The subtlety of the Buddha-dharma is described by Chih-i as follows:

“The hundred realms and the thousand suchnesses are the objective realm of the Buddha, and only Buddhas … can exhaust such principle [reality]. It is like a huge box: its cover has to be correspondingly huge too. With the unlimited Buddha-knowledge, [the Buddha] illuminates the vast and great Buddhahood and objective realm. For [the Buddha] to reach to the bottom [of this reality] is called ‘following his own will.’ If [the Buddha] illuminates the characteristics of the nine other Dharma realms from beginning to end without leaving out a thread or a mustard seed, this is called ‘following another’s will.’ On the basis of these two dharmas [of following the Buddha’s own will and another’s will], [the Buddha] manifests the Traces of the ten realms, either showing his own body or another’s body, and either speaking the words following his own will or the words following another’s will. Both his own will and another’s will are inconceivable, and both his own body and the body of another are extremely subtle and quiescent. [Ultimately,] all of them are neither Relative nor Ultimate, and yet, [they] are capable of responding to the Relative of the nine realms and the Ultimate of the one realm, causing no loss or decrease to the Buddha-dharma.” (Vol 2, Page 81)

Related to the Dharma of Sentient Beings that is composed of the Relative and the Ultimate, the Dharma of Buddha further explains the Buddha’s knowledge that concerns the Relative and the Ultimate, from which the profundity and vastness of objective reality is revealed. According to Chih-i, this objective reality is only penetrated by the Buddha with the Twofold Knowledge in terms of the Relative and the Ultimate. With this Twofold Knowledge, the Buddha is able to embrace the other nine realms, and to utilize all possible expedient means to teach and transform living beings. Therefore, the Twofold Knowledge of the Relative and the Ultimate is subtle and represents the subtlety of the Buddha-dharma. Chih-i asserts that the Dharma of Buddha is not something separate from our empirical world, and in fact, is part of the same reality. Its subtlety is reflected in the fact that the Twofold Knowledge of the Relative and the Ultimate can only be penetrated by the Buddha. Its subtlety is also reflected in the fact that only the Buddha with the Twofold Knowledge can exhaust the vastness of objective reality. (Vol. 2, Page 80)

Chih-i argues that although each realm is differentiated from other realms as having different definitions of the Ten Suchnesses, together, they constitute the Ultimate Truth that consists of the relative and ultimate reality. In other words, the relative and the ultimate are coexistent as a polar concept and are contained within each other in terms of soteriological significance. On the one hand, without the relative of the nine realms, the ultimate of the Buddha-realm cannot be substantiated, and without the ultimate, the relative does not have any validity, two of which form a polar concept existing interdependently. On the other hand, if the relative does not contain the ultimate, then the attainment of Buddhahood would not be possible; if the ultimate does not contain the relative, then the Buddha would not undertake his task of teaching and saving beings. Only if the ultimate is already contained in relative as the cause for Buddhahood, can the attainment of Buddhahood as the effect be possible, whereby all beings in the nine realms are grounded to be able to eventually enter the Buddha-realm; only if the relative is contained in the ultimate, can the Buddha’s endless soteriological activities of saving beings be realistic. (Vol. 2, Page 80)

With regard to the Ten Suchnesses in the Buddha-realm, “appearance” refers to the Buddha-nature as the Conditional Cause (Yiian-yin) of Buddhahood, i.e., the merits living beings accumulate; “nature” refers to the Buddha-nature as the Understanding Cause (Ch., Liao-yin; Skt., vyan͂janahetu) of Buddhahood, i.e., the wisdom of beings; “substance” refers to the Buddha-nature as the Fundamental Cause (Cheng-yin) of Buddhahood, i.e., the pure and tranquil mind as the ultimate truth beings possess; “power” refers to the Buddha’s initial aspiration for enlightenment that surpasses that of the Two Vehicles; “function” refers to the Buddha’s performance of the Four Great Vows; “causes” refers to the Buddha’s grand adornment of knowledge and wisdom; “conditions” refers to the Buddha’s grand adornment of blessings and virtues; “effects” refers to the repetitive effects of the state of unsurpassed enlightenment in which each thought of the Buddha is integrated with the mind of great awakening; “retributions” refers to the fruit of mahāparinirvāṇa, and the last suchness “beginning-and-end-ultimately-alike” conveys the truth of the Middle Way, meaning that the Threefold Truth inherent in sentient beings at the beginning stage of practice is not different from the Threefold Truth revealed at the final stage of enlightenment. This is to say, both types of the Threefold Truth denote the same aspects (i.e., Emptiness, the Provisional, and the Middle Way), and both are based on the same reality consisting of causes and conditions. Chih-i supports his statement by explaining that in terms of the truth of Emptiness, sentient beings and the Buddha are inherently not different, since they are empty of substantial Being. When this non-distinction is spoken of in terms of the truth of the Provisional, it means that the Ten Dharma-realms are interpenetrating and mutually inter-existent. Sentient beings are the same as the Buddha, in a sense that they all inherently possess the Buddha-nature. The Buddha and sentient beings are the same, considering that everyone can attain Buddhahood as long as one makes efforts through diligent practices like the Buddha did in his previous lives before his enlightenment. With regard to the truth of the Middle Way, “ultimately alike” means that all of ignorant men and sages are part of reality that constitute the Ultimate Truth. (Vol. 2, Page 79)

(4) The characteristics of the Ten Suchnesses are defined in the group of bodhisattvas and Buddhas

The meaning of the Ten Suchnesses concerning the fourth group of bodhisattvas and Buddhas (P’u-sa Fo) is described in three categories regarding the bodhisattvas of various levels of attainment: the bodhisattva of the Tripiṭaka Teaching, the bodhisattva of the Common Teaching, and the bodhisattvas of the Separate Teaching.

With regard to the bodhisattva of the Six Perfections” (Liu-tu P’usa) (of the Tripitaka Teaching), “appearance,” “nature,” “substance,” “power,” and “function” are discussed in terms of the bodhisattva’s blessings and virtues, which are derived from practicing the Six Perfections (pāramitās). “Causes” refers to wholesome karman, for the bodhisattva still abides in the human world. “Conditions” refers to affliction (Ch., Fa-nao; Skt., kleśa), for the bodhisattva has not severed defilement. “Effects” refers to the bodhisattva’s severance of bonds by means of thirty-four mental states. “Suchness of its retributions” refers to the Ten Suchnesses the bodhisattva is endowed with.” With regard to the bodhisattva of the Common Teaching (T’ung-chiao P’u-sa), “appearance,” “nature,” “substance,” “power,” “function,” “causes,” “conditions,” and “effects” are discussed from the perspective of non-defilement. “Retributions” means that the bodhisattva receives retribution before the sixth of the Ten Stages, and does not receive any retribution starting from the sixth of the Ten Stages. This is because on the Sixth Stage, the bodhisattva completely severs wrong attitudes and do not receive any rebirth, given that the action of their vow to assist sentient beings is not the retribution per se resulted from real karman. Thus, he is endowed with nine suchnesses but not ten (e.g. “retributions” is not included).

With regard to the bodhisattva of the Separate Teaching (Piehchiao P’u-sa), because of his cultivation of the Middle Way, and his gradual progress in contemplation, the bodhisattva embraces the Ten Dharma-realms. (Vol. 2, Page 78)