船山哲學中的「自然」意味著一種與「人為」不同的自發性運作方式，它無法為人的知能所穿透，也不能被理解為作為根據的終極因或造物主，而是一種自發性、自本自根的以自正性命為指向的秩序，關聯著一種終極無為宇宙觀。船山以人之天、物之天、天之天三個概念將自然區分為人的自然、物之自然與宇宙之自然三個層面，人的自然規定了人的性分，人對其自然的深化與拓展，不過是回歸自身，上不同天，下不混物，而是立於人道之獨，這樣，「人之自然」便不再同質於物之自然與宇宙之自然，因為它包含了圍繞著人的本性的提升與轉化而展開的積極的歷史文化創造，這是與通常的自然觀念極為不同的。

The concept of “natural” in Chuanshan’s philosophy means a spontaneous operation mode different from “man-made”. It cannot be penetrated by human knowledge and cannot be understood as the ultimate cause or creator as a basis. Nature means a spontaneous, self-based order, which is ultimately associated with an ultimate inaction cosmology. Chuanshan uses the three concepts of “renzhitian”, “wuzhitian” and “tianzhitian” to divide nature into three levels: the nature of man, the nature of the thing, and the nature of the universe. The nature of man dictates the nature of man. “Renzhitian” stipulates the unique nature of human beings, and the deepening and expansion of its nature is just a return to itself, which is different from the heavens and the earth in the top, and is not confused with other things in the bottom, but is based on the Dao of mankind. In this way, “renzhitian” encompasses the active historical and cultural creation around the promotion and transformation of human nature.