Zhang Zai 張載 (1020–1077) was a seminal figure in the early development of Neo-Confucian philosophy and Zheng meng 正蒙 (Rectifying the Ignorant) is his representative philosophical work. This annotated translation is the first English translation of the book. The "ignorant" in the title is a critical reference to followers of Daoism and Buddhism. The book's positive agenda—developed in response to what Zhang saw as the philosophical flaws in Daoist and Buddhist teachings—is devoted to outlining key ideas informing Zhang's metaphysics and moral philosophy, in which his philosophical revitalization of the concept of qi 氣 (vital stuff) plays a key role, and subsequently provided an important contribution to the development of Neo-Confucian thought, as evidenced in philosophical discourse on the relationship between li 理 (principle) and qi. For Zhang, qi is the vital stuff that constitutes all things but is by no means limited to physical substantiality. Yet equally important in Zhang's metaphysics is the concept of taixu 太虛 (Supreme Void). The relationship between the Supreme Void and qi embodies the principle that "fundamental state and function" (ti yong 體用) are inseparable. The aphoristic and cryptic style that Zhang adopted for Zheng meng undoubtedly stimulated the development of the rich body of exegesis on Zheng meng in the Ming and Qing periods, as well as in contemporary mainland China and Taiwan, where prominent scholars continue to diverge widely about how key concepts in the book should be interpreted.