One who is an obedient son and respectful brother, and yet likes defying superiors—rare! One who doesn’t like defying superiors, and yet likes raising rebellion—has never this been.

This says, that if a person is capable of a virtuous service to parents and elders, then his heartmind will be harmonious and compliant. He will rarely like to defy superiors, and will certainly not like to raise rebellion.

– Zhu Xi 朱熹

此言人能孝弟，則其心和順，少好犯上，必不好作亂也。

The noble man focuses efforts on the root; when the root is established the Way will grow lifelong. That which family affection and brotherly respect are, they act as humanity's root?

This says that, in all matters, the noble man concentrates his efforts and abilities on the root. Once this foundational root is established, its way by itself will grow lifelong. As for family affection and brotherly respect (xiao 孝),ᵃ given that it is the foundation of one’s good nature, if learners devote themselves to this, then from this the way of humanity (ren 仁)ᵇ will grow.

– Zhu Xi 朱熹

言君子凡事專用力於根本，根本既立，則其道自生。若上文所謂孝弟，乃是為仁之本，學者務此，則仁道自此而生也。

° ° °

To be affectionate with family and respectful of elders is to comply with virtue. Therefore, one who is like this would not like to defy authority. How then would there arise incidents contrary to moral principle throwing norms into disorder? Virtue has its root, and when that root is established, its way will grow sufficiently large.

Family affection and brotherly respect are conducted in the home, after that humanityᵇ and loveᶜ reach to outside things. This is what is meant by “affectionate to his parents, and humane to the people.”² Thus the practice of humanity takes family affection and brotherly respect as its root. When discussing human nature, we regard humanity as the root of family affection and brotherly respect.

Someone asked: “Family affection and brotherly respect act as the root of humanity?” Does this phrase not assert that through family affection and brotherly respect, humanity can be attained?

No. This says that the practice of humanity begins with family affection and brotherly respect—these are one matter of humanity. To call them the root of humane conduct then is acceptable. But to say they are the root of humanity itself, is not acceptable. For humanity is the nature, while family affection and brotherly respect are its function. Within human nature there is only humanity, rightness, ritual and wisdom—these four, and nothing more.ᵈ

Where would family affection and brotherly respect come in? Humanity presides over love, and there is no greater love than the love for parents. Hence the text reads “that which family affection and brotherly respect are, they are the root of acting humanely!”³

– Cheng Yi 程颐

孝弟，順德也，故不好犯上，豈復有逆理亂常之事。德有本，本立則其道充大。孝弟行於家，而後仁愛及於物，所謂親親而仁民也。故為仁以孝弟為本。論性，則以仁為孝弟之本。或問：「孝弟為仁之本，此是由孝弟可以至仁否？」曰：非也。謂行仁自孝弟始，孝弟是仁之一事。謂之行仁之本則可，謂是仁之本則不可。蓋仁是性也，孝弟是用也，性中只有箇仁、義、禮、智四者而已，曷嘗有孝弟來。然仁主於愛，愛莫大於愛親，故曰孝弟也者，其為仁之本與！

Definitions from Zhu Xi

Part 1: Youzi was a pupil of Kongzi named Ruo 若. To virtuously serve father and mother acts as xiao 孝; virtuously serving elder brothers acts as di 弟. Fan shang 犯上 means to work against those who are above. Xian 鮮 is rare or few. Zuo luan 作亂, then it follows, represents the affairs of treason and struggles.

Part 2: Wu 務 is to concentrate one’s efforts on. Ben 本 is like the root of a plant. Ren 仁 is the principle of love and the character of the heartmind. Wei ren 為仁 is just like saying “to behave with humanity.” Yu 與 is a term of doubt, a retreat out of modesty, one does not dare to speak simplified words.

Footnotes

ᵃ Xiao 孝 (“family affection” of an “obedient son”) is defined by Zhu Xi as shan shi 善事, which is literally a “good deed,” but must be from a place of virtue and ongoing, thus a “virtuous service.” How could mere obedience in itself act as the root of one’s humanity?

ᵇ Ren 仁 (“humanity”) is man’s good nature. It is inborn, yet must be cultivated through practice or lost by neglect. It is the principle underlying love.

ᶜ Ai 愛 (“love”) is an expressed fondness for, beginning with family affection and extending to general compassion. It is the external manifestation of humanity.

ᵈ Siduan 四端 (“Four Beginnings”) are ren 仁 (“humanity”), yi 義 (“rightness”), li 禮 (“ritual”), and zhi 智 (“wisdom”). These come from the Mengzi, 2A:6.

¹ You Ruo 有若 (518-457 BC) was a pupil of Kongzi. It is believed that he started his own school after the teacher’s passing. Chengzi theorized that the pupils of Youzi and Zengzi compiled the Discourses, hence he is referred to here with the honorific zi 子 (“master”).

² Quotes The Mengzi, “He is affectionate to his parents and humane to the people.” [7A.45, tr. Chan]

³ There is a linguistic issue of how to parse the ancient phase 為仁之本: “acts as the root of humanity” or “the root of acting humanely.” Chengzi says it is the latter: humanity is inborn, thus already present, but needs to manifest in actions (xing 行, in conduct).

Comment: Note the parallel between the opening and closing lines: 其為人 “his acts as a human” and 其為仁 “his acts humane,” with xiaodi 孝弟 “a virtuous service to family” in between acting as the transformer.

The Confucian tradition only speaks of practicing humanity, not of [intellectually] knowing humanity. This is about putting the way of humanity into practice—the root of humane behavior is discussed in terms of real matters. – Zhu Xi 朱熹 , Yulei 20:1.2:71 & 20

For more info, see the Collected Conversations of Master Zhu on this verse.