Cheng Yi gave Neo-Confucianism a durable vocabulary of principle, moral seriousness, and disciplined learning that later became central to Zhu Xi's synthesis.
Intellectual setting
With his brother Cheng Hao, Cheng Yi responded to Song-dynasty Buddhist and Daoist influence by renewing Confucian classical learning as a program of moral metaphysics.
Key ideas
Principle
Each thing has a normative pattern or principle; moral cultivation requires grasping those principles rather than following private desire.
Investigating things
Learning proceeds by sustained attention to affairs, texts, and conduct so that knowledge and action become responsive to moral principle.
Legacy
Later Cheng-Zhu orthodoxy made his formulations authoritative in East Asian education, while Wang Yangming and others challenged the separation of investigation from immediate moral knowing.