Summa Th. II-II EN Qu.34


We must how consider the vices opposed to charity: (1) hatred, which is opposed to love; (2) sloth and envy, which are opposed to the joy of charity; (3) discord and schism, which are contrary to peace; (4) offense and scandal, which are contrary to beneficence and fraternal correction.

Under the first head there are six points of inquiry:

(1) Whether it is possible to hate God?

(2) Whether hatred of God is the greatest of sins?

(3) Whether hatred of one's neighbor is always a sin?

(4) Whether it is the greatest of all sins against our neighbor?

(5) Whether it is a capital sin?

(6) From what capital sin does it arise?

Whether it is possible for anyone to hate God?

Objection: 1. It would seem that no man can hate God. For Dionysius says (Div. Nom. iv) that "the first good and beautiful is an object of love and dilection to all." But God is goodness and beauty itself. Therefore He is hated by none.
2. Further, in the Apocryphal books of 3 Esdras 4:36,[39] it is written that "all things call upon truth . . . and (all men) do well like of her works." Now God is the very truth according to Jn 14,6. Therefore all love God, and none can hate Him.
3. Further, hatred is a kind of aversion. But according to Dionysius (Div. Nom. i) God draws all things to Himself. Therefore none can hate Him.

On the contrary It is written (Ps 73,23): "The pride of them that hate Thee ascendeth continually," and (Jn 15,24): "But now they have both seen and hated both Me and My Father."
I answer that As shown above (I-II 29,1), hatred is a movement of the appetitive power, which power is not set in motion save by something apprehended. Now God can be apprehended by man in two ways; first, in Himself, as when He is seen in His Essence; secondly, in His effects, when, to wit, "the invisible things" of God . . . "are clearly seen, being understood by the things that are made" (Rm 1,20). Now God in His Essence is goodness itself, which no man can hate---for it is natural to good to be loved. Hence it is impossible for one who sees God in His Essence, to hate Him.Moreover some of His effects are such that they can nowise be contrary to the human will, since "to be, to live, to understand," which are effects of God, are desirable and lovable to all. Wherefore again God cannot be an object of hatred if we consider Him as the Author of such like effects. Some of God's effects, however, are contrary to an inordinate will, such as the infliction of punishment, and the prohibition of sin by the Divine Law. Such like effects are repugnant to a will debased by sin, and as regards the consideration of them, God may be an object of hatred to some, in so far as they look upon Him as forbidding sin, and inflicting punishment.

Reply to Objection: 1. This argument is true of those who see God's Essence, which is the very essence of goodness.
2. This argument is true in so far as God is apprehended as the cause of such effects as are naturally beloved of all, among which are the works of Truth who reveals herself to men.
3. God draws all things to Himself, in so far as He is the source of being, since all things, in as much as they are, tend to be like God, Who is Being itself.

Whether hatred of God is the greatest of sins?

Objection: 1. It would seem that hatred of God is not the greatest of sins. For the most grievous sin is the sin against the Holy Ghost, since it cannot be forgiven, according to Mt 12,32. Now hatred of God is not reckoned among the various kinds of sin against the Holy Ghost, as may be seen from what has been said above (Question [14], Article [2]). Therefore hatred of God is not the most grievous sin.
2. Further, sin consists in withdrawing oneself from God. Now an unbeliever who has not even knowledge of God seems to be further away from Him than a believer, who though he hate God, nevertheless knows Him. Therefore it seems that the sin of unbelief is graver than the sin of hatred against God.
3. Further, God is an object of hatred, only by reason of those of His effects that are contrary to the will: the chief of which is punishment. But hatred of punishment is not the most grievous sin. Therefore hatred of God is not the most grievous sin.

