TL;DR: Wang Chong (27-97 CE) criticized day selection arts in the Lunheng: he held that the good or ill outcome of an action is decided not by the date but by ming (fate) and timing. The chapters Jiri, Biansui, Nansui and Jieshu refute the day-taboo books, the belief that failing to choose a day brings spirit-caused misfortune, the moving-house rules that avoid Tai Sui, and the art of judging houses by surname. He pointed out that people often choose a day and meet disaster, or break a taboo and gain fortune. It is one of the earliest surviving critiques of day selection (trạch cát) arts.
Wang Chong and the Lunheng: the context of a dissenting voice
Wang Chong (王充, 27-97 CE) lived under the Eastern Han, served as a minor official and then returned home to write. He left the Lunheng (論衡), a collection of essays discussing ming, qi, ghosts and spirits, customs, and the divination arts of his time. Beside discussing ming, the Lunheng also contains a less often mentioned part: criticism of the custom of selecting days, of taboos, and of belief in ghosts and spirits.
The chapters directly related to this topic sit in juan 23 to 25 of the Lunheng: Sihui (四諱, the four great taboos of popular custom), Jiri (譏日, criticizing the day-taboo books), Bushi (卜筮, on turtle-shell and yarrow divination), Biansui (辨祟, sorting out the belief in spirit-caused misfortune), Nansui (難歲, questioning the Tai Sui taboo) and Jieshu (詰術, questioning the art of judging houses by surname). This is one of the earliest surviving texts criticizing day selection (trạch cát) arts.
Jiri: how did Wang Chong criticize the custom of avoiding days?
The chapter Jiri opens by observing that people, already believing in taboos of years and months, also believe in taboos of days: when a great affair ends in disaster they say a year or month was offended, when a small one does they say a forbidden day was not avoided (世俗既信歲時，而又信日)[1]. He takes the best-known day-taboo books and examines each in turn: the burial calendar (葬歷), the sacrifice calendar that avoids the xueji and yuesha days, the hair-washing book (沐書), the book on cutting clothes, and the builders' book for choosing a day to raise a house.
His method is to compare acts of the same kind. The hair-washing book says: "Wash on a Tý day and people will love you; wash on a Mão day and your hair turns white" (子日沐，令人愛之。卯日沐，令人白頭). Wang Chong asks back: would someone as ugly as Momu be loved for washing on a Tý day, would a girl of fifteen go grey for washing on a Mão day; washing the hands, the feet and the body removes dirt just as washing the hair does, yet no one chooses a day for them. Against the sacrifice calendar he points out that butchers everywhere kill thousands of animals a day without choosing lucky or unlucky days, and those who die early are not necessarily butchers (海內屠肆，六畜死者日數千頭，不擇吉凶，早死者未必屠工也).
The chapter also mentions the custom of not starting to learn writing on a Bính day, because Cangjie was said to have died on a Bính day, and the rite of not playing music on Tý and Mão days, because the Yin and Xia dynasties fell on such days. Wang Chong holds that these avoidances come from grief for the ancients and "do not necessarily bring calamity" (殆有所諱，未必有凶禍也). He concludes that the law of the true king decides affairs by whether the human matter is right or not, and does not ask whether the day is lucky (王法舉事以人事之可否，不問日之吉凶).
Wang Chong's argument rests on two pillars. The first is ming: the chapter Minglu says "there is a ming of life and death, long life and early death, and also a ming of nobility and lowliness, poverty and wealth" (有死生壽夭之命，亦有貴賤貧富之命)[1]. The second is timing: the chapter Biansui says "fortune and misfortune arrive with the times; life and death arrive with ming" (禍福之至，時也；死生之到，命也).
Biansui: how did Wang Chong refute the belief that ghosts and spirits cause harm?
The chapter Biansui (辨祟) sets out the popular view of the time: illness, death and punishment all come from breaking ground, moving house, sacrificing, burying, travelling, taking office or marrying without choosing a lucky day and without avoiding the year and month, thereby offending ghosts and spirits[1]. Wang Chong calls this idle talk (如實論之，乃妄言也) and shows how the belief sustains itself: good outcomes are credited to the chosen day, bad ones blamed on a broken taboo, while "often people choose a day and meet disaster, or break a taboo and gain fortune" (多或擇日而得禍，觸忌而獲福).
He points to cases involving many people at once: the four hundred thousand Zhao soldiers buried by Qin at Changping all died together, yet when they left home they had not necessarily failed to choose an hour; Jie and Zhou did wrong and did not die early, kings You and Li acted lawlessly and did not die young. On illness he writes: "Human illness rarely does not come from wind, damp, food and drink" (人之疾病，希有不由風濕與飲食者), yet people lie in wind and damp and then take money to ask which spirit is to blame.
The chapter ends with a test: let ten people live in one house, choose lucky days for every sacrifice and marriage, and break no taboo all year round; after a hundred years, will any of them not have died? His conclusion is that life and death have their own ming and are not caused by offending the year and month (人之死生竟自有命，非觸歲月之所致).
