The subtlety of the dharma is illustrated by the Ten Subtleties in the door of the Traces and in the door of the Origin. The door of the Traces (Chi-men) is the theme of the first fourteen chapters of the Lotus Sūtra, in which the Buddha presents himself as the historical manifestation, Śākyamuni. The door of the Origin (Pen-men) is the theme of the latter half of the Lotus Sūtra, in which the fundamental and eternal Buddha is for the first time displayed. The Ten Subtleties in the Traces are elucidated under five divisions. The Ten Subtleties in the Origin are interpreted in ten aspects. The category of the Ten Subtleties is Chih-i’s endeavor to incorporate all the theories and divisions in Buddhism, so that Buddhism can be presented as a coherent whole, constituted by the cause and effect of Buddhahood. (Vol. 2, Page 90)

The … Buddha-nature as the Triple Cause (Conditional Cause, Understanding Cause, and Fundamental Cause) of Buddhahood corresponds with the Three Tracks. The Buddha-nature as the Conditional Cause of Buddhahood (Yüan-yin Fo-hsing) refers to the inherent potential and propensity for Buddhahood within all sentient beings (which allows them to practice and build up the proper causes and conditions for attaining Buddhahood), and it corresponds to the Track of the Accomplishment (Tzu-ch’eng Kui), which is to perform the deeds required to realize the wisdom of a Buddha. The Buddha-nature as the Understanding Cause of Buddhahood (Liao-yin Fo-hsing) refers to the inherent potential for wisdom in all sentient beings, and it corresponds to the Track of the Illumination of Wisdom (Kuan-chao-kui), which destroys delusions and reveals the true nature of reality. The Buddha-nature as the Fundamental Cause of Buddhahood (Cheng-yin Fo-hsing) refers to the fact that all beings are inherently endowed with the Ultimate Truth where they all participate in the true nature of reality, and it corresponds to the Track of the Real Nature (Chen-hsin-kui), which is non-illusory and non-differentiated. See Swanson, Foundations of T’ien-t’ai Philosophy, pp. 133-134, and p.306, note 201; Lee Chih-fu, Miao-fa Lienhua-ching Hsüan-i Yen-chiu, vol. 1, pp. 185-186. (Vol. 2, Page 88)

The Liu-chi (Six Identities) is a system of realizing the truth set up by Chih-i to indicate six gradual ascending levels of attaining Buddhahood. These levels are all identified with the uniformity of the principal substance. They represent six levels of attainment in the fifty-two stages of the Perfect Teaching.

1. Li Chi-fo: all sentient beings by principle are Buddhas, for they inherently possess the Buddha-nature, even if they have not heard the Buddha dharma.
2. Ming-tzu Chi-yo: this is to understand that all dharmas contain the Buddha-dharma, and this understanding is derived from hearing the Buddha’s teaching that all sentient beings by principle are Buddhas. This is the stage when beings have just heard the teaching of the Buddha.
3. Kuanhsing Chi-fo: this is to contemplate that all dharmas contain the Buddhadharma. This is the stage of the Five Preliminary Grades of Disciples (Wup’in Ti-tzu JVei).
4. llsiang-ssu Chi-fo: this is the attainment of Śrāvaka enlightenment, which resembles true enlightenment of the Buddha upon severing false views and wrong attitudes within the three realms. This is the stage of the Ten Faith (Shih-hsin Wei),
5. Fen-cheng Chi-foe. this is the stage in which one realizes the Middle Way more and more, and has less and less ignorance, which is the stage from the Ten Dwellings (Shih-chu Wei) to the Preliminary Enlightenment (Teng-chüeh Wei).
6. Chiu-ching Chi-yo: this is the ultimate stage of Buddhahood, and the stage of Perfect or Subtle Enlightenment (Miao-chüeh Wei). (Vol. 2, Page 85)

By addressing that contemplating the mind is about the mind being neither self-generated nor other-generated, Chih-i demonstrates how truth can be realized through negation:

“In the case of empty space, if the mind that contemplates originates itself, then the mind does not need to rely on causes and conditions. Since the mind relies on causes and conditions, the mind has no power of self-generation. Since the mind has no power of self-generation, conditions cannot generate either. Since the mind and its condition have no [independent] existence, how can they be jointly substantial? If they cannot be obtained in conjunction, they cannot originate at all when they are in separation. If there is not even one single self-generation possible, how could there exist a hundred realms and a thousand dharmas? Because the mind is empty, everything that is created by the mind is empty. This emptiness is also empty. Such emptiness is not empty. Applying this Emptiness to the case of the Provisional, the Provisional is not provisional either. If there is neither Provisional nor Emptiness, it is ultimately pure and tranquil [the middle way].”

This passage stresses the significance of the mind contemplation. The method of contemplating the mind through negation is described as a way to realize the Middle Way-Ultimate Truth. By negating the mind that arises by its own or by another, one realizes the truth of Emptiness. By negating the substantiality of Emptiness and the Provisional, this prevents one from being attached to either of them, through which the truth as the Middle Way is realized. (Vol. 2, Page 82)

The all-embracing feature of the mind contemplation is revealed by the unity of the three categories of Dharma in the quotation from the Avatamsakasūtra:

“The mind, Buddha, and sentient beings are of no distinction.”

Chih-i points out that what mind contemplation can achieve is described by yet another quote from the Avatamsakasūtra:

“When one’s mind traverses the Dharma-realm, taking it as if it is empty space, then one will know the objective realm of all Buddhas.”

Chih-i believes that this quotation, in terms of the mind traversing the Dharma-realm, suggests that mind is related to the Threefold Truth, and that contemplating the mind is the means to attain the Threefold Truth. Chih-i explains:

“The Dharma-realm is identical to the Middle Way. Empty space is identical to Emptiness. The mind and Buddhas are identical to the Provisional. The three together are identical to the objective realm of all Buddhas. This means that if one contemplates [the thought of] one’s mind, one can still be endowed with all the Buddha-dharmas.”

The all-embracing feature of the mind is further emphasized by Chih-i as he holds that contemplating the mind is about one thought embracing reality as a whole:

“In the case of one’s mind traversing the Dharma-realm, when contemplating the mutual opposition of a sensation and its object, one thought arises in the mind which must belong to one of the ten realms. When [one thought] belongs to one realm, it at once embraces one hundred realms and one thousand dharmas. The one thought is replete with all [aspects of reality].”

This passage addresses that all characteristics of reality are contained in the rising of one thought. Therefore, contemplating the mind is the most practical method in reaching truth. (Vol. 2, Page 81-82)

For Chih-i, mind contemplation is the most accessible way to approach the Ultimate Truth, because Dharma of Sentient Beings is too broad and Dharma of Buddha is too high in approaching the Ultimate Truth. Contemplating mind, on the other hand, is related to the Threefold Truth and to the all-embracing feature of the mind. As the Ultimate Truth concerns the Threefold Truth and is all embracing, mind contemplation is proved to be the ultimate approach of penetrating the Ultimate Truth. (Vol. 2, Page 81)