Summa Th. II-II EN Qu.73 a.2

Whether backbiting is a mortal sin?

Objection: 1. It would seem that backbiting is not a mortal sin. For no act of virtue is a mortal sin. Now, to reveal an unknown sin, which pertains to backbiting, as stated above (Article [1], ad 3), is an act of the virtue of charity, whereby a man denounces his brother's sin in order that he may amend: or else it is an act of justice, whereby a man accuses his brother. Therefore backbiting is not a mortal sin.
2. Further, a gloss on Pr 24,21, "Have nothing to do with detractors," says: "The whole human race is in peril from this vice." But no mortal sin is to be found in the whole of mankind, since many refrain from mortal sin: whereas they are venial sins that are found in all. Therefore backbiting is a venial sin.
3. Further, Augustine in a homily On the Fire of Purgatory [*Serm. civ in the appendix to St. Augustine's work] reckons it a slight sin "to speak ill without hesitation or forethought." But this pertains to backbiting. Therefore backbiting is a venial sin.

On the contrary It is written (Rm 1,30): "Backbiters, hateful to God," which epithet, according to a gloss, is inserted, "lest it be deemed a slight sin because it consists in words."
I answer that As stated above (Question [72], Article [2]), sins of word should be judged chiefly from the intention of the speaker. Now backbiting by its very nature aims at blackening a man's good name. Wherefore, properly speaking, to backbite is to speak ill of an absent person in order to blacken his good name. Now it is a very grave matter to blacken a man's good name, because of all temporal things a man's good name seems the most precious, since for lack of it he is hindered from doing many things well. For this reason it is written (Si 41,15): "Take care of a good name, for this shall continue with thee, more than a thousand treasures precious and great." Therefore backbiting, properly speaking, is a mortal sin. Nevertheless it happens sometimes that a man utters words, whereby someone's good name is tarnished, and yet he does not intend this, but something else. This is not backbiting strictly and formally speaking, but only materially and accidentally as it were. And if such defamatory words be uttered for the sake of some necessary good, and with attention to the due circumstances, it is not a sin and cannot be called backbiting. But if they be uttered out of lightness of heart or for some unnecessary motive, it is not a mortal sin, unless perchance the spoken word be of such a grave nature, as to cause a notable injury to a man's good name, especially in matters pertaining to his moral character, because from the very nature of the words this would be a mortal sin. And one is bound to restore a man his good name, no less than any other thing one has taken from him, in the manner stated above (Question [62], Article [2]) when we were treating of restitution.

Reply to Objection: 1. As stated above, it is not backbiting to reveal a man's hidden sin in order that he may mend, whether one denounce it, or accuse him for the good of public justice.
2. This gloss does not assert that backbiting is to be found throughout the whole of mankind, but "almost," both because "the number of fools is infinite," [*Qo 1,15] and few are they that walk in the way of salvation, [*Cf. Mt 7,14] and because there are few or none at all who do not at times speak from lightness of heart, so as to injure someone's good name at least slightly, for it is written (Jc 3,2): "If any man offend not in word, the same is a perfect man."
3. Augustine is referring to the case when a man utters a slight evil about someone, not intending to injure him, but through lightness of heart or a slip of the tongue.

Whether backbiting is the gravest of all sins committed against one's neighbor?

Objection: 1. It would seem that backbiting is the gravest of all sins committed against one's neighbor. Because a gloss on Ps 108,4, "Instead of making me a return of love they detracted me," a gloss says: "Those who detract Christ in His members and slay the souls of future believers are more guilty than those who killed the flesh that was soon to rise again." From this it seems to follow that backbiting is by so much a graver sin than murder, as it is a graver matter to kill the soul than to kill the body. Now murder is the gravest of the other sins that are committed against one's neighbor. Therefore backbiting is absolutely the gravest of all.
2. Further, backbiting is apparently a graver sin than reviling, because a man can withstand reviling, but not a secret backbiting. Now backbiting is seemingly a graver sin than adultery, because adultery unites two persons in one flesh, whereas reviling severs utterly those who were united. Therefore backbiting is more grievous than adultery: and yet of all other sins a man commits against his neighbor, adultery is most grave.
3. Further, reviling arises from anger, while backbiting arises from envy, according to Gregory (Moral. xxxi, 45). But envy is a graver sin than anger. Therefore backbiting is a graver sin than reviling; and so the same conclusion follows as before.
4. Further, the gravity of a sin is measured by the gravity of the defect that it causes. Now backbiting causes a most grievous defect, viz. blindness of mind. For Gregory says (Regist. xi, Ep 2): "What else do backbiters but blow on the dust and stir up the dirt into their eyes, so that the more they breathe of detraction, the less they see of the truth?" Therefore backbiting is the most grievous sin committed against one's neighbor.

