The healing practice known as yi since ancient times was constituted from the astronomical observations of movements of such bodies as the sun, the moon, Jupiter, Saturn, Mercury, Mars, and Venus in relation to phenomena and activities of things on earth.
From earth, we see planets move from east to west, south to north. The movement of such heavenly bodies creates different conditions on earth. The most obvious influence is the sun.
When the sun rises, the observers’ ground becomes warmer, when the sun sets the observers’ ground becomes cooler. The warmth we call yang, and the cool we call yin. This, we might say, is where yinyang theory is grounded.
The east is where the sun rises, it is the beginning of the day, so it represents the rise of yang. The west is where the sun goes down, it is the end of the day, so it represents the rise of yin. When the sun rises in the east we get up, and when the sun goes down in the west we settle down to rest.
When the sun moves north of the earth’s equator, plants in the north begin to sprout, and when the sun moves south of the equator, plants in the north wither. When the sun is at its most northern extent in relation to the earth’s equator, the northern hemisphere is warmest or has the most of yang. Similarly, when the sun is at its most southern extent the northern side of the earth is coolest or has the most of yin. When we talk about warmth or cool, it is always from the position of the observer, the east, west, north, south, and middle are the five basic positions that carry different yinyang qualities. This is where the wuxing theory is grounded.
The position of the planets in relation to earth can be divided further into the east, southeast, south, southwest, northwest, north, northeast, upper-middle, and bottom middle, this is the 10 天干 tiangan (heavenly stems).
The earth rotates on its axis and around the sun 360 degrees, which is divided into 12 periods or times. This is the 12 地支dizhi (earthly branches). As the rotation of earth is the main reason that the planets appear to change positions in relation to earth, which provides different yinyang conditions on the ground, so dizhi cannot be separated from tiangan. In other words, tiangan and dizhi together form the yinyang conditions of the observers.
Tiangan has five basic positions, di zhi has six basic periods of time, the combination of position and time influences all human activities. The study of the yinyang combination of position and time is the base of 五运六气 wuyun liuqi (five movements six qi).
To demonstrate the yinyang creation on the ground through the planets and earth movement, the ancient Chinese scholars created He Tu and Luo Shu (cosmological diagrams). Then the ancient scholars created八卦bagua to give a simple and direct illustration of yinyang conditions at the time and position.
All things including humans are created and actioned upon by wuyun liuqi, and our illnesses are caused by all things that block our yun (movement) with the yun of the planets above and our qi with the qi of the earth. When one understands the yunqi of things surrounding us, and knows the yunqi of our bodies, then one can utilize the material or immaterial to correct illnesses, which makes one a yi scholar and healer.
In conclusion, to be an adept yi practitioner, one needs to know about 1: the terms of yin and yang. 2: The terms of wuxing. 3: The system of tiangan and dizhi. 4: A basic knowledge of astronomical phenomena. 5: The tia gan dizhi calendar. 6. He Tu, and Luo Shu. 7: Bagua. 8: The wuyun liuqi of the human body and spirit. 9: The wuyun liuqi of meridians and points. 10: The wuyun liuqi of herbs. 11: How to treat illnesses through an understanding of wuyun liuqi of herbs and meridian and points.
The above 11 contents are the system of yi.
For people who don’t know the Chinese language, it is important to learn some of the Chinese characters to be able to read illustrations and charts. For modern Chinese learners, it is also good to know the ancient meanings of Chinese characters as the classical meanings of the words are the meanings in the classical yi texts and they are often different to their modern meaning. For this reason, I have been posting Chinese characters on Facebook and on zijiepan.com. Ideally, an outstanding yi practitioner would be able to read classical Chinese texts in order to attain the most direct insights into yi.