 The Qingjing jing (Book of Clarity and Quiescence; Kohn 1993: 24–29) is another influential work, also dating from the Tang period and also spoken by Laozi. It states that the innate clarity and quiescence of the mind and the spirit are defiled by passion and lust owed to the separation of original Unity into the two complementary principles. Only by realizing that mind, forms, and individual objects are devoid of an underlying nature is it possible to awaken to their fundamental emptiness. This is attained by contemplation, and leads one to the recovery of the “clarity and quiescence” mentioned in the title (an expression derived from the Daode jing, sec. 45). Among the main uses of this work was, and still is, its daily recitation by Quanzhen monks, nuns, and adepts.