On the contrary It is more grievous to sin by deed than by word. But backbiting is a sin of word, while adultery, murder, and theft are sins of deed. Therefore backbiting is not graver than the other sins committed against one's neighbor.
I answer that The essential gravity of sins committed against one's neighbor must be weighed by the injury they inflict on him, since it is thence that they derive their sinful nature. Now the greater the good taken away, the greater the injury. And while man's good is threefold, namely the good of his soul, the good of his body, and the good of external things; the good of the soul, which is the greatest of all, cannot be taken from him by another save as an occasional cause, for instance by an evil persuasion, which does not induce necessity. On the other hand the two latter goods, viz. of the body and of external things, can be taken away by violence. Since, however, the goods of the body excel the goods of external things, those sins which injure a man's body are more grievous than those which injure his external things. Consequently, among other sins committed against one's neighbor, murder is the most grievous, since it deprives man of the life which he already possesses: after this comes adultery, which is contrary to the right order of human generation, whereby man enters upon life. In the last place come external goods, among which a man's good name takes precedence of wealth because it is more akin to spiritual goods, wherefore it is written (Pr 22,1): "A good name is better than great riches." Therefore backbiting according to its genus is a more grievous sin than theft, but is less grievous than murder or adultery. Nevertheless the order may differ by reason of aggravating or extenuating circumstances.The accidental gravity of a sin is to be considered in relation to the sinner, who sins more grievously, if he sins deliberately than if he sins through weakness or carelessness. In this respect sins of word have a certain levity, in so far as they are apt to occur through a slip of the tongue, and without much forethought.

Reply to Objection: 1. Those who detract Christ by hindering the faith of His members, disparage His Godhead, which is the foundation of our faith. Wherefore this is not simple backbiting but blasphemy.
2. Reviling is a more grievous sin than backbiting, in as much as it implies greater contempt of one's neighbor: even as robbery is a graver sin than theft, as stated above (Question [66], Article [9]). Yet reviling is not a more grievous sin than adultery. For the gravity of adultery is measured, not from its being a union of bodies, but from being a disorder in human generation. Moreover the reviler is not the sufficient cause of unfriendliness in another man, but is only the occasional cause of division among those who were united, in so far, to wit, as by declaring the evils of another, he for his own part severs that man from the friendship of other men, though they are not forced by his words to do so. Accordingly a backbiter is a murderer "occasionally," since by his words he gives another man an occasion for hating or despising his neighbor. For this reason it is stated in the Epistle of Clement [*Ad Jacob. Ep. i], that "backbiters are murderers," i.e. occasionally; because "he that hateth his brother is a murderer" (1Jn 3,15).
3. Anger seeks openly to be avenged, as the Philosopher states (Rhet. ii, 2): wherefore backbiting which takes place in secret, is not the daughter of anger, as reviling is, but rather of envy, which strives by any means to lessen one's neighbor's glory. Nor does it follow from this that backbiting is more grievous than reviling: since a lesser vice can give rise to a greater sin, just as anger gives birth to murder and blasphemy. For the origin of a sin depends on its inclination to an end, i.e. on the thing to which the sin turns, whereas the gravity of a sin depends on what it turns away from.
4. Since "a man rejoiceth in the sentence of his mouth" (Pr 15,23), it follows that a backbiter more and more loves and believes what he says, and consequently more and more hates his neighbor, and thus his knowledge of the truth becomes less and less. This effect however may also result from other sins pertaining to hate of one's neighbor.

Whether it is a grave sin for the listener to suffer the backbiter?

