Si Mountain in the 24 Mountains of Feng Shui: Meaning and In-depth Interpretation

Where is the Si Mountain on the compass, and why is its position derivable rather than something to memorise?

The Si Mountain lies at roughly 142.5° to 157.5° on the compass ring, measured from the 0° mark at true North and turning clockwise. It is the 11th mountain of the 24. This position is not a number to be memorised, but something derived from two simple rules.

First, the 360° ring is divided evenly among 24 mountains, so each mountain is exactly 15° wide. Second, the central mountain of each of the eight directions carries the name of that direction. The Southeast direction is centred at 135°, and its middle mountain is Xun (Tốn), sitting at 135°, roughly 127.5° to 142.5°. Counting one more mountain of 15° clockwise from Xun brings us to Si, that is 142.5° to 157.5°. Counting one mountain back gives Chen (Thìn), that is 112.5° to 127.5°.

This counting method applies to all 24 mountains, so you only need to remember the order of the mountain names and the anchors of the four cardinal directions to reconstruct the entire degree ring. There is no need to consult a separate table for each mountain.

Which palace does the Si Mountain belong to in the Later Heaven bagua, and which three mountains share that palace?

The Si Mountain belongs to the Xun palace in the Later Heaven bagua. The three mountains sharing the Xun palace are Chen, Xun and Si. Of these, Chen is a Earthly Origin dragon, Xun is a Heavenly Origin dragon, and Si is a Human Origin dragon.

A distinction must be drawn between palace and direction, because this is where many articles lump the two together. The Southeast direction is one of the eight directions, each 45° wide. The Xun palace is one of the eight palaces of the Later Heaven bagua, and it too corresponds to 45° Southeast. But palace is a trigram concept, used to assign trigram names, palace five elements, and family relationships according to the Bagua; whereas direction is a purely positional concept. When we say "the Si Mountain belongs to the Xun palace", we are speaking of trigram governance. When we say "the Si Mountain belongs to the Southeast direction", we are speaking of position. The two statements do not replace each other.

One easily confused point: the four principal trigrams Kan, Li, Zhen and Dui have no mountain bearing their name, because those four positions are already occupied by the four branches Zi, Wu, Mao and You. Only the four trigrams Qian, Kun, Gen and Xun have mountains bearing the trigram name. So there is no such thing as "the Si Mountain belongs to another trigram" in any school using the 24 mountain system. Its palace on the Later Heaven compass is Xun, and Xun alone.

What is the five element of the Si Mountain, and why do two answers not contradict each other?

Considering the five element of the earthly branch that gives the mountain its name, Si belongs to the Fire element. This is the five element attached to the Si earthly branch under the 12 branch system, independent of its position on the compass.

Considering the five element of the palace containing it on the Later Heaven compass, Si sits within the Xun palace, and the Xun palace belongs to the Wood element.

These two statements do not contradict each other because they speak of two different things. One speaks of the element of the Si earthly branch. One speaks of the element of the Xun trigram. Both are correct within their own frame of reference, and no feng shui school uses a different system for dividing the 24 mountains. The problem only arises when a writer mixes the two statements without declaring the frame, leaving readers to think that "the Si Mountain belongs to Fire" and "the Si Mountain belongs to Wood" are a contradiction. In fact they are two layers of information stacked on the same mountain.

What is the Three Origins dragon of the Si Mountain, and what does that mean when choosing mountain and facing?

The Si Mountain is a Human Origin dragon. Among the three mountains sharing the Xun palace, Chen is an Earthly Origin dragon, Xun is a Heavenly Origin dragon, and Si is a Human Origin dragon. These three mountains cannot substitute for one another, even though they share a palace and a direction.

The reason lies in the fact that the Three Origins dragon classifies mountains by qi role, not by position. Earthly Origin dragon, Heavenly Origin dragon and Human Origin dragon have different combination rules when establishing the facing, when collecting the dragon, and when fixing the configuration. A house facing exactly Xun and a house facing exactly Si may both fall within 45° Southeast, yet belong to two different origin dragons, so the interpretation under the Three Origins system is not the same.

In other words, knowing "the house faces Southeast" is not enough to apply the Three Origins rules. You must know whether the specific mountain is Chen, Xun or Si, because each mountain corresponds to one origin dragon. This is why, in practice, people measure to the degree rather than only to the direction.

