I answer that, Mitigation of the pains of hell can be understood in two ways: first, as though one were delivered from the punishment which he already deserved, and thus, since no one is delivered from punishment unless he be absolved from guilt, (for an effect is not diminished or taken away unless its cause be diminished or taken away), the pain of hell cannot be mitigated by works done without charity, since they are unable to remove or diminish guilt. Secondly, so that the demerit of punishment is hindered; and thus the aforesaid works diminish the pain of hell---first because he who does such works escapes being guilty of omitting them---secondly, because such works dispose one somewhat to good, so that a man sins from less contempt, and indeed is drawn away from many sins thereby.
These works do, however merit a diminution or postponement of temporal punishment, as in the case of Achab (3 Kgs. 21:27, seqq.), as also the acquisition of temporal goods.
Some, however, say that they mitigate the pains of hell, not by subtracting any of their substance, but by strengthening the subject, so that he is more able to bear them. But this is impossible, because there is no strengthening without a diminution of passibility. Now passibility is according to the measure of guilt, wherefore if guilt is not removed, neither can the subject be strengthened.
Some again say that the punishment is mitigated as to the remorse of conscience, though not as to the pain of fire. But neither will this stand, because as the pain of fire is equal to the guilt, so also is the pain of the remorse of conscience: so that what applies to one applies to the other.
This suffices for the Replies to the Objections.