On the contrary The best is opposite to the worst, according to the Philosopher (Ethic. viii, 10). But hatred of God is contrary to the love of God, wherein man's best consists. Therefore hatred of God is man's worst sin.
I answer that The defect in sin consists in its aversion from God, as stated above (Question [10], Article [3]): and this aversion would not have the character of guilt, were it not voluntary. Hence the nature of guilt consists in a voluntary aversion from God.Now this voluntary aversion from God is directly implied in the hatred of God, but in other sins, by participation and indirectly. For just as the will cleaves directly to what it loves, so does it directly shun what it hates. Hence when a man hates God, his will is directly averted from God, whereas in other sins, fornication for instance, a man turns away from God, not directly, but indirectly, in so far, namely, as he desires an inordinate pleasure, to which aversion from God is connected. Now that which is so by itself, always takes precedence of that which is so by another. Wherefore hatred of God is more grievous than other sins.

Reply to Objection: 1. According to Gregory (Moral. xxv, 11), "it is one thing not to do good things, end another to hate the giver of good things, even as it is one thing to sin indeliberately, and another to sin deliberately." This implies that to hate God, the giver of all good things, is to sin deliberately, and this is a sin against the Holy Ghost. Hence it is evident that hatred of God is chiefly a sin against the Holy Ghost, in so far as the sin against the Holy Ghost denotes a special kind of sin: and yet it is not reckoned among the kinds of sin against the Holy Ghost, because it is universally found in every kind of that sin.
2. Even unbelief is not sinful unless it be voluntary: wherefore the more voluntary it is, the more it is sinful. Now it becomes voluntary by the fact that a man hates the truth that is proposed to him. Wherefore it is evident that unbelief derives its sinfulness from hatred of God, Whose truth is the object of faith; and hence just as a cause is greater than its effect, so hatred of God is a greater sin than unbelief.
3. Not everyone who hates his punishment, hates God the author of punishments. For many hate the punishments inflicted on them, and yet they bear them patiently out of reverence for the Divine justice. Wherefore Augustine says (Confess. x) that God commands us to bear with penal evils, not to love them. On the other hand, to break out into hatred of God when He inflicts those punishments, is to hate God's very justice, and that is a most grievous sin. Hence Gregory says (Moral. xxv, 11): "Even as sometimes it is more grievous to love sin than to do it, so is it more wicked to hate justice than, not to have done it."

Whether hatred of one's neighbor is always a sin?

Objection: 1. It would seem that hatred of one's neighbor is not always a sin. For no sin is commanded or counselled by God, according to Pr 8,8: "All My words are just, there is nothing wicked nor perverse in them." Now, it is written (Lc 14,26): "If any man come to Me, and hate not his father and mother . . . he cannot be My disciple." Therefore hatred of one's neighbor is not always a sin.
2. Further, nothing wherein we imitate God can be a sin. But it is in imitation of God that we hate certain people: for it is written (Rm 1,30): "Detractors, hateful to God." Therefore it is possible to hate certain people without committing a sin.
3. Further, nothing that is natural is a sin, for sin is a "wandering away from what is according to nature," according to Damascene (De Fide Orth. ii, 4,30; iv, 20). Now it is natural to a thing to hate whatever is contrary to it, and to aim at its undoing. Therefore it seems that it is not a sin to hate one's I enemy.

On the contrary It is written (1Jn 2,9): "He that . . . hateth his brother, is in darkness." Now spiritual darkness is sin. Therefore there cannot be hatred of one's neighbor without sin.
I answer that Hatred is opposed to love, as stated above (I-II 29,2); so that hatred of a thing is evil according as the love of that thing is good. Now love is due to our neighbor in respect of what he holds from God, i.e. in respect of nature and grace, but not in respect of what he has of himself and from the devil, i.e. in respect of sin and lack of justice.Consequently it is lawful to hate the sin in one's brother, and whatever pertains to the defect of Divine justice, but we cannot hate our brother's nature and grace without sin. Now it is part of our love for our brother that we hate the fault and the lack of good in him, since desire for another's good is equivalent to hatred of his evil. Consequently the hatred of one's brother, if we consider it simply, is always sinful.

