「Bi-Ak」is the performance theory of Mukcius. His theory is unique in many points. First, it is a criticism on performances rather than a philosophy of art. While this is the theoretical principles, but that is the explanation how the art worked in the age of Chinese Warring States. Mukcius considered how confucian scholar`s doctrine of performance showed its limits in practice. Second, he argued the uselessness of art. In other words, he stressed the tasks of art by opposing itself. Third, he explained the need of art in the view of common people not of the nobles. In his time, the nobles were the main agents of art, for performance was one of political means. Mukcius pointed the harmful consequences of the confucian doctrine and criticised the helplessness of art in the troubled times. Furthermore, he claimed that the art as amusement for the nobles should be discarded. Nevertheless, he didn`t deny the ideals of the confucian doctrine. For him, newness in performance is the restoration of the original ideals of it. 「Bi-Ak」asks what art should not miss, what it should keep in spite of the rapid changes of society. It is a starting point of the theory of art by Mukcius. He teaches us that the true experiment and progression of performance is to restore the original ideals of it.