Zhou Dunyi’s Taiji philosophy presents a vision of reality in which a single, supreme principle underlies all things and gives rise to the entire cosmos. Taiji, the “Supreme Ultimate,” is described as the undifferentiated source of existence, a fundamental reality that precedes all particular forms while containing within itself both being and non-being in harmonious unity. From this ultimate principle there arises a dynamic process rather than a static structure, so that the cosmos is understood as an ordered unfolding grounded in Taiji. All things, despite their diversity, share this same underlying principle and thus belong to a single, coherent whole.

Within this unfolding, the first differentiation is expressed through movement and stillness. From movement arises yang, associated with activity and creativity; from stillness arises yin, associated with quiescence and receptivity. These two are not absolute opposites but complementary aspects whose ceaseless interaction drives all transformation. As yin and yang alternate and interpenetrate, they generate the Five Phases or Five Elements—wood, fire, earth, metal, and water—which function as dynamic modes of change rather than inert substances. Through the interplay of yin, yang, and the Five Phases, the myriad phenomena of the universe, including the natural world and human beings, come forth.

This cosmology is not merely speculative; it is inseparable from a vision of human life and moral cultivation. Human beings receive the vital patterns of heaven and earth and thus embody the same principles that structure the cosmos. Because of this shared foundation, it is possible for humans to understand and harmonize with the natural order. Moral self-cultivation, grounded in sincerity and inner tranquility, becomes the way to align one’s heart-mind with Taiji itself. The sage is the one who most fully realizes this alignment, embodying the unity of cosmic principle and human virtue and living in profound harmony with the ongoing cycles of movement, rest, and return that characterize reality as a whole.