This paper studies how ideas diffuse and shape elite political behavior in an autocratic setting by tracing the spread of the Wang Yangming “School of Mind” in late imperial China. Using more than 24,000 texts from 1000 to 1900, we construct two exposure measures—the frequency of core concepts and the count of associated authors—and add an alternative semantic-similarity measure that compares prefecture texts to a corpus of Yangming’s writings using embedding-based cosine similarity from a classical-Chinese language model. A difference-in-differences specification shows a sharp rise in exposure after 1500, especially in prefectures with greater lecture influence. We then relate exposure to the emergence of Donglin reformers during 1604–1627 and find a strong positive association that is robust across measures and controls. The evidence indicates that ideas stressing individual agency and accountability diffused through elite discourse and were linked to greater reformist mobilization within an autocratic system.