「積善成德」是荀子再三強調的工夫進路，本文將試圖探究荀子何以會對此一工夫進路充滿信心，並且又為何要以此作為其工夫進路的核心？換句話說，積善成德何以可能，又為何必要？本文認為積善成德之所以可能的主要原因有二：一是荀子預設了具有道德義涵的天君之心，二是荀子肯定了情欲之性的可轉化性，前者是積善成德的積極根據，後者則是其消極的基礎。而積善成德之所以必要，也有兩個主要因素：一是荀子對情欲之性的戒懼，情欲之性具有強大的負面驅力，是使人為惡的根源，二是荀子對理想人格的期許，理想人格乃仁且智的聖人境界，是人為學的最終目標，而無論是希望轉化情欲之性或者成就理想人格，都必須透過不斷地為學積善才能達成。

“Ji-shan-cheng-de” is an approach of moral practice that is emphasized by Xunzi. This article will explore why Xunzi has confidence in the approach and takes it as a core. In other words, is Ji-shan-cheng-de possible and necessary, This article thinks that there are two principal factors that make Ji-shan-cheng-de possible: one is that Xunzi's Tian-jun-zhi-xin has moral meaning; the other is that Xunzi's Qing-yu-zhi-xing has the character of transformation. The former is a positive root and the latter is a negative basis. There are also two principal factors that make Ji-shan-cheng-de necessary: one is that Xunzi’s caution against Qing-yu-zhi-xing, which has a powerful and negative force and is the root of evil; the other is that Xunzi's expectations for an ideal personality, which is a realm of benevolent and wise sage and is the goal of self-cultivation. Only through constantly accumulating merits can we reach the above goal.