  Recent Chinese studies generally place the commentary at the end of the Han period, although some Japanese scholars would date it to as late as the sixth century C.E. It is probably a second-century C.E. work and reflects the influence of the “Huang-Lao” (Yellow Emperor and Laozi) tradition, which flourished during the early Han dynasty (A. Chan 1991a). Called in early sources the Laozi zhangju, it belongs to the genre of zhangju literature, prevalent in Han times, which one may paraphrase as commentary by “chapter and sentence.” Its language is simple; its imagination, down-to-earth. The Heshanggong commentary shares with other Han works the cosmological belief that the universe is constituted by qi, the energy-like building blocks of life and the vital constituent of the cosmos, variously translated as “vital energy,” “life-force,” or “pneuma.” On this basis, interpreting the text in terms of yin-yang theory, the Laozi is seen to disclose not only the mystery of the origins of the universe but also the secret to personal well-being and sociopolitical order.