The existence and identity of both substance and function are agreed upon by religious thinkers and philosophers alike. Among them Ch'an masters are unrivalled in terms of giving rise to function from substance and talking about substance and function only after sudden awakening，i.e. the illumination of one's own mind and view of one's nature. In modern times, however，some people criticized the Ch'an School as lacking the concepts of substance and function，while others drew the conclusion that it does not differentiate between these concepts. The present paper intends to correct these extreme views and misunderstandings. Firstly，the characteristics of the Ch'an School in comparison with the teaching schools are demonstrated by virtue of the school's formation and cultivation methods. Secondly，a comprehensive synthesis of the pertinent remarks made by enlightened Ch'an masters reveals the essential substance and function concept of the Ch'an School：(1)"Mind," "nature，""one thing," and other expressions skilfully used by Ch'an Masters are all different terms denoting the same "substance". (2)There is no right and wrong, good and evil，sorrow and joy in this substance which is pure by itself. (3)It transcends all measurements and verbal formation，leaves no traces, can neither be know through knowledge nor pursued by reason. (4)Substance is formless and immaterial. Neither does it arise not perish, neither come nor go. It is to be found everywhere in the universe and，based on it，function arises continously. (5)Substance is neither empty nor existing，yet both empty as well as existing. Manifesting itself in accordance with objects, it can be great or small. It is the master of everything. Thus the relationship between substance and function is one of identity. (6)The function of substance is incesant. It encompasses all activities yet cannot be limited within their scope. Not in its entirety active and not resting in inactivity，it can do everything. (7)In relation to man，it is not diminished in a bewildered worldling and not increased in a hloy man. Neither interrupted nor uninterrupted，neither turbulent nor calm，it can nowhere be applied intentionally. The subtlety and transcendence of this substance and function concept excels all other philosophies. This is proven in the following section in which its characteristics are discussed. When philosophers discourse of substance and function，they develop their ideas based on feeling or reasoning wherefore their theories differ completely. The neo-Confucianists of the Sung Dynasty are a good illustration of this fact. They tried to find out by logical deduction what cannot be found in this way. On the other hand，Ch'an masters realize substance and function through sudden enlightenment which perceives directly. The expressions they used may differ but their actual meaning is identical. Moreover，their sudden enlightenment has to be certified by a master which excludes the possibility of mistaken "awakening". Thus no other philosophy can compete with t