Objection: 1. It would seem that the listener who suffers a backbiter does not sin grievously. For a man is not under greater obligations to others than to himself. But it is praiseworthy for a man to suffer his own backbiters: for Gregory says (Hom. ix, super Ezech): "Just as we ought not to incite the tongue of backbiters, lest they perish, so ought we to suffer them with equanimity when they have been incited by their own wickedness, in order that our merit may be the greater." Therefore a man does not sin if he does not withstand those who backbite others.
2. Further, it is written (Si 4,30): "In no wise speak against the truth." Now sometimes a person tells the truth while backbiting, as stated above (Article [1], ad 3). Therefore it seems that one is not always bound to withstand a backbiter.
3. Further, no man should hinder what is profitable to others. Now backbiting is often profitable to those who are backbitten: for Pope Pius [*St. Pius I] says [*Append. Grat. ad can. Oves, caus. vi, qu. 1]: "Not unfrequently backbiting is directed against good persons, with the result that those who have been unduly exalted through the flattery of their kindred, or the favor of others, are humbled by backbiting." Therefore one ought not to withstand backbiters.

On the contrary Jerome says (Ep ad Nepot. lii): "Take care not to have an itching tongue, nor tingling ears, that is, neither detract others nor listen to backbiters."
I answer that According to the Apostle (Rm 1,32), they "are worthy of death . . . not only they that" commit sins, "but they also that consent to them that do them." Now this happens in two ways. First, directly, when, to wit, one man induces another to sin, or when the sin is pleasing to him: secondly, indirectly, that is, if he does not withstand him when he might do so, and this happens sometimes, not because the sin is pleasing to him, but on account of some human fear.Accordingly we must say that if a man list ens to backbiting without resisting it, he seems to consent to the backbiter, so that he becomes a participator in his sin. And if he induces him to backbite, or at least if the detraction be pleasing to him on account of his hatred of the person detracted, he sins no less than the detractor, and sometimes more. Wherefore Bernard says (De Consid. ii, 13): "It is difficult to say which is the more to be condemned the backbiter or he that listens to backbiting." If however the sin is not pleasing to him, and he fails to withstand the backbiter, through fear negligence, or even shame, he sins indeed, but much less than the backbiter, and, as a rule venially. Sometimes too this may be a mortal sin, either because it is his official duty to cor. rect the backbiter, or by reason of some consequent danger; or on account of the radical reason for which human fear may sometimes be a mortal sin, as stated above (Question [19], Article [3]).

Reply to Objection: 1. No man hears himself backbitten, because when a man is spoken evil of in his hearing, it is not backbiting, properly speaking, but reviling, as stated above (Article [1], ad 2). Yet it is possible for the detractions uttered against a person to come to his knowledge through others telling him, and then it is left to his discretion whether he will suffer their detriment to his good name, unless this endanger the good of others, as stated above (Question [72], Article [3]). Wherefore his patience may deserve commendation for as much as he suffers patiently being detracted himself. But it is not left to his discretion to permit an injury to be done to another's good name, hence he is accounted guilty if he fails to resist when he can, for the same reason whereby a man is bound to raise another man's ass lying "underneath his burden," as commanded in Dt 21,4 [*Ex 23,5].
2. One ought not always to withstand a backbiter by endeavoring to convince him of falsehood, especially if one knows that he is speaking the truth: rather ought one to reprove him with words, for that he sins in backbiting his brother, or at least by our pained demeanor show him that we are displeased with his backbiting, because according to Pr 25,23, "the north wind driveth away rain, as doth a sad countenance a backbiting tongue."
3. The profit one derives from being backbitten is due, not to the intention of the backbiter, but to the ordinance of God Who produces good out of every evil. Hence we should none the less withstand backbiters, just as those who rob or oppress others, even though the oppressed and the robbed may gain merit by patience.

Q74: OF TALE-BEARING [*'Susurratio,' i.e. whispering] (TWO ARTICLES)

We must now consider tale-bearing: under which head there are two points of inquiry:

(1) Whether tale-bearing is a sin distinct from backbiting?

(2) Which of the two is the more grievous?

Whether tale-bearing is a sin distinct from backbiting?

