TL;DR: Thai Nguyên is the can chi of the conception month, taken from the month pillar by advancing the can one step and the branch three steps, so a Kỷ Tỵ month yields Canh Thân. Thai Tuc is taken from the day pillar by the same one-step can and three-step branch advance, but it is the least documented of the three. Menh Cung in Bát Tự is calculated from the month branch and hour branch, entirely different from the Menh Cung of Tử Vi, which is placed from the Dan palace by month and hour. All three belong to the outer methods, and today's Tử Bình community splits into two camps: some still use them, others have dropped them as confusing.
What Is Thai Nguyên and Where Does It Come From?
Thai Nguyên is the can chi of the conception month, the month in which the mother conceived the child, counted back roughly ten months before birth. The common method is to take the can chi of the birth month pillar and advance one step in the can and three steps in the branch. For example, someone born in a Kỷ Tỵ month has Thai Nguyên of Canh Thân: the can Ky advances one step to Canh, and the branch Ty advances three steps to Than. This is the method recorded in the classical texts of the Uyên Hải Tử Bình Toàn Tập group, in the section discussing the rules for raising Thai Nguyên.
A distinction is needed here: one thing is the can chi of Thai Nguyên, another is its nap am. The can chi gives the pair of characters, while the nap am gives the element, and most classical interpretations use the nap am to compare against the native destiny. The book Tử Vi Kinh Nghiem, lower volume, contains a full nap am table of the sixty hoa giap, from Giáp Ngọ Ất Mùi as Sa Trung Kim to Nhâm Tuất Quý Hợi as Đại Hải Thủy, and this table is used for both Tử Vi and Tứ Trụ when one needs to look up the element of a can chi pair.
The Thai Nguyên Formula in Practice
- Step one: identify the can chi of the month pillar by the solar terms calendar, not by the ordinary lunar calendar.
- Step two: advance the can one step along the cycle Giap, At, Binh, Dinh, Mau, Ky, Canh, Tan, Nham, Quy.
- Step three: advance the branch three steps along the cycle Ty, Suu, Dan, Mao, Thin, Ty, Ngo, Mui, Than, Dau, Tuat, Hoi.
- Step four: look up the nap am of the resulting can chi pair if you want to interpret by element.
What Is Thai Tuc and How Does It Differ from Thai Nguyên?
Thai Tuc is also an auxiliary pillar, but it is taken from the day pillar instead of the month pillar, then likewise advances the can one step and the branch three steps. In other words, Thai Nguyên describes the qi at the moment life took form, while Thai Tuc describes the qi at the person themselves, which is why it is taken from the day pillar, the pillar of the self. This is the fundamental difference between the two methods, and also why many books place Thai Tuc in the supporting group rather than the primary group.
Notably, external documentation on Thai Tuc is far thinner than on Thai Nguyên. In the sources gathered for this article, Thai Tuc appears almost only as a name accompanying Thai Nguyên in sections on raising rules, without a separate chapter explaining its use in detail. The presentation here therefore stops at the formula and its place in the structure, without going deep into specific interpretation, because going deeper would be speculation rather than cross-checked knowledge.
How Is Menh Cung in Bát Tự Calculated?
Menh Cung in Bát Tự is calculated from the month branch and hour branch, without using the can. The common method is to count from the palace of the birth month along a fixed cycle, then add the number of palaces according to the birth hour to arrive at the destiny palace. This palace carries an earthly branch, and from that branch one looks up the can to form a complete pillar when needed.
This point must be stated clearly because the books do not agree. Some books calculate Menh Cung by counting forward from Dan by month and then by hour, others count backward, others use a pre-made lookup table instead of a formula, and the results sometimes differ by one palace. So when reading a chart that records Menh Cung, one should ask which convention the chart maker used. This article does not choose one school as standard, only notes that this is an unresolved point and that learners need to know it to avoid confusion.
Distinguishing Bát Tự Menh Cung from Tử Vi Menh Cung
These two share a name but differ completely in placement, and this is the most common point of confusion.
| Criterion | Bát Tự Menh Cung | Tử Vi Menh Cung |
|---|---|---|
| Source data | Month branch and hour branch | Birth month and birth hour, placed from the Dan palace |
| Reference system | The twelve earthly branches by solar terms | The twelve palaces on the Tử Vi chart |
| Result | One earthly branch, with can looked up if needed | One of the twelve palaces of the chart, with its main star |
| Role | Auxiliary pillar supporting the Tứ Trụ | The governing palace of the whole chart |
The table shows that simply looking at the source data is enough to tell them apart. Bát Tự Menh Cung has no main star, no Tứ Hóa, no accompanying Than palace. Tử Vi Menh Cung has all of those, and according to Dau So Tinh Thanh volume 1, Menh Cung is also compared against Thái Tuế, the palace of the birth year branch, to increase accuracy when judging fortune and misfortune.
