Vol II No. 5
Daily Thought

Thomas Aquinas: Is Sloth a Mortal Sin?

by William J. Martin




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.

Sloth is not listed literally as what violates any of the Ten Commandments. The Commandments make no mention of sloth. So perhaps sloth is not a mortal sin.


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.

Sloth does not seem to be a mortal sin in a spiritual sense either. For aversion of the mind from a spiritual good may be merely a consequence of human nature which cannot possibly live up to all the Divine Counsels at all times. Perhaps sloth is merely the intellectual or spiritual inability to will the good at all times.


Further, no mortal sin is to be found in a perfect man. But sloth is to be found in a perfect man: for John 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.

Sloth can be found in the most perfect of the Desert Fathers. No doubt, if sloth is found in the perfect man, then it mustn’t really be a mortal sin. Perhaps it is a vexatious enemy that harasses and threatens a man against his reason and his will. 

On the Contrary: It is written (2 Cor. vii. 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.

Sloth is sorrow that fails to hope in the Divine good. Sloth thus is of the world and consumed with its finite limitations and created imperfections. Sloth avoids the Divine Good because the good of the world has molded and defined the expectations and hopes of the sinner away from any transcendent perfection.

I answer that, 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 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.

Sloth destroys the spiritual life because it stands opposed to the Divine Virtue of Charity. Through Charity, God dwells in us and we dwell in Him. Charity yields joy in God as the sinner is made into a saint through Divine Grace. The experience of the Charity makes a man joyful and thankful for God’s condescending movement into his soul. Sloth is sorrow and despair over the spiritual good that God longs to bring alive in the human soul. It is a mortal sin because it rejects the life that God brings to the soul through His Charity.

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 imperfection. 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 reason in the dislike, horror and detestation of the Divine good on account of the flesh utterly prevailing over the spirit. On this case it is evident that sloth is a mortal sin.

Sloth is a venial sin if it does not reach the level of the consent of reason. If it remains in the body or the sensuality or the appetite it might be better called laziness or lethargy. The body often resists the soul’s pursuit of the spiritual good. But if sloth is consented to in the soul by reason because a man despairs of the spiritual good, then sloth is a mortal sin. A man might grow to hate and despise the possibility of the efficacious nature of Divine Grace. He might think God too perfect to desire any involvement in human life. Or he might grow impatient at the pace in which Grace operates on his life. He might give up on Grace because he cannot perceive or see its effects in himself or others. He might decide that his sin is too great for God to overcome and conquer. Or perhaps the power of the flesh is so strong that it overcomes the spirit in a man, and for that reason a man succumbs to despairing over the spiritual good. So a man might reject the spiritual good of God’s Grace because of his body or because of his soul, because the flesh possesses him or because his soul refuses to hope. Whatever the reason, sloth is a mortal sin if a man uses his mind to reject the power of God’s Grace in human life and thus fails to pursue it.

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.

Sloth is directly set against keeping the Sabbath Day holy and refuses to rest in God. It is thus implicitly present in the Fourth Commandment. Sloth is thus the willful refusal to keep God’s Day holy and to rest in it because the slothful man does not see or perceive that any good can come out of it.

Reply to Objection 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.

Sloth is a turning of the mind away from the Divine Good. We are made to adhere and cleave to the spiritual good of God’s Grace in order that our natures might be perfected. If a man is sorry about having to do something for God’s sake or because God wills it, this is mortal sin of sloth. A slothful man may either flee the spiritual good by entering into a state of physical or spiritual torpor or through a busy-ness that is equally fatal. In both cases either the increase or decrease of activity is slothful unto death because the sinner is fleeing the spiritual good.

However, sloth induces us to avoid not only pure goodness. It induces us to avoid all pain, sorrow, or threats to a limited good. Sloth moves us to avoid the spiritual good out of fear for spiritual pain and suffering. So sloth can be motivated by the fear for what the spiritual good might demand of us in the process of its purification of our souls. The slothful man is more often than not immersed in earthly pleasures. So the virtue that opposes and overcomes sloth is zeal. But to cultivate zeal we must come to know God’s Charity, His goodness, and His desire to fill our hearts with the effects of His Grace.

Reply to Objection 3. Imperfect movements of sloth are to be found in holy men, but they do not reach to the consent of reason.

Holy men like the Desert Fathers are tempted and tried by sloth. It does not, however, reach the consent of reason in them. They resist it and they flee from it by pursuing with much zeal the Charity of God’s Grace. Dearest brethren, let us do the same. Amen.