Acedia is a Greek word that names a state of languor or torpor, of unconcern or dissatisfaction with one's condition or action in the world. In a strong case it can keep one from being able to perform one's duties. The term acedia was used first used in Christianity by monks and other ascetics who lived solitary lives, and were tempted to become listless and inert, or begin longing to be elsewhere or to do something other than what they were doing. Evagrius numbers acedia as of the eight bad thoughts, and St. Thomas Aquinas (following Gregory the Great) numbers it as one of the seven capital vices (so-called because they are the source of many kinds of sin). Though related to depression, acedia is not considered entirely the same in the monastic and Christian tradition. It is usually seen as naming a fault, which is subject to one's will, rather than simply a psychological state. Acedia is to spiritual health something like what depression is to mental health.
The signs or symptoms of acedia may be bodily or psychological, and again, pertaining to sadness or to its consequent tedium or languor. Bodily signs range from mere sleepiness to general sickness or debility. It produces feelings of ill health, making a person feel unable to fulfill his duties.
Some psychological signs are a lack of attention to prayer, an overall dissatisfaction with life, and boredom, showing itself in a general laziness or refusal to work or to pray.
2094. One can sin against God's love in various ways... Acedia or spiritual sloth goes so far as to refuse the joy that comes from God and to be repelled by divine goodness.
Temptations in Prayer
2733 Another temptation, to which presumption opens the gate, is acedia. The spiritual writers understand by this a form of depression due to lax ascetical practice, decreasing vigilance, carelessness of heart. "The spirit indeed is willing, but the flesh is weak" (Mat 26:41). The greater the height, the harder the fall. Painful as discouragement is, it is the reverse of presumption. The humble are not surprised by their distress; it leads them to trust more, to hold fast in constancy.
Summa Theologiae, II-II 35:1
Proceeding thus to the first. It seems that acedia is not a sin.
1. For we are neither praised nor blamed for passions, according to the Philosopher in Ethics II. But acedia is a certain passion, since it is a species of sadness, as Damascene says, as was established above. Therefore acedia is not a sin.
2. Further, no bodily shortcoming that happens at fixed hours has the account of sin. But acedia is such, since Cassian says in Monastic Institutes X, "acedia disturbs the monk above all around the sixth hour, like an intermittent fever, afflicting the soul of the one it lays low with burning fires at regular and fixed intervals." Therefore acedia is not a sin.
3. Further, that which comes from a good root does not seem to be a sin. But acedia comes from a good root; for Cassian says in the same book, that "acedia comes from someone's groaning that he does not have spiritual fruit, and thinking that other monasteries and those which are a long way off are much better than the one he dwells in"; this seems to pertain to humility, [and thus to be no sin.]
4. Further, one should flee from every sin, according to Sirach 21:2, "flee from sin as from a serpent." But Cassian says in the same book, "we have learned from experience not to turn away from the assault of acedia by fleeing, but to overcome it by resisting." Therefore acedia is not a sin.
But against this, that which is forbidden in Sacred Scripture is a sin. But acedia is forbidden, for it is said in Sirach 6:26, "bow down your shoulder and carry her," i.e., spiritual wisdom, "and be not morose [subject to acedia] in her bands." Therefore acedia is a sin.
It should be said that acedia, according to Damascene, is a certain oppressive sadness, which so depresses man's mind that he can do nothing freely, as things which are acidic are also cold. And therefore acedia implies a certain weariness in working, as is evident from what the Gloss says about Psalm 106:8, "their soul abhorred all meat"; and some say that acedia is a torpor of the mind that neglects to begin good things. Now such sadness is always bad, sometimes in itself, sometimes with respect to its effect. For sadness in itself is bad when it concerns that which is apparently bad and truly good, as conversely delight is bad when it concerns that which is apparently good and truly bad. Therefore since spiritual good is truly good, sadness that concerns spiritual good is bad in itself. But also sadness that concerns something truly bad is bad with respect to its effect if it weighs a man down so much as to draw him totally away from good work; hence the Apostle in 2 Cor 2:7, does not want "the penitent to be absorbed by greater sadness" about sin. But since acedia, as we take it here, names sadness regarding spiritual good, it is bad in both ways: in itself, and with respect to its effect. And therefore acedia is a sin, since evil in appetitive movements we call a sin, as is evident from what was said above.
Replies to Objections:
1. To the first, therefore, it should be said that passions in themselves are not sins, but they are blameworthy insofar as they are applied to something bad, just as they are praised on account of their being applied to something good. Hence sadness in itself names something neither praiseworthy nor blameworthy, while moderate sadness about something bad names something praiseworthy, and sadness about something good, and immoderate sadness name something blameworthy. And in this way acedia is set down as a sin.
2. To the second it should be said that the passions of the sensitive appetite can both be venial sins in themselves, and incline the soul to mortal sin. And since sensitive appetite has a bodily organ, it follows that by a bodily change man becomes more disposed to some sin. Thus it can happen that according to certain bodily changes arising at definite times, certain sins assail us more. But every bodily lack of itself disposes to sadness. And therefore those who are fasting, around midday, when they begin to feel the lack of food, and to be pressed by the sun's heat, are more attacked by acedia.
3. To the third it should be said that it pertains to humility for a man, considering his own defects, not to extol himself. But it does not pertain to humility, but rather to ingratitude, for a man to despise the good things that he has from God. And acedia follows from this contempt, for we are saddened about the things that we reckong as bad or worthless. Thus one ought to extol the good things that others have, in such a way as not to despise the good things God has given to oneself, since thus they would make one sad.
4. To the fourth it should be said that sin is always to be fled, but the assault of sin is sometimes to be overcome by fleeing, other times by resisting. By fleeing, when the continual thought increases the incentive to sin, as happens with lust; hence it is said in 1 Cor 6:18, "flee fornication." By resisting, when persevering thought takes away the incentive to sin which arises from some light thought. And this happenes in acedia, since the more we think about spiritual goods, the more pleasing they become to us, and thus acedia ceases.
Acedia & Me: A Marriage, Monks, and a Writer's Life by Kathleen Norris - a series of meditations on acedia in the desert monks Anthony the Great and Evagrius, how acedia manifests itself in the modern world, etc.
Seven principles of the spiritual life by Fr. Thomas Bolin