"Jang" means "to store, keep, or hide", "Bu" means "to keep just for a limited period of time, like a station". The concept of this "Jang" and "Bu" is the foundation for understanding the physiology described in Korean Medicine. The five Jang organs refer to the Liver, Heart, Spleen, Lung, and the Kidney. The five Jang organs "jang(store)" spirit in it thus the name. The six Bu organs refer to the Gall Bladder, Pericardium, Stomach, Large Intestine, and the Urinary Bladder. The capitalization of the organs that are also dealt with in Western medicine is to show that although each capitalized organ is similar to the Western medical counterpart, there exists some amount of differences in the functions they actually exert throughout the body.

The relationship among the Five Jang organs is the relationship among the Five phases. The inter-promoting relationship among the Five phases can be understood easily. "Water generating Wood" refers to a bud sprouting out of a seed, while "Wood generating Fire" refers to the growing bud, which eventually blossoms to hybridize, the "Fire generating Soil". When it bears fruits and gets rid of all the moisture to gather only the Yang-Ki, it has reached the stage of "Soil generating Metal". When this Yang-Ki is well kept within the fruit, it is called "Metal generating Water".

When it comes to inter-controlling relationships, it becomes a little more complicated. Let's first take "Wood controlling Soil" into consideration. The activity of Wood is getting the reserved Yang Ki in the Water. Why should it restrict Soil? Soil, located consecutive to the Fire, is in charge of controlling the infinitely extending force. And because Soil already has in itself some Dampness, it can said to be Eum. However, although it is Eum, it is different from Water, in that it contains Dampness, which has Eum within the Yang. This enables Soil to communicate with the Fire. Soil is where the Yang and the Eum meet together, the combining of the Heavenly Ki and the earthly Ki. Thus, Wood breaks this bond to sprout buds, while the Soil combines again the separated Heavenly Ki and the earthly Ki.

Since there are according roles for each phases, why does the Wood need to control the Soil? The environment around us is not that simple as it appears to be. Wood Ki is exerted in the spring to help sprouting, but without the help of Soil on the moment of hybridization, it wouldn't be able to sprout. The function of Soil is not only existent in putting the Eum and the Yang together. Wood gradually pulls Yang Ki from Water, while the Soil destructs the Water to obtain the Yang Ki. So if it were not for Wood‘s control, the Water might as well be destroyed down to decaying. Soil always functions to put the Eum and Yang together, and Wood has to get over this to generate Fire.

Next, let's take a look into "Fire controlling Metal". In the transformation of Eum and Yang, the two changes into each other once they reach the climax. How come the Fire(which is Yang) control the Metal(which is Eum)? Water is the basis of inborn constitution, and the Soil, the basis of acquired constitution. The transformation from Fire to Metal, that is from Yang to Eum is the world of SaSang, which is the world of objectivity and lifelessness. When it comes to the world of life(the world of Five phases), it always passes through Soil, the step of Eum-Yang combination before moving from Eum to Yang. This step in between is the foundation for prolonging life. Fire has to control Metal to prevent it from collecting the Yang Ki in before Eum-Yang combination. Some say that the Five phases does make sense, but putting late summer after summer from the four seasons is only for matching it to the Five phases. This is true in terms of objective observations. But when Soil, the self with spirit that faces the universe, is added to the world of Sasang, the world of subjectivity, it then becomes the world where subjectivity and objectivity coexist. Five phases is the expression of the self entering substances to induce change. Thus, putting late summer shows the perspective of looking at the changes of seasons not as objective but rather as subjective creature, with some will that also has life.

Let's look at "Soil controlling Water". Water is the basis of inborn constitution, and the Soil, the basis of acquired constitution. This also means that Water is death and Soil is life. This is because the process from Wood to Soil via Fire is the developmental process for organisms to bear fruits, while the process from Metal to Water is the process of dying.

The Spleen and the Stomach belong to Soil, then how is Soil related to digestion? Soil helps digestion by acting against the acquired constitution to pull out the Yang Ki in the seed to make it utilized. However, Wood also acts to pull out the Yang Ki captured within Water. The difference exists in that, Wood gradually pulls out Essence with the help of Water, while Soil destroys Water to pull Yang Ki out. Soil contains a lot of heat, that came from Fire, so it is not that easy for Water to exert itself. The activity of Water is possible only after Metal dries the Dampness into Water, and wrap the Fire-heat up with Yang Ki, the shape adequate for entering Water.

Let's take "Metal controlling Wood". This can easily be understood with understanding of the functions of Water. Water and Fire are in antithetic relationship, while Metal and Wood play complementary roles by being in between the two. Metal helps Ki move from Fire into Water, so it needs to inhibit Wood from taking Yang Ki out from Water. Trees wrapping fruits with tough and thick rinds to remove moisture is to isolate the effects of Wood or Soil.

Then, what is "Water controlling Fire"? In fact, Water is not afraid of the Fire, but afraid of the Soil. Water doesn't have the ability to control Soil. However, the Soil cannot win over Water unless with the help of Fire. Water takes advantage of this to control Soil. Transformation of the Five Phases is for the storing and releasing of Ki, and this movement of Ki is just vicissitudes of Fire. Fire is Yang, which should be controlled by Eum, but Metal is being controlled by Fire, while Wood and Soil cannot be functioned well enough without the help of Fire. This is why Water gets Metal's help to control Fire. This is the most important and central process of inter-controlling of the Five Phases. Conversely in inter-promoting relationships, where it is more important to activate the movement of Ki, the activities of Wood and Fire are more critical.