Considered to be one of the most central concepts within the Zhongyong 中庸, the notion of the “Mean” or “centrality” (zhong 中) occupies a key position within Zhu Xi’s psychological and ethical thought. The term occurs several times in the opening lines of the work, presented alternately as part of the semantic compounds zhonghe 中和 and shizhong 時中. Despite the distinct differences between the two instances of zhong as they functioned within Zhu Xi’s reading of the text, recent approaches have failed to provide a complete account of their relation, thereby hindering a full understanding of the role of centrality within Zhu Xi’s psychological thought. It is the aim of the current paper to elaborate upon and address this issue. In the first section, I examine Zhu Xi’s reading of the phrase shizhong, providing evidence to support Daniel Gardner’s recent suggestion that Zhu interpreted this instance of zhong as an explicitly situational balancing of one’s emotional state. In the second section, I address the relationship between zhong and he, demonstrating that Zhu instead framed this instance of zhong as a primarily hypothetical ideal informed by one’s inborn nature (xing 性), existing only prior to actual concrete practice. In the third section, I argue that Zhu Xi maintained a strong thematic and perspectival boundary between the two instances of zhong, in contrast with recent interpretations of the term. While zhonghe was adopted to describe the hypothetical initial state or “substance” (ti 體) of one’s psychology in an abstract ontological sense, shizhong reflected its application or “function” (yong 用) within the concrete social world.