Western medicine places strong emphasis on the physical structures of the body, which are made up of different organic and inorganic substances, proteins, tissues and cells. These substances form the physiological basis of humans. Traditional Chinese medicine (TCM), on the other hand, views life a little differently. Instead of emphasizing discrete body components with cells being the basic building blocks, the body is seen as a whole entity with connecting parts that work together to sustain life. Some parts have more energetic properties while others have more material characteristics. The interaction between the different parts is vital to the individual's being so they are often referred to as fundamental substances. Qi (pronounced chee), blood and body fluids are the most important fundamental substances necessary for sustaining a healthy, prosperous life.
The ancient Chinese people believed qi was the most fundamental entity making up the world. They thought everything in the universe resulted from the movement and change of qi. The Chinese character for "qi" is the same word used for air or gas, and it is thought to have the same properties as these substances. Qi can be interpreted as the "life energy" or "life force," which flows within us. Sometimes, it is known as the "vital energy" which directly guides our bodies.
In TCM theory, qi is the vital substance constituting the human body. It also refers to the physiological functions of organs and meridians. In fact, it may be difficult to find one equivalent English word or phrase that completely describes the nature of qi. Most often, qi is best defined according to its functions and properties.