 Taiji and wuji are opposed, apparently contradictory, expressions. Signifying the most basic complementarity, namely, that between yin and yang, taiji is the most primitive and original form of li. It is quintessential li, or elementary form (patterning). Signifying something unbounded and free of polarity, wuji describes the unformed primal qi whence yin and yang emerge through the taiji impulse. It is quintessential qi, pure potentiality. Hence, Zhou Dunyi’s proposition, “Wuji er taiji” (Free from polarity, and yet the supreme polarity), expresses the identity of opposites (li and qi) that gives rise to the initial impulse of  phenomena.[23]  In the next step of this impulse, yin and yang are formed. They complement taiji as pure energy to pure form, thus expressing another dimension of the li-qi complementarity.