 The idea of the Dao (Way, Path, Guide) emerged during the Warring States period in China (fifth to second centuries BCE), when the reigning idea of Tian (Heaven) as a kind of personal god or God started to shatter along with the rest of the imperial structures of the Zhou Dynasty. Chinese thinkers faced their version of the problem of evil: “Why is Tian letting this chaos persist?” and added “Where is the dao to harmony?” (Perkins 2019; Miller 2003: 37). An extended debate arose among different schools of thought arguing for different answers (Zürn 2018: 300ff), including two schools that have endured: the early Ru (Confucian) thinkers who said the dao could be brought back into the human world by reestablishing right social relationships and customs, and the early or  proto-Daoists[44]  who found a new focus in the dao in the impersonal, consistent patterns of the non-human natural world. The Daodejing (ca. sixth to fourth centuries BCE, hereafter “DDJ”) is the earliest Daoist text that reads these natural patterns as evidence of a single force or principle of all that there is—as a single metaphysical ultimate—and “tentatively”, as Perkins (2019) says well, names this ultimate “the dao” or in some translations “the Dao” or “Dao”. Though this entry will focus mainly on the Daoist tradition and use the word “Dao” (hereafter not italicized) to refer to it, the res in question runs under other important names and concepts in both the Daoist and Ru traditions, including Taiji (Great Ultimate or Grand One), Xuan Tian (Dark Heaven), Zhen (Truth or noumenal Reality) and conjoined with Tian as Tiandao in Ruism.