Tiyong

Tiyong or essence-function is a key concept in Chinese philosophy and East Asian Buddhism. It is a compound of two terms: "essence" (Chinese: 體; pinyin: tǐ), the absolute reality, cause, or source of all things, and "function" (yòng, 用), the manifestations of ti, which make up the impermanent and relative concrete reality. Ti and yong do not represent two separate things, but aspects of the same non-dual process.

The meanings of the term essence-function can also expand to include the following polarities: internal/external, root/branch, hidden/manifest, stillness/movement, fundamental/superficial. The basic idea can be found in ancient Chinese texts like the I Ching and Mencius. The term was widely adopted by Chinese Buddhists and became a major theme in Chinese Buddhism. 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). Essence-function thought remains an important doctrinal theme in East Asian Buddhism.