The Lord Confronts the Disobedience of Adam & Eve; The Expulsion from Paradise
(Mid 12th Century)
Nave Mosaics from Palatine Chapel
Palermo, Sicily

St. Thomas Aquinas on the Corruption of Human Nature as an Effect of Sin

The purpose of this series is to understand and explain the theological rationale underlying Sessions Five and Six of the Council of Trent, particularly insofar as it drew from the work of St. Thomas Aquinas. To review this series, see Part 1, which introduces the series, and Part 2, on the essence of original sin.

Aquinas addresses the effects of sin in Questions 85-87 of Pars Prima Secundae of his Summa Theologica. The effects of sin, according to Aquinas, are three-fold: corruption, stain, and debt. In Question 85 he considers the corruption of the good of nature. In Question 86 he considers the stain on the soul. And in Question 87 he considers the debt of punishment. In this post, I will present a short overview of Aquinas’ teaching in Question 85 on the corruption of nature as an effect of sin.

Sin Diminishes the Good of Human Nature

In the first article, Aquinas teaches that sin diminishes the good of nature [diminuat bonum naturae]. First he explains the three ways in which human nature is good. He writes:

The good of human nature is threefold. First, there are the principles of which nature is constituted, and the properties that flow from them, such as the powers of the soul, and so forth. Secondly, since man has from nature an inclination to virtue, as stated above (60, 1; 63, 1), this inclination to virtue is a good of nature. Thirdly, the gift of original justice, conferred on the whole of human nature in the person of the first man, may be called a good of nature.¹

Let’s look more carefully at these three ways, according to Aquinas, that human nature can be good. First, human nature is good in the very principles of nature (i.e. the principles out of which nature is constituted) and in the properties that follow upon these principles. By ‘principles’ here he is referring to the internal principles of form and matter.²  From our form and matter we have the properties and powers that are natural to members of our kind. Aquinas gives as an example the powers of the soul, since the soul’s powers follow from the kind of soul that it is. A rational soul, for example, has by its very nature the power of rationality. Why are these principles good? They are good because one of the three ways in which a thing is perfect is that in which its being consists, [quod in suo esse constituitur], and everything is good insofar as it is perfect.³

Second, human nature is good in its natural inclination to virtue. Man’s reason, according to Aquinas, naturally comes to know both the first principles of knowledge and the first principles of action.⁴  The very first principle of action, for example, is that good should be done and evil avoided. These first principles, according to Aquinas, are the nurseries [seminalia] of the intellectual and moral vitues. Furthermore, man’s will, according to Aquinas, has a natural appetite for the-good-which-is-according-to-reason [naturalis appetitus boni quod est secundum rationem].⁵

The third way in which human nature can be good is by way of the gift of original righteousness, which I discussed in Part 2 when explaining the “harmony of original justice.” These three ways in which human nature can be good are not equally affected by sin. Aquinas writes:

Accordingly, the first-mentioned good of nature is neither destroyed nor diminished by sin. The third good of nature was entirely destroyed through the sin of our first parent. But the second good of nature, viz. the natural inclination to virtue, is diminished by sin. Because human acts produce an inclination to like acts, as stated above (Question 50, Article 1). Now from the very fact that thing becomes inclined to one of two contraries, its inclination to the other contrary must needs be diminished. Wherefore as sin is opposed to virtue, from the very fact that a man sins, there results a diminution of that good of nature, which is the inclination to virtue.⁶

So according to Aquinas, the good of human nature in its very principles, is neither destroyed nor diminished by sin. Sin does not make us into a different species, let alone into a species of lesser goodness. After sin we remain in essence human (i.e. rational animal), even though in our behavior we fall short of what we are by nature.⁷  By contrast, the good we had in the gift of original righteousness, i.e. the harmony of original justice, was entirely destroyed by Adam’s sin.

But according to Aquinas the second good of human nature, that is, the good of our natural inclination to virtue, is diminished [diminuitur] by sin. This is because our actions affect our inclinations. An inclination or disposition is an act in potency. Dispositions exist in powers of the soul. If a particular power of the soul can operate in different ways, then repeated acts in one particular way by means of that power implant in that power a potency to act in that particular way. This is how habits are formed. And this is what Aquinas is talking about when he says that “human acts produce an inclination to like acts”. Now, if something becomes inclined to one of two contraries (e.g. good or evil), it follows that its inclination to the other contrary must be diminished. Therefore, since sin is the contrary of virtue, then from the fact that a man sins, it follows that the good that consists in his inclination to virtue must diminish.

