Qi is the fundamental life energy of the universe. It is invisible and is found in everything - air, water, food, sunlight, etc. In the body, it is the invisible life force that creates and animates life. We are all born with qi inherited from our parents and we also acquired additional qi throughout life from the food we eat and the air we breathe. In addition to what we consume, the level and quality of our qi also depends on the state of physical, mental and emotional balance.
Qi as universal life force energy is a foundation of Chinese Medical theory. It encompasses the idea that all things in the universe are interconnected and composed of energy at various levels of vibration and are constantly changing and transforming; just as the water in the ocean today becomes the clouds in the sky tomorrow and the rain upon the earth the next day. Without Qi or life force, nothing could exist.
The direct meanings of yin and yang in Chinese are bright and dark sides of an object. Chinese philosophy uses yin and yang to represent a wider range of opposite properties in the universe: cold and hot, slow and fast, still and moving, masculine and feminine, lower and upper, etc. In general, anything that is moving, ascending, bright, progressing, hyperactive, including functional disease of the body, pertains to yang.
The characteristics of stillness, descending, darkness, degeneration, hypo-activity, including organic disease, pertain to yin. The function of yin and yang is guided by the law of unity of the opposites. In other words, yin and yang are in conflict but at the same time mutually dependent. The nature of yin and yang is relative, with neither being able to exist in isolation. Without "cold" there would be no "hot"; without "moving" there would be no "still"; without "dark", there would be no "light".
The most illustrative example of yin-yang interdependence is the interrelationship between substance and function. Only with ample substance can the human body function in a healthy way; and only when the functional processes are in good condition, can the essential substances be appropriately refreshed. The opposites in all objects and phenomena are in constant motion and change: The gain, growth and advance of the one mean the loss, decline and retreat of the other. For example, day is yang and night is yin, but morning is understood as being yang within yang, afternoon is yin within yang, evening before midnight is yin within yin and the time after midnight is yang within yin. The seed (Yin) grows into the plant (Yang), which itself dies back to the earth (Yin).
This takes place within the changes of the seasons. Winter (Yin) transforms through the Spring into Summer (Yang), which in turn transforms through Autumn into Winter again. Because natural phenomena are balanced in the constant flux of alternating yin and yang, the change and transformation of yin-yang has been taken as a universal law. Traditional Chinese medicine holds that human life is a physiological process in constant motion and change. Under normal conditions, the waxing and waning of yin and yang are kept within certain bounds, reflecting a dynamic equilibrium of the physiological processes. When the balance is broken, disease occurs. Typical cases of disease-related imbalance include excess of yin, excess of yang, deficiency of yin, and deficiency of yang.
Meridians are energy channels. They can be likened to the wiring of a house, or the veins and arteries through which our blood flows, except that they have no discrete physical structure. They run through our physical bodies but they cannot be dissected or found surgically. Meridians are part of the body's subtle energy anatomy and have no concrete form. Humans are not unique in having meridians - dogs, cats, horses, and all mammals seem to have energy meridians.
Despite their intangible nature, we know that meridians exist because their impact can be felt. Sedating (weakening) or strengthening the various meridians has a noticeable impact on energy levels, mood and adaptability, health, immunity, thinking and cognition, and more. Some of the meridians are yin and some are yang, and each corresponds to an element and specific emotional tendencies.
Children are sometimes able to feel the flow of energy in their own meridians (somewhat like growing pains) when energy of a meridian is out of balance. People who are intuitive can sometimes see or sense the energy of other people's meridians and tell whether their flow is healthy and strong (Donna Eden is known for her ability to sense what people need for energetic balance).
The 14 meridians are the Central, Governing, Circulation/Sex, Bladder, Gall Bladder, Heart, Kidney, Large Intestine, Liver, Lung, Small Intestine, Spleen, Stomach, and Triple Warmer.