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
Western philosophers have often been divided into some major branches, or schools, based either on the questions typically addressed by people working in different parts of the field, or notions of ideological undercurrents. In the ancient world, the most influential division of the subject was the Stoics' division of philosophy into logic, ethics, and physics (conceived as the study of the nature of the world, and including both natural science and metaphysics). In contemporary philosophy, specialties within the field are more commonly divided into metaphysics, epistemology, ethics and aesthetics (the latter two of which together comprise axiology, or value theory). Logic is sometimes included as a main branch of philosophy, sometimes as a separate science philosophers happen to work on, and sometimes just as a characteristically philosophical method applying to all branches of philosophy.