It is known generally that koan were used to control the religious system by the Edo bakufu (Japanese feudal government headed by a shogun) in ways such as that where a priest could not become chief priest unless he could solve a certain amount of koan, or that of koan being used to demonstrate the experience of a priest along with horo (the number of years from the time when a person became a priest and received the religious precepts).
近世には一定の数の公案を解かないと住職になれない等、法臘の他に僧侶の経験を表す基準となるなど、江戸幕府の宗教統制にも利用された事は一般に知られている。