One of the main academic issues in the 16th century Chosun
is Heavenly Mandate. They explained the good nature of the
human being related to Heavenly Mandate. This is of course a
very traditional Confucian idea, but the elaboration of this
thought is made by Chosun Confucianism. Toegye participates
in that discussion dominantly. He modifies the existing The
Diagram of Heavenly Mandate and emphasizes the concept of
Li based on Heavenly Mandate through it. In the 16th century
Chosun academia where Zhuxi’s philosophy was being adopted
at a full scale, such an attempt by Toegye can be evaluated as
an effort to differentiate from the understandings of the past
and contemporary scholars. This analysis is confirmed by the
fact that he had noted the differences between The Diagram of
Supreme Ultimate and The Diagram of Heavenly Mandate.
Specifically, he explained Li as Heavenly Mandate with the
condition that Li and Gi are wondrously united and
consolidated. In that way, while he found the basis of morality
from the Heavenly Mandate which is a kind of moral
imperative, he definitely claimed that the Heavenly Mandate is
Li only when it is combined with Gi. In other words, When
combined with Gi, Li exerts the power to intervene with the
world just like a kind of moral command. This means that
rather than explaining morality of humans through the Supreme
Ultimate, it is necessary to find the basis of human morality
through the Heavenly Mandate. The division regarding these
two concepts is distinguished from the interpretation of the
scholars in the past. Through this differentiation, I can say that
Toegye reconstructed the theory on morality systematically.