Reply to Objection: 1. By the commandment of God (Ex 20,12) we must honor our parents---as united to us in nature and kinship. But we must hate them in so far as they prove an obstacle to our attaining the perfection of Divine justice.
2. God hates the sin which is in the detractor, not his nature: so that we can hate detractors without committing a sin.
3. Men are not opposed to us in respect of the goods which they have received from God: wherefore, in this respect, we should love them. But they are opposed to us, in so far as they show hostility towards us, and this is sinful in them. In this respect we should hate them, for we should hate in them the fact that they are hostile to us.

Whether hatred of our neighbor is the most grievous sin against our neighbor?

Objection: 1. It would seem that hatred of our neighbor is the most grievous sin against our neighbor. For it is written (1Jn 3,15): "Whosoever hateth his brother is a murderer." Now murder is the most grievous of sins against our neighbor. Therefore hatred is also.
2. Further, worst is opposed to best. Now the best thing we give our neighbor is love, since all other things are referable to love. Therefore hatred is the worst.

On the contrary A thing is said to be evil, because it hurts, as Augustine observes (Enchiridion xii). Now there are sins by which a man hurts his neighbor more than by hatred, e.g. theft, murder and adultery. Therefore hatred is not the most grievous sin.Moreover, Chrysostom [*Hom. x in the Opus Imperfectum, falsely ascribed to St. John Chrysostom] commenting on Mt 5,19, "He that shall break one of these least commandments," says: "The commandments of Moses, Thou shalt not kill, Thou shalt not commit adultery, count for little in their reward, but they count for much if they be disobeyed. On the other hand the commandments of Christ such as, Thou shalt not be angry, Thou shalt not desire, are reckoned great in their reward, but little in the transgression." Now hatred is an internal movement like anger and desire. Therefore hatred of one's brother is a less grievous sin than murder.
I answer that Sins committed against our neighbor are evil on two counts; first by reason of the disorder in the person who sins, secondly by reason of the hurt inflicted on the person sinned against. On the first count, hatred is a more grievous sin than external actions that hurt our neighbor, because hatred is a disorder of man's will, which is the chief part of man, and wherein is the root of sin, so that if a man's outward actions were to be inordinate, without any disorder in his will, they would not be sinful, for instance, if he were to kill a man, through ignorance or out of zeal for justice: and if there be anything sinful in a man's outward sins against his neighbor, it is all to be traced to his inward hatred.On the other hand, as regards the hurt inflicted on his neighbor, a man's outward sins are worse than his inward hatred.

Reply to Objection: 1. This suffices for the Replies to the Objections.

Whether hatred is a capital sin?

Objection: 1. It would seem that hatred is a capital sin. For hatred is directly opposed to charity. Now charity is the foremost among the virtues, and the mother of all others. Therefore hatred is the chief of the capital sins, and the origin of all others.
2. Further, sins arise in us on account of the inclinations of our passions, according to Rm 7,5: "The passions of sins . . . did work in our members to bring forth fruit unto death." Now all other passions of the soul seem to arise from love and hatred, as was shown above (I-II 25,1 I-II 25,2). Therefore hatred should be reckoned one of the capital sins.
3. Further, vice is a moral evil. Now hatred regards evil more than any other passion does. Therefore it seems that hatred should be reckoned a capital sin.

On the contrary Gregory (Moral. xxxi) does not reckon hatred among the seven capital sins.
I answer that As stated above (I-II 84,3 I-II 84,4), a capital vice is one from which other vices arise most frequently. Now vice is contrary to man's nature, in as much as he is a rational animal: and when a thing acts contrary to its nature, that which is natural to it is corrupted little by little. Consequently it must first of all fail in that which is less in accordance with its nature, and last of all in that which is most in accordance with its nature, since what is first in construction is last in destruction. Now that which, first and foremost, is most natural to man, is the love of what is good, and especially love of the Divine good, and of his neighbor's good. Wherefore hatred, which is opposed to this love, is not the first but the last thing in the downfall of virtue resulting from vice: and therefore it is not a capital vice.