Objection: 1. It would seem that tale-bearing is not a distinct sin from backbiting. Isidore says (Etym. x): "The susurro [tale-bearer] takes his name from the sound of his speech, for he speaks disparagingly not to the face but into the ear." But to speak of another disparagingly belongs to backbiting. Therefore tale-bearing is not a distinct sin from backbiting.
2. Further, it is written (Lv 19,16): "Thou shalt not be an informer [Douay: 'a detractor'] nor a tale-bearer [Douay: 'whisperer'] among the people." But an informer is apparently the same as a backbiter. Therefore neither does tale-bearing differ from backbiting.
3. Further, it is written (Si 28,15): "The tale-bearer [Douay: 'whisperer'] and the double-tongued is accursed." But a double-tongued man is apparently the same as a backbiter, because a backbiter speaks with a double tongue, with one in your absence, with another in your presence. Therefore a tale-bearer is the same as a backbiter.

On the contrary A gloss on Rm 1,29-30, "Tale-bearers, backbiters [Douay: 'whisperers, detractors']" says: "Tale-bearers sow discord among friends; backbiters deny or disparage others' good points."
I answer that The tale-bearer and the backbiter agree in matter, and also in form or mode of speaking, since they both speak evil secretly of their neighbor: and for this reason these terms are sometimes used one for the other. Hence a gloss on Si 5,16, "Be not called a tale-bearer [Douay: 'whisperer']" says: "i.e. a backbiter." They differ however in end, because the backbiter intends to blacken his neighbor's good name, wherefore he brings forward those evils especially about his neighbor which are likely to defame him, or at least to depreciate his good name: whereas a tale-bearer intends to sever friendship, as appears from the gloss quoted above and from the saying of Pr 26,20, "Where the tale-bearer is taken away, contentions shall cease." Hence it is that a tale-bearer speaks such ill about his neighbors as may stir his hearer's mind against them, according to Si 28,11, "A sinful man will trouble his friends, and bring in debate in the midst of them that are at peace."

Reply to Objection: 1. A tale-bearer is called a backbiter in so far as he speaks ill of another; yet he differs from a backbiter since he intends not to speak ill as such, but to say anything that may stir one man against another, though it be good simply, and yet has a semblance of evil through being unpleasant to the hearer.
2. An informer differs from a tale-bearer and a backbiter, for an informer is one who charges others publicly with crimes, either by accusing or by railing them, which does not apply to a backbiter or tale-bearer.
3. A double-tongued person is properly speaking a tale-bearer. For since friendship is between two, the tale-bearer strives to sever friendship on both sides. Hence he employs a double tongue towards two persons, by speaking ill of one to the other: wherefore it is written (Si 28,15): "The tale-bearer [Douay: 'whisperer'] and the double-tongued is accursed," and then it is added, "for he hath troubled many that were peace."

Whether backbiting is a graver sin than tale-bearing?

Objection: 1. It would seem that backbiting is a graver sin than tale-bearing. For sins of word consist in speaking evil. Now a backbiter speaks of his neighbor things that are evil simply, for such things lead to the loss or depreciation of his good name: whereas a tale-bearer is only intent on saying what is apparently evil, because to wit they are unpleasant to the hearer. Therefore backbiting is a graver sin than tale-bearing.
2. Further, he that deprives. a man of his good name, deprives him not merely of one friend, but of many, because everyone is minded to scorn the friendship of a person with a bad name. Hence it is reproached against a certain individual [*King Josaphat] (2Ch 19,2): "Thou art joined in friendship with them that hate the Lord." But tale-bearing deprives one of only one friend. Therefore backbiting is a graver sin than tale-bearing.
3. Further, it is written (Jc 4,11): "He that backbiteth [Douay:,'detracteth'] his brother . . . detracteth the law," and consequently God the giver of the law. Wherefore the sin of backbiting seems to be a sin against God, which is most grievous, as stated above (Question [20], Article [3]; I-II 73,3). On the other hand the sin of tale-bearing is against one's neighbor. Therefore the sin of backbiting is graver than the sin of tale-bearing.

