有關〈孟子〉書中孟子、告子的四個辯論，歷來討論甚多，本文嘗試再做詮釋，認為「性猶杞柳」及「性猶湍水」之辯，都是二人就同一比喻而各說各話：告子認為人性無善無不善，以人性為仁義，必須後天的加工改造；孟子則認為人性本善，以人性為仁義，必須順人性的發展。至于「生之謂性」之辯，孟子承認一切生物皆有生之自然之質（食與色），但以人與禽獸不同，不可以食、色為人之性；告子則認為食、色乃普遍於一切人乃至生物而為其根本，故可謂人之性。還有「義內」之辯，告子之「義外」是說義由內心所發，卻由外在對象決定；孟子之「義內」則是義由內發，亦由內定。但此內發內定實際上是一超越內外而合內外之說。本文亦涉及告子「不得於言，勿求於心；不得於心，勿求於氣」的解釋，認為這其實是分別訴諸理智（言）、意志（心）及情感（氣）以求不動心的說法。本文並從〈孟子〉書中有關告子的資料歸納告子人性論的大概。

　　　　　There have been discussions by scholars about the four debates between Mencius (371-289 B.C.?) and Kao Tzu (c. 420-c. 350 B.C.) in the Book of Mencius, which are the topics to be re-examined in this essay. The author thinks that in the debates of “Human nature is like the willow tree” and “Human nature is like whirling water,” the two thinkers express their views on human nature through their different interpretations of the same analogies. Kao Tzu thinks that human nature is indifferent to good and evil, and to turn human nature into humanity and righteousness requires transformation of human nature; Mencisu thinks that human nature is good and one should not violate human nature in order to attain humanity and righteousness. In the debate of “What is inborn is called nature,” Mencius admits that desiring food and sex is inborn in all living beings, but since humans are different from animals, desiring food and sex should not be regarded as human nature. Kao Tazu, however, advocates that desiring food and sex should be regarded as human nature since it is inborn and is the most fundamental not only in animals but also in human beings. As for the debate on whether righteousness is “external” in the sense that although the sense of respect grows out of the min-and-heart, the content and the degree of respect are always determined by external objects. Mencius regards righteousness as “internal,” which means that it grows out of the is determined by one’s mind-and-heart. It should be noted that mencius’ notion of “internal” actually embodies a meaning that transcends “internal” and “external.” In addition to the four debates, this essay also explains Kao Tzu’s idea of “unperturbed mind” in terms of the mind being unperturbed by means of the intellect, the will and emotion. This essay also gives a general description of Kao Tzu’s system of thought.