Xue Er(simplified Chinese: 学而; traditional Chinese: 學而) is the first book of the Analects of Confucius. According to Zhu Xi, a Confucian philosopher in the 12th century, the book Xue Er is the base of moral improvement because it touches upon the basic principals of being a "gentleman"(君子).  Name Xué(學) Ér(而) consist of two separate Chinese characters. The first character Xué denotes "to learn" as a verb or "the research of something" as a noun. The following character Ér signifies a conjunction between two actions. The titles of the Analects of Confucius are usually related to the first phrase of a given book. Likewise, the book Xue Er's initial sentence in Classical Chinese starts with "Xue Er": 學(Xué)而(Ér)時(Shí)習(Xí)之(Zhī),不(Bú)亦(Yì)說(Yuè)乎(Hū)？
The Master said, "Is it not pleasant to learn with a constant perseverance and application?
Note that although the English translation used only one verb "to learn", In the Classical Chinese text, there are two verbs: 學(Xué, to learn) and 習(Xí, to practice). Content Xing Bing's commentary of the Analects Lunyu Zhengyi(論語正義) listed several key words of the book Xue Er. The key words include: Gentleman(君子), filial piety(孝弟), humaneness(仁人), doing one's best(忠), trust(信), the foundation of a nation(道國之法) and the principles of an appropriate friendship(主友之規). In the book, Confucius opted for hospitality towards strangers and tolerance of ignorance. Confucius also emphasized on the importance of self introspection(through examples from his disciple Zengzi and his own sayings). Sources
^ Zhu, Xi (2016). 四書章句集注. Taipei: 國立臺灣大學出版中心. ISBN 9789863501626. ^ James, Legge (2013). The Analects (The Revised James Legge Translation). e-artnow. ISBN 9788074848605. ^ Chin, Annping (2014). The Analects. Penguin. ISBN 9780698153516. ^ Lunyu Zhushu (論語注疏). Peking University Publishing house. 2000. ISBN 97