「氣」論是船山哲學的核心，然而山之「氣」，則具有與傳統氣論學派之說極為不同的涵義。在船山系統中，必須清楚區隔「氣之實」與「氣之名」之不同。前者之氣乃等同於宇宙本體；後者之氣，則只是人類詮釋本體之實蘊時所立的一個名言、概念、具有特殊的、確定的義涵。因此，氣之「實」與氣之「名」之間，具有「無限」與「有限」、「全體」與「一端」的不同。本文綜船山論的內涵；同時透過與傳統要氣論之說：漢代氣化宇宙論；宋儒張柱渠之氣論；明儒羅整庵、王廷相之氣論等，來與其說比較，豁顯船山論之義理特色與殊勝之處。

Chi, the vital force, was the very importance philosophical idea to Wang Chun-Shan. The contents of Chi in his philosophical system, it had very different meanings that distinguished to the traditional chi theory. In Wang’s philosophical system, we must make the differentiation between the Shin (reality) and the Ming (name) about the idea of Chi. In the latter, chi was only a concept that had the special determined meanings, whose contents attributed to human explaining the universal entity. And so the Shin of Chi was infinite while the Ming of Chi was finite; one was substance in total, and the other was one aspect of the substance. The present writer synthesized the contents of Wang’s Chi theory to compare Wang’s with the major traditional Chi theory. They included the chi-cosmology in the Han Dynasty、the Chi theory of Chang Tsai in the Sung Dynasty、the Chi theory of Wang Ting-Hsiang and Lo chin-shun in the Ming Dynasty. And then we can make clear to the philosophical characters and superiority of his chi theory.