Objection 1. It would seem that suffrages profit those who are in hell. For it is written (2 Maccabees 12:40): "They found under the coats of the slain some of the donaries of the idols... which the law forbiddeth to the Jews," and yet we read further on (2 Maccabees 12:43) that Judas "sent twelve thousand drachms of silver to Jerusalem... to be offered for the sins of the dead." Now it is clear that they sinned mortally through acting against the Law, and consequently that they died in mortal sin, and were taken to hell. Therefore suffrages profit those who are in hell.
Objection 2. Further, the text (Sent. iv, D, 45) quotes the saying of Augustine (Enchiridion cx) that "those whom suffrages profit gain either entire forgiveness, or at least an abatement of their damnation." Now only those who are in hell are said to be damned. Therefore suffrages profit even those who are in hell.
Objection 3. Further, Dionysius says (Eccl. Hier.): "If here the prayers of the righteous avail those who are alive, how much more do they, after death, profit those alone who are worthy of their holy prayers?" Hence we may gather that suffrages are more profitable to the dead than to the living. Now they profit the living even though they be in mortal sin, for the Church prays daily for sinners that they be converted to God. Therefore suffrages avail also for the dead who are in mortal sin.
Objection 4. Further, in the Lives of the Fathers (iii, 172; vi, 3) we read, and the Damascene relates in his sermon [De his qui in fide dormierunt] that Macarius discovered the skull of a dead man on the road, and that after praying he asked whose head it was, and the head replied that it had belonged to a pagan priest who was condemned to hell; and yet he confessed that he and others were assisted by the prayers of Macarius. Therefore the suffrages of the Church profit even those who are in hell.
Objection 5. Further, the Damascene in the same sermon relates that Gregory, while praying for Trajan, heard a voice from heaven saying to him: "I have heard thy voice, and I pardon Trajan": and of this fact the Damascene adds in the same sermon, "the whole East and West are witnesses." Yet it is clear that Trajan was in hell, since "he put many martyrs to a cruel death" [De his qui fide dormierunt]. Therefore the suffrages of the Church avail even for those who are in hell.
On the contrary, Dionysius says (Eccl. Hier. vii): "The high priest prays not for the unclean, because by so doing he would act counter to the Divine order," and consequently he says (Eccl. Hier. vii) that "he prays not that sinners be forgiven, because his prayer for them would not be heard." Therefore suffrages avail not those who are in hell.
Further, Gregory says (Moral. xxxiv, 19): "There is the same reason for not praying then" (namely after the judgment day) "for men condemned to the everlasting fire, as there is now for not praying for the devil and his angels who are sentenced to eternal punishment, and for this reason the saints pray not for dead unbelieving and wicked men, because, forsooth, knowing them to be already condemned to eternal punishment, they shrink from pleading for them by the merit of their prayers before they are summoned to the presence of the just Judge."
Further, the text (Sent. iv, D, 45) quotes the words of Augustine (De Verb. A post. Serm. xxxii): "If a man depart this life without the faith that worketh by charity and its sacraments, in vain do his friends have recourse to such like acts of kindness." Now all the damned come under that head. Therefore suffrages profit them not.
I answer that, There have been three opinions about the damned. For some have said that a twofold distinction must be made in this matter. First, as to time; for they said that after the judgment day no one in hell will be assisted by any suffrage, but that before the judgment day some are assisted by the suffrages of the Church. Secondly, they made a distinction among those who are detained in hell. Some of these, they said, are very bad, those namely who have died without faith and the sacraments, and these, since they were not of the Church, neither "by grace nor, by name" [Cf. Oratio ad Vesperas, Fer. ii, post Dom. Pass.] can the suffrages of the Church avail; while others are not very bad, those namely who belonged to the Church as actual members, who had the faith, frequented the sacraments and performed works generically good, and for these the suffrages of the Church ought to avail. Yet they were confronted with a difficulty which troubled them, for it would seem to follow from this (since the punishment of hell is finite in intensity although infinite in duration) that a multiplicity of suffrages would take away that punishment altogether, which is the error of Origen (Peri Archon. i; cf. Gregory, Moral. xxxiv): and consequently endeavored in various ways to avoid this difficulty.
Praepositivus [Gilbert Prevostin, Chancellor of the See of Paris, A.D. 1205-9 said that suffrages for the damned can be so multiplied that they are entirely freed from punishment, not absolutely as Origen maintained, but for a time, namely till the judgment day: for their souls will be reunited to their bodies, and will be cast back into the punishments of hell without hope of pardon. But this opinion seems incompatible with Divine providence, which leaves nothing inordinate in the world. For guilt cannot be restored to order save by punishment: wherefore it is impossible for punishment to cease, unless first of all guilt be expiated: so that, as guilt remains for ever in the damned, their punishment will nowise be interrupted.
