程顥、程頤稱宇宙的本體為「理」，這個本體是實存性的實有，宇宙萬物都是由這個本體所創生。至於人的本性，程頤明確提出「性即理也，所謂理，性是也。」這樣的說法，可以推論出：性＝理，也就是用「理」去界定「性」的範疇與內涵，所以說二程是「以理為性」。這樣的理與性，有總體義，有分殊義。總體義的理與性，是指宇宙的本體；分殊義的性，則是指人物所稟受的本體，而這個分殊的本體，也即是總體的本體。 因為分殊的本體即是宇宙的本體，所以，人本身便涵蘊有這個本體，而心是人的主宰，所以程顥認為，人只須當處認取自身的本體，不須向外追尋，所以說「只心便是天」。價值落在現象界，由此再往前推，就可以得出：即事物即是天理，所以說「灑掃應對，形而上者在焉」。 在宇宙本體與個別本體的整個理論系統，二程是用「理一分殊」的方式開展出來的，其中的理，是指宇宙的本體，分殊則是指個別的本體。而二程所主張「以理為性」的理，正是指宇宙的本體；性，雖然有總體義和分殊義，這裡的「性」，側重在指個別的本體，也就是「理一分殊」中的「分殊」。 綜上所論，二程在宇宙的本體和人的心性的所有理論，都是以「以理為性」為核心思想，再以「理一分殊」的思想及方法所架構出來的。

Cheng, Hao and Cheng, Yi called the noumenon of the universe “Li.” This noumenon is substantially existing, and all God’s creation is created from this noumenon. As for the nature of human beings, Cheng, Hao proposed “Sing-ji-li-ye, suo-wei-li, sing-shih-ye” clearly. From this kind of statement, I can infer that “Sing” is equal to “Li. ” That is, using “Li” to define the connotation and category of “Sing.” Therefore, I can say that refers to two Mr. Chengs’ “Yi-li-wei-sing.” “Li” and “Sing” of this kind have overall meanings and individual meanings. “Li” and “Sing” of overall meanings indicate the noumenon of the universe; “Sing” of individual meanings mean the noumenon people and objects are endowed with. The individual noumenon is also the overall noumenon. Because the individual noumenon is also the noumenon of the universe, a person contains the noumenon himself/herself. The mind is the master of a person. Therefore, Cheng, Hao thought a person has to recognize the noumenon of himself/herself only, and does not have to search it outside. Because of “Jhih-sin-bian-shih-tian,” the value fulfills on the phenomenon circles. Then I can infer that things are the justice of nature. Hence, “The etiquette of daily life has metaphysics in itself.” Two Mr. Chengs developed the entire theoretic systems of the universe noumenon and the individual noumenon with “Li-yi-fen-shu.” “Li” means the noumenon of the universe, and “Fen-shu” signifies the individual noumenon. “Li” of “Yi-li-wei-sing” the two Mr. Chengs advocated is exactly the noumenon of the universe. Although “Sing” has the overall meaning and the individual meaning, “Sing” here lays special emphasis on the individual noumenon, namely “Fen-shu” of “Li-yi-fen-shu.” To sum up, all of the two Mr. Chengs’ theories on the noumenon of the universe and the nature of the human beings take “Yi-li-wei-sing” to be the core thought. The theories then were constructed with the thought and method of “Li-yi-fen-shu.”