Confucius said "respect ghosts and spirits but keep them at a distance" (kính quỷ thần nhi viễn chi). Wang Chong goes further: in the chapter Jiri he writes "the hundred sacrifices have no ghosts, the dead have no awareness" (百祀無鬼，死人無知), and holds that sacrifice serves to repay merit and show that kindness is not forgotten.
Nansui: how did Wang Chong question the custom of avoiding Tai Sui?
The chapter Nansui (難歲) targets the Yixi fa (移徙法), the rules for moving house, which say: "Moving toward Tai Sui is unlucky; moving with one's back to Tai Sui is also unlucky" (徙抵太歲凶，負太歲亦凶)[1]. Under these rules, moving toward Tai Sui is called Suixia and moving away from it is called Suipo; in a year when Tai Sui stands at Tý, no one may move house along the north-south line, and building and marriage must avoid it too. Tai Sui here is the spirit of the year, which practitioners believe stands at one earthly-branch position each year.
Wang Chong presses the point: if Tai Sui hated people moving house, everyone who moved would meet disaster; if it hated people bumping into it, everyone walking the roads north or south would suffer (則道上之人南北行者皆有殃). He asks further: a year is only a name for accumulated days and months, so if the year has a spirit, do the day, the month and the hour have spirits too (歲而有神，日月時亦復有神乎)? He concludes that people cannot live without moving, and when practitioners see someone die they blame an earlier move, which is why the talk of Tai Sui has been passed down without end (工伎之人，見今人之死，則歸禍於往時之徙).
Table: The chapters criticizing day selection in the Lunheng
| Chapter | Chinese name | Object of criticism | Main argument |
|---|---|---|---|
| Jiri | 譏日 | Burial calendar, sacrifice calendar, hair-washing book, clothes-cutting book, house-building day book | Among acts of the same kind only one must wait for a day; the true king judges whether the matter is right, not the day |
| Biansui | 辨祟 | The belief that failing to choose days or offending the year brings spirit-caused misfortune | People often choose a day and meet disaster, or break a taboo and gain fortune; life and death follow ming |
| Nansui | 難歲 | Moving-house rules that avoid Tai Sui and Suipo | People walking north or south on the roads are not harmed; if the year has a spirit, so must the day, month and hour |
| Jieshu | 詰術 | Judging houses by the five tones of the surname (圖宅術) | A house is to a person what a nest or den is to birds and beasts; nests and dens have no Giáp Ất order, nor do houses |
Did Wang Chong completely deny day selection arts?
Not entirely. Wang Chong keeps the day rules found in the ritual classics: he cites the Book of Rites, "inner affairs use soft days, outer affairs use hard days" (內事以柔日，外事以剛日), and reads it as a way of separating inner from outer affairs, not of judging fortune (剛柔以慎內外，不論吉凶以為禍福)[1]. In the chapter Biansui he writes that the sage first settles an affair by what is right, and only then consults divination to show that he does not decide alone (聖人舉事，先定於義。義已定立，決以卜筮，示不專己). What he denies is the view that dates decide fortune, and that breaking a taboo will be punished by ghosts and spirits.
This is an important point when reading the Lunheng today: Wang Chong is not a modern materialist. He still believes in ming, but his ming is the qi received at birth, not the intervention of deities according to a calendar.
How did the Lunheng influence the Vietnamese day selection tradition?
The sources of this article do not show that the Lunheng changed the custom of choosing days in Vietnam. Hiệp kỷ biện phương thư, a day selection manual compiled under the Qing, translated into Vietnamese by Vũ Hoàng and Lân Bình (Mũi Cà Mau Publishing House, 1998), opens its section on rules with the line that the spirits and influences used in choosing days were handled in antiquity by the Kiến Trừ, Kham dư and Tùng thần schools[3]. Under Tai Sui, the same manual quotes the very line of the Yixi fa that the Lunheng recorded in order to refute it (徙抵太歲凶，負太歲亦凶), as evidence for the names Suixia and Suipo, and still treats Suipo as the most baleful spirit (歲破為最凶之神).
Trần Trọng Kim in Nho giáo (1930) introduced Wang Chong to Vietnamese readers through his theory of ming and encounter, quoting the Lunheng: "Advancement lies in meeting the right occasion, retreat in not meeting it" (進在遇，退在不遇)[2]. He also remarked that men such as Dong Zhongshu, Yang Xiong and Wang Chong put forward their own insights, but their influence "could not change the current of conventional learning".
How can we read the Lunheng today for preservation and counter-argument?
Today, many Vietnamese still consult good and bad days before great matters: marriage, breaking ground, opening a business, traveling. This is part of traditional culture, reflecting the wish for peace of mind and respect for natural rhythms. Reading Wang Chong does not mean completely rejecting tradition, but understanding that this tradition was questioned as early as the Eastern Han, and that choosing days can be useful as a psychological ritual, but should not be given the power to decide fate.
Nhật Nguyệt's suggestion: keep the ritual as part of culture, but do not let it cause excessive anxiety or useless expense.
