TL;DR: Tam Hợp is a group of three zodiac animals four years apart that combine into the frame of one element (Thân, Tý, Thìn into Water); Lục Hợp is a set of six pairs of Địa Chi matched by yin and yang, for example Tý with Sửu and Dần with Hợi. Folk custom often uses these two relations to read the ages of parents and children, but that is an interpretation within a divination system, not a verified law of nature. The books differ in whether they also count Tương Xung, Tương Hại and the Thiên Can, and even in whether the pair Ngọ and Mùi transforms into a new element or only combines.
What are Tam Hợp and Lục Hợp in the 12 zodiac animals?
Tam Hợp groups the 12 Địa Chi into four sets of three, each set made of three zodiac animals four years apart that combine into the frame (cục) of one element. Lục Hợp is six pairs of Địa Chi matched by a yin and yang pairing. Both are relations among the branches, used by divination books as classification tools, not a law about family life.
The naming and the grouping of Tam Hợp are recorded in introductory divination books, in which the 12 Địa Chi are ordered Tý, Sửu, Dần, Mão, Thìn, Tị, Ngọ, Mùi, Thân, Dậu, Tuất, Hợi, and each branch carries its own element and yin or yang quality[1]. From that basis the groups Tam Hợp, Lục Hợp, Tương Xung and Tương Hại are derived.
Why do the 12 zodiac animals have Tam Hợp and Lục Hợp?
The mechanism rests on two axes: the order of the 12 branches and the five elements. A Tam Hợp group is three branches evenly spaced around the circle of 12, making an equilateral triangle on the Địa Chi circle. Each branch has its own element, but the books say the three together transform into one element: Thân (Metal), Tý (Water) and Thìn (Earth) combine into Water. Lục Hợp forms on a different axis: pairing a yang branch with a yin branch by the convention of the books, and each pair also transforms into an element.
The 12 branches are divided into yin and yang by odd and even position: Tý, Dần, Thìn, Ngọ, Thân, Tuất are yang; Sửu, Mão, Tị, Mùi, Dậu, Hợi are yin. As for elements, Dần and Mão belong to Wood, Tị and Ngọ to Fire, Thân and Dậu to Metal, Tý and Hợi to Water, Thìn, Tuất, Sửu and Mùi to Earth[1]. These are the elements of the single branches; the element a Tam Hợp group transforms into is a separate matter, shown in the table below.
Table of Tam Hợp and Lục Hợp for the 12 zodiac animals
The table below is a quick reference. The "Element" column is the element of each single branch; the "Tam Hợp group" column gives the group of three with the element the group transforms into; the "Lục Hợp pair" column gives the paired branch by the convention of the books.
| Zodiac animal | Địa Chi | Element | Tam Hợp group (transforms into) | Lục Hợp pair |
|---|---|---|---|---|
| Tý | Tý | Water | Thân, Tý, Thìn (into Water) | Sửu |
| Sửu | Sửu | Earth | Tị, Dậu, Sửu (into Metal) | Tý |
| Dần | Dần | Wood | Dần, Ngọ, Tuất (into Fire) | Hợi |
| Mão | Mão | Wood | Hợi, Mão, Mùi (into Wood) | Tuất |
| Thìn | Thìn | Earth | Thân, Tý, Thìn (into Water) | Dậu |
| Tị | Tị | Fire | Tị, Dậu, Sửu (into Metal) | Thân |
| Ngọ | Ngọ | Fire | Dần, Ngọ, Tuất (into Fire) | Mùi |
| Mùi | Mùi | Earth | Hợi, Mão, Mùi (into Wood) | Ngọ |
| Thân | Thân | Metal | Thân, Tý, Thìn (into Water) | Tị |
| Dậu | Dậu | Metal | Tị, Dậu, Sửu (into Metal) | Thìn |
| Tuất | Tuất | Earth | Dần, Ngọ, Tuất (into Fire) | Mão |
| Hợi | Hợi | Water | Hợi, Mão, Mùi (into Wood) | Dần |
The element of each branch, the Tam Hợp groups with the element they transform into, and the Lục Hợp pairs in this table follow the lists of the cited book[1]. Note that the table is only a reference tool, not a claim that a person born in the year of the Tý gets along or clashes with a person born in the year of the Sửu in real life.