On the contrary It is written (Si 5,17): "An evil mark of disgrace is upon the double-tongued; but to the tale-bearer [Douay: 'whisperer'] hatred, and enmity, and reproach."
I answer that As stated above (Question [73], Article [3]; I-II 73,8), sins against one's neighbor are the more grievous, according as they inflict a greater injury on him: and an injury is so much the greater, according to the greatness of the good which it takes away. Now of all one's external goods a friend takes the first place, since "no man can live without friends," as the Philosopher declares (Ethic. viii, 1). Hence it is written (Si 6,15): "Nothing can be compared to a faithful friend." Again, a man's good name whereof backbiting deprives him, is most necessary to him that he may be fitted for friendship. Therefore tale-bearing is a greater sin than backbiting or even reviling, because a friend is better than honor, and to be loved is better than to be honored, according to the Philosopher (Ethic. viii).

Reply to Objection: 1. The species and gravity of a sin depend on the end rather than on the material object, wherefore, by reason of its end, tale-bearing is worse than backbiting, although sometimes the backbiter says worse things.
2. A good name is a disposition for friendship, and a bad name is a disposition for enmity. But a disposition falls short of the thing for which it disposes. Hence to do anything that leads to a disposition for enmity is a less grievous sin than to do what conduces directly to enmity.
3. He that backbites his brother, seems to detract the law, in so far as he despises the precept of love for one's neighbor: while he that strives to sever friendship seems to act more directly against this precept. Hence the latter sin is more specially against God, because "God is charity" (1Jn 4,16), and for this reason it is written (Pr 6,16): "Six things there are, which the Lord hateth, and the seventh His soul detesteth," and the seventh is "he (Pr 6,19) that soweth discord among brethren."


We must now speak of derision, under which head there are two points of inquiry:

(1) Whether derision is a special sin distinct from the other sins whereby one's neighbor is injured by words?

(2) Whether derision is a mortal sin?

Whether derision is a special sin distinct from those already mentioned?

Objection: 1. It would seem that derision is not a special sin distinct from those mentioned above. For laughing to scorn is apparently the same as derision. But laughing to scorn pertains to reviling. Therefore derision would seem not to differ from reviling.
2. Further, no man is derided except for something reprehensible which puts him to shame. Now such are sins; and if they be imputed to a person publicly, it is a case of reviling, if privately, it amounts to backbiting or tale-bearing. Therefore derision is not distinct from the foregoing vices.
3. Further, sins of this kind are distinguished by the injury they inflict on one's neighbor. Now the injury inflicted on a man by derision affects either his honor, or his good name, or is detrimental to his friendship. Therefore derision is not a sin distinct from the foregoing.

On the contrary Derision is done in jest, wherefore it is described as "making fun." Now all the foregoing are done seriously and not in jest. Therefore derision differs from all of them.
I answer that As stated above (Question [72], Article [2]), sins of word should be weighed chiefly by the intention of the speaker, wherefore these sins are differentiated according to the various intentions of those who speak against another. Now just as the railer intends to injure the honor of the person he rails, the backbiter to depreciate a good name, and the tale-bearer to destroy friendship, so too the derider intends to shame the person he derides. And since this end is distinct from the others, it follows that the sin of derision is distinct from the foregoing sins.

Reply to Objection: 1. Laughing to scorn and derision agree as to the end but differ in mode, because derision is done with the "mouth," i.e. by words and laughter, while laughing to scorn is done by wrinkling the nose, as a gloss says on Ps 2,4, "He that dwelleth in heaven shall laugh at them": and such a distinction does not differentiate the species. Yet they both differ from reviling, as being shamed differs from being dishonored: for to be ashamed is "to fear dishonor," as Damascene states (De Fide Orth. ii, 15).
2. For doing a virtuous deed a man deserves both respect and a good name in the eyes of others, and in his own eyes the glory of a good conscience, according to 2Co 1,12, "Our glory is this, the testimony of our conscience." Hence, on the other hand, for doing a reprehensible, i.e. a vicious action, a man forfeits his honor and good name in the eyes of others---and for this purpose the reviler and the backbiter speak of another person---while in his own eyes, he loses the glory of his conscience through being confused and ashamed at reprehensible deeds being imputed to him---and for this purpose the derider speaks ill of him. It is accordingly evident that derision agrees with the foregoing vices as to the matter but differs as to the end.
3. A secure and calm conscience is a great good, according to Pr 15,15, "A secure mind is like a continual feast." Wherefore he that disturbs another's conscience by confounding him inflicts a special injury on him: hence derision is a special kind of sin.

Whether derision can be a mortal sin?

