Eastern philosophy
The "Dao De Jing" ("Tao-Te-Ching," c. 4th century BCE), traditionally attributed to Laozi, and the "Nan Hua Jing" ("Zhuang Zi") are considered the key texts of the tradition. The first organized form of Taoism, the Tianshi (Celestial Masters') school arose in the 2nd century CE. Xuanxue ("deep learning", also "Neo-Taoism") was a major philosophical movement influenced by Confucian scholarship, which focused on the interpretation of the "Yijing," "Daodejing," and "Zhuangzi" and which flourished during the third to sixth centuries CE. The most important philosophers of this movement were He Yan, Wang Bi, the Seven Sages of the Bamboo Grove, Ge Hong and Guo Xiang. Thinkers like He Yan and Wang Bi focused on the deep nature of Tao, which they saw as being best exemplified by the term "Wu" (nothingness, non-being, negativity).
Doctor of the Church
In the Eastern Church three Doctors were pre-eminent: Saint John Chrysostom, Saint Basil the Great, and Gregory of Nazianzus. The feasts of these three saints were made obligatory throughout the Eastern Empire by Leo VI the Wise. A common feast was later instituted in their honour on 30 January, called "the feast of the three Hierarchs". In the Menaea for that day it is related that the three Doctors appeared in a dream to John Mauropous, Bishop of Euchaita, and commanded him to institute a festival in their honour, in order to put a stop to the rivalries of their votaries and panegyrists. This was under Alexius Comnenus (1081–1118; see "Acta SS.", 14 June, under St. Basil, c. xxxviii). But sermons for the feast are attributed in manuscripts to Cosmas Vestitor, who flourished in the tenth century. The three are as common in Eastern art as the four are in Western. Durandus (i, 3) remarks that Doctors should be represented with books in their hands. In the West analogy led to the veneration of four Eastern Doctors, Saint Athanasius being added to the three hierarchs.