What is the Xuan 玄？

Laozi used the term "Xuan" (玄) many times in Tao Te Ching, such as "Xuan 之又玄 (Xuan and yet more Xuan), the gateway to all wonders" and "Xuan 德 (Xuan virtue) is deep and far-reaching". Its meaning is "profound, dim, and remote", serving as a description of "Dao" (道) and "De" (德).

Laozi Xiang'er Zhu (《老子想尔注》) states: "Xuan is heaven. The ancient immortals could uphold faith in the subtle and wonderful, communicating with heaven." Taoism holds that advocating "non-existence" or "existence" is a one-sided bias. Therefore, one should "neither adhere to existence nor non-existence" and "conform to the middle way"—this is what is called "Xuan". It is believed that "又玄 (yet more Xuan)" refers to "Chongxuan" (重玄，double Xuan).

Viewing all things and phenomena in the world through the thought of Chongxuan, Taoism advocates eliminating all oppositions such as hardness and softness, movement and stillness, existence and non-existence, goodness and evil, right and wrong from mental cognition, so as to reach the 虚无 (emptiness) state of "the 泯 (annihilation) of both the realm and wisdom" and "the forgetting of both the perceiver and the perceived". All these embody the philosophical speculative characteristics in Taoist doctrines.