天台智者大師發揮龍樹《中論》義，提出一心三觀之觀法，表面看似為我們了解世間的一切法提供了一認識論上之理論。但觀一切法之所以可能，則仍須有一作為觀者的主體，本文即嘗試探討智者大師有關主體的理論，其如何由論述主體的各種特性如空寂、一念三千和一心三觀等，繼而把主體歸結為不可思議，並檢討若循其主體理論，或可避免哲學上有關真心、妄心等有關主體特性之各種爭辯之問題。

Chih-i was the first master creating a philosophical system in the School of T’ien-t’ai. From his philosophy, subject played an important role when the main ideas in his philosophy were more or less based on the characteristics of subject. Paradoxically, Chih-i considered that the more one understood the nature of subject, the less extent should one think of it. As a result, subject is inconceivable even though subject had its characteristics and functions. This paper aims at discussing how such subjectivity theory of Chih-i constructs and discusses the possible issues raised from his theory.