What Are These Three Methods Used For?
According to the classical texts cited in the Uyên Hải Tử Bình Toàn Tập group, Thai Nguyên is seen as the starting point of formation, representing the conception stage and the initial seed for the entire later destiny structure. A common interpretation is to compare the nap am of Thai Nguyên with the nap am of the native destiny or with the hour pillar: if they are mutually generating it is considered favorable, if mutually overcoming it is considered unfavorable. Some Bát Tự texts give an example of someone born in a Canh Tý month in a Tân Mùi year, with Thai Nguyên of Tân Mão; Tân Mão carries Wood nap am while Tân Mùi carries Earth nap am, and Wood overcomes Earth, so it is considered unfavorable for the native destiny.
Also according to that group of documents, Thai Nguyên meeting a noble is said to indicate hidden blessings, meeting punishment, clash, overcome or harm is said to indicate a harder life, meeting Loc is seen as being born into a well-off family, meeting Tuần Không is seen as lesser. These are traditional sayings, not certain conclusions about fate, and the old books themselves stress the need to cross-check with reality rather than speculate on paper alone.
Menh Cung in Bát Tự is usually used as an additional layer of comparison: seeing whether the destiny palace generates or overcomes the element of the day master, then weighing it further in interpretation. Some Bát Tự texts give an example with a Giap Wood day master, where a Menh Cung of Earth or Water is considered favorable, while if it overcomes or is clashed, other factors must be examined carefully before concluding.
Where Do the Schools Disagree?
The first point is whether to use them at all. On the Ly So Viet Nam forum, in a thread discussing the five pillars, many Tử Bình students argue that the four pillars alone are already complex enough, that adding Thai Nguyên makes it confusing, and they choose to drop both Thai Nguyên and Menh Cung. The opposite side cites a passage from Tử Vi Đẩu So saying that Tử Bình four-pillar practitioners who rarely use the conception pillar are making a great omission, and calls the structure of four pillars plus two characters of the conception pillar the five pillars, ten characters in total.
The second point is the Bát Tự Menh Cung formula. As said above, the books do not record it identically, some count forward, some backward, some use a lookup table. Learners should state clearly which convention they use rather than assume their book's method is the universal standard.
The third point is the degree of importance. One view holds that even if the birth date and hour meet many favorable factors, if Thai Nguyên is violated, those good factors are greatly reduced. Another view holds the opposite, seeing Thai Nguyên as only an auxiliary layer of information, not enough to overturn conclusions drawn from the four main pillars. Some Bát Tự texts, when discussing the role of Thai Nguyên, stress that in the end it must still be verified through real life, not left at theory.
Why Is Thai Tuc Rarely Mentioned in Practice?
Two reasons can be seen from the sources themselves. First, Thai Tuc has no separate interpretive system recorded as a chapter like Thai Nguyên, so learners find it hard to find a basis for using it. Second, once Thai Nguyên describes the qi at conception and the day pillar describes the self, Thai Tuc lies in between, overlapping in function with both sides, so it is easily seen as redundant. This is an observation based on the state of the documentation, not a claim that Thai Tuc is useless. Those who want to use Thai Tuc should consult the classical texts that have a section on raising Thai Tuc directly, because external sources on this topic are very thin.
What to Note When a Chart Includes These Three Items?
Technically, most current Tứ Trụ chart programs output only four pillars. To print Thai Nguyên, Thai Tuc and Menh Cung as well, three calculation functions must be added before outputting results, because the default calculation core does not include them. These three functions take the month pillar, the day pillar, and the pair of month branch and hour branch as input, then return the corresponding can chi according to the formulas given. When adding them, the Menh Cung convention being used should be stated clearly to avoid mismatch with other tools.
In interpretation, these three items should be seen as an auxiliary layer of information. They can help clarify context further, but should not replace the analysis of the five elements, the ten gods, and the luck cycles of the four main pillars. And as said, where the books differ, both directions should be presented rather than silently choosing one.
