所謂中國儒家的道德哲學是以孟荀為代表的兩種不同的系統，即一為道德理想主義的自律道德系統，一為道德現實主義的他律道德系統。他們都是繼孔子而起的儒家大家。然而，他們兩個人的基本觀點與價值取向有所不同，而其學問義理也隨之不同。這麼緣故的線索可能在孔子所謂「性相近也，習相遠也」此一段文章找得到。因為，筆者認為孟荀之學問義理決定於如何解釋這「性相近，習相遠」的「性」。此是自古以來許多學者所論的熱門課題，但學者們有不同所見，議論分岐。筆者認為，簡要地可說「性」有兩個不同的意指：一是「氣質之性」，二是「義理之性」。孔子所說的「性」也有兩種不同的解釋可能性。其實，《論語》裡面，指「義理之性」的「性」以外，還有情慾、材質、氣質之性。因此，如果從孤立地角度看，可解釋為「氣質之性」等等。但是，由《論語》整個義理系統（孔子學說以「仁」為主）看，應該指「義理之性」而言。筆者也認定，孔子所說的「性相近」的「性」有著一點模糊性。所以，後來產生兩個不同的義理系統，即孟荀哲學系統。 孟子是以「性相近」的「性」為「義理之性」而建立儒家內聖之學的根基，荀子則是把它規定「氣質之性」（情慾之性）而強調後天的人為學習，即繼承孔子的客觀精神之一面而闡明外王之學。筆者認為，在孟荀兩個人為什麼「同宗而異路」，這樣質疑提出之下，要探討如下的問題：第一，孟荀哲學的基本觀點如何，第二，由「荀子非孟子」看孟荀人性論的不同點。第三，孟荀對道德修養的含意。

Two outstanding figures of moral philosophy of Confucianism are certainly Mengzi and Xunzi who stand for the moral idealism and the moral empiricism. Mengzi emphasized that the autonomy of moral agency whilst the Xunzi claimed that men need the moral discipline above all. They have different academic stances, backgrounds and point of views. However, it is obvious that they are come from the same root, the Confucius. It is said that the difference of these two are made during they elucidated what Confucius said “By nature, men are nearly alike; by practice, they get to wide apart” and Mengzi and Xunzi both thought that they realized the states of Confucius profoundly. They found the significant of “nature” and the understanding of the each one's “nature” between these two paragons made their differences. Of course, the argument of “nature” is one of philosophical categories and it has long history of discussions and assertions. However, through the research, I analyzed that the Confucius' “nature” has two attributions those are “metaphysical nature” and “physical nature” and alongside of contexts of the Confucius' the Analects the “metaphysical nature” has its validity. In spite of Confucius context, there are dispute of “nature”, because Xunzi insisted that the “nature」 as “physical” but Mengzi argued that is “metaphysical”. Mengzi claimed the “metaphysical nature” and he developed it as the innate virtue and learning of the sage, on the other hand, Xunzi emphasized the discipline and acquired learning from the political and cultural leader. Through the essay, I would like to demonstrate that why and how the two Confucians generated different philosophical thinking even they shared the same origin. Firstly, it is displaying that the basic structure of Mengzi and Xunzi's ideas. Secondly, the difference between these two and their disputes are demonstrated. Finally, it is illustrating that the meaning of the moral cultivation of these two confucian the light of their philosophies of “human nature”.