論者多以「中和」來看待〈書譜〉的論點，而在這「中和」的語境下，所充斥的多是「兼通」思維。筆者認為孫過庭的「兼通」處處以「法」為本質，雖然推論他也認為書藝的最上乘是「法」與「意」的「兼通」，但卻不是等值的「兼通」，而是以「法」為主體的「法中見意」。本文透過「以王羲之為兼通典範」、「真草兼通的必要性」、「通會之際的具體內容」三個部分來說明〈書譜〉所體現以「法」為本質的「兼通」思想。尤其是在「通會之際的具體內容」中，筆者以孫過庭的「平正－險絕－平正」三階段論述為綱領，分析其所統攝的各項審美指標，而這些審美指標最後所對應的，都是「法－意－法」的元素。最後本文以「尚法為本、中和為體、兼通為用」來總結〈書譜〉的理論體系。

Calligraphy theorists mostly view the perspectives in Sun Guoting's Treatise on Calligraphyin a context of ＂moderateness,＂ within which the mindset of ＂fusion＂ plays an important part. However, while Sun argues that the ultimate state of calligraphy art is the fusion of principles (fa) and spirit (yi), principles are still the main body, as in ＂writing the spirit with principles (yi fa xieyi)＂, and ＂seeing the spirit from principles (fa zhongjianyi). This study aims to explicate the mindset of fusion with principles as its main component expressed in the Treatise on Calligraphy. The study consists of three sections: (1) Wang Xizhi as the model of ＂fusion;＂ (2) The Necessity of fusion in true grass script (zhencao); (3) Explicating state-of-the-art calligraphy (tung hui zhi ji). In the third section of this study, the perspectives of the author are stated in reference of Sun Guoting's ＂Stable-Unstable-Stable＂ theory with a view to analyzing the aesthetic criteria it has included. These aesthetic criteria are ultimately corresponding to the components of ＂Principles-Spirit-Principles.＂ The study summarizes the theory system in Treatise on Calligraphyas ＂Moderateness as the body, principles as the foundation, fusion as the way of application.＂