Where does Eight Mansions place the Si Mountain, and what are the limits of that placement?

According to Eight Mansions, the Si Mountain belongs to the Xun palace, and the Xun palace belongs to the East Four Mansions. Thus a house sitting Si and facing Hai, as well as a house sitting Hai and facing Si, are both classified in the East Four Mansions group.

The limits of this placement need to be stated clearly. Eight Mansions uses only the palace, not the mountain. It does not distinguish Chen, Xun and Si from one another, because all three belong to the Xun palace. So when an article says "the Si Mountain suits people of East Four destinies", that statement is correct but lacks resolution: the same statement is also true for the Chen Mountain and the Xun Mountain. To distinguish the three mountains within the same palace, you must move to another system, for example the Three Origins dragon or Xuan Kong Flying Stars.

In other words, Eight Mansions is a coarse interpretation layer by eight palaces, useful for matching destiny trigram with sitting and facing, but it cannot replace the interpretation layers that require 15° resolution.

How does Xuan Kong Flying Stars use the Si Mountain, and where do the schools disagree?

Xuan Kong Flying Stars uses the Si Mountain in two main places. First, the Si Mountain lies within the Xun palace, so when building the star chart, it is affected by the star flying into the Xun palace for the period under consideration. Second, when doing fine division, each 15° mountain is further subdivided to examine different star layers, and Si is one fine division unit within the 24 mountain layer.

Where the Xuan Kong branches disagree is in how yin and yang are assigned to each mountain. Some branches assign yin and yang by the mountain's root stem and branch, some assign by the mountain's position within the palace, and the results can diverge for certain mountains. This difference affects whether the star chart is calculated as forward flying or reverse flying, so two masters using two different branches can produce two different star charts from the same house.

One thing should be said plainly: this is a real disagreement between branches, not a mistake by the student. Readers should ask clearly which branch the interpreter is using before comparing results, rather than assuming there is only one correct assignment.

How does measurement error affect determining the Si Mountain?

Each mountain is only 15° wide, so a small deviation crosses into another mountain. The Si Mountain has two degree boundaries at its ends: 142.5° and 157.5°. The adjacent mountain below is Xun, roughly 127.5° to 142.5°. The adjacent mountain above is Wu (Ngọ), roughly 157.5° to 172.5°.

That means if the compass needle reads 142°, you are in Xun, not Si. If it reads 158°, you have already moved into Wu. A shift of just half a degree near the boundary changes the mountain, changes the origin dragon, and changes the entire interpretation under the Three Origins system. So when measuring, the compass should be placed at the centre of the house, kept away from metal, electronic devices and magnetic objects, and it is worth measuring several times at different moments to filter out interference.

One practical note: many modern houses have steel structures, refrigerators, speakers and phones within range. Environmental error can be larger than the error of the compass itself. In that case, the conclusion "this house is on the Si Mountain" should be recorded together with a level of certainty, rather than asserted as an absolute fact.

Which parts of this article are cultural knowledge rather than prediction?

The cultural knowledge parts include: the position of the Si Mountain at 142.5° to 157.5°, the fact that it is the 11th mountain, the fact that it belongs to the Xun palace and the Southeast direction, the fact that it is a Human Origin dragon, the fact that the Xun palace belongs to the East Four Mansions, and the fact that its opposite mountain is Hai. These are structural facts of the 24 mountain system, verifiable by counting and cross-checking against the compass.

The parts that are not prediction, but are often presented as prediction, include: every statement that the Si Mountain will bring wealth, health, reputation or good or bad marriage to the household head. Such statements belong to the interpretation layer, depending on the period, the star chart, the land configuration, the measurement, and the branch being used. They are not results derived from the name of the Si Mountain itself.

The correct way to read is to separate the two layers: the structural layer is fixed and learnable, the interpretation layer depends on the frame of reference and must have that frame declared. An article that mixes the two layers without naming the system leaves readers thinking there is a contradiction, or thinking feng shui is a rigid predictive system. Both are misunderstandings of the nature of the 24 mountains.

Quick reference table: the Si Mountain

Overview article on the topic: What is feng shui? Foundational principles and how to apply them