Within the School of Yin-Yang, Qi is understood as the fundamental, all-pervading stuff of reality, the vital force or “substance-energy” from which all things arise. Heaven, earth, and the myriad beings are seen as different configurations of this Qi, denser in material forms and more refined in spiritual or subtle phenomena. Yin and yang themselves are not separate substances but complementary modes or phases of Qi’s activity—dark and light, passive and active, dense and rarefied. In this sense, Qi serves as the ontological basis of the cosmos, the underlying continuity beneath all apparent diversity.

Qi is also the dynamic principle of change that animates the universe. The ceaseless alternation and mutual transformation of yin and yang are made possible by the movement and transformation of Qi. Natural cycles—such as the seasons, climatic shifts, and the rhythms of growth and decay—are interpreted as patterned flows of Qi, following predictable pathways of increase, decrease, and renewal. The Five Phases (wuxing) are understood as characteristic patterns or modes of Qi’s cyclical transformation, giving a structured account of how change unfolds in the world.

At the same time, Qi functions as the mediating link between the cosmos, nature, and human life. Human bodies, emotions, health, and fortune are all expressions of Qi in particular configurations, shaped by the interplay of yin-yang and the Five Phases. When Qi flows harmoniously, yin and yang complement one another and a state of balance is maintained; when Qi becomes stagnant, excessive, or deficient, imbalance and disharmony arise. Thus, harmony in the body, in the environment, and in society is seen as a matter of aligning with the proper patterns and timing of Qi.

Because of this, Qi becomes a unifying explanatory concept that allows the School of Yin-Yang to synthesize cosmology, metaphysics, and practical life. The same principles of Qi’s movement and transformation are applied to understand phenomena as diverse as weather, governance, and ethical conduct. Material and spiritual realms are not sharply divided but are viewed as different expressions of one continuous field of Qi in varying states of concentration and refinement. Through this lens, the world appears as an intricate web of interdependent processes, all sustained and animated by the ceaseless circulation of Qi.