Within Zhou Dunyi’s Taiji philosophy, yin and yang are understood as two inseparable aspects of a single, ultimate reality. Both arise from Taiji, the Supreme Ultimate, which is the undifferentiated source of all things. Movement from this source gives rise to yang, while stillness gives rise to yin, so neither exists in isolation. Their apparent duality is therefore only relative, for they remain rooted in one unified ground. Rather than being hostile or mutually exclusive, they are complementary polarities that complete each other and make wholeness possible.

The relationship between yin and yang is characterized by ceaseless interaction and transformation. Yang is associated with movement and initiation, while yin is associated with stillness and receptivity, yet each continually gives way to the other. When one aspect reaches an extreme, it naturally turns into its counterpart, forming a cyclical rhythm that prevents stagnation and sustains harmony. In this way, yin and yang are mutually dependent and co-defining: there is no meaningful yang apart from yin, and no yin apart from yang. Each contains the implicit tendency toward the other, and their dynamic balance maintains a living equilibrium rather than a rigid symmetry.

From the interplay of yin and yang arise the Five Phases (wuxing), through which the myriad things of the cosmos are generated. All natural processes and human affairs can be seen as expressions of this ongoing alternation and balance. The same pattern that shapes the heavens and earth also informs human nature and social order, so that cosmology and ethics are woven together. To live in attunement with this vision is to recognize that genuine harmony does not come from suppressing one pole in favor of the other, but from allowing their rhythmic transformation to unfold in due measure.