Tianlun 天論 "Discourse on Heaven" is the title of several texts, one of which constitutes a chapter in the book Xunzi 荀子 (ch. 17), while another writing of that title was compiled by the Tang-period master Liu Yuxi 劉禹錫 (772-842).
In his chapter on Heaven, Xun Kuang 荀況 (Xunzi, 313-238 BCE) holds that natural phenomena like the movements of the celestial bodies, the four seasons, waxing and waning of Yin and Yang or the growth and vanishing of the ten thousand beings were results of "divinity" (shen 神), as a result of completion, but without having a shape – this is what is called tian 天 "Heaven", i.e. nature. The phenomena in relation to Heaven/the sky were completely regular and permanent (tian xing you chang 天行有常) and could not be influenced by moral or immoral behaviour of worldly rulers. This was because Heaven, earth, and man had different realms of their own. Heaven/the sky determined the four seasons, the earth the various resources, and man was master over the governance (of social affairs and of the natural environment). This means that Heaven, Earth and man are "able to form a triad" (nen san 能參) by division of labour.
Xun Kuang's view was thus opposed to the older Confucian master Meng Ke 孟軻 (Mengzi 孟子, 385-304 or 372-289 BCE), who believed that the comportment of a ruler had an influence on the Heavenly mandate bestowed upon him. Xunzi also contradicts the Daoist belief in the mysticism of nature.
In a kind of verse, the author asks "how can glorifying Heaven and contemplating it be as good as tending its creatures and regulating them?", and "How can obeying Heaven and singing it hymns of praise be better than regulating what Heaven has mandated and using it?" (Knoblock 1994: III, 20-21) He stresses that from the human viewpoint, it was far better to care for the governance of things and of society instead of asking for supernatural aspects. In Confucian terms, "the proper congruity between ruler and subject, the proper affection between father and son, and the proper separation of duties between husband and wife" (Knoblock 1994: III, 19) was the core issue, and not "monstrosities" (yao 祅) or "prodigies among the myriad things" (wanwu zhi guai 萬物之怪) as "cryptic messages from the Sky-God" (Knoblock 1994: III, 4, 19).
Liu Yuxi's text is a clarification of similar writing called Tianshuo 天說 "Explanations on Heaven", by which Liu Zongyuan 柳宗元 (773-819) criticized Han Yu's 韓愈 (768-824) belief (laid down in his essay Tianming lun 天命論) that Heaven was able to reward by merits and to punish by disaster. Liu Zongyuan held that Heaven and man did not have a relation towards each other (tian ren bu xiang yu 天人不相與). "The Dark (xuan 玄) one above" was called the sky/Heaven, the Yellow one below the earth, the mixture in-between "primordial breath" (yuanqi 元氣), and cold and heat were called Yin and Yang. In spite of their hugeness, Heaven and earth were not different from trees and bushes (da guoluo ye 大果蓏也 "[like] huge melons"), and were therefore not able to reward or punish humans for proper of indecent conduct. Merits and misfortune were products of man himself, and not of Heaven.
Liu Yuxi believed that Liu Zongyuan's text was not clear enough, and compiled his 3-chapters long treatise to "complete the discourse" (yi ji qi bian 以極其辨). He explained that Heaven and man worked in a kind of division of labour in two spheres, where each of the two parts had advantages. Heaven as the "actor" with the greatest shape (you xing zhi da zhe 有形之大者) worked in the sphere of nature, where man as the best of all moving beings (dongwu zhi you zhe 動物之尤者) was powerless, while humans were able to control and give shape to society, where Heaven was useless. Heaven was competent in the generating of the ten thousand beings (tian zhi suo neng zhe, sheng wanwu ye 天之所能者，生萬物也), while man was proficient in governing them (ren zhi suo neng zhe, zhi wanwu ye 人之所能者，治萬物也). The reason why Heaven is looking down upon the earth was because it is unable to govern the world; and the reason for man looking up to Heaven/the sky was because man is unable to predict by himself frost and heat.
In the two spheres, Heaven and man were thus able to vanquish each other (tian yu ren jiao xiang sheng 天與人交相勝) and could not substitute each other. What Heaven was able to do, could not be carried out by man (tian zhi neng, ren gu bu neng 天之能，人固不能也), and vice versa. Moral concepts, for instance, could not be applied to nature, while things like rules, standards, orders, rewards and punishment, right and wrong, were made by man, and not by Heaven.
There was no mutual influence (ganying 感應) between Heaven and man. This was not just objectively true, but also subjectively. In times of peace and under the rule of worthy men, the "standards were in grand operation" (fa da xing 法大行) or – in less favourable situations - "slightly slackening" (fa xiao chi 法小弛). Principles were then "clarified" (li ming 理明), and men did not believe in the powers of Heaven. Yet in times of political and social disturbance, when the "standards were slackening to a critical extent" (da fa chi 法大弛) and "the principles were obscured" (li mei 理昧) under the rule of ignorant tyrants, men were inclined to believe that Heaven had indeed influence on the world.
In a letter to Liu Yuxi (Da Liu Yuxi Tianlun shu 答劉禹錫天論書), Liu Zongyuan confirmed the soundness of this tenet and coined the formula that "Heaven does not influence man" (fei tian yu hu ren 非天預乎人).
The text of Liu Zongyuan's Tianshuo is included in the collected writings Hedong Xiansheng ji 河東先生集 and Liu Zongyuan ji 柳宗元集, that of Liu Yuxi's is found in the collected writings Liu Binke wenji 劉賓客文集.