在儒家思想史上，以孔子儒家為代表的原始儒家在倫理學意義上探討了「孝應如何行」，卻未進一步論證「孝存在何以可能」這一關鍵性問題，也就是「孝」存在之正當性問題。《孝經》與《春秋繁露》的作者先後從天人關係的層面上，將「孝」論證為「天之道」的自我展現與自我運動。朱熹繼而從「理」形而上高度為孝存在之正當性辯護。「人理」出於天理，通人理也就是通天理。天理渾然不可分，天理與仁、義、禮、智、信、孝的關係不是本原與派生物之間的關係，而是本原與屬性之間的關係。仁義禮智孝並非由理「旋次生出」，理是人倫道德的「總名」，仁義禮智信孝則是天理之「件數」。經過儒學史上的三次論證，儒家孝道存在之正當性得以確立，思辨性不斷增強。儒家孝道不僅實現了「形式上的系統」，也實現了「實質上的系統」。

In the philosophical history of Confucianism, the original Confucianism, represented by Confucius, explored "how to perform filial piety" on the level of ethical meaning without further arguing about the critical question of "how is filial piety ever possible," namely, of the existential legitimacy of "filial piety." The authors of "The Classic of Filial Piety and Rich Dew of the Spring and Autumn Annals" respectively argued that "filial piety" was the self-demonstration and self-movement of the "way of heaven" in terms of the relationship between heaven and man. Ju Xi argued for the existential legitimacy of filial piety on the metaphysical level of "li" (理 principle). The "li of man" originates in the li of heaven; understanding the li of man equals to knowing the li of heaven. The li of heaven is whole and indivisible. The relationship between the li of heaven and "benevolence, righteousness, propriety, wisdom, fidelity, filial piety" is not one between the origin and the derivatives but between the origin and the attributes. "Benevolence, righteousness, propriety, wisdom, fidelity, filial piety" do not derive from li; li is the "general name" of the morality of human ethics, while "benevolence, righteousness, propriety, wisdom, fidelity, filial piety" are the "items" of the Ii of heaven. After the three argumentations in the history of Confucianism, the existential legitimacy of the Confucian doctrine of filial piety has been established and its speculation successively reinforced. The Confucian doctrine of filial piety fulfills not only the "formal system" but also the "substantial system."