“The Great Ultimate is therefore the cosmic heart (xin) as both the pole star (jíxīng 極星) and the human heart. In the Xici (Appended Statements, a portion of the Yijing), the Great Ultimate is the prime principle of the world, and in the Xuanxue (Arcane Learning) milieu it is deemed to be cognate with the Emptiness and the Taiyi.”
“Zhōu Dūnyí 周敦頤 (1017-73), in particular, associated it with the Taoist term wuji (Ultimateness, Boundless, Infinite; lit., “without a ridgepole”) in the famous phrase wújí ér tàijí 無極而太極. This phrase can mean either that wújí and tàijí are one and the same thing, or that wújí comes first followed by tàijíi. While Neo-Confucians tended to endorse the first meaning, most Taoists adopted the second: for them the tàijí is the beginning of the world, but the wújí is the unknowable Dao itself.”
“The tàijí is the positive way of cognition and the wújí the apophatic one, two aspects that are complimentary in the divine knowledge, or knowing ignorance, both knowing and ignoring, neither knowing or ignoring. In the body, the tàijí is represented by the kidneys because the right one symbolizes the Great Yin (tàiyīn 太陰) and the left one the Minor Yang (or Young Yang, shăoyáng 少陽), hence the passage from Yin to Yang.”
Isabelle Robinet is the author of all citations here. There is a random order of them, just in the way I like to reread my synopsis from time to time to keep myself in the form. By the way, Encyclopedia of Taoism doesn’t practice tones’ settings but I do.