《文心雕龙·丽辞》
大自然赋予万物的形体，必然是成双成对；这种自然规律所起的作用，使事物不可能孤独形成。
造化赋形，支体必双，神理为用，事不孤立。
Nature provides form to all things. It must come in pairs. Such is the performance of the natural law, which makes it impossible for things to form in isolation.