Summa Theologica, by St. Thomas Aquinas, [1947], at sacred-texts.com
We must now consider the contrary vices; (1) despair; (2) presumption. Under the first head there are four points of inquiry:
(1) Whether despair is a sin?
(2) Whether it can be without unbelief?
(3) Whether it is the greatest of sins?
(4) Whether it arises from sloth?
Objection 1: It would seem that despair is not a sin. For every sin includes conversion to a mutable good, together with aversion from the immutable good, as Augustine states (De Lib. Arb. ii, 19). But despair includes no conversion to a mutable good. Therefore it is not a sin.
Objection 2: Further, that which grows from a good root, seems to be no sin, because "a good tree cannot bring forth evil fruit" (Mat. 7:18). Now despair seems to grow from a good root, viz. fear of God, or from horror at the greatness of one's own sins. Therefore despair is not a sin.
Objection 3: Further, if despair were a sin, it would be a sin also for the damned to despair. But this is not imputed to them as their fault but as part of their damnation. Therefore neither is it imputed to wayfarers as their fault, so that it is not a sin.
On the contrary, That which leads men to sin, seems not only to be a sin itself, but a source of sins. Now such is despair, for the Apostle says of certain men (Eph. 4:19): "Who, despairing, have given themselves up to lasciviousness, unto the working of all uncleanness and [Vulg.: 'unto'] covetousness." Therefore despair is not only a sin but also the origin of other sins.
I answer that, According to the Philosopher (Ethic. vi, 2) affirmation and negation in the intellect correspond to search and avoidance in the appetite; while truth and falsehood in the intellect correspond to good and evil in the appetite. Consequently every appetitive movement which is conformed to a true intellect, is good in itself, while every appetitive movement which is conformed to a false intellect is evil in itself and sinful. Now the true opinion of the intellect about God is that from Him comes salvation to mankind, and pardon to sinners, according to Ezech. 18:23, "I desire not the death of the sinner, but that he should be converted, and live" [*Vulg.: 'Is it My will that a sinner should die . . . and not that he should be converted and live?' Cf. Ezech. 33:11]: while it is a false opinion that He refuses pardon to the repentant sinner, or that He does not turn sinners to Himself by sanctifying grace. Therefore, just as the movement of hope, which is in conformity with the true opinion, is praiseworthy and virtuous, so the contrary movement of despair, which is in conformity with the false opinion about God, is vicious and sinful.
Reply to Objection 1: In every mortal sin there is, in some way, aversion from the immutable good, and conversion to a mutable good, but not always in the same way. Because, since the theological virtues have God for their object, the sins which are contrary to them, such as hatred of God, despair and unbelief, consist principally in aversion from the immutable good; but, consequently, they imply conversion to a mutable good, in so far as the soul that is a deserter from God, must necessarily turn to other things. Other sins, however, consist principally in conversion to a mutable good, and, consequently, in aversion from the immutable good: because the fornicator intends, not to depart from God, but to enjoy carnal pleasure, the result of which is that he departs from God.
Reply to Objection 2: A thing may grow from a virtuous root in two ways: first, directly and on the part of the virtue itself; even as an act proceeds from a habit: and in this way no sin can grow from a virtuous root, for in this sense Augustine declared (De Lib. Arb. ii, 18,19) that "no man makes evil use of virtue." Secondly, a thing proceeds from a virtue indirectly, or is occasioned by a virtue, and in this way nothing hinders a sin proceeding from a virtue: thus sometimes men pride themselves of their virtues, according to Augustine (Ep. ccxi): "Pride lies in wait for good works that they may die." In this way fear of God or horror of one's own sins may lead to despair, in so far as man makes evil use of those good things, by allowing them to be an occasion of despair.
Reply to Objection 3: The damned are outside the pale of hope on account of the impossibility of returning to happiness: hence it is not imputed to them that they hope not, but it is a part of their damnation. Even so, it would be no sin for a wayfarer to despair of obtaining that which he had no natural capacity for obtaining, or which was not due to be obtained by him; for instance, if a physician were to despair of healing some sick man, or if anyone were to despair of ever becoming rich.
