At the end of August 1552, Jesuit missionary Xavier reached ShangChuan Island, GuangDong, China. It marked the beginning of the cultural exchange between China and Europe.

In the next two centuries, more than 100 European missionaries entered China. For successful missionary work, they followed their pledge of poverty, chastity and obedience, took the strategies which accord with Chinese psychology, such as “making up for Confucianism”, “bending with Confucianism”, exert all their strength and wisdom, hope to bring China into the territory of God. But they encountered an almost insurmountable obstacle, Chinese Characters and Chinese Language. They spend 2 or 3 hours on Chinese learning every day, even that, they need spend 10-15 years to speak Chinese skillfully.

In this case, While Joachim Bouvet, Jean Francoise Foucquet, Joseph Henri Marie de Prémare were preaching Catholicism in China, A group of Sinologists in Europe launched the Chinese Key project,started looking for keys to master Chinese quickly.
In February 1674, Andreas Muller announced that he had found Clavis Sinica. On November 1697, Christian Mentzel told Leibniz that he found a better Clavis Sinica, Regretfully, Although they all claimed to have found Clavis Sinica,none of them had published books. Their research aroused Leibniz’s great interest. Leibniz put forward 14 questions about Chinese learning, including three main problems:
(1) Are there any primitive components in Chinese characters? If yes, how many of them?
(2) Are there any structural rules in Chinese characters? If yes, how many of them?
(3) What are the word formation methods of Chinese characters?
For the next 350 years, no one answered Leibniz's question.