The source of this classic comes from Shi Shuo Xin Yu Literature: "When Xie An was young, please ask Ruan Guanglu to say' White Horse Theory'. Thank you for your theory. If you had thanked me at that time, you would not have understood Ruan immediately, and then ask each other. Ruannai sighed:' Not only can people be said, but even asking for help can't be obtained!' "
Xie An (A.D. 320-385, the word Anshi, a man) in the Jin Dynasty once asked about the "White Horse Theory" when he was young (he was a doctor with an open mind, also known as Ruan Guanglu). Ruan Yu's knowledge is not extensive, but he is good at delving into some difficult problems, and is good at induction and refinement. When he makes the most difficult questions concise, he can make the truth very profound, clear and really penetrating. Xie An asked him to talk about "White Horse Theory", but he found the right person. The so-called "white horse theory" is the proposition that "white horse is not a horse" put forward by Gongsunlong School during the Warring States Period. This proposition reveals the difference between things and concepts, individuals and general, and also contains the idea that everything is separable. Ruan Yu told Xie An seriously, but at that time Xie An couldn't immediately understand what Ruan Yu said, but he seemed to understand something, so he asked carefully again and again. Ruan Yu lamented: "Not only are there very few people who can tell the white horse theory, but even fewer people can understand the truth of the white horse theory."