① Three immaterial “openings” that make it possible to return to one’s true Nature (xing), one’s true Existence (ming), and Emptiness (xuwu).
⊛ What are the three essentials? The Opening of reverting to the root (guigen), the Barrier of returning to the mandate (fuming), and the Valley of Empty Non-Being (xuwu). These are the three essentials. Someone refers to the mouth and the nose as the three essentials, but this is wrong. 或問何謂三要？曰：歸根之竅，復命之關，虛無之谷，是謂三要。或指口鼻為三要者，非也。 (Li Daochun, The Harmony of the Center: An Anthology, chap. 3)
② Body, mind, intention.
⊛ Body, mind, and intention are the three essentials. 身、心、意為三要。 (Li Daochun, The Harmony of the Center: An Anthology, chap. 3)
③ In Li Daochun’s exposition of Neidan, a term understood in different ways according to different levels of Neidan. ⓐ Precepts, concentration, and wisdom. ⓑ Body, mind, and Intention (yi). ⓒ The three Cinnabar Fields. ⓓ Mouth and nose (nostrils).
⊛ In the Supreme One Vehicle, the “three essentials” are precepts, concentration, and wisdom. . . . In the higher vehicle, the “three essentials” are body, mind, and Intention. . . . In the middle vehicle, the three essentials are the Great Abyss, the Crimson Palace, and the Room of the Essence. . . . In the lower vehicle, the three essentials are the mouth and the nose. 〔最上一乘，以〕戒定慧為三要。. . . 〔上乘者，以〕身心意為三要。 . . . 〔中乘者，以〕太淵，絳宮，精房為三要。 . . . 〔下乘者，以〕口鼻為三要。 (Li Daochun, The Harmony of the Center: An Anthology, chap. 2, trans. in Taoist Internal Alchemy: An Anthology of Neidan Texts, pp. 179-182 passim)