Qi was originally a philosophic concept. The ancients believed that the world changes and things in the world can transform from one to another, so when they tried to explain the world with a common substance, they determined that the substance must have two properties: invisibility and motion. As it is invisible or has no certain shape, it can create various kinds of things; and as it is moving, things in the world are always changing and may transform from one to another. Air, the original meaning of Qi, is just such a substance which cannot be seen but the movement of which, as wind, can be felt. This was extended to mean that the most basic substance of the world, and its movement and change can explain the generation, development and change of all things in the world.

The ancient Chinese philosophy holds that Qi is this most basic substance constituting the world. Accordingly, TCM also believes that Qi is the most fundamental substance in the construction of the human body and in the maintenance of its life activities. As a whole, Qi in the cosmos takes two patterns of existence, diffused Qi and coagulated Qi. The former is more vigorous, cannot be detected directly and exists everywhere. The latter is manifested as various kinds of things that can be seen or that have certain shapes. In order to survive, coagulated Qi must communicate with diffused Qi and its generation as well as its ending results from movement of the diffused Qi. That means, when the diffused Qi coagulates, it creates substantial matter, while if it separates, the matter disappears. Therefore, any substantial matter can be regarded as a special process of the movement of Qi, and life, in essence, is the course of Qi's ascending, descending, exiting and entering movements in given conditions.v