There is a simple rule for using Na Jia aka Hidden stems in Bazi. Strictly speaking Na Jia is part of Yi Jing. Bridge between stems and trigrams are represented by this system. Na Jia is derived in Later Heaven sequence, using both Early and Later Heaven arrangement. Gender is represented in Early Heaven and we use yang polarity for male and yin polarity for female. With this tool we go through the Later Heaven stem sequence.
The first prenatal pair is Qian- Kun, so Kun, which is only one palace away from the exalted position, is the starting point. Yang Qian uses Jia and yin Kun uses Yi. We see that in the Later Heaven Qian- Kun order starts at Kun. Now it is the time to place the fire stems. The next trigram to be used is Dui. In Early Heaven Dui’s yin-yang opposite is Gen. Dui is yin and its stem is Ding, while Gen is male and its stem is Bing. Going in the clockwise direction of Later Heaven in search for the earth stems, the next trigram to be used is Kan. In Early Heaven Kan’s yin-yang opposite is Li. Kan is male and its stem is Wu, while Li is female and its stem is Ji. We continue to search the metal stems. The next trigram to be used is Zhen. In Early Heaven Zhen’s yin-yang opposite is Xun. Zhen is yang and its stem is Geng, while Xun is female and its stem is Xin. At this point all trigrams are used, but there are ten stems and only eight trigrams. So, we start the new circle and use the pair Qian- Kun again. Qian is male, yang and its secondary stem is Ren, while Kun is female and yin and its corresponding secondary stem is Gui.
This stem-trigram connection had a major role in developing Feng Shui formula for San He 24 Mountains. On the Earth level the polarity of the stems/mountains follows the functional polarity of the trigrams. Gui stem follows Kun and the function of Kun is yang in the most cases (its gender is yin, but Kun as exposed mother is quite yang). The youngest son (Gen) has a male gender, but functionally he is of yin polarity (young child, dependent on his mother). For other trigrams the gender polarity and functional polarity are the same. In this way the polarity for all the mountains with stems can be ascertained. Exception is the mountain of Geng, which has yin polarity in San He 24 Mountains. This is because the 24 mountains should have 12 yang mountains and 12 yin mountains. Without yin polarity of the Geng mountain there would be 13 yang and 11 yin mountains. So, one mountain has to be sacrificed and should use a yin polarity instead of the expected yang polarity. The Zhen-Xun pair is the last offspring pair in the circle, so Zhen’s stem Geng has the weakest position and follows the higher order, adopting the yin position. Well, this seems to be a little bit forced solution, slightly unnatural and this is perhaps the weakest part of San He Mountain formula.
However, in modern times Na Jia formula has another and well known variant. Because there is no Wu and Ji stem in the mountains, some people cast them out and use Gui for Kan and Ren for Li. The logic behind this is in pairing of the postnatal and prenatal Heaven position in search for the substitute stems. Li connects with Qian, and Qian brings in Ren. Kan connects with Kun, and Kun brings in Gui stem. This approach is theoretically weak: the order of five elements in the postnatal Heaven is broken. If the earth stems are cast out, fire should be used for Kan and Li, metal for Gen and Dui and water for Zhen and Xun. However, this is not the case. Early Heaven pattern is also broken. When the standard and older formula is examined in the context of the Early Heaven, the opposite sequence is gradual and symmetric: Qian-Kun (wood), Dui-Gen (fire), Li-Kan (earth), Zhen-Xun (metal)- Qian-Kun (water). If we introduce water in the pair Li-Kan, the order is corrupted. In the imaginary view Kan with Gui becomes too strong water, while Wu stem encircles water and Ji stems prevents spreading of the fire. The rule of water Na Jia stems in the pair of Li-Kan is not a valid formula!
However, the Na Jia formula can also be used as the secondary tool in Bazi. The key concept of Na Jia is the attachment of the Na Jia stem to the particular trigram. Na Jia stem is the ally and the follower of its trigram. When knowing that, one can connect the situations in the Bazi chart with the ally relationship between the particular trigram and its Na Jia.
For example: we have Bing and Ding stems and Wu branch in the pillars. The strong fire of Li is present in this chart. This fire will have a good relationship with Ji stem, because Ji stem follows the fire of Li. If the fire is too strong, Ji earth will probably be of little help in the reducing of its power. If you have Hai- Mao- Wei trinity with strong wood, this wood belongs to the trigram Zhen and Geng stem is friend of Zhen. So, if your wood is too strong, Geng metal will be probably of moderate help because it will be a little bit reluctant to cut the trees. Hai- Mao- Wei trinity, however, is less connected to Zhen then Jia, Mao and Yi group. So Geng will still be usable. If you have Chen and Si together and also some wood in the chart, this is the wood connection with Xun and Xun makes Xin metal for its ally. So, Xin metal will not be so usable to control the excess of the wood. If there is a lot of Wei branches in the pillars, this is strongly connected with Kun palace and the element of earth. If there is Yi stem in the pillars, this stem will be probably quite unusable for controlling the excess earth, because Yi stem is a loyal friend of the Kun palace.
All these can be used ONLY at the secondary level of analysis. It can be used for fine tuning. Bear in mind:
- Mountains of particular trigram are more connected to this trigram than San he and San hui (those with the central branch belonging to the trigram). San he and San hui are more dispersed and also carry other influences. Mountains activate stronger alliance between Na Jia and its trigram and San he/ San hui can activate only a weaker alliance.
- If trigram’s mountains are not found in a cluster, Na Jia effect will also be weaker.
- San he must include central branch in this approach because this central branch is a part of trigram’s mountains. So, if you have only Hai and Wei and no Mao in the chart, there is almost no activation of trigram Zhen.
- Chen – Si, Wei – Shen, Xu- Hai and Chou – Yin mountains activate only weaker alliance between Na Jia and the trigram, because the central trigram can’t be found in Bazi. These branches MUST be found together in the pillars (neighbors).
- If the stem of Na Jia is quite strong in the chart and has the controling or weakening relationsip with the useful element, for example, there will not be strong Na Jia alliance and the stem will still attack the controlled element (controling relationship like fire controling metal, etc.) or drain the element (like earth drains fire, etc)… For example: if one has Jia, Mao and Yi in the pillars, trigram Zhen is activated and geng metal serves as its Na Jia. But if the same pillars have strong metal presence in the chart like Geng Shen pillar with the support from the season, Geng metal will be just a little bit less sharp and dominant and it will still attack the Jia wood.