Tasan Chŏng Yag-yong 茶山 丁若鏞 is in large part interpreted as either 1) pro-Catholic under the guise of Confucianism or, 2) a primitive, 'original' Confucian with no deep relevance to Western Learning. The notion of a personified Heaven, or 'a lord above' (上帝), in Tasan's work naturally provokes the image of the God of Western religion or the fearful Heaven of ancient Confucianism, which in turn causes researchers to assume that such a view was held only by those who were against Neo-Confucianism or even "pro-Catholic" (親西派). What is interesting, however, is that the writings of Kyŏnggi Southerners - the faction to which Tasan ideologically belonged, who were neither against Neo-Confucianism nor even anti-Catholic (攻西派), make frequent reference to a personified Heaven with power and authority. This article first reviews how Tasan's contemporaries envisioned Heaven by examining the letters and manuscripts of such Kyŏnggi Southerners as Ch'ae Che-gong 蔡濟恭, An Chŏng-bok 安鼎福 and Yi Ka-hwan 李家煥. It shall be demonstrated that a number of thinkers before Tasan had already described such key notions as an 'inclination' (嗜好) towards goodness as the true nature (本性) of Heaven. The second part of this article describes Tasan's theory of human mind, especially the three elements of its immaterial core, namely, nature (性), capability (才), and implementation (行事). It will be argued that Tasan's explanation of the human mind bears a striking resemblance to the traits of Heaven as narrated by the Kyŏnggi Southerners previously examined. The final part explores the significance of Heaven in the worldview of Kyŏnggi Southerners and the philosophy of Tasan. For them, Heaven was not an omnipotent being waiting to judge our lives after death, but the object of a 'humane relationship' (人倫) - like a father, a king, or a teacher, along with all their accompanying strengths and weaknesses.