Objection: 1. It would seem that derision cannot be a mortal sin. Every mortal sin is contrary to charity. But derision does not seem contrary to charity, for sometimes it takes place in jest among friends, wherefore it is known as "making fun." Therefore derision cannot be a mortal sin.
2. Further, the greatest derision would appear to be that which is done as an injury to God. But derision is not always a mortal sin when it tends to the injury of God: else it would be a mortal sin to relapse into a venial sin of which one has repented. For Isidore says (De Sum. Bon. ii, 16) that "he who continues to do what he has repented of, is a derider and not a penitent." It would likewise follow that all hypocrisy is a mortal sin, because, according to Gregory (Moral. xxxi, 15) "the ostrich signifies the hypocrite, who derides the horse, i.e. the just man, and his rider, i.e. God." Therefore derision is not a mortal sin.
3. Further, reviling and backbiting seem to be graver sins than derision, because it is more to do a thing seriously than in jest. But not all backbiting or reviling is a mortal sin. Much less therefore is derision a mortal sin.

On the contrary It is written (Pr 3,34): "He derideth [Vulg.: 'shall scorn'] the scorners." But God's derision is eternal punishment for mortal sin, as appears from the words of Ps 2,4, "He that dwelleth in heaven shall laugh at them." Therefore derision is a mortal sin.
I answer that The object of derision is always some evil or defect. Now when an evil is great, it is taken, not in jest, but seriously: consequently if it is taken in jest or turned to ridicule (whence the terms 'derision' and 'jesting'), this is because it is considered to be slight. Now an evil may be considered to be slight in two ways: first, in itself, secondly, in relation to the person. When anyone makes game or fun of another's evil or defect, because it is a slight evil in itself, this is a venial sin by reason of its genus. on the other hand this defect may be considered as a slight evil in relation to the person, just as we are wont to think little of the defects of children and imbeciles: and then to make game or fun of a person, is to scorn him altogether, and to think him so despicable that his misfortune troubles us not one whit, but is held as an object of derision. In this way derision is a mortal sin, and more grievous than reviling, which is also done openly: because the reviler would seem to take another's evil seriously; whereas the derider does so in fun, and so would seem the more to despise and dishonor the other man. Wherefore, in this sense, derision is a grievous sin, and all the more grievous according as a greater respect is due to the person derided.Consequently it is an exceedingly grievous sin to deride God and the things of God, according to Is 37,23, "Whom hast thou reproached, and whom hast thou blasphemed, and against whom hast thou exalted thy voice?" and he replies: "Against the Holy One of Israel." In the second place comes derision of one's parents, wherefore it is written (Pr 30,17): "The eye that mocketh at his father, and that despiseth the labor of his mother in bearing him, let the ravens of the brooks pick it out, and the young eagles eat it." Further, the derision of good persons is grievous, because honor is the reward of virtue, and against this it is written (Jb 12,4): "The simplicity of the just man is laughed to scorn." Such like derision does very much harm: because it turns men away from good deeds, according to Gregory (Moral. xx, 14), "Who when they perceive any good points appearing in the acts of others, directly pluck them up with the hand of a mischievous reviling."

Reply to Objection: 1. Jesting implies nothing contrary to charity in relation to the person with whom one jests, but it may imply something against charity in relation to the person who is the object of the jest, on account of contempt, as stated above.
2. Neither he that relapses into a sin of which he has repented, nor a hypocrite, derides God explicitly, but implicitly, in so far as either's behavior is like a derider's. Nor is it true that to commit a venial sin is to relapse or dissimulate altogether, but only dispositively and imperfectly.
3. Derision considered in itself is less grievous than backbiting or reviling, because it does not imply contempt, but jest. Sometimes however it includes greater contempt than reviling does, as stated above, and then it is a grave sin.


We must now consider cursing. Under this head there are four points of inquiry:

(1) Whether one may lawfully curse another?

(2) Whether one may lawfully curse an irrational creature?

(3) Whether cursing is a mortal sin?

(4) Of its comparison with other sins.

Whether it is lawful to curse anyone?

