The causes for attaining Buddhahood should be understood in three ways. First, each of the ten dharma realms from hell to Buddha contain the other nine realms. All possible realms of experience are more or less present in each facet of experience. Those of us who are predominantly human can, depending on our past and present actions, experience the realm of hell or heaven. Second, the first nine dharma realms from hell to bodhisattvahood are integrated with that of Buddhahood. All things possess the potential for Buddhahood and, given the right conditions, can attain perfect enlightenment. Third, the ten dharma realms are all simultaneously empty of substantial Being yet conventionally existent, thus partaking in the threefold truth of reality. These three categories also are three different ways of saying the same thing: that reality is one yet many, threefold yet a unity, neither completely different nor wholly the same. Thus reality, dharma, is best described by the term “subtle.”

The result of Buddhahood is also understood in three ways. First, the essence of reality, or Buddhahood, pervades the entire universe. Buddhahood is not a separate realm detached from our world of experience, but an integral and fundamental part of it. Second, the Buddha did not first attain enlightenment around two thousand years ago under a tree in India, but attained Buddhahood in the incalculable past, or for eternity. Third, the Buddha always has, is, and always will manifest himself in various forms for the benefit of teaching sentient beings and leading them to enlightenment.

It is the Lotus Sūtra which clarifies the meaning of “dharma” in these six ways, therefore it is worthy of the title “subtle.” The other Sūtras, classified by Chih-i according the scheme of the five flavors are subtle in some parts and crude in others, except for the Hinayāna Teachings, which are only crude, and the Lotus Sūtra, which is only subtle.

In terms of “contemplating the mind,” the correct and subtle way is to contemplate the mind as including all other minds and that of the Buddha, not as being detached and separate from other minds. Second, one should contemplate one’s mind as being equal to that of the Buddha. Third, one should contemplate one’s mind and the mind of other sentient beings and the Buddha as being simultaneously empty of substantial being yet conventionally existent.

The “six identities,” a T’ien-t’ai interpretation of the interpenetration and identity of the fifty-two stages leading to Buddhahood should be understood in the same way, that one dharma interpenetrates and contains all other dharmas and stages of attainment.

Finally, this is all summarized in terms of the “four categories of oneness.” The interpenetration of all dharmas is the content of the “oneness of reality.” The unity of the Five Flavors is the content of the “oneness of teaching.” The integrated nature of the mind and of all minds, the subject and object of contemplation, is the content of the “oneness of practice.” The interpenetration and unity of all the levels of attainment as taught in the concept of the Six Identities is the content of the “oneness of persons.”