In the East Asian Buddhist context, the term was further expanded and linked to classic Buddhist ideas and polarities like: nirvaṇa and saṃsāra, Buddhahood and sentient being, original enlightenment and initial enlightenment, ultimate truth and relative truth, principle and phenomena (理事), and the One Mind and its functions (in the Awakening of Faith in the Mahayana).
[4][dead link] According to Buddhologist A. Charles Muller:T'i originally means body or substance, and refers to the more internal, essential, hidden, important aspects of a thing.
[2] In Chinese philosophy, a major application of t'i-yung is to understand the human mind or spirit (sheng) as "essence," and individual words, thoughts and actions as the function.
In Confucian texts, the concept is applied to the fundamental quality of jen ("humanity," "benevolence") which expresses itself in various "functions", like as propriety (li) and filial piety (hsiao).
[7] According to Sung-bae Park the concept of essence-function is used by East Asian Buddhists "to show a non-dualistic and non-discriminate nature in their enlightenment experience," but does not exclude notions of subjectivity and objectivity.
[9] According to Charles Muller, essence-function thought "has its origins deep in the recesses of early Chou thought in such seminal texts as the Book of Odes, Analects, I ching and Tao te ching, became formally defined and used with regularity in the exegetical writings of Confucian/Neo-Taoist scholars of the Latter Han and afterward.
"[2] Tiyong thought further developed in the Wei (220–265) – Jin (266–420) period of Chinese history, when "Unification of the Three Teachings" ideology was dominant, striving for a theoretical reconciliation of Confucianism, Daoism, and Buddhism.
The first philosopher to systematically use the ti-yong schema was Wang Bi (226–249) in his commentary to Daodejing, chapter 22, when he discussed the metaphysical relation between non-being (wu) and being (you).
The concept developed further with the introduction of Buddhism in China, adapting Buddhist philosophy to a Chinese frame of reference.
But this does not tell how the absolute is present in the relative world: To deny the duality of samsara and nirvana, as the Perfection of Wisdom does, or to demonstrate logically the error of dichotomizing conceptualization, as Nagarjuna does, is not to address the question of the relationship between samsara and nirvana -or, in more philosophical terms, between phenomenal and ultimate reality [...] What, then, is the relationship between these two realms?
[15]The Awakening of Mahayana Faith, a key text in Chinese Buddhism, also employs Essence-Function and combines it with Yogacara, Buddha-nature and Madhyamaka philosophy, to produce a unique worldview.
[21] Wonhyo developed t'i-yung theory into its most influential form in his commentary on the Ta ch'eng ch'i hsin lun (Treatise on the Awakening of Mahayana Faith).