船山之天道論，以宇宙本體為「氣」。但其義理內涵與傳統其它氣論學派之說，在實質上大相逕庭。這是因為，人嘗試去詮釋本體時，他不得不使用「語言」來指稱之。作為言說的需要，當船山說本體「其實，氣也」時，所謂氣之「實」乃等同於宇宙本體自身。這與人類詮釋本體之實蘊時，所建立之具有特殊的、確定的義涵之名言、概念－氣之「名」，並不相同。氣之「實」與氣之「名」之間，具有「無限」與「有限」、「全體」與「一端」的差異。當「此」端既立，與此端相對之「彼」端也必然同時成立；須「合兩端於一體」乃能得其全。由於天道無限，「合兩端於一體」的綜合過程將無窮地進行。船山以「陰陽」總稱一切兩端，在天道一元論的前提下，富有方法論的意識，他以「陰陽」觀念發展出一套頗為有效的理論。本文歸納船山「陰陽」的三用法：分別是「陰陽名、實之分的方法」、「陰陽之合說與分說之異的方法」、「陰陽之肇生者與所生者層次不同的方法」，以總論「陰陽」觀念的方法論涵義。

As far as the metaphysics of Wang Chuan-Shan was concerned, he asserted that the universal substance was Chi. The contents of Chi in his philosophical system were different from those of traditional Chi theory. Trying to explain it, we must use the language to indicate the universal substance. When Wang interpreted that the Shin (reality) of the universal substance was Chi, Chi was equal to the substance itself. It was different from 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. When one aspect was set up, another opposite aspect must come into existence too. We must synthesize two opposite aspects to each other into an organic whole. Because the intension of the universal entity was infinite, the synthetic process will continuously proceed. Wang generally called all of two opposite aspects Yin-Yang. On the basic of the monism full of methodological consciousness, Wang had applied the idea of Yin-Yang to develop an effective metaphysics. The present writer concluded it's methodological meanings with three usages of Yin-Yang, as ‘the differences between the Shin (reality) and the Ming (name) of Yin-Yang.’ ‘whether Yin and Yang were to be separated or combined, it was different.’ ‘compared Yin-Yang as the entity that created the universe with Yin-Yang created by the universe.’