完整的原文为：子曰：“由，诲汝知之乎！知之为知之，不知为不知，是知也。”，出自《论语·为政》，是孔子告诫学生仲由（字子路）的一句名言，意思是：孔子说：“子路，告诉你对待知和不知的态度吧（即对待学问的态度）！知道就是知道，不知道就是不知道，这样才是真正的智慧。”早在2500年前，孔子就指出了养成踏实认真的学习态度极其重要，只有承认自己有所知、有所不知，才能更好地学习，从而取得进步。

孔子的政治主张、伦理思想、道德观念和教育原则在国外也影响深远。“清末怪杰”辜鸿铭精通英、法、德、拉丁、希腊、马来亚等9种语言，他的译文为：To know what it is that you know, and to know what it is that you do not know, — that is understanding.

“书销中外六十本，诗译英法惟一人”的翻译界泰斗许渊冲则译为：To admit what you know and what you do not know, that is knowledge.

香港著名翻译家刘殿爵（D. C. Lau）的版本是：To say you know when you know, and to say you do not when you do not, that is knowledge.

著名翻译家林戊荪的译文同出一脉：Say you know when you know, and say you don't know when you don't, that is true knowledge.

美国翻译家、汉学家伯顿·华兹生（Burton Watson）对此的理解则是：When you know, to know you know. When you don’t know, to know you don’t know. That’s what knowing is.

美国诗人庞德（Ezra Pound）的译文颇有些不走寻常路：To know is to act knowledge, and, when you do not know, not to try to appear as if you did, that’s knowing.

以上均是中外著名学者、翻译大师的智慧结晶，值得我们学习和借鉴。如按照“Chinglish”的译法，将这句话译为“know is know, no know is no know, is know”，肯定是不可取的。