This paper examines the so-called three main treatises of the T'ien-t'ai Sect, i.e. Fa Hua Hsuen Yi, Fa Hua Wen Chu, and Mou Ho Chih Kuan, to investigate Master Chih-i's mind philosophy. Master Chih-i first proposed the concept of "mind of one thought of ignorance" to explain the illusory nature of mind as the root of the birth of samsaric and changing world. This is the negative function of mind. Yet, mind has also a positive function, i.e. to recognize things and even to realize truth. Therefore, mind is also the root of enlightement, realizing Buddhahood, and obtaining liberation. In this context, mind has two dimensions of ignorance and dharmata which originate in the same mind. In regard to the relationship between mind and all things, Chih-i held that mind possesses all things. Although the ignorant mind possesses all things, the pure mind also possesses all things. In this point, chih-i stressed more on the former. He proposed the concept of "three thousand worlds in one thought" which means that the mind of one thought always arises and disappears together with one of the multiple staes. So, the mind of one thought arises and calms down with all things simultaneously. Arising is function and calming down is no-function. In function, the mind and all things arises simultaneously: in no-function, the mind and all things calms down simultaneously. Chih-i called it "the inconceivable state". This argument shows that the mind can maintain all things and thus prevent the from totally negated.
In the field of practive, Chih-i proposed the technique of "triple contemplation in one mind". It consists of two sides: the mind to be contemplated and the mind to contemplate. The former is to contemplate the ignorant mind of one thought by means of the triple contemplation: emptiness, provisionality and the middle. The latter is to use the pure mind as the mind to contemplate, i.e. to contemplate the three dimensions of emptiness, provisionality and the middle of the object. In the former contemplation, the practitioner has to contemplate emptiness first, provisionality next, and the middle last. This is the contemplation method of "pieh chiao". If one contemplates the three dimensions of emptiness, provisionality and the middle simultaneously, one has to contemplate the interpenetration and correlation of emptiness, provisionality and the middle. This is the contemplation method of sudden spontaneity. This is also the contemplation method of "yuan chiao". Chih-i promotedthe latter one.