Zhou Dunyi’s Taiji philosophy understands duality as something that arises within, and never apart from, an original unity. Taiji, the Supreme Ultimate, is that undifferentiated source from which the “Two Principles” of yin and yang emerge. Through movement, Taiji gives rise to yang; through stillness, it gives rise to yin. Duality is therefore not an independent or rival reality, but a functional differentiation within a single underlying ground. What appears as two is always rooted in one.

Within this framework, yin and yang are complementary rather than antagonistic. They stand as interdependent polarities—light and dark, active and receptive, firm and yielding—that define and complete one another. Each contains the seed of the other, and they constantly alternate and transform into one another. This ceaseless interaction is the basis of all change and the engine of cosmic creativity. From their dynamic interplay arise the manifold phenomena of the cosmos.

Taiji philosophy thus portrays duality as both necessary and provisional: necessary for the manifestation of the world, yet always grounded in a more fundamental unity. The apparent opposition of yin and yang never breaks the continuity of Taiji; instead, it reveals how the one reality expresses itself in patterned contrast. To recognize this is to see that harmony does not lie in abolishing one pole in favor of the other, but in discerning their proper balance and mutual regulation. In this way, the vision of Taiji both affirms the reality of duality in experience and gently points beyond it to the unity that pervades and sustains it.