Sin Cannot Remove the Entire Good of Human Nature

In Article 2, Aquinas argues that sin cannot remove the entire good of human nature. He first shows that this must be true, on account of the ontological relation between good and evil. In the Sed contra he writes:

Augustine says (Enchiridion xiv) that “evil does not exist except in some good.” But the evil of sin cannot be in the good of virtue or of grace, because they are contrary to it. Therefore it must be in the good of nature, and consequently it does not destroy it entirely.⁸

The Manichees were dualists who held that good and evil were two fundamental principles, neither more fundamental than the other. St. Augustine (354-430) had been a ‘hearer’ among the Manichees for nine years, until in 383 he encountered the renowned Manichee named Faustus, and started seeing problems with Manichaeism. In 386, as a professor of rhetoric in Milan, he encountered the Neo-Platonic alternative to the dualist philosophy of the Manichees. The Neo-Platonists explained evil not as a principle equally fundamental to goodness, but rather as a privation of goodness. This position was philosophically superior to that of the Manichees, and later, as a Christian, St. Augustine found that it fit beautifully with the data of Christian revelation. It treated being and goodness as the same in referent, differing only in sense (i.e. concept). Because being and goodness are the same in referent, therefore a privation of goodness is also a privation of being. Therefore, there could be no such thing as pure evil, for it would have no being.

That conclusion grounds the argument that Aquinas makes here. The evil of sin is in some sense present in sinful man. But because there can be no such thing as pure evil, therefore evil can exist only parasitically in some good. Since sin cannot be in virtue or in grace, because they are contrary to sin, therefore sin in man must be in the good of man’s nature. But if sin entirely destroyed the good of human nature, then sin could not exist in the good of human nature. Therefore, because sin is present in man, it follows that sin does not entirely destroy the good of human nature.

In his Responseo Aquinas continues:

As stated above (Article 1), the good of nature, that is diminished by sin, is the natural inclination to virtue, which is befitting to man from the very fact that he is a rational being; for it is due to this that he performs actions in accord with reason, which is to act virtuously. Now sin cannot entirely take away from man the fact that he is a rational being, for then he would no longer be capable of sin. Wherefore it is not possible for this good of nature to be destroyed entirely.⁹

Here he refers back to his argument in article 1, to show that the good of nature that is diminished by sin is the natural inclination to virtue. We have this natural inclination to virtue because we are by nature rational beings, and our rational power is by nature our highest power. Furthermore, what makes an action virtuous is that it is in accord with reason. So in order for a being to sin, that being must have a rational nature, because a non-rational being (e.g. a plant or a cat) cannot sin. But since sin does not make us no longer capable of sin, therefore sin cannot make us into something other than a rational being by nature. And since our natural inclination to virtue follows from the very fact that we are rational beings by nature, therefore because sin cannot make us into something other than a rational being by nature, it follows that sin cannot entirely destroy our natural inclination to virtue, even though sin can diminish our natural inclination to virtue.

In the last section of his argument in this article, Aquinas explains that our natural inclination to virtue lies between our rational nature and virtue. Our natural inclination to virtue has as its root [radice] our rational nature, and has as its term and end the good of virtue. Because our rational nature cannot be diminished by sin, therefore our natural inclination to virtue cannot be diminished at its root. But, our natural inclination to virtue can be diminished with respect to attaining its end (i.e. virtue), because by sin an obstacle [impedimentum] is placed against its attaining its end. Since our natural inclination to virtue cannot be diminished at its root, but only at its term, therefore our natural inclination to virtue cannot be destroyed entirely, because the root of this inclination always remains [semper manet radix talis inclinationis].

The Four Wounds of Nature Consequent Upon Sin

In the third article, Aquinas explains the four wounds consequent upon sin. He writes:

As a result of original justice, the reason had perfect hold over the lower parts of the soul, while reason itself was perfected by God, and was subject to Him. Now this same original justice was forfeited through the sin of our first parent, as already stated (81, 2); so that all the powers of the soul are left, as it were, destitute of their proper order, whereby they are naturally directed to virtue; which destitution is called a wounding of nature.¹⁰

First, he briefly describes what original justice was, and the general result of its loss. I have discussed already in Part 2 of this series Aquinas’ explanation of original justice (also called original righteousness). By the loss of this original justice through Adam’s sin, the powers of the soul were left, as it were, destitute of their proper order [destitutae proprio ordine], whereby they were naturally ordered to virtue [quo naturaliter ordinantur ad virtutem]. This destitution of their proper order, he says, is called a wounding of nature [vulneratio naturae]. He continues:

Again, there are four of the soul’s powers that can be subject of virtue, as stated above (Question 61, Article 2), viz. the reason, where prudence resides, the will, where justice is, the irascible, the subject of fortitude, and the concupiscible, the subject of temperance. Therefore in so far as the reason is deprived of its order to the true, there is the wound of ignorance; in so far as the will is deprived of its order of good, there is the wound of malice; in so far as the irascible is deprived of its order to the arduous, there is the wound of weakness; and in so far as the concupiscible is deprived of its order to the delectable, moderated by reason, there is the wound of concupiscence.¹¹

There are four wounds of nature consequent upon sin, because the soul has four powers that can be subject to virtue: reason [ratio], in which is the virtue of prudence [prudentia], will [voluntas], in which is the virtue of justice, the irascible appetite [irascibilis], in which is the virtue of fortitude, and the concupiscible appetite [concupiscibilis], in which is the virtue of temperance [temperantia]. These four virtues are called the cardinal or ‘hinge’ virtues, because all the other moral virtues depend upon them. Insofar as reason is deprived of its order to the true, there is the wound of ignorance. Insofar as the will is deprived of its order to the good, there is the wound of malice [malitiae], which Aquinas describes as a certain proneness of the will to evil [pronitate voluntatis ad malum].¹²  Insofar as the irascible appetite is deprived of its order to the arduous good, there is the wound of weakness [infirmitatis]. And insofar as the concupiscible appetite is deprived of its order to the delectable-moderated-by-reason [delectabile moderatum ratione], there is the wound of concupiscence. Aquinas continues:

Accordingly these are the four wounds inflicted on the whole of human nature as a result of our first parent’s sin. But since the inclination to the good of virtue is diminished in each individual on account of actual sin, as was explained above (Question 1, Article 2), these four wounds are also the result of other sins, in so far as, through sin, the reason is obscured, especially in practical matters, the will hardened to evil, good actions become more difficult and concupiscence more impetuous.¹³

These four wounds were inflicted on the whole of human nature as a result of Adam’s sin. But these four wounds are not the same as original sin. Original sin is the loss of the third good described in Article 1 above, namely, the good of original righteousness. But the four wounds, though consequent on sin, are due to the loss (in the sense of diminution, not total destruction) of the second good described in Article 1 above, namely, the good of our natural inclination to virtue. Therefore, since original righteous was wholly destroyed upon Adam’s sin, original sin cannot be made worse by additional sinful acts. By contrast, because human acts produce an inclination to like acts in the very powers through which those acts are performed, and because the four wounds are wounds to the powers in their natural inclinations to their respective virtues, therefore the four wounds can be made worse by additional sinful acts.¹⁴

Death and Other Bodily Defects are not Natural to Man, but are a Result of Sin

In Articles 5 and 6 Aquinas argues that death and bodily defects are results of sin, and are not natural to man. According to Aquinas in Article 5, sin is the cause of death and of all bodily defects, because sin removed the original justice our first parents enjoyed. By this original justice the lower powers of the soul were held subject to reason, without any disorder whatsoever. But original justice was not only the ordered harmony of the powers of the soul to each other; it also included the subjection of the whole body to the soul, without any bodily defect.¹⁵  Therefore, by the loss of original justice, our first parents lost the perfect subjection of the body to the soul. This is why the body is now subject to defect and corruption (i.e. bodily decay).

We might then ask why, when all our sin, both original and actual, is removed at baptism, the defects of the body remain. Aquinas answers:

Both original and actual sin are removed by the same cause that removes these defects, according to the Apostle (Romans 8:11): “He . . . shall quicken . . . your mortal bodies, because of His Spirit that dwelleth in you”: but each is done according to the order of Divine wisdom, at a fitting time. Because it is right that we should first of all be conformed to Christ’s sufferings, before attaining to the immortality and impassibility of glory, which was begun in Him, and by Him acquired for us. Hence it behooves that our bodies should remain, for a time, subject to suffering, in order that we may merit the impassibility of glory, in conformity with Christ.¹⁶

According to Aquinas God does not without reason allow us to suffer in these decaying bodies during this present life. Through our suffering, we are conformed to Christ’s sufferings, and may merit the impassibility of glory, in conformity with Christ.

In Article 6 Aquinas argues that death and bodily defects are not natural to man. He writes:

[W]e must observe that the form of man which is the rational soul, in respect of its incorruptibility is adapted to its end, which is everlasting happiness: whereas the human body, which is corruptible, considered in respect of its nature, is, in a way, adapted to its form, and, in another way, it is not.¹⁷

Aquinas has argued elsewhere that the form of man, which is the rational soul, is incorruptible, by which he means that it naturally subsists per se; it is naturally not in potency to dissolution so as to cease to exist.¹⁸  Here he says that the human soul, in respect of its incorruptibility, is adapted to its end, which is everlasting happiness. But the human body, which is corruptible, is in one way adapted to its form, and in another way is not.

As an illustration Aquinas notes that the smith, in order to make a knife, chooses a matter that is hard and can be sharpened. Since iron meets these criteria, the smith chooses to use iron to make the knife. But iron by its very nature is also breakable and disposed to rust. Those qualities of iron are not the reasons the smith chooses to use iron in order to make the knife. Aquinas then concludes:

In like manner the human body is the matter chosen by nature in respect of its being of a mixed temperament, in order that it may be most suitable as an organ of touch and of the other sensitive and motive powers. Whereas the fact that it is corruptible is due to a condition of matter, and is not chosen by nature: indeed nature would choose an incorruptible matter if it could. But God, to Whom every nature is subject, in forming man supplied the defect of nature, and by the gift of original justice, gave the body a certain incorruptibility, as was stated in the I, 97, 1. It is in this sense that it is said that “God made not death,” and that death is the punishment of sin.¹⁹

Just as iron is breakable and disposed to rust, though those are not the qualities for which it is chosen to be the knife’s matter, so likewise the body is corruptible due to a condition of matter (for matter is naturally corruptible) though its corruptibility was not the reason it was chosen to be that which the soul informed. More suited to the nature of the soul would have been an incorruptible body. But in forming man, God supplied [supplevit] the defect of nature [defectum naturae], and by the gift of original justice, which ordered the corruptible body to the incorruptible soul, gave to the body a certain incorruptibility [incorruptibilitatem quandam]. By “certain incorruptibility” here Aquinas means a mediated incorruptibility, one that is extrinsic to the body as such, and dependent upon its ordered  relation to something else. By the gift of original justice the body was not made intrinsically incorruptible, but by this gift the body was made incorruptible-by-relation to the soul. So when Adam and Eve forfeited their original justice through sin, they thereby forfeited the mediated incorruptibility their bodies had enjoyed. Death thus entered into the world, through sin.

“[A]s through one man sin entered into the world, and death through sin, and so death spread to all men ….” (Romans 5:12)

Part 4 can be found here.

1. Summa Theologica I-II Q.85 a.1. co.
2. See his work titled De principiis naturae [On the Principles of Nature].
3. Aquinas explains this three-fold goodness elsewhere when he says: “For everything is called good according to its perfection. Now perfection of a thing is threefold: first, according to the constitution of its own being; secondly, in respect of any accidents being added as necessary for its perfect operation; thirdly, perfection consists in the attaining to something else as the end.” [Summa Theologica I Q.6 a.3 co.]
4. Those are the first principles of speculative reason and the first principles of practical reason, respectively.
5. Summa Theologica I-II Q.63 a.1
6. Summa Theologica I-II Q.85 a.1. co.
7. He defends this claim in the next article.
8. Summa Theologica I-II Q.85 a.2. sc.
9. Summa Theologica I-II Q.85 a.2. co.
10. Summa Theologica I-II Q.85 a.3. co.
11. Summa Theologica I-II Q.85 a.3. co.
12. Summa Theologica I-II Q.85 a.3 ad 2
13. Summa Theologica I-II Q.85 a.3. co.
14. I am passing over Article 4 in order to shorten and simplify this summary of Question 85.
15. Cf. Summa Theologica I Q.97 a.1
16. Summa Theologica I-II Q.85 a.5 ad 2
17. Summa Theologica I-II Q.85 a.6 co.
18. Summa Theologica I Q.75 a.6
19. Summa Theologica I-II Q.85 a.6 co.