Abstract
Qixue氣學 is a school that can compete with Lixue理學 and Xinxue心學 in the works of modern historians of Chinese philosophy. Although neglected for a long time, it remains one of the few schools that can be connected to materialism. Qixue is a significant concept, but those who introduce it often confuse its xiantian mode先天型 with its houtian mode後天型. In the xiantian mode, qi氣 is regarded as the action of the substance, and thus belongs to the category of metaphysics. On the contrary, qi is a materialistic term in the houtian mode, which is a branch of natural philosophy based on the theory of finite human nature. Both of these two modes borrowed the word qi to refute Zhu Xi's朱熹 division of li理 and qi, and the metaphysics of kong空 and wu無 of Buddhism and Taoism. This article takes Liu Zongzhou劉宗周, Luo Qinshun羅欽順, and Zhang Zai張載 as examples. They represented three kinds of xiantian mode thought respectively, but all based their philosophies on the theory of infinite human nature. The xiantian mode is still a school within Lixue; the houtian mode looked for a new way to develop.