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).
Western philosophy
Some problems discussed throughout this period are the relation of faith to reason, the existence and unity of God, the object of theology and metaphysics, the problems of knowledge, of universals, and of individuation. The prominent figure of this period was Augustine of Hippo (one of the most important Church Fathers in Western Christianity) who adopted Plato's thought and Christianized it in the 4th century and whose influence dominated medieval philosophy perhaps up to end of the era but was checked with the arrival of Aristotle's texts. Augustinianism was the preferred starting point for most philosophers (including Anselm of Canterbury, the father of scholasticism) up until the 13th century.