當探討萬物根源的問題時，由於哲學思考的本性，恆不免地必須持「一本」之論。根據「一本」，要怎麼解釋萬物差異現象的問題？以「氣」為萬物根源之論，在漢以後成為通行的學說。但氣有運動變化，性質駁雜不純，實不足以為萬物一源的本體。宋儒以氣是形下之器，並以天道為主宰氣之生化的形上本體；由天道可說萬物一本，由氣化則可解釋萬殊的成因。唯其形上、形下二分之說，不無天道二元論之疑，且對氣的來源欠缺合理的說明。明儒論理氣之說者，大都主張天地一氣，理乃氣之理。但或因其以氣一理一，以至於無法說明萬殊的問題；或為說明萬殊的現象，謂氣萬理萬，而導致多元氣論的結果，無法維持「一本」之說。船山雖亦主本體一氣之論，然其氣論涵義則與傳統其他氣論之說大異。從船山觀點來看，氣雖是純一之體，卻全備天下之雜多萬殊。天地間存在著陰陽、五行，乃至萬物之氣，但是，所有這類的氣都不是具有自性而能永恆常在的實體，亦即二、五與萬殊之氣等並「無其專氣」。氣之實體才是永恆常在之體，萬物都是其「體」之「用」所化生。氣之「體」即於「此」體之上能發生無窮之用，而化生無盡之物。從本體來說，氣唯一體；從作用來說，氣則有萬殊。根據「體用」的觀念，船山得以合理解釋全體存在如何可能既是異、又是一的問題。

Owing to the nature of philosophical thinking, it is unavoidable to advocate monism when we considered the variety of things. Still, the problem has always been how could we explain the manifoldness of phenomena through the ultimate 'One'? Since Han Dynasty it has become a universal accepted idea that all things are only modifications of Chi. But Chi could not be viewed as the ultimate one of all things, because it possesses the qualities of movement and change, it is heterogeneous. Following the view of 'The Book of Change', the Confucian scholars in Sung dynasty asserted that Chi is a concept belonging to phenomena, while Ten-Toa was the creating substance that creates all things and governs all the movements and changes of Chi. Accordingly, Tian-Tao is the oneness and Chi is the manifold. But this way of viewing the relation between the one and the many would lead to a conclusion that implies a ontological dualism of Li-Chi, and the question of the origination of the many would still remain unexplained. Confucian scholars in Ming Dynasty asserted without exception the affinity of Li and Chi. If one holds that Li and Chi are both the one, that would cause a result of being unable to explain the many. But if one maintains that Chi and Li are both the many, that would lead to a pluralism, which would force one to abandon the preferred ontological monism. The metaphysics of Wang Chuan-Shan builds a way out of this dilemma. First, the creative powers and orders of all things are actually everywhere the same and identical, the creative power and substance of all things are 'The One'. Second, besides the creative substance, power, and order of the universe and of all things, there is manifold functions of Chi, i.e. besides the oneness of Chi, there is the manifoldness of the same. Although there are diversity of Chi, i.e. the infinite complexity of the phenomena, but they are for their parts changeable and not permanent. The universal substance of Chi is, however, permanent and all-present, and the diversity of things are its creatures. Viewed from the universal substance of it, Chi is "The One", from functions, it is diversified. Wang Chuan-Shan can therefore, through the concepts of Ti (substance) and Yong (functions), explain how it is possible that Chi is one, on the one hand, and simultaneously many, on the other.