"In the Eight Trigrams Kan represents “Water” while Li represents “Fire.” However, the everyday terms for water and fire are also often used. Kan and Li training has long been of major importance to Qigong practitioners. In order to understand why, you must understand these two words, and the theory behind them.
"First you should understand that through Kan-Li and Yin-Yang are related, Kan and Li are not Yin and Yang. Kan is Water, which is able to cool your body down and make it more Yin, while Li is Fire, which warms your body and makes it more Yang. Kan and Li are the methods or causes, while and Yang are the results. When Kan and Li are adjusted or regulated correctly, Yin and Yang will be balanced and interact harmoniously.
"Qigong practitioners believe that your body is always too Yang, unless you are sick or have not eaten for a long time, in which case your body is always too Yang. Since your body is always Yang, it is degenerating and burning out. It is believed that this is the cause of aging. If you are able to use Water to cool down your body, you will be able to slow down the degeneration process and thereby lengthen your life. This is the main reason why Chinese Qigong practitioners have been studying ways of improving the quality of the Water in their bodies, and of reducing the quantity of Fire. I believe that as a Qigong practitioner you should always experiment. If you earnestly ponder and experiment, you will be able to grasp the trick of adjusting them.
"If you want to adjust them, you must understand that Water and Fire mean many things in your body. The first concerns your Qi. Qi is classified as Fire or Water. When your Qi is not pure and causes your body to heat up and your mental/spiritual body to become unstable (yang), it is classified as Fire Qi. The Qi which is pure and is able to cool both your physical and spiritual bodies (make them more Yin) is considered Water Qi. However, your body can never be purely Water. Water can cool down the Fire, but it must never totally quench it, because then you would be dead. It is also said that Fire Qi is able to agitate and stimulate the emotions, and from the emotions generate a “mind.” This mind is called Xin, and is considered the “Fire mind”, Yang mind, or emotional mind. On the other hand, the mind that Water Qi generates is calm, steady, and wise. This mind is called Yi, and is considered to be the “Water mind” or wisdom mind. If you spirit is nourished by Fire Qi, although your spirit may be high, it will be scattered and confused (a Yang spirit). Naturally, if the spirit is nourished and raised up by the Water Qi, it will be firm and steady (a Yin mind). When your Yi is able to govern your emotional Xin effectively, your will (strong emotional intention) can be firm.
"Theoretically, a Qigong practitioner would like to keep his body in a state of Yin-Yang balance, which means the “center point of the Yin and Yang forces. This center point is commonly called “Wuji” (no extremities). In order to reach this goal, you must first understand your body’s Yin and Yang so that you can balance so that you can balance them by adjusting your Kan and Li. Theoretically, between the two extremes of Yin and Yang are millions of paths (i.e., different Kan and Li methods) which can lead you to the neutral center.
"[You can see that the theory of Yin and Yang and the methods of Kan and Li are the root of training in all Chinese Qigong styles. Without this root, the essence of Qigong practice would be lost.]" *
* Dr. Yang, Jwing-Ming, The Essence of Taiji Qigong