TCM classic Huangdi Neijing, or Canon of Medicine, holds that life consists of "qi" ("qi" belongs to the classical philosophical category, referring to the basic element which constitutes everything in the world). The balance and harmony of the internal environment of the human body, the wholism and unity of the human body and the external surroundings are the foundation for man to live and exist. In normal cases, the adjustment of the human body can adapt the internal environment to the changes of the external natural environment to maintain normal physiological functions.

If human activities violate the patterns of natural changes, or abnormal and violent changes occur in the external natural surroundings, the regulatory function of the human body will fail to adapt itself to the situation, destroying the relative balance of the internal and external surroundings and consequently giving rise to disease. Therefore, "conforming to nature" is the first requirement for health preservation. More information, please read Women Qi and Blood.

Essence, qi and spirit are the basic substances essential to vital activities.

Essence is the basic material for constituting the human body and promoting the growth and development of the human body. Essence is divided into "congenital essence" and "acquired essence". Congenital essence is inherited from the parents. After birth, the nutritious cream derived form the diet is called acquired essence. Congenital essence and acquired essence can be transformed into each other and supplement mutually to form the dynamic foundation of vital activities. If essence is deficient, vital activities will decline, causing premature ageing and susceptibility to diseases. More information, please read TCM Women Meridians.

Qi is the important substance for constituting life, too. The sufficiency or deficiency of qi determines the strength of the life force and the length of the life span. The vital phenomena are the ascending, descending, coming-in and coming-out of the functional activities of qi.

Spirit is a general term for vital activities of body and also the outward manifestation of vital activities of the human body. It includes mentality, consciousness, thinking, movement, perception, etc. Essence and blood are the material foundation for spirit. And sufficient essence and qi bring on prosperous spirit. Therefore, whether life is healthy or not can be judged by inspecting the state of spirit.

It can be seen from the above that vital activities are determined by the conditions of essence, qi, spirit and visceral functions. Abundant essence, qi and spirit, the balance of visceral qi and blood ensure good health and freedom from diseases, insusceptibility to aging, and extension of life span. More information, please read Gynecological cause of Disease.