Yubon once confessed that he sincerely liked the idiom of ‘shishiqiushi(seeking of truth from facts ;實事求是)’ for all his life. His discussion of the nature a window to peek at such an attitude.