Reply to Objection: 1. As stated in Phys. vii, text. 18, "the virtue of a thing consists in its being well disposed in accordance with its nature." Hence what is first and foremost in the virtues must be first and foremost in the natural order. Hence charity is reckoned the foremost of the virtues, and for the same reason hatred cannot be first among the vices, as stated above.
2. Hatred of the evil that is contrary to one's natural good, is the first of the soul's passions, even as love of one's natural good is. But hatred of one's connatural good cannot be first, but is something last, because such like hatred is a proof of an already corrupted nature, even as love of an extraneous good.
3. Evil is twofold. One is a true evil, for the reason that it is incompatible with one's natural good, and the hatred of such an evil may have priority over the other passions. There is, however, another which is not a true, but an apparent evil, which, namely, is a true and connatural good, and yet is reckoned evil on account of the corruption of nature: and the hatred of such an evil must needs come last. This hatred is vicious, but the former is not.

Whether hatred arises from envy?

Objection: 1. It seems that hatred does not arise from envy. For envy is sorrow for another's good. Now hatred does not arise from sorrow, for, on the contrary, we grieve for the presence of the evil we hate. Therefore hatred does not arise from envy.
2. Further, hatred is opposed to love. Now love of our neighbor is referred to our love of God, as stated above (Question [25], Article [1]; Question [26], Article [2]). Therefore hatred of our neighbor is referred to our hatred of God. But hatred of God does not arise from envy, for we do not envy those who are very far removed from us, but rather those who seem to be near us, as the Philosopher states (Rhet. ii). Therefore hatred does not arise from envy.
3. Further, to one effect there is one cause. Now hatred is caused by anger, for Augustine says in his Rule that "anger grows into hatred." Therefore hatred does not arise from envy.

On the contrary Gregory says (Moral. xxxi, 45) that "out of envy cometh hatred."
I answer that As stated above (Article [5]), hatred of his neighbor is a man's last step in the path of sin, because it is opposed to the love which he naturally has for his neighbor. Now if a man declines from that which is natural, it is because he intends to avoid that which is naturally an object to be shunned. Now every animal naturally avoids sorrow, just as it desires pleasure, as the Philosopher states (Ethic. vii, x). Accordingly just as love arises from pleasure, so does hatred arise from sorrow. For just as we are moved to love whatever gives us pleasure, in as much as for that very reason it assumes the aspect of good; so we are moved to hate whatever displeases us, in so far as for this very reason it assumes the aspect of evil. Wherefore, since envy is sorrow for our neighbor's good, it follows that our neighbor's good becomes hateful to us, so that "out of envy cometh hatred."

Reply to Objection: 1. Since the appetitive power, like the apprehensive power, reflects on its own acts, it follows that there is a kind of circular movement in the actions of the appetitive power. And so according to the first forward course of the appetitive movement, love gives rise to desire, whence follows pleasure when one has obtained what one desired. And since the very fact of taking pleasure in the good one loves is a kind of good, it follows that pleasure causes love. And in the same way sorrow causes hatred.
2. Love and hatred are essentially different, for the object of love is good, which flows from God to creatures, wherefore love is due to God in the first place, and to our neighbor afterwards. On the other hand, hatred is of evil, which has no place in God Himself, but only in His effects, for which reason it has been stated above (Article [1]), that God is not an object of hatred, except in so far as He is considered in relation to His effects, and consequently hatred is directed to our neighbor before being directed to God. Therefore, since envy of our neighbor is the mother of hatred of our neighbor, it becomes, in consequence, the cause of hatred towards God.
3. Nothing prevents a thing arising from various causes in various respects, and accordingly hatred may arise both from anger and from envy. However it arises more directly from envy, which looks upon the very good of our neighbor as displeasing and therefore hateful, whereas hatred arises from anger by way of increase. For at first, through anger, we desire our neighbor's evil according to a certain measure, that is in so far as that evil has the aspect of vengeance: but afterwards, through the continuance of anger, man goes so far as absolutely to desire his neighbor's evil, which desire is part of hatred. Wherefore it is evident that hatred is caused by envy formally as regards the aspect of the object, but dispositively by anger.


