This paper shows two different features of the Korean traditional cosmology, one definitely associated with the I-Ching system, and the other with the Western astronomical knowledge, during the eighteenth century. This means that the Korean traditional cosmology was not competing against Western astronomical knowledge. Korean literati, such as Kim Sŏng'mun(1658-1735) and Sŏ Myŏng'ung(1716-1787) suggested an advanced, but conservative cosmology associated with the I-Ching system, and adapted the Western astronomy for it. It was not until the late eighteenth century that some literati, like Sŏ Hosu(1738-1799), Hong Taeyong(1731-1783), and Chŏng Yakchŏn(1758-1816), came to categorically reject the traditional correlative synthesis. Yet, their critical and anti-traditional discourses had come to and originated from the advanced cosmological discourses associated with the I-Ching system.