Tong (同commonality) and yi (异difference) are opposing concepts that underpin a fundamental relationship among things. When distinct boundaries separate one thing from another, it implies that these two entities share some similarities while also showing differences in various aspects. The assessment of commonality and difference among things is crucial for their recognition and arrangement. In ancient times, many believed that things should be arranged in a rational manner according to an overall order, which was established on the basis of clear definition and accurate comprehension of the commonality and difference among things. Some others advocated acknowledging the relativity of the concepts of commonality and difference and thus breaking away from the constraints of such a relationship in the cognitive dimensions.

Rites are the basis for determining proper human relations, clarifying ambiguities, differentiating between things, and telling right from wrong. (The Book of Rites)

From the standpoint of difference, the liver and the gallbladder may appear worlds apart, just as the states of Chu and Yue. Yet, when viewed through the lens of commonality, all things can be seen as the same. (Zhuangzi)