We must now consider the vices opposed to the joy of charity. This joy is either about the Divine good, and then its contrary is sloth, or about our neighbor's good, and then its contrary is envy. Wherefore we must consider (1) Sloth and (2) Envy.

Under the first head there are four points of inquiry:

(1) Whether sloth is a sin?

(2) Whether it is a special vice?

(3) Whether it is a mortal sin?

(4) Whether it is a capital sin?

Whether sloth is a sin?

Objection: 1. It would seem that sloth is not a sin. For we are neither praised nor blamed for our passions, according to the Philosopher (Ethic. ii, 5). Now sloth is a passion, since it is a kind of sorrow, according to Damascene (De Fide Orth. ii, 14), and as we stated above (I-II 35,8). Therefore sloth is not a sin.
2. Further, no bodily failing that occurs at fixed times is a sin. But sloth is like this, for Cassian says (De Instit. Monast. x, [*De Institutione Caeobiorum]): "The monk is troubled with sloth chiefly about the sixth hour: it is like an intermittent fever, and inflicts the soul of the one it lays low with burning fires at regular and fixed intervals." Therefore sloth is not a sin.
3. Further, that which proceeds from a good root is, seemingly, no sin. Now sloth proceeds from a good root, for Cassian says (De Instit. Monast. x) that "sloth arises from the fact that we sigh at being deprived of spiritual fruit, and think that other monasteries and those which are a long way off are much better than the one we dwell in": all of which seems to point to humility. Therefore sloth is not a sin.
4. Further, all sin is to be avoided, according to Si 21,2: "Flee from sins as from the face of a serpent." Now Cassian says (De Instit. Monast. x): "Experience shows that the onslaught of sloth is not to be evaded by flight but to be conquered by resistance." Therefore sloth is not a sin.

On the contrary Whatever is forbidden in Holy Writ is a sin. Now such is sloth [acedia]: for it is written (Si 6,26): "Bow down thy shoulder, and bear her," namely spiritual wisdom, "and be not grieved [acedieris] with her bands." Therefore sloth is a sin.
I answer that Sloth, according to Damascene (De Fide Orth. ii, 14) is an oppressive sorrow, which, to wit, so weighs upon man's mind, that he wants to do nothing; thus acid things are also cold. Hence sloth implies a certain weariness of work, as appears from a gloss on Ps 106,18, "Their soul abhorred all manner of meat," and from the definition of some who say that sloth is a "sluggishness of the mind which neglects to begin good."Now this sorrow is always evil, sometimes in itself, sometimes in its effect. For sorrow is evil in itself when it is about that which is apparently evil but good in reality, even as, on the other hand, pleasure is evil if it is about that which seems to be good but is, in truth, evil. Since, then, spiritual good is a good in very truth, sorrow about spiritual good is evil in itself. And yet that sorrow also which is about a real evil, is evil in its effect, if it so oppresses man as to draw him away entirely from good deeds. Hence the Apostle (2Co 2,7) did not wish those who repented to be "swallowed up with overmuch sorrow."Accordingly, since sloth, as we understand it here, denotes sorrow for spiritual good, it is evil on two counts, both in itself and in point of its effect. Consequently it is a sin, for by sin we mean an evil movement of the appetite, as appears from what has been said above (Question [10], Article [2]; I-II 74,4).

