「本性論」在探討吾人是否本具成就生命圓滿之質素，這在生命實踐哲學上是一重要論題，在中國主要哲學流派之儒釋道三家中，除道家外類皆明言人具此本質，故本文乃對道家始祖老子進行探究，以瞭知其對「本性論」之主張。 本文首依牟宗三先生「主觀體證境界」之詮釋系統，將老子哲學定位爲生命實踐哲學，它所追求之理想是「聖」，而聖之內涵爲「道」，故本文主要便在探究：在老子哲學系統中，「道」是否本具於吾人「性」中。 嚴格本性論需證明三命題：「吾人本具成聖質素」(本具)、「人人皆具成聖質素」(皆具)、「人人圓具成聖質素」(圓具)。本文依《老子》主「爲道」乃向內求取，且是經由銷解生命負面情愫，以創造「道」呈顯之有利條件，而讓「道」自然呈顯；據此證明「吾人本具成聖質素」。至於「皆具」與「圓具」，因《老子》僅五千言，限於資料，無法詳盡縝密論述此等主張；本文僅透過《老子》近似之論與消極性之證明入路，而謂《老子》在某種程度上亦主張「皆具」與「圓具」。 故本文以爲道家老子與儒釋兩家哲人，對本性論看法並無二致，雖然《老子》未做文字上明白宣示，但經由本文之探究，可知《老子》當是主張吾人本具成聖質素。

”True nature theory” intends to examine whether people have natural characters to achieve a satisfactory life, which is an important issue in the philosophy of life practice. Among Chinese mainstream philosophy in three schools of Confucianism, Buddhism and Taoism, theories suggest that humans are provided with this natural character except Taoism. This study intends to investigate ”true nature theory” by Lao-tzu, the ancestor of Taoism. Based on the interpretation system of ”state of subjective testimony” by Mr. Mou Tsung-san, we position the philosophy of Lao-tzu as a life practice philosophy. It pursues the ideal of ”holiness” with the content of ”doctrine”. This study intends to investigate: in the system of Lao-tzu philosophy, if ”doctrine” exists in humans' ”nature”. True nature theory needs to prove three assumptions: ”humans are provided with the nature of being a whole person” (originally provided), ”everyone is provided with the nature of being a whole person” (all provided), ”everyone is satisfactorily provided with the nature of being a whole person” (satisfactorily provided). Based on the theory of Lao Tzu, ”practice the doctrine” is to self-demand. It is to eliminate negative feelings and create a condition that is beneficial to demonstrate ”doctrine” so that the ”doctrine” can be naturally presented. So, it proves ”humans are originally provided with the nature of being a whole person”. As to ”all provided” and ”satisfactorily provided”, limited by the 5000 words of Lao-tzu, it cannot be explained in detail concerning the arguments. We can only argue that, to some extent, Lao Tzu suggests ”all provided” and ”satisfactorily provided” through Lao Tzu theories on similarity and inactivity. Hence, our study suggests that there is no difference regarding the theory of true nature among Taoism Lao-tzu, Confucianism and Buddhism. Without clear written statement by Lao Tzu, our study indicates Lao Tzu believes that humans are provided with the nature of being a whole person.