李塨早年追隨顏元，頗受影響。李塨高与舉亍後，與學界交流密˱。後拜毛奇齡為師，習其經學之業。晚年專心於經學著述，撰有諸經傳注。李塨雖稱終身奉行顏元之說，但是在學術著述上，顯然與顏元躬行「實學」的宗旨背離。本文試圖由李塨生平之師從與學術交流狀況入手，分析其學術轉向的背景與意義。 李塨的經學傳注著作多於「實學」，希望以「學問」充實「實學」的內容。李塨忽略「形式」有時候會決定「意義」。李塨雖言經傳著述為擴充顏元之學而作，但是採取此種注經形式而產生的意義，尉遠離顏元「習行」之學。李塨沒有意識到形式、方法的侷限，他更沒有認識到思想觀點在其間會產生巨大的扭曲。李塨沒有把握住顏元思想另一個核心：「行」，反而由轉回文獻上進行議論，未能進一步拓展「實學」內涵。如此，則顏元雖有開拓、反思，然後繼者卻走回傳統，創新未能成，傳統未能遍，則顏李學派沒落的結局自然可知。

As a disciple in his early years, Li Gong was strongly influenced by Yan Yuan. When passed the state examination, Li Gong actively involved with the academic circles. Later on, he became a disciple of Mao Qi-Ling and studied the classics with him. In his old age, Li Gong concentrated on Confucian Classic studies and wrote a lot of commentaries. Claiming himself as a lifelong follower of Yan Yuan; however, Li Gong's academic works seemingly deviate from the principle of “practical learning” proposed by Yan Yuan. This paper starts off with Li Gong's apprenticeship and academic exchanges to analyze the background and significance of his academic transformation. Li Gong’s commentaries tend to put more emphasis on “practical learning” in the hope of supplementing its contents with practical knowledge. Li Gong failed to notice that “forms” may at times define “meanings.” Li Gong claimed that his commentary writings were intended to expand Yan Yuan’s learning, however, the meanings derived from his annotated styles deviate from Yan Yuan's “practical activities.” Li Gong was not aware of the constraints of forms and approaches. Neither did he perceive that thoughts and ideas contained within may engender massive distortions. Li Gong did not preserve the core value of “action” in Yan Yuan' thoughts. Instead, he reverted to literature discussions and failed to expand the contents of “practical learning.” In so doing, Yan Yuan elaborated and reflected on the learning. However, his disciples fell short of creativity and tradition, and consequently leading to the demise of Yan Li School.