Tiandui "Responses on Heaven" is a philosophical essay written during the Tang period 唐 (618-907) by Liu Zongyuan 柳宗元 (773-819), as a response to the famous elegiac rhapsody Tianwen 天問 "Questions to Heaven" written during the late Warring States period 戰國 (5th cent.-221 BCE) by Qu Yuan 屈原 (c. 340-278 BCE).
Qu's poem consists of a series of more than 170 questions on nature, history, mythology and society without giving or expecting answers. Liu Zongyuan, living a thousand years later, answers each single question of Qu by providing reasons from the viewpoint of a mature and rather scientific Confucian state philosophy that re-emerged after centuries of Buddhist and Daoist dominance.
Liu holds that before the ten thousand beings took shape, in the very beginning of the cosmos, everything was concentrated in "originary breath" (yuanqi 元氣) as a kind or archaic matter. The quickness and slowness of the movement of this breath generated Yin and Yang, the coaction of which produced concrete objects like Heaven, Earth, and the ten thousand beings. The latter were formed spontaneously (ziran 自然), and not – like in Western thought – by intentional creation. Logically, there was no supernatural power like Heaven who could steer the fate of humans or the emergence and ruin of states. The destiny of humans and states was the result of human action alone. "Immortals" (xian 仙) did not exist. Even if the length of individual lives was different, every human being would die in the end (duan chang bu qi, xian ge you zhi 短長不齊,咸各有止).
Concerning the rich mythology in Qu Yuan's poem and the poet's questions on natural phenomena, Liu Zongyuan provided his own analysis and explanation.
The "answers" are written in four-syllable verses.
The text can be found in Liu's collected writings Liu Zongyuan ji 柳宗元集 or Hedong Xiansheng ji 河東先生集. An annotated edition of both texts, Tianwen Tiandui zhu 天問天對注, was as published in 1973 by the Shanghai Renmin Press 上海人民出版社.