Reply to Objection: 1. Passions are not sinful in themselves; but they are blameworthy in so far as they are applied to something evil, just as they deserve praise in so far as they are applied to something good. Wherefore sorrow, in itself, calls neither for praise nor for blame: whereas moderate sorrow for evil calls for praise, while sorrow for good, and again immoderate sorrow for evil, call for blame. It is in this sense that sloth is said to be a sin.
2. The passions of the sensitive appetite may either be venial sins in themselves, or incline the soul to mortal sin. And since the sensitive appetite has a bodily organ, it follows that on account of some bodily transmutation a man becomes apt to commit some particular sin. Hence it may happen that certain sins may become more insistent, through certain bodily transmutations occurring at certain fixed times. Now all bodily effects, of themselves, dispose one to sorrow; and thus it is that those who fast are harassed by sloth towards mid-day, when they begin to feel the want of food, and to be parched by the sun's heat.
3. It is a sign of humility if a man does not think too much of himself, through observing his own faults; but if a man contemns the good things he has received from God, this, far from being a proof of humility, shows him to be ungrateful: and from such like contempt results sloth, because we sorrow for things that we reckon evil and worthless. Accordingly we ought to think much of the goods of others, in such a way as not to disparage those we have received ourselves, because if we did they would give us sorrow.
4. Sin is ever to be shunned, but the assaults of sin should be overcome, sometimes by flight, sometimes by resistance; by flight when a continued thought increases the incentive to sin, as in lust; for which reason it is written (1Co 6,18): "Fly fornication"; by resistance, when perseverance in the thought diminishes the incentive to sin, which incentive arises from some trivial consideration. This is the case with sloth, because the more we think about spiritual goods, the more pleasing they become to us, and forthwith sloth dies away.

Whether sloth is a special vice?

Objection: 1. It would seem that sloth is not a special vice. For that which is common to all vices does not constitute a special kind of vice. But every vice makes a man sorrowful about the opposite spiritual good: for the lustful man is sorrowful about the good of continence, and the glutton about the good of abstinence. Since then sloth is sorrow for spiritual good, as stated above (Article [1]), it seems that sloth is not a special sin.
2. Further, sloth, through being a kind of sorrow, is opposed to joy. Now joy is not accounted one special virtue. Therefore sloth should not be reckoned a special vice.
3. Further, since spiritual good is a general kind of object, which virtue seeks, and vice shuns, it does not constitute a special virtue or vice, unless it be determined by some addition. Now nothing, seemingly, except toil, can determine it to sloth, if this be a special vice; because the reason why a man shuns spiritual goods, is that they are toilsome, wherefore sloth is a kind of weariness: while dislike of toil, and love of bodily repose seem to be due to the same cause, viz. idleness. Hence sloth would be nothing but laziness, which seems untrue, for idleness is opposed to carefulness, whereas sloth is opposed to joy. Therefore sloth is not a special vice.

On the contrary Gregory (Moral. xxxi, 45) distinguishes sloth from the other vices. Therefore it is a special vice.
I answer that Since sloth is sorrow for spiritual good, if we take spiritual good in a general way, sloth will not be a special vice, because, as stated above (I-II 71,1), every vice shuns the spiritual good of its opposite virtue. Again it cannot be said that sloth is a special vice, in so far as it shuns spiritual good, as toilsome, or troublesome to the body, or as a hindrance to the body's pleasure, for this again would not sever sloth from carnal vices, whereby a man seeks bodily comfort and pleasure.Wherefore we must say that a certain order exists among spiritual goods, since all the spiritual goods that are in the acts of each virtue are directed to one spiritual good, which is the Divine good, about which there is a special virtue, viz. charity. Hence it is proper to each virtue to rejoice in its own spiritual good, which consists in its own act, while it belongs specially to charity to have that spiritual joy whereby one rejoices in the Divine good. In like manner the sorrow whereby one is displeased at the spiritual good which is in each act of virtue, belongs, not to any special vice, but to every vice, but sorrow in the Divine good about which charity rejoices, belongs to a special vice, which is called sloth.

Reply to Objection: 1. This suffices for the Replies to the Objections.

Whether sloth is a mortal sin?