Objection 1: It would seem that there can be no despair without unbelief. For the certainty of hope is derived from faith; and so long as the cause remains the effect is not done away. Therefore a man cannot lose the certainty of hope, by despairing, unless his faith be removed.
Objection 2: Further, to prefer one's own guilt to God's mercy and goodness, is to deny the infinity of God's goodness and mercy, and so savors of unbelief. But whoever despairs, prefers his own guilt to the Divine mercy and goodness, according to Gn. 4:13: "My iniquity is greater than that I may deserve pardon." Therefore whoever despairs, is an unbeliever.
Objection 3: Further, whoever falls into a condemned heresy, is an unbeliever. But he that despairs seems to fall into a condemned heresy, viz. that of the Novatians, who say that there is no pardon for sins after Baptism. Therefore it seems that whoever despairs, is an unbeliever.
On the contrary, If we remove that which follows, that which precedes remains. But hope follows faith, as stated above (Q[17], A[7]). Therefore when hope is removed, faith can remain; so that, not everyone who despairs, is an unbeliever.
I answer that, Unbelief pertains to the intellect, but despair, to the appetite: and the intellect is about universals, while the appetite is moved in connection with particulars, since the appetitive movement is from the soul towards things, which, in themselves, are particular. Now it may happen that a man, while having a right opinion in the universal, is not rightly disposed as to his appetitive movement, his estimate being corrupted in a particular matter, because, in order to pass from the universal opinion to the appetite for a particular thing, it is necessary to have a particular estimate (De Anima iii, 2), just as it is impossible to infer a particular conclusion from an universal proposition, except through the holding of a particular proposition. Hence it is that a man, while having right faith, in the universal, fails in an appetitive movement, in regard to some particular, his particular estimate being corrupted by a habit or a passion, just as the fornicator, by choosing fornication as a good for himself at this particular moment, has a corrupt estimate in a particular matter, although he retains the true universal estimate according to faith, viz. that fornication is a mortal sin. In the same way, a man while retaining in the universal, the true estimate of faith, viz. that there is in the Church the power of forgiving sins, may suffer a movement of despair, to wit, that for him, being in such a state, there is no hope of pardon, his estimate being corrupted in a particular matter. In this way there can be despair, just as there can be other mortal sins, without belief.
Reply to Objection 1: The effect is done away, not only when the first cause is removed, but also when the secondary cause is removed. Hence the movement of hope can be done away, not only by the removal of the universal estimate of faith, which is, so to say, the first cause of the certainty of hope, but also by the removal of the particular estimate, which is the secondary cause, as it were.
Reply to Objection 2: If anyone were to judge, in universal, that God's mercy is not infinite, he would be an unbeliever. But he who despairs judges not thus, but that, for him in that state, on account of some particular disposition, there is no hope of the Divine mercy.
The same answer applies to the Third Objection, since the Novatians denied, in universal, that there is remission of sins in the Church.
Objection 1: It would seem that despair is not the greatest of sins. For there can be despair without unbelief, as stated above (A[2]). But unbelief is the greatest of sins because it overthrows the foundation of the spiritual edifice. Therefore despair is not the greatest of sins.
Objection 2: Further, a greater evil is opposed to a greater good, as the Philosopher states (Ethic. viii, 10). But charity is greater than hope, according to 1 Cor. 13:13. Therefore hatred of God is a greater sin than despair.
Objection 3: Further, in the sin of despair there is nothing but inordinate aversion from God: whereas in other sins there is not only inordinate aversion from God, but also an inordinate conversion. Therefore the sin of despair is not more but less grave than other sins.
On the contrary, An incurable sin seems to be most grievous, according to Jer. 30:12: "Thy bruise is incurable, thy wound is very grievous." Now the sin of despair is incurable, according to Jer. 15:18: "My wound is desperate so as to refuse to be healed." [*Vulg.: 'Why is my wound,' etc.] Therefore despair is a most grievous sin.
I answer that, Those sins which are contrary to the theological virtues are in themselves more grievous than others: because, since the theological virtues have God for their object, the sins which are opposed to them imply aversion from God directly and principally. Now every mortal sin takes its principal malice and gravity from the fact of its turning away from God, for if it were possible to turn to a mutable good, even inordinately, without turning away from God, it would not be a mortal sin. Consequently a sin which, first and of its very nature, includes aversion from God, is most grievous among mortal sins.