For this reason the followers of Gilbert de la Porree devised another explanation. These said that the process in the diminution of punishments by suffrages is as the process in dividing a line, which though finite, is indefinitely divisible, and is never destroyed by division, if it be diminished not by equal but by proportionate quantities, for instance if we begin by taking away a quarter of the whole, and secondly, a quarter of that quarter, and then a quarter of this second quarter, and so on indefinitely. In like manner, they say by the first suffrage a certain proportion of the punishment is taken away, and by the second an equally proportionate part of the remainder. But this explanation is in many ways defective. First, because it seems that indefinite division which is applicable to continuous quantity cannot be transferred to spiritual quantity: secondly, because there is no reason why the second suffrage, if it be of equal worth, should diminish the punishment less than the first: thirdly, because punishment cannot be diminished unless guilt be diminished, even as it cannot be done away unless the guilt be done away: fourthly, because in the division of a line we come at length to something which is not sensible, for a sensible body is not indefinitely divisible: and thus it would follow that after many suffrages the remaining punishment would be so little as not to be felt, and thus would no longer be a punishment.
Hence others found another explanation. For Antissiodorensis [William of Auxerre, Archdeacon of Beauvais] (Sent. iv, Tract. 14) said that suffrages profit the damned not by diminishing or interrupting their punishment, but by fortifying the person punished: even as a man who is carrying a heavy load might bathe his face in water, for thus he would be enabled to carry it better, and yet his load would be none the lighter. But this again is impossible, because according to Gregory (Moral. ix) a man suffers more or less from the eternal fire according as his guilt deserves; and consequently some suffer more, some less, from the same fire. wherefore since the guilt of the damned remains unchanged, it cannot be that he suffers less punishment. Moreover, the aforesaid opinion is presumptuous, as being in opposition to the statements of holy men, and groundless as being based on no authority. It is also unreasonable. First, because the damned in hell are cut off from the bond of charity in virtue of which the departed are in touch with the works of the living. Secondly, because they have entirely come to the end of life, and have received the final award for their merits, even as the saints who are in heaven. For the remaining punishment or glory of the body does not make them to be wayfarers, since glory essentially and radically resides in the soul. It is the same with the unhappiness of the damned, wherefore their punishment cannot be diminished as neither can the glory of the saints be increased as to the essential reward.
However, we may admit, in a certain measure, the manner in which, according to some, suffrages profit the damned, if it be said that they profit neither by diminishing nor interrupting their punishment, nor again by diminishing their sense of punishment, but by withdrawing from the damned some matter of grief, which matter they might have if they knew themselves to be so outcast as to be a care to no one; and this matter of grief is withdrawn from them when suffrages are offered for them. Yet even this is impossible according to the general law, because as Augustine says (De Cura pro Mort. xiii)--and this applies especially to the damned--"the spirits of the departed are where they see nothing of what men do or of what happens to them in this life," and consequently they know not when suffrages are offered for them, unless this relief be granted from above to some of the damned in spite of the general law. This, however, is a matter of great uncertainty; wherefore it is safer to say simply that suffrages profit not the damned, nor does the Church intend to pray for them, as appears from the authors quoted above.
Reply to Objection 1. The donaries to the idols were not found on those dead so that they might be taken as a sign that they were carried off in reverence to the idols: but they took them as conquerors because they were due to them by right of war. They sinned, however, venially by covetousness: and consequently they were not damned in hell, and thus suffrages could profit them. or we may say, according to some, that in the midst of fighting, seeing they were in danger, they repented of their sin, according to Psalm 77:34, "When He slew them, then they sought Him": and this is a probable opinion. Wherefore the offering was made for them.
Reply to Objection 2. In these words damnation is taken in a broad sense for any kind of punishment, so as to include also the punishment of purgatory which is sometimes entirely expiated by suffrages, and sometimes not entirety, but diminished.
Reply to Objection 3. Suffrage for a dead person is more acceptable than for a living person, as regards his being in greater want, since he cannot help himself as a living person can. But a living person is better off in that he can be taken from the state of mortal sin to the state of grace, which cannot be said of the dead. Hence there is not the same reason for praying for the dead as for the living.
Reply to Objection 4. This assistance did not consist in a diminishment of their punishment, but in this alone (as stated in the same place) that when he prayed they were permitted to see one another, and in this they had a certain joy, not real but imaginary, in the fulfillment of their desire. Even so the demons are said to rejoice when they draw men into sin, although this nowise diminishes their punishment, as neither is the joy of the angels diminished by the fact that they take pity on our ills.
Reply to Objection 5. Concerning the incident of Trajan it may be supposed with probability that he was recalled to life at the prayers of blessed Gregory, and thus obtained the grace whereby he received the pardon of his sins and in consequence was freed from punishment. The same applies to all those who were miraculously raised from the dead, many of whom were evidently idolaters and damned. For we must needs say likewise of all such persons that they were consigned to hell, not finally, but as was actually due to their own merits according to justice: and that according to higher causes, in view of which it was foreseen that they would be recalled to life, they were to be disposed of otherwise.
Or we may say with some that Trajan's soul was not simply freed from the debt of eternal punishment, but that his punishment was suspended for a time, that is, until the judgment day. Nor does it follow that this is the general result of suffrages, because things happen differently in accordance with the general law from that which is permitted in particular cases and by privilege. Even so the bounds of human affairs differ from those of the miracles of the Divine power as Augustine says (De Cura pro Mort. xvi).
Source: Summa Theologica (New Advent)