How does folk custom read the ages of parents and children?
In folk custom, people often take the lunar ages of father, mother and child and compare them by the two relations Tam Hợp and Lục Hợp to guess the level of harmony. The common method is: if the child's age falls in a Tam Hợp group with the father's or mother's age, it is considered favorable; if it is a Lục Hợp pair, it is considered very compatible; if it falls into Tương Xung or Tương Hại, it is considered a clash.
This way of reading is usually passed down by word of mouth from experience, with no original text setting a unified rule. People often cite examples: father born in the year of the Dần, child in the year of the Ngọ or Tuất, belongs to the Tam Hợp group Dần, Ngọ, Tuất; mother born in the year of the Tý, child in the year of the Sửu, belongs to the Lục Hợp pair Tý and Sửu. Conversely, Tý with Ngọ is Tương Xung, Dần with Thân is Tương Xung, so they are considered unfavorable.
Ages here follow the lunar year, which changes at Tết, not on 1 January. Tết of Đinh Mùi falls on 6 February 2027, so a child born on 5 February 2027 is still a Bính Ngọ child for folk age reading and Tử Vi. Bát Tự changes the year at Lập Xuân (8:42 on 4 February 2027, Vietnam time), so the same child has the year pillar Đinh Mùi. Each year can be checked against the ages of both father and mother with the Child's birth year by parents' ages tool.
In their definitions, divination books only state which branches combine or clash; they say nothing about affection between parents and children. The folk extension from branch relations to human relations is an added interpretation, not part of the original definition.
Where do the books differ?
The first difference lies in the definition itself. Tử vi đẩu số tinh thành lists six Lục Hợp pairs, each transforming into an element: Tý and Sửu into Earth, Dần and Hợi into Wood, Mão and Tuất into Fire, Thìn and Dậu into Metal, Tị and Thân into Water, Ngọ and Mùi into Earth. The book notes a view that Ngọ and Mùi only combine without transforming, and the compiler sides with Ngọ and Mùi becoming Earth because Ngọ Fire generates Mùi Earth[1].
The second difference is whether additional relations are counted. Some books consider Tương Xung, Tương Hại and Tương Phá alongside Tam Hợp and Lục Hợp, so the same pair of ages can be considered both compatible and clashing depending on the book: Dần and Hợi are a Lục Hợp pair but also sit in the same Tứ Hành Xung group of Dần, Thân, Tị, Hợi. The third difference is whether the Thiên Can of the birth year is also considered or only the Địa Chi. Books that consider only the branch are simpler, but they leave out the can, which has its own five transforming pairs: Giáp and Kỷ into Earth, Ất and Canh into Metal, Bính and Tân into Water, Đinh and Nhâm into Wood, Mậu and Quý into Fire[2].
Should Tam Hợp and Lục Hợp decide family matters?
Tam Hợp and Lục Hợp should not be used as the sole basis for judging the relation between parents and children, and even less for deciding important matters such as having a child, adopting a child or separating. This is a classification tool of a divination system, not a scientific conclusion about psychology or heredity.
Folk belief still keeps the reading of a family's ages as a cultural practice, especially when choosing a birth year or discussing compatibility. Its value lies in creating a shared language to talk about harmony, not in any predictive ability.
No research has shown that a Tam Hợp or Lục Hợp relation between the ages of parents and children has a causal link with family harmony or health. Divination documents record only conventions, without empirical evidence.
Nhật Nguyệt's suggestion when reading a family's ages
If you want to use Tam Hợp and Lục Hợp as a cultural conversation, treat it as one reference layer, on a par with understanding each person's character, circumstances and actual behavior. State clearly which convention you follow, for example whether you consider only the Địa Chi of the birth year or also the can, so that different people consulting different books do not end up with different results.
When a pair of ages is considered clashing by one book but compatible by another, present both rather than choosing one side. The most honest way is to say clearly that this is folk belief, not something verified, and not to use it to assign a fixed character to a child or an adult.
