于斌的「三知論」之範圍包含「知人」、「知物」、「知天」等三個範疇，也是儒家傳統中所稱的格物致知，格物即于斌所指稱的「知物」，也是在現代學術分類中的自然科學，「知人」與「知天」，于斌將其歸類為致知，也以社會科學及宗教科學分別指稱。而于斌所謂的宗教科學是含括天主教神學，因此「三知論」若以Thomas S. Kuhn研究方法論中的「科學典範」（scientific paradigms）來理解，則可視其為相當獨特的科學典範。天主教社會訓導既探究人文科學與社會科學範疇的課題，更深入倫理神學的領域，在人文科學與社會科學的研究上，也屬於相當特別的一種研究方法論之科學典範。而人文社會科學中的理論典範（theoretical paradigms）只有受歡迎程度與用途多寡之差別，並不似自然科學的理論典範會有偽誤及被淘汰的情況。本研究將于斌的「三知論」與天主教社會訓導之方法論進行比較，在天主教社會訓導之方法論的文獻探究中，將以《天主教教理》（Catechism of the Catholic Church）、《信仰與理性》（Fides Et Ratio）、《信德之光》（Lumen Fidei）、《真理的光輝》（Veritatis Splendor）等文獻為中心，並從Kuhn科學研究典範的角度進行探析，希望透過此研究方法與途徑，能在天主教社會訓導之方法論上，獲致不同的研究視野與發現。

Cardinal Paul Yu Pin’s “three principles of knowing” consists in three categories: “knowing human,” “knowing nature,” and “knowing God.” It also implies the principle of “investigating things to gain knowledge” in Confucian tradition. “Investigating things” is Cardinal Yu’s principle of “knowing nature” and it could be said to be what is categorized as natural science in modern scholarship. The principles: “knowing human” and “knowing God” are categorized by Cardinal Yu as “gaining knowledge” in respect to the social science and religious science respectively. Religious science in Cardinal Yu, includes Catholic theology. Hence, in view of Thomas S. Kuhn’s research methodology— “Scientific paradigms,” the “three principles of knowing” can be considered as a unique scientific paradigm. Catholic social doctrine not only discusses problematics in the area of the human sciences and social sciences, it also deeply engages in discourses around moral theology. In human science and social science research, there also exist a related special kind of research methodological scientific paradigm. While the theoretical paradigms of natural science has the virtue of being able to be falsified and eliminated, the theoretical paradigms of the humanistic science and social science are valued by their popularity. This article is meant to make a comparison between the methodologies of Cardinal Yu’s “three principles of knowing” and that of the Catholic social doctrine. The following texts: Catechism of the Catholic Church, Fides et Ratio, Lumen Fidei, Veritatis Splendor, would be the focus of the literature review for the Catholic social doctrine. They will be analyzed in light of Kuhn’s scientific paradigm, with the hope to gain diverse research visions and findings regarding the methodology of Catholic social doctrine.