Buddhist terminology put forward by Xuanzang, a monk in the Tang Dynasty in China. Also known as "knowledge only". "quantity", people's understanding; "Bi", knowledge gained through reasoning. "Truth only knows quantity" is the truth knowledge that the only knowers believe that things cannot exist independently without "knowledge".

According to legend, when Xuanzang was studying in India, Mahayana Master Prajna wrote more than 700 Odes to Mahayana, denouncing the contradiction of epistemology: color is not difficult to see with eyes, and it is also difficult to see with eyes. He presented the paper to the king of Japan and asked for a debate with learned scholars. At that time, Xuanzang was the only knowledgeable scholar who volunteered to participate in the war. To this end, he wrote a 1600-word "Theory of Controlling Evil". "Truth only knows quantity" is its core content.

Knowledge-only learning was introduced into China in the Southern and Northern Dynasties and reached its peak in the Tang Dynasty.