Dangran (当然), literally meaning “should be so,” is often used to describe the fact that something should exist or work in a specific manner, or the fact that someone should behave in a certain way. It implies some degree of legitimacy and reasonableness, indicating that the functioning of things and the conduct of people should adhere to legitimate rules and reasonable manners. The Song Dynasty scholar Zhu Xi (1130-1200) believed that these rules come from and embody tianli (天理the natural principles). Therefore, exploring the rules of dangran is the primary focus of qiongli (穷理exhausting principles).