One of Zhu Xi’s (1130-1200) most important texts, the Preface to the Mean and Commonality 中庸序 (date of composition: 1189) is organised as a long recontextualisation and commentary on a sixteen character long passage from the Old Text Shangshu 古文尚書. His commentary tantalisingly describes the text as telling us something of importance regarding the nature of the mind and its role in one’s interactions with the world. What he there writes has typically been interpreted as espousing an ideal of strict self-denial and a subjugation of the self to moral laws. This thesis argues that his meaning is almost precisely the opposite; by reading of the Preface in light of near-contemporary discussions of the text with his students. It argues that Zhu in the Preface elaborates a responsive theory of the mind and on that basis a theory of moral action as moral responsiveness. His responsive theory of the mind sets out to describe the sorts of things that give shape to one’s responses to the outside world; this includes the state of one’s body, brute contingency and most importantly one’s moral nature. The theory of moral action developed on this basis is one that seeks to describe how one can avoid being a victim of the whims of fate, and even in the most adverse conditions lead a flourishing life; not free from contingency but in a creative co-existence with it. The way this thesis achieves this result is by taking the commentary form seriously; where previous interpreters have assumed Zhu to be a systematic philosopher deriving doctrines from abstract principles, this thesis reconstructs what Zhu says as attempts to interpret a text. It does this in three steps, divided over three chapters: It first reconstructs the lively debate that was taking place during the Northern and Southern Song Dynasties on precisely how to interpret the passage from the Counsels of the Great Yu; it then reconstructs the assumtptions Zhu ascribes to the text by interpreting several arguments Zhu makes as arguments for a particular reading of a text; in the last chapter these assumptions are read back into the Shangshu text through the lens of several illustrations Zhu uses to arrive at the picture of responsive action described above.