Wulilun 物理論 "On the order of things" was an essay on metaphysics written by the Three Empires-period 三國 (220-280) philosopher Yang Quan 楊泉 (dates unknown, died after 280 CE), courtesy name Deyuan 德淵. The essay was originally 16-juan long, but only fragments are preserved. They were collected by the Qing-period 清 (1644-1911) scholar and publisher Sun Xingyan 孫星衍 (1753-1818) and can be found in his series Pingjinguan congshu 平津館叢書.
Yang Quan hailed from the commandery of Guiji 會稽 (today's Shaoxing 紹興, Zhejiang), according to other sources from the princedom of Liang 梁國 (close to modern Shangqiu 商丘, Henan), but was never able to gain access to an official position. Instead, he engaged in philosophical discussions and research on astronomy, geography, the calendar, economy, agriculture and medicine. Of his writings, fragments are preserved of a book called Taiyuanjing 太元經 or Taixuanjing 太玄經 (an imitation of Yang Xiong's 揚雄 Taixuanjing 太玄經, original 14 juan, fragments collected by Ma Guohan 馬國翰 in his Yuhanshanfang jiyi shu 玉函山房輯佚書), and of his 2 juan of collected writings (wenji 文集), (parts of) the rhapsodies Wuhu fu 五湖賦, Zanshan fu 贊善賦, Zhiji fu 織機賦, Canfu 蠶賦, Yangxing fu 養性賦 and Caoshu fu 草書賦 have survived, as well as a piece called Qingci 請辭 (see Yan Kejun's 嚴可均 collection Quan Sanguo wen 全三國文).
In his arguments Yang Quan often referred to older or contemporary writers, in particular from the book Fuzi 傅子. For this reason some editions mixed up these two books, for instance, the encyclopaedic collection Yilin 意林 from the Tang period 唐 (618-907). The Qing-period editor Ye Dehui 葉德輝 (1864-1927) carefully separated the two texts from each other. The surviving fragments of the Wulilun are also found in the series Longxijingshe congshu 龍溪精舍叢書, Hanxuetang congshu 漢學堂叢書 and Huangshi yishu kao 黃氏逸書考.
The book describes Yang's concept of nature and touches many issues in fieldwork and the trades. He defines the slow process of ploughing and sowing as the root of agriculture, and the hurried process of harvest as its ends. He maintains that the character of the soil was an important precondition of cultivation, yet scholars did usually not pay attention to the many types of soil. Yang establishes half a dozen of soil categories with designations similar to concepts in geomancy (fengshui): guifeng 龜龍, qifeng 麟風, gongnu 弓弩, doushi 鬥石, shuzhang 舒張, bisai 閉塞, yinzhen 隱真 (good), jingmao 景卵 (bad), haoying 膏英 (good) and jijiao 塉角 (bad). The way of cultivating of the soil was thus to be adapted to its quality, in order to achieve the best results, with high stalks, long ears and large grains. Yet the seasons would also influence the readiness of the soil to accept seeds.
Yang also shortly describes water wheels (fanche 翻車) used to irrigate fields and orchards. The use of them allowed even children to bring into effect the work of a hundred persons. He acknowledged that the construction of boats (goulu 䑦𦪇) was the masterly business of craftsmen. In relation to the wider nature, Yang compared the spider webs or beehives with the miraculous products of craftsmen. The conception for the artwork, like round or square, came out of the master's heart, and the skill out if his hands. Without refined skills and excellent ideas, no such work would be possible. Yang also mentions a vehicle with a compass (zhinanche 指南車) or the famous sword of Ruan Shi 阮師, and some aspects of medicine.
Water was the element which "established" (li 立) Heaven and Earth, while "breath" (qi 氣) completed (cheng 成) them. "Breath" could be divided into pure and turbid, and in fact, water was also a kind of breath, but "lighter than the breath of earth and stone". From this assumption it can be seen that qi was rather to be perceived a kind of dense or less dense matter. Each object was an accumulation of breath/matter (qi ji 氣積), or a transformation of breath into a vessel (qi taohua 氣陶化). The density of this accumulation was defined by the dispersion (boliu 播流) of Yin and Yang 陰陽. The earth therefore had a shape, but Heaven, as an expression of the revolving "originary breath" (yuanqi 元氣) had no physical structure (tian wu ti 天無體) and just possessed "brightness" (haoran 皓然) as a feature. The universe itself was a limitless "expanded night" (xuanye 宣夜, a concept of Qie Meng 郄萌). Yet Yang also maintained that objects or creatures came into being by receiving "breath" (wu shou qi er han sheng 物受氣而含生).
Yang rejected the belief that living beings were in possession of a soul, just like an extinguished fire would not leave back any glow. Man lived because he had obtained breath, and would die if his essence was consumed (ren han qi er sheng, jing jin er si 人含氣而生，精盡而死). Yang thus stands in the tradition of the Later Han period philosophers Huan Tan 桓譚 (23 BCE-56 CE) and Wang Chong 王充 (23 BCE-56 CE) and stood in opposition to the popular religion of Buddhism that assumes the existence of extra-bodily factors. Yang Quan like rejected the assumption that all objects had come out of nothing (xuwu 虛無, wu 無) which was part of the Daoist conception of the universe and was vividly discussed by the "School of the Mystery" (xuanxue 玄學) during the third century. Yang directly criticized the "pure talks" (qingtan 清談) of his contemporaries and maintained that they would dulge into discussions about the single hair of a tiger, but not have an idea about the pattern of its fur. Their disputes were just the noise of croaking frogs or chirring cicadas.
Of Yang's theories on human nature, not much is known. He criticized that there were persons with the appearance of a saint (Yao 堯) and the behaviour of a tyrant (Jie 桀). In the political sphere, Yang seems to have inclined towards a less rigorous government which would prohibit the influential clans or court cliques to oppose the imperial power.