Objection: 1. It would seem that sloth is not a mortal sin. For every mortal sin is contrary to a precept of the Divine Law. But sloth seems contrary to no precept, as one may see by going through the precepts of the Decalogue. Therefore sloth is not a mortal sin.
2. Further, in the same genus, a sin of deed is no less grievous than a sin of thought. Now it is not a mortal sin to refrain in deed from some spiritual good which leads to God, else it would be a mortal sin not to observe the counsels. Therefore it is not a mortal sin to refrain in thought from such like spiritual works. Therefore sloth is not a mortal sin.
3. Further, no mortal sin is to be found in a perfect man. But sloth is to be found in a perfect man: for Cassian says (De Instit. Caenob. x, l) that "sloth is well known to the solitary, and is a most vexatious and persistent foe to the hermit." Therefore sloth is not always a mortal sin.

On the contrary It is written (2Co 7,20): "The sorrow of the world worketh death." But such is sloth; for it is not sorrow "according to God," which is contrasted with sorrow of the world. Therefore it is a mortal sin.
I answer that As stated above (I-II 88,1 I-II 88,2), mortal sin is so called because it destroys the spiritual life which is the effect of charity, whereby God dwells in us. Wherefore any sin which by its very nature is contrary to charity is a mortal sin by reason of its genus. And such is sloth, because the proper effect of charity is joy in God, as stated above (Question [28], Article [1]), while sloth is sorrow about spiritual good in as much as it is a Divine good. Therefore sloth is a mortal sin in respect of its genus. But it must be observed with regard to all sins that are mortal in respect of their genus, that they are not mortal, save when they attain to their perfection. Because the consummation of sin is in the consent of reason: for we are speaking now of human sins consisting in human acts, the principle of which is the reason. Wherefore if the sin be a mere beginning of sin in the sensuality alone, without attaining to the consent of reason, it is a venial sin on account of the imperfection of the act. Thus in the genus of adultery, the concupiscence that goes no further than the sensuality is a venial sin, whereas if it reach to the consent of reason, it is a mortal sin. So too, the movement of sloth is sometimes in the sensuality alone, by reason of the opposition of the flesh to the spirit, and then it is a venial sin; whereas sometimes it reaches to the reason, which consents in the dislike, horror and detestation of the Divine good, on account of the flesh utterly prevailing over the spirit. In this case it is evident that sloth is a mortal sin.

Reply to Objection: 1. Sloth is opposed to the precept about hallowing the Sabbath day. For this precept, in so far as it is a moral precept, implicitly commands the mind to rest in God: and sorrow of the mind about the Divine good is contrary thereto.
2. Sloth is not an aversion of the mind from any spiritual good, but from the Divine good, to which the mind is obliged to adhere. Wherefore if a man is sorry because someone forces him to do acts of virtue that he is not bound to do, this is not a sin of sloth; but when he is sorry to have to do something for God's sake.
3. Imperfect movements of sloth are to be found in holy men, but they do not reach to the consent of reason.

Whether sloth should be accounted a capital vice?

Objection: 1. It would seem that sloth ought not to be accounted a capital vice. For a capital vice is one that moves a man to sinful acts, as stated above (Question [34], Article [5]). Now sloth does not move one to action, but on the contrary withdraws one from it. Therefore it should not be accounted a capital sin.
2. Further, a capital sin is one to which daughters are assigned. Now Gregory (Moral. xxxi, 45) assigns six daughters to sloth, viz. "malice, spite, faint-heartedness, despair, sluggishness in regard to the commandments, wandering of the mind after unlawful things." Now these do not seem in reality to arise from sloth. For "spite" is, seemingly the same as hatred, which arises from envy, as stated above (Question [34], Article [6]); "malice" is a genus which contains all vices, and, in like manner, a "wandering" of the mind after unlawful things is to be found in every vice; "sluggishness" about the commandments seems to be the same as sloth, while "faint-heartedness" and "despair" may arise from any sin. Therefore sloth is not rightly accounted a capital sin.
3. Further, Isidore distinguishes the vice of sloth from the vice of sorrow, saying (De Summo Bono ii, 37) that in so far as a man shirks his duty because it is distasteful and burdensome, it is sorrow, and in so far as he is inclined to undue repose, it is sloth: and of sorrow he says that it gives rise to "spite, faint-heartedness, bitterness, despair," whereas he states that from sloth seven things arise, viz. "idleness, drowsiness, uneasiness of the mind, restlessness of the body, instability, loquacity, curiosity." Therefore it seems that either Gregory or Isidore has wrongly assigned sloth as a capital sin together with its daughters.

