The Confucian works in particular have been of key importance to Chinese culture and history, as a set of works known as the "Four Books and Five Classics" were, in the 12th century AD, chosen as the basis for the Imperial examination for any government post. These nine books therefore became the center of the educational system. They have been grouped into two categories: the "Five Classics", allegedly commented and edited by Confucius, and the Four Books. The "Five Classics" are: