The 15 Rules of Determining Mortal Sins

Translation of Bl. Denys the Carthusian

Summa Peccati, Lib. I, Art. XXI

Introduction to the rules by which one is able to know which sins are mortal and which are venial

“Do not any unjust thing in judgment, in rule, in weight, or in measure” (Lev. 19:35). Vices frequently put on the appearance of virtues, and things which are deadly are regarded as wholesome. For the most cunning enemy, those whom he cannot deceive through evident evils, he attempts to ensnare and overcome through apparent goods. This assault and this work belong to the noonday demon, as Bernard says, who (as the Apostle testifies) “transformeth himself into an angel of light” (2 Cor. 11:14; cf. Ps. 90:6). Therefore it is necessary, both for confessors and for penitents, and especially for preachers of the word of God, that they be able to discern which sins are mortal, in what way, and for what reason, according to certain and solid rules. For this reason, concerning this matter, I shall now introduce certain orderly rules, as judicial laws, insofar as the Lord shall grant it.

FIRST RULE: Whatever is contrary to the natural law is, according to its genus (*ex suo genere*), a mortal sin; although at times, on account of the smallness of the act or the prevention or surprise of reason, it may be venial, as also happens in other sins which are mortal according to its genus (*ex suo genere*).

The natural law is that which right and well-disposed purely natural reason dictates to all. This law, as regards its affirmative precepts, is expressed in Matthew, where the Savior says: “All things therefore whatsoever you would that men should do to you, do you also to them” (Matt. 7:12). But as regards the negative precepts, it is found in Tobias, where it is read: “See thou never do to another what thou wouldst hate to have done to thee by another” (Tob. 4:16). Nevertheless, this negative prohibition is sufficiently understood within that affirmative precept uttered by Christ. Hence, as has been stated above (art. 3, 8, 18, 19), Thomas and other doctors affirm that a sin is mortal if it is against the law, whether it be against the written law or the natural law. And in Book 2, Distinction 42, Durandus writes that every sin is against the natural law, or the inspired law, or one derived from them. Finally, according to the holy Doctors, the written law and even the evangelical law presuppose and are founded upon the natural law, and add certain things to it; therefore the natural law binds under mortal sin. Moreover, the natural law is a certain expression and image and resplendence of the eternal and uncreated law; therefore the Most High Lawgiver requires it to be fulfilled by all. For this reason He impressed and, as it were, inscribed it upon the reason of all, and did not merely set it forth in books, as Isidore teaches (cf. Rom. 2:15). **Furthermore**, commenting on that passage of Isaiah: “They have transgressed the laws, they have changed the ordinance, they have broken the everlasting covenant” (Isa. 24:5), Jerome understands by ordinance the natural law implanted in the hearts of all, for the transgression of which the Lord declares that He will condemn the reprobate. Therefore, to act against the natural law is a mortal sin; and a sin is so much the more unjust and more deadly the more it is opposed to the natural law.

But if it be objected that, according to Ambrose, sin is a transgression of the divine law, and that the natural law is distinguished from the divine law, it must be answered that the natural and divine laws, although they are formally distinct, nevertheless materially coincide; because the natural law can also be called divine, insofar as it is expressed in Sacred Scripture and proceeds immediately from the eternal law (cf. Rom. 7:12).

SECOND RULE: Whatever is opposed to justice and is done against the precepts of the Decalogue is, by its very genus (*ex suo genere*), mortal.

For the Prophet says to the Lord: “Thou hast despised all them that fall off from thy judgments; for their thought is unjust” (Ps. 118:118). And again: “Neither shall the unjust remain before thy eyes” (Ps. 5:6). Likewise: “Cursed are they who decline from thy commandments” (Ps. 118:21). This is evident from the explanation of St. Bonaventure, introduced in the nineteenth article. Hence also in Book 2, Distinction 35, he asserts that a sin exists whether it be against the law of nature, against the written law, or against the evangelical law. The same is evident from the fact that the precepts of the Decalogue are of natural law, or of the natural dictate of reason, according to all doctors, although the observance of the Sabbath, as regards the determination of time, was not of the natural law. Hence, according to Estius, the Decalogue was a certain renovation of the natural and unwritten law. Moreover, the precepts of the Decalogue concern acts of justice. Therefore in Jeremiah it is said: “Cursed be he that doth the work of God deceitfully” (Jer. 48:10). Or, as another translation has it, “negligently,” which comes to the same thing. For he performs the work of God deceitfully who does it without due diligence and thus withholds just honor from the Creator. And this is to do the work of God negligently, which is directly against justice and against the natural and divine law, because both natural reason and Sacred Scripture dictate that service must be rendered reverently and diligently to God Most High, the Prince of immense majesty.

THIRD RULE: Whatever is contrary to the evangelical and divine law is a mortal sin.

For in the evangelical law not only are the precepts of the Decalogue contained, but many others are added to them by Christ, who did not come to destroy the law, but to fulfill and perfect it, as is clear in Matthew (Matt. 5:17), where the precepts added by Christ are described, and likewise in Luke, where many things are found which, according to one interpretation, are counsels, but according to another are precepts, as is evident concerning reconciliation to be made, the avoidance of oaths, and the love of enemies (Matt. 5:23–24, 34; 5:44; Luke 6:27), also concerning giving to everyone that asks, lending, and similar matters (Matt. 5:42; Luke 6:30). But others are absolute precepts, although some of them are not expressed in the form of a command, as that saying: “Whosoever shall say to his brother, Thou fool, shall be in danger of hell fire” (Matt. 5:22). Moreover, that these bind under mortal sin is evident from the fact that Christ, at the end of these teachings, said: “Every one that heareth these my words and doth them not, shall be like a foolish man that built his house upon the sand” (Matt. 7:26). This is also clear from what He again declares in Matthew: “Not every one that saith to me, Lord, Lord, shall enter into the kingdom of heaven, but he that doth the will of my Father who is in heaven,” that is, His precepts (Matt. 7:21). Hence He speaks again: “If thou wilt enter into life, keep the commandments” (Matt. 19:17).

The divine law is divided into the evangelical law and the Mosaic law. Now in the law of Moses three kinds of precepts are contained, namely moral, judicial, and ceremonial. The moral precepts were those contained in the Decalogue, either explicitly or implicitly and directly; but the ceremonial precepts were, as it were, certain determinations of the moral precepts regarding rite and the manner of divine worship, that is, concerning the manner of observing justice in relation to God; while the judicial precepts were determinations of the moral precepts regarding the manner of observing justice among men, as Alexander of Hales in his Summa, Thomas likewise in the Prima Secundae (q. xcix, a. 4), and William of Paris in the book On Faith and Laws explain. Moreover, those ceremonial precepts were figures of the mysteries of Christ; therefore, once the Gospel of God was promulgated, they were forbidden. Likewise, those judicial precepts cease in the evangelical law, although some of them may be renewed and instituted in the New Testament by a prelate or a ruler, as Thomas asserts in the Prima Secundae (q. civ, a. 3). Therefore the saying of Blessed Ambrose, “Sin is the transgression of the divine law and disobedience to the heavenly commandments,” is not to be understood of the ceremonial and judicial precepts of the Old Testament.

FOURTH RULE: Whatever is contrary to the precepts of the Church is mortal.

This is proved from what the Son of God asserts in Matthew: “And if he will not hear the church, let him be to thee as the heathen and the publican” (Matt. 18:17). Now by the name of the Church a universal synod may be understood, concerning which Augustine speaks in the book Against Faustus: “Such is the authority of the Church that I would not believe the Gospel unless the authority of the Church moved me.” The name of the Church can also signify any Supreme Pontiff or Apostolic Lord, to whom every one of the faithful is bound to obey in all things more than any inferior or even his own prelate, as Raymond teaches in his Summa, and Thomas and Bonaventure in the Second Book of Sentences (Distinction 44). Chrysostom also, commenting on Matthew, and Durandus, who was of the Order of St. Francis, and Thomas in the Secunda Secundae, understand by “the Church” in the aforesaid words an ecclesiastical prelate (q. xxxiii, a. 8, ad 4). Therefore one must obey the general decrees of councils, and likewise the canons of the Supreme Pontiffs, as divine precepts, which, alas, is very poorly observed, because sins are committed everywhere against ecclesiastical liberty and against the privileges of religious, nor does the clergy any longer care for the decrees and canons regulating and concerning their own state.

FIFTH RULE: Whoever does not obey his superior who has legitimate jurisdiction over him, in matters that concern that superior’s authority, jurisdiction, or preeminence, sins mortally.

This is clear from what has already been said. For he acts or omits to act against what justice requires, and against the words of Christ, who said: “He that heareth you, heareth me; and he that despiseth you, despiseth me” (Luke 10:16). And Peter of Tarentaise [Bl. Innocent V] testifies to this near the end of the second book of the Sentences. Hence prompt obedience is owed to secular princes, judges, parents, and one’s own superiors, since the Apostle says to the Romans: “He that resisteth the power, resisteth the ordinance of God; And they that resist, purchase to themselves damnation” (Rom. 13:2). And elsewhere: “Servants, be obedient to your carnal masters, Not serving to the eye, as pleasing men” (Eph. 6:5–6; Col. 3:22). Indeed, the prince of the Apostles commands in his first canonical epistle: “Servants, be subject to your masters in all fear, Not only to the good and gentle, but also to the froward” (1 Pet. 2:18).

SIXTH RULE: Whatever is contrary to the charity of God or of one’s neighbor is mortal.

This has already been shown at length above (art. xviii), and the divine Apostle teaches it most clearly in the First Epistle to the Corinthians, to such an extent that he says: “And if I should deliver my body to be burned, and have not charity, it profiteth me nothing” (1 Cor. 13:3). From this Alexander of Hales on the Third Book of Sentences, and William of Auxerre in his Summa conclude that if someone, from unformed faith and servile fear, were to endure death for the faith, he would nonetheless be damned. For charity is the life of the soul, nor can anything be accepted or pleasing to God without it. Therefore the Apostle John affirms many things concerning this in his first epistle, saying: “Whosoever hateth his brother is a murderer” (1 John 3:15). And not only is whatever is contrary to charity mortal, but also whatever directly opposes any virtue that falls under a precept, because this too is contrary to the precept itself and overturns what justice requires and the order of charity.

THE SEVENTH RULE: Whoever exposes himself to moral danger sins mortally.

This is evident from the authority of St. Augustine, who asserts this. And the meaning is this: whoever doubts, when doing or omitting something, whether it is mortal, such that he does not have a more probable judgment for one side than for the other, but stands, as it were, in equilibrium, or even judges it more probably to be mortal, and yet does or omits such a thing, sins mortally, even if the act itself is in fact venial. For such a person behaves foolishly and sins against true wisdom and prudence. For the Savior commands: “Be ye therefore wise as serpents” (Matt. 10:16). And Paul says: “Become not unwise” (Eph. 5:17). Hence Ss. Thomas, Bonaventure, and others unanimously say on the Fourth Book of Sentences (Distinction XVII) that one who doubts whether any sin is mortal is bound to confess it, otherwise he would sin mortally, even if the sin were not in fact mortal, because he would be committing himself to the danger or risk of spiritual death. Hence accidental homicide is not excused when a person ought probably to have judged that homicide or something similar could result from his action. Indeed, according to St. Bonaventure on the Fourth Book, distinction seventeen, a man is bound to confess venial sins committed deliberately, lest he expose himself to danger; because many who think they are sinning venially, in fact sin mortally.

EIGHTH RULE: Whoever does not avoid a probable and proximate occasion of mortal sin, sins mortally.

This is clear from what has already been said. For such a person exposes himself to danger, especially if he has at times experienced that from such an occasion he has fallen mortally. And thus they sin mortally who, without necessity, approach persons and places where they probably know that they will fall, and who do not avoid embraces, touches, and kisses, from which, by their own experience, they know that they have sinned, or have been so gravely aroused or polluted. Concerning such occasions of sin, Hugh of St. Victor says: He cannot avoid sin who does not avoid the occasions of sin.

NINTH RULE: Not only does one sin mortally who performs a work forbidden by a precept, but also one who, with deliberation, consents to a forbidden pleasure.

This is clear from what was said in the nineteenth article. Moreover, as Thomas of Argentina says in his Compendium, morose delectation is a mortal sin. Nor is a delight called morose unless it arises from the consent of reason.

On this matter St. Thomas writes more fully in the Prima Secundae, question seventy-four, article eight, saying: Some have held that consent to a forbidden delight is only a venial sin. Others have said that it is a mortal sin; and this position is the truer one. Nevertheless, the two opinions can be reconciled in some way. For someone can, for example, take delight either in the thought of fornication insofar as that thought has the character of an object, insofar as the will or reason reflects upon its own act, or in the act of fornication that is thought about. Now a thought of fornication is not of itself always mortal, but sometimes venial, as when it clings uselessly to the mind apart from a precept. Indeed, at times it is free from all sin, as when someone thinks about it in order to argue against it or to discuss it. Moreover, the same judgment applies to such a thought and to the delectation that follows it; therefore consent to such a delight is not a mortal sin. But consent to a delight that follows a thought about the act of fornication is a mortal sin. For this delight does not occur unless a person’s affection is conformed to the act about which he is thinking, since no one takes delight except in something that is in harmony with his affection. Finally, what Augustine asserts in book twelve of *On the Trinity* accords with this: “Because of sins of thought, even without the will to carry them out, but with the will to take delight in them, the whole man will be condemned. For to consent to such a delight is nothing other than to consent that one’s affection be inclined toward the act which such delight follows.” It is also said in the *Summa Pisana*, drawing on the words of Thomas (ST, Prima Secundae, Q. LXXIV, Art. 6, ad 3): “A delight is called morose not because of length of time, but because deliberating reason lingers over it, and does not repel it, but willingly embraces the thought from which it is caused; such thoughts must be repelled as soon as they touch the mind.”

TENTH RULE: Not only does one sin mortally who carries out a forbidden act, but also he who firmly intends to do it.

For such a will is reckoned as the deed itself, since in it there is a complete turning away from God. Hence the Judge of all consciences says: “Whosoever shall look on a woman to lust after her, hath already committed adultery with her in his heart” (Matt. 5:28). Therefore Jerome says in his Epistles: “A thought is sinful once it has given consent to the suggestion.”