Dosan Sibigok consists of ‘Eonji Yukok(言志 六曲)’ and ‘Eonhak Yukok’'(言學 六曲). This thesis focuses on how the structures of two Yukoks(六曲) are intimately connected to one another and how Toegye's Yigicheolhak(a kind of philosophy) is reflected in his works. First of all, let's examine the relationship between ‘Dosanjapyeoung’ and ‘Dosan Sibigok’. Two works show a world view of Toegye, an ethicist who had tried to understand an abstruse principle of Taegeukyeomgye. They are connected deeply to each other. At first, Toegye created a chinese poem, ‘Dosanjabyeoung’ to express his joy in Dosan and then he wrote ‘Dosan Sibigok’, which was written in Korean, to depict his emotion which he couldn't express with chinese letters.
In the epilogue of ‘Dosan Sibigok’, he wrote that he had composed two ‘Dosan Yukoks’ by imitating Yukga of farewell. One was ‘Eonji Yukok’ and another was ‘Eonhak Yukok’. He also wrote that his work called ‘Dosan Yukok’ was a style of Yukga. In this respect, ‘Eonji(言志)’ and ‘Eonhak(言學)’. are well organized each other. Especially, they have something in common in their last stanza. Both of them are related to Gunjajido(君子之道, a way of man of virtue) of Bieunjang(費隱章) in the doctrine of the mean <中庸>. They sing ‘a way of nature’ and ‘a way of human being’ in common.
‘Eonji Yukok’ shows the world view of Juriron(主理論) (a theory of Neo-confucianism). Toegye inherited Juryeomgye's point of view in literature, which had a moral value. His poems were based on virtue and his ideal poem was Doyeonmyoung's Chungdamhana(冲澹閑雅). In ‘Eonji Yukok’, he desired people to realize and pursue a way of man of virtue. That is, ‘Eonji 1’ shows a poetic self to try to be in harmony with nature and ‘Eonji 2’ reveals that he wanted to live in an age of peace. ‘Eonji 3’ presents his enthusiastic will to train a lot of talented people. ‘Eonji 4’ reveals that he would long for the king and he would be loyal to him, not forgetting pimiirin (彼美一人, a king) even though he was living in a beautiful scenery of Dosan. ‘Eonji 5’ shows his thought of being in government service(出處觀) so that he tried not to forget the world even though he lived in nature. In ‘Eonji 6’, the poet desired people to realize a reason why Eoyakyeonbi (魚躍鳶飛, a very active state) and Unyoungcheongwang(雲影天光, a harmonious state) were repeated and rotated, depicting the beauty of four seasons.
Toegye wrote about an attitude, a mind and a way for study in the later Yukgok, calling ‘Eonhak’. In ‘Eonhak’, he insisted on keeping studying and cultivating mind, based on ‘gyoung’(敬, respect). In ‘Eonhak 1’, he recommended people to read a lot of books for study (萬卷生涯), and to rid themselves of greed and to appreciate the arts (往來風流) for self-discipline. In ‘Eonhak 2’, he recommended that to be wise men they should practice a way in which ancient people had done. In ‘Eonhak 3’, he resolved that he would devote himself to his studies and self-discipline as ancient saints had done. In ‘Eonhak 4’, he wrote that people should not stop a way in which they had performed and they should keep practicing it without being distracted. In ‘Eonhak 5’, Toegye decided that people should keep studying and maintain self-discipline like everlasting nature. ‘Eonhak 6’ also emphasizes on ceaseless study and self- discipline. Bieunjang(費隱章) in the doctrine of the mean <中庸> is recited in ‘Eonhak 6’, which is related closely to the contents expressed ‘Eonji 6’. As mentioned above, ‘Eonji’ and ‘Eonhak’ harmonizes with each other and has unity in various aspects.