Objection: 1. It would seem unlawful to curse anyone. For it is unlawful to disregard the command of the Apostle in whom Christ spoke, according to 2Co 13,3. Now he commanded (Rm 12,14), "Bless and curse not." Therefore it is not lawful to curse anyone.
2. Further, all are bound to bless God, according to Da 3,82, "O ye sons of men, bless the Lord." Now the same mouth cannot both bless God and curse man, as proved in the third chapter of James. Therefore no man may lawfully curse another man.
3. Further, he that curses another would seem to wish him some evil either of fault or of punishment, since a curse appears to be a kind of imprecation. But it is not lawful to wish ill to anyone, indeed we are bound to pray that all may be delivered from evil. Therefore it is unlawful for any man to curse.
4. Further, the devil exceeds all in malice on account of his obstinacy. But it is not lawful to curse the devil, as neither is it lawful to curse oneself; for it is written (Si 21,30): "While the ungodly curseth the devil, he curseth his own soul." Much less therefore is it lawful to curse a man.
5. Further, a gloss on Nb 23,8, "How shall I curse whom God hath not cursed?" says: "There cannot be a just cause for cursing a sinner if one be ignorant of his sentiments." Now one man cannot know another man's sentiments, nor whether he is cursed by God. Therefore no man may lawfully curse another.

On the contrary It is written (Dt 27,26): "Cursed be he that abideth not in the words of this law." Moreover Eliseus cursed the little boys who mocked him (2R 2,24).
I answer that To curse [maledicere] is the same as to speak ill [malum dicere]. Now "speaking" has a threefold relation to the thing spoken. First, by way of assertion, as when a thing is expressed in the indicative mood: in this way "maledicere" signifies simply to tell someone of another's evil, and this pertains to backbiting, wherefore tellers of evil [maledici] are sometimes called backbiters. Secondly, speaking is related to the thing spoken, by way of cause, and this belongs to God first and foremost, since He made all things by His word, according to Ps 32,9, "He spoke and they were made"; while secondarily it belongs to man, who, by his word, commands others and thus moves them to do something: it is for this purpose that we employ verbs in the imperative mood. Thirdly, "speaking" is related to the thing spoken by expressing the sentiments of one who desires that which is expressed in words; and for this purpose we employ the verb in the optative mood.Accordingly we may omit the first kind of evil speaking which is by way of simple assertion of evil, and consider the other two kinds. And here we must observe that to do something and to will it are consequent on one another in the matter of goodness and wickedness, as shown above (I-II 20,3). Hence in these two ways of evil speaking, by way of command and by way of desire, there is the same aspect of lawfulness and unlawfulness, for if a man commands or desires another's evil, as evil, being intent on the evil itself, then evil speaking will be unlawful in both ways, and this is what is meant by cursing. On the other hand if a man commands or desires another's evil under the aspect of good, it is lawful; and it may be called cursing, not strictly speaking, but accidentally, because the chief intention of the speaker is directed not to evil but to good.Now evil may be spoken, by commanding or desiring it, under the aspect of a twofold good. Sometimes under the aspect of just, and thus a judge lawfully curses a man whom he condemns to a just penalty: thus too the Church curses by pronouncing anathema. In the same way the prophets in the Scriptures sometimes call down evils on sinners, as though conforming their will to Divine justice, although such like imprecation may be taken by way of foretelling. Sometimes evil is spoken under the aspect of useful, as when one wishes a sinner to suffer sickness or hindrance of some kind, either that he may himself reform, or at least that he may cease from harming others.

Reply to Objection: 1. The Apostle forbids cursing strictly so called with an evil intent:
2. and the same answer applies to the Second Objection.
3. To wish another man evil under the aspect of good, is not opposed to the sentiment whereby one wishes him good simply, in fact rather is it in conformity therewith.
4. In the devil both nature and guilt must be considered. His nature indeed is good and is from God nor is it lawful to curse it. On the other hand his guilt is deserving of being cursed, according to Jb 3,8, "Let them curse it who curse the day." Yet when a sinner curses the devil on account of his guilt, for the same reason he judges himself worthy of being cursed; and in this sense he is said to curse his own soul.
5. Although the sinner's sentiments cannot be perceived in themselves, they can be perceived through some manifest sin, which has to be punished. Likewise although it is not possible to know whom God curses in respect of final reprobation, it is possible to know who is accursed of God in respect of being guilty of present sin.

Summa Th. II-II EN Qu.73 a.2