依據《聖經》在〈創世紀〉的記載，人類始祖由於違反天主的訓戒而犯了原罪。因著原罪就將人之本性區分為兩種不同的狀態：分別為未犯原罪之前的純真狀態，以及因犯原罪而遭天主剝奪部分能力的墮落狀態。這其中的差別主要在於前者擁有來自天主的超性恩賜——原始正義。 創世紀第一章：「天主看了他所造的一切，認為樣樣都很好。」（1, 31）宗徒保祿指出：「天主所造的樣樣都好。」（弟前4, 4）即言天主造人原本是很正直的，人被造得樣樣都好，不該有任何的罪惡在其中，天主把人造得易於行善。德訓篇說：「天主造人原很正直，但人卻發明了許多詭計。」（7, 29）而以上所謂這一切的正直，指的即是天主特別給予人類始祖的超性恩賜原始正義，使得人得以易於行善與天主合一，並使人得以遠離一切的痛苦與死亡。 原始正義概念實際上是與整個基督宗教的原罪連繫在一起的，也是說明人性墮落狀態所不可或缺的內涵。本文即是以天使博士對原始正義概念的說明做出解析，目的有二：1. 指出何謂原始正義以說明人性於原罪前後的差別。2. 藉由原始正義恩賜與本性關聯說明人在純真狀態擁有原始正義的狀況中為何還能犯下原罪。

According to Genesis 3, the ancestors of human race committed original sin by breaking God’s precepts. Due to original sin, human nature is separated into two states: the innocent state before committing original sin and the fallen state after committing original sin. The difference in between is mostly that the former state is bestowed with God’s transcendental gift—original justice. “And God saw every thing that he had made, and, behold, it was very good” (Genesis 1: 31). “For every creature of God is good,” as Paul the Apostle pointed out (Timothy 4: 4), indicates that human race is made to be upright; everything about men is made to be good, and there should be nothing sinful. God made human beings inclined toward doing good. “God hath made man upright; but they have sought out many inventions” (Ecclesiastes 7: 29). This very uprightness refers to God’s transcendental gift to the ancestors of the human race, original justice, which inclines human race toward doing good and being with God as well as keeps them away from sufferings and death. The concept of original justice is actually associated with original sin, and its immanence is essential in explaining the fallen state of human nature. This article analyzes Aquinas’s explanation about the concept of original justice to reach two goals: first, to point out the differences between the states of human nature before and after original sin by explicating the content of original justice; second, through differentiating “original justice” from “human nature” to explain why our forefathers, even in the innocent state, could still commit original sin.