On the contrary The same Gregory (Moral. xxxi, 45) states that sloth is a capital sin, and has the daughters aforesaid.
I answer that As stated above (I-II 84,3 I-II 84,4), a capital vice is one which easily gives rise to others as being their final cause. Now just as we do many things on account of pleasure, both in order to obtain it, and through being moved to do something under the impulse of pleasure, so again we do many things on account of sorrow, either that we may avoid it, or through being exasperated into doing something under pressure thereof. Wherefore, since sloth is a kind of sorrow, as stated above (Article [2]; I-II 85,8), it is fittingly reckoned a capital sin.

Reply to Objection: 1. Sloth by weighing on the mind, hinders us from doing things that cause sorrow: nevertheless it induces the mind to do certain things, either because they are in harmony with sorrow, such as weeping, or because they are a means of avoiding sorrow.
2. Gregory fittingly assigns the daughters of sloth. For since, according to the Philosopher (Ethic. viii, 5,6) "no man can be a long time in company with what is painful and unpleasant," it follows that something arises from sorrow in two ways: first, that man shuns whatever causes sorrow; secondly, that he passes to other things that give him pleasure: thus those who find no joy in spiritual pleasures, have recourse to pleasures of the body, according to the Philosopher (Ethic. x, 6). Now in the avoidance of sorrow the order observed is that man at first flies from unpleasant objects, and secondly he even struggles against such things as cause sorrow. Now spiritual goods which are the object of the sorrow of sloth, are both end and means. Avoidance of the end is the result of "despair," while avoidance of those goods which are the means to the end, in matters of difficulty which come under the counsels, is the effect of "faint-heartedness," and in matters of common righteousness, is the effect of "sluggishness about the commandments." The struggle against spiritual goods that cause sorrow is sometimes with men who lead others to spiritual goods, and this is called "spite"; and sometimes it extends to the spiritual goods themselves, when a man goes so far as to detest them, and this is properly called "malice." In so far as a man has recourse to eternal objects of pleasure, the daughter of sloth is called "wandering after unlawful things." From this it is clear how to reply to the objections against each of the daughters: for "malice" does not denote here that which is generic to all vices, but must be understood as explained. Nor is "spite" taken as synonymous with hatred, but for a kind of indignation, as stated above: and the same applies to the others.
3. This distinction between sorrow and sloth is also given by Cassian (De Instit. Caenob. x, 1). But Gregory more fittingly (Moral. xxxi, 45) calls sloth a kind of sorrow, because, as stated above (Article [2]), sorrow is not a distinct vice, in so far as a man shirks a distasteful and burdensome work, or sorrows on account of any other cause whatever, but only in so far as he is sorry on account of the Divine good, which sorrow belongs essentially to sloth; since sloth seeks undue rest in so far as it spurns the Divine good. Moreover the things which Isidore reckons to arise from sloth and sorrow, are reduced to those mentioned by Gregory: for "bitterness" which Isidore states to be the result of sorrow, is an effect of "spite." "Idleness" and "drowsiness" are reduced to "sluggishness about the precepts": for some are idle and omit them altogether, while others are drowsy and fulfil them with negligence. All the other five which he reckons as effects of sloth, belong to the "wandering of the mind after unlawful things." This tendency to wander, if it reside in the mind itself that is desirous of rushing after various things without rhyme or reason, is called "uneasiness of the mind," but if it pertains to the imaginative power, it is called "curiosity"; if it affect the speech it is called "loquacity"; and in so far as it affects a body that changes place, it is called "restlessness of the body," when, to wit, a man shows the unsteadiness of his mind, by the inordinate movements of members of his body; while if it causes the body to move from one place to another, it is called "instability"; or "instability" may denote changeableness of purpose.

Summa Th. II-II EN Qu.34