Thomas Aquinas was an Italian friar, a Catholic priest, and the Doctor of the Church in the 13th century. He was one of the best theologians in Western Europe in the Medieval Ages. His work titled Summa Theologiae highlighted the accomplishment of theology of the period. A lot of his teachings, especially sacraments and grace, are controversial, but on original sin, it is good. His answer to Question 82, Prima Secundæ Partis (First Part of the Second Part), Summa Theologiae, concerning the original sin, is summarized.
Question 1: Is original sin a habit?
According to Aquinas, original sin is a habit.
He explained that habit is two-fold. The first kind of habit is one’s inclination to act, like our framework of knowledge or worldview (“science”) and virtues are habits. Original sin, as a lack of original righteousness, is not a habit in this sense. The second kind is “the disposition of a complex nature.” Original sins, as the lack of original justice, means the souls have been spiritually corrupted, and being impossible not to sin. This impossibility not to sin is the disposition of the corrupted souls, and from this point of view, original sin is a habit. This answered the Objection 1 he listed.
It is true that with the definition of the first kind, evil habits have to be acquired through a wicked act. It contradicts that the original sin is not something we acquire. However, using the definition of the second kind of habit, we are inborn with evil habits because of the original sins. Aquinas thus disputed the Objection 3.
Then Aquinas discussed about the Objection 2 regarding the original sin and the actual sin. While an actual sin is an act beyond a permissible limit, the original sin is basically a disposition, passed on from Adam and Eve, to perform an actual sin. Even if one is asleep, he is regarded as being sinful, unlike what the Objection 2 claims.
Question 2: Are there several original sins in one man? How does Aquinas defend himself?
According to Aquinas, there is only one, instead of many, original sin in one man.
Aquinas cited from John 1:29, where John the Baptist said, “Behold the lamb of God, who takes away the sin of the world.” The “sin” here refers to the original sin, and it is clearly singular, not plural. Objection 1 quoted a verse in Psalm: “Behold I was conceived in iniquities, and in sins did my mother conceive me.” But these sins are actual sins like pride, disobedience etc., instead of the original sin. He thus disputed Objection 1.
Aquinas explained it with the cause and essence of it. The cause of the original sin is the first sin committed by Adam and Eve, and the sinful state was then passed on to us. Therefore, there is only one original sin. For the essence of it, the original sin refers to the disposition of a corrupted human nature. This disposition is numerically one. He illustrated with the sickness analogy: the original sin is like the cause of of the sickness, and various symptoms like the various actual sins. In this way, he disputed Objection 2, because the various sins in one man stem from one original sin; and he also replied to Objection 3, because it is this numerically one original sin infects different parts of the soul, which does not make this original sin to be plural.
Question 3: Is original sin the same thing as concupiscence?
According to Aquinas, the original sin is materially concupiscence, but formally the lack of original justice. Given that the original sin is the lack of original justice, man is no longer submitting to the will of God, but pursue the cause of things other than God, or “mutable good” according to him. This desire for other things other than God is concupiscence, or spiritual lust. This makes the original sin materially concupiscence. From the context, Aquinas’ concupiscence is not limited to inappropriate sexual desires.
Objection 1 argued that concupiscence is natural to man so that it cannot be of the original sin which is contrary to the human nature. But Aquinas stated that the act of concupiscence is beyond the permissible boundary, as in the corrupted human nature, and thus it is of the original sin.
Objection 2 argued that the sins are of a wide diversity besides concupiscence, but Aquinas added that these sins stem all from concupiscence, the pursuit of things other than God. The original sin, as the misplaced passion because of the lack of original justice, is therefore concupiscence.
Aquinas argued in a previous question (Question 77) that man is motivated by a strong passion instead of intellect. The corrupted nature of human being made man pursue inappropriate passion, even though his intellect should not have led him to. Original sin is thus concupiscence, although it comprises of ignorance. Hence, he disputed Objection 3.
Question 4: Is original sin equally in all of us?
According to Aquinas, original sin is equally in all of us.
Aquinas explained that as the original sin is simply the lack of original justice, there is no degree of it, as it is just the entire righteousness was removed. In addition, since all of our original sin is equally related to the sin of Adam and Eve, it is evident that no one’s original sin is greater than the other. This disputed Objection 1, which argued acts of concupiscence can be of various degrees, that this concupiscence is not something of continuous degree, but simply the lack of righteousness (a value of a binary variable). It similarly disputed Objection 2, because as in the sickness analogy, while the severity of the sickness is continuous, the cause of sickness is one.
Objection 3 cited Augustine’s quote: “lust transmits the original sin to the child.” And this lust, believably sexual in nature, is of various degrees, implying that the original sin is not equal in all of us. However, Aquinas disputed this objection that the original sin is transmitted to children even without lust.