Intellectual setting
Zhang Zai served briefly in the Song bureaucracy and studied alongside his nephews, the brothers Cheng Hao and Cheng Yi, before retiring to teach near Hengqu in Shaanxi. He wrote during the eleventh-century revival of Confucian philosophy that reacted against the long dominance of Buddhism and Daoism in Chinese intellectual life, seeking to answer their metaphysics with a distinctively Confucian cosmology grounded in qi.
Key ideas
The Supreme Void is qi, not nothingness
Against Buddhist and Daoist treatments of ultimate reality as empty or nonbeing, Zhang Zai argued that the "Supreme Void" (taixu) is identical with qi in its most dispersed, formless state, so that determinate things are qi that has temporarily integrated into form and will eventually disintegrate back into the void, making change itself, rather than a static substrate, fundamental.
The Western Inscription and cosmic kinship
In his short essay the Ximing ("Western Inscription"), Zhang Zai described Heaven and Earth as father and mother and all people and things as one's siblings sharing a single body, grounding ethical obligation - including the Confucian virtue of filial care - in a cosmology of universal kinship rather than in convention alone.
Legacy
Zhang Zai's account of qi and the Supreme Void became a foundational reference point for later Neo-Confucian metaphysics, and the Ximing was singled out by Zhu Xi for inclusion in the core Neo-Confucian curriculum; his cosmic-kinship ethics continued to be cited by later Chinese and Korean Confucians as a model for grounding universal moral concern in a coherent metaphysics of qi.