Now unbelief, despair and hatred of God are opposed to the theological virtues: and among them, if we compare hatred of God and unbelief to despair, we shall find that, in themselves, that is, in respect of their proper species, they are more grievous. For unbelief is due to a man not believing God's own truth; while the hatred of God arises from man's will being opposed to God's goodness itself; whereas despair consists in a man ceasing to hope for a share of God's goodness. Hence it is clear that unbelief and hatred of God are against God as He is in Himself, while despair is against Him, according as His good is partaken of by us. Wherefore strictly speaking it is more grievous sin to disbelieve God's truth, or to hate God, than not to hope to receive glory from Him.
If, however, despair be compared to the other two sins from our point of view, then despair is more dangerous, since hope withdraws us from evils and induces us to seek for good things, so that when hope is given up, men rush headlong into sin, and are drawn away from good works. Wherefore a gloss on Prov. 24:10, "If thou lose hope being weary in the day of distress, thy strength shall be diminished," says: "Nothing is more hateful than despair, for the man that has it loses his constancy both in the every day toils of this life, and, what is worse, in the battle of faith." And Isidore says (De Sum. Bono ii, 14): "To commit a crime is to kill the soul, but to despair is to fall into hell."
Objection 1: It would seem that despair does not arise from sloth. Because different causes do not give rise to one same effect. Now despair of the future life arises from lust, according to Gregory (Moral. xxxi, 45). Therefore it does not arise from sloth.
Objection 2: Further, just as despair is contrary to hope, so is sloth contrary to spiritual joy. But spiritual joy arises from hope, according to Rom. 12:12, "rejoicing in hope." Therefore sloth arises from despair, and not vice versa.
Objection 3: Further, contrary effects have contrary causes. Now hope, the contrary of which is despair, seems to proceed from the consideration of Divine favors, especially the Incarnation, for Augustine says (De Trin. xiii, 10): "Nothing was so necessary to raise our hope, than that we should be shown how much God loves us. Now what greater proof could we have of this than that God's Son should deign to unite Himself to our nature?" Therefore despair arises rather from the neglect of the above consideration than from sloth.
On the contrary, Gregory (Moral. xxxi, 45) reckons despair among the effects of sloth.
I answer that, As stated above (Q[17], A[1]; FS, Q[40], A[1]), the object of hope is a good, difficult but possible to obtain by oneself or by another. Consequently the hope of obtaining happiness may be lacking in a person in two ways: first, through his not deeming it an arduous good; secondly, through his deeming it impossible to obtain either by himself, or by another. Now, the fact that spiritual goods taste good to us no more, or seem to be goods of no great account, is chiefly due to our affections being infected with the love of bodily pleasures, among which, sexual pleasures hold the first place: for the love of those pleasures leads man to have a distaste for spiritual things, and not to hope for them as arduous goods. In this way despair is caused by lust.
On the other hand, the fact that a man deems an arduous good impossible to obtain, either by himself or by another, is due to his being over downcast, because when this state of mind dominates his affections, it seems to him that he will never be able to rise to any good. And since sloth is a sadness that casts down the spirit, in this way despair is born of sloth.
Now this is the proper object of hope---that the thing is possible, because the good and the arduous regard other passions also. Hence despair is born of sloth in a more special way: though it may arise from lust, for the reason given above.
This suffices for the Reply to the First Objection.
Reply to Objection 2: According to the Philosopher (Rhet. i, 11), just as hope gives rise to joy, so, when a man is joyful he has greater hope: and, accordingly, those who are sorrowful fall the more easily into despair, according to 2 Cor. 2:7: "Lest . . . such an one be swallowed up by overmuch sorrow." Yet, since the object of hope is good, to which the appetite tends naturally, and which it shuns, not naturally but only on account of some supervening obstacle, it follows that, more directly, hope gives birth to joy, while on the contrary despair is born of sorrow.
Reply to Objection 3: This very neglect to consider the Divine favors arises from sloth. For when a man is influenced by a certain passion he considers chiefly the things which pertain to that passion: so that a man who is full of sorrow does not easily think of great and joyful things, but only of sad things, unless by a great effort he turn his thoughts away from sadness.