Many people study the traditional chinese metaphysics, eg flyingstar fengshui, four-pillars bazi, chinese divination, etc... by hard memorising the theory and formula, so as the same for later application. In fact, there is no harm going by this way, as usually this is the way to begin with and go through, prior to move on to next higher level. No matter for feng shui, bazi and chinese divinations, the need of finding out the useful god from it as the key to open the door for fortune telling, luck forecasting, plays a very important step in the whole TCM methodology. Therefore, able to derive the "useful god" and into the right understanding on it for appropriate use, would drive the higher degree of accuracy in the foretune telling and luck forecasting. Apart from the wriiten methods passing down from the ancient time to now for such, the "gan ying" human mind interaction with what he see, hear and feel to determine on selecting the "useful god" and also the intepretation for application, is very essential and major portion of it. This would also show the diferences between a super and powerful TCM master and an ordinary TCM follower or practioner. How the "gan ying" links to the processes of the TCM in application?

In the ancient china song dynasty, great TCM master Shao Yong had written in his book 《皇極經世觀物外篇 Huang Ji Jing Shi Guan Wu Wai Pian, advocating the the study and reseach of "Yi Xue" cannot go without anyone of the four fundamental components, numerology, imagology (look alike imaging, picture), words (description, meaning) and conceptual view derived.
宋代 邵雍在 其驚世著作 《皇極經世觀物外篇》   主張研究易學 "數象言意" 四者不可缺一。 

Numerology is built on (derived from) the objects and components in the image (picture). Therefore by going through the structural numbers derived could help to compose the image in whole. By looking at the image, would lead to decribing it in words. Therefore, by going through the word description, could help to compose the conceptual view for it. Image (picture) is built from shape and form, numbers are established for quantity and quality, naming and terms are builts from word description, conceptual view and idea are built for application. These four components are closely interacted with and linked to each others so cannot live with anyone of them.
數為象設, 循數觀象, 觀象玩辭, 以辭會意。 象起於形，數起於質，名起於言，意起於用。“象、數、言、意四者，缺一不可”。

Image (picture ) and number, such as, trigram picture, trigram number, yi-gua picture, yi-number. Words into conceptual view and idea are meant from the reflection (impression, interaction ) from image and number. Master Shao Yong said, "Conception gives word description, word description gives image, image gives numbers. Therefore, when the numbers are established, the image must exist already. Once the image is there, the word description is used. When word description is used, the conceptual view and idea come out."
象數包括卦象、卦數、易圖、易數﹔言意就是象數之中所反映出的義理。 邵雍説：有意必有言，有言必有象，有象必有數。數立則象生，象生則言用，言用則意顯。

He said, " yi (yi-jing, yi-xue) has image of concept, image of words, image of numbers". From this, it can be seen that out of the above-mentioned four components the image is considered as much crucial among others. As we know, the yi-diagram is in principle composed from several trigrams in special orders and forms, and the "Early-heavenly trigram diagram" of Master Shao Yong was invented from arrangement of the 64 trigrams in specific order and form for presenting the movement of yin yang at growth and decline as per the yin yang lifecycle.
又説, 《易》有“意象”、“言象”、“數象”，則見其於“象數言意”四者之中，特別注重“象”。所謂 “易圖” 主要是指用卦象構成的圖而言，而邵雍的《先天圖》就是以卦象構成的一幅“寓卦之生變與陰陽消長之數” 的易圖。 

Number (numerology) is establised as per the yi xue, yin yang principle theory for Heaven and Earth, when the TCM is no long based on and connect to this principles, such foretune telling and luck forecasting methods are then classified as magical or religious power away from the yi-xue based metaphysics stream and lineage. 天下之數出乎理，違乎理則入於術。... 

Therefore, the four components cannot be lack of one in the yi-jing yi xue foundationed Traditional Chinese Metaphysics.
"數象言意" 四者不可缺一, 這可就是中國術數學的基本法吧!      
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Think about, when you are onsite conducting a feng shui survey check for yin or yang mansion, what do you see, what do you feel, what inspires and interact your mind deriving into an image, numbers, concepts representing the yi yang and five-elements engery, and what and where is the "useful god" energy to address. Similar ways when reading a person's bazi, or in a chinese divination fortune telling and luck forecasting.

Dont foreget, what you see and hear and feel, may be different from others. There is a fengshui jargon, the mountain you see in eyes may not be the mountain, the water you see in eyes may not be the water.