Classic Chinese philosophy believes that the primary state of the universe is qi, the constant movement of which produces all the things in the universe, including life. Thus people in ancient China thought that the accumulation of qi would produce life while the dispersion of qi would put an end to life. Qi is very active and in constant motion. Qi is also extremely fine and invisible.
In the theory of TCM, Qi is the most essential substance that makes up the body and maintains life activities. All vital substances, organs and meridians in the body are formed by the motion, transformation and accumulation of qi.
Qi is an important and unique concept of TCM and is defined and sub-categorised into different types according to its function within the body. This includes: nutrient (ying) qi, defensive (wei) qi and pectoral (zong) qi.