According to the teaching of the Church, the source of indulgences is this spiritual treasury in which are contained all the merits of Christ, the Blessed Mother and the Saints. The custody of this treasury is given over to the Church which acts as the administrator in dispensing these spiritual riches to the faithful.
This power She has exercised even in the earliest times as is evident from the words of St. Paul in writing to the Corinthians," "And to whom you have pardoned anything, I also: for, what I have pardoned, if I have pardoned anything, for your sakes have I done it in the person of Christ." It is true that the form of indulgences as they exist in the Church today differ from the form in earlier days. These differences however, are merely accidental and in no way effect the essentials which have always remained unchanged.
Although all indulgences are essentially the same, by reason of the effect produced in the soul of the recipient they are divided into plenary and partial. The first as its name signifies remits the entire temporal punishment due to sin. "Unless it has been expressly stated to the contrary a plenary indulgence may be gained only once in the same day, although the same work may be performed many times." There are, however, some notable exceptions to this law in the toties quoties indulgences granted to all the faithful who visit a Franciscan Church on the Feast of Portiuncula, to all who recite one third part of the Rosary in the presence of the Blessed Sacrament," the indulgence granted to all the faithful who visit a Church of the Rosary Confraternity from noon on the Saturday preceding the feast of Rosary Sunday to midnight of the feast itself, and the indulgence granted to all who visit any Church from noon on the Feast of All Saints Day to midnight of the Feast of All Souls.13 The first three of these indulgences are applicable to both the living and the dead, while the last may be applied only to the souls in Purgatory. On the other hand, a partial indulgence is one which remits only a portion of the temporal punishment due to sin. It may be partial either by reason of the manner granted, e.g. an indulgence of seven years, or because of the defect of disposition on the part of the recipient. A partial indulgence of this latter sort is one which is converted from a plenary into a partial, because the subject, on account of his imperfect disposition is unable to gain it as a plenary indulgence. As a matter of fact, the gaining of a plenary indulgence is very difficult, since, according to the common teaching of theologians, a prerequisite is that the subject be free from all sin and affection to even the slightest venial sin. The entire effect of the indulgence would not be lost, because, it is explicitly stated in the Code, "a plenary indulgence is understood as granted in such a way, that if anyone is not able to gain it fully, nevertheless, one may gain it partially according to the disposition one has."
By reason of its duration an indulgence may be either perpetual or temporal. Perpetual are those which are conceded without limit of time in perpetuity or until their revocation. Temporary are those which have been given for a determined period, e.g. for three years, and this time having elapsed, the indulgence ceases. By reason of the manner of gaining them, an indulgence may be local, personal or real. Local indulgences are those which are affixed to a determined place or thing in a determined place, e.g. to a church, altar, or a statue permanently located in a church. Real indulgences are those annexed to some movable thing, e.g. to rosaries, medals and the like. Indulgences of this sort differ from local indulgences in this that they are attached to some movable thing, whereas, local are attached to some immovable thing. Thirdly, personal indulgences are those conceded to certain individuals or moral persons without any determination as to place.
Lastly, indulgences may be either general or particular, according as they are granted to all the faithful or are limited to certain classes of persons. Likewise they may be divided into those which are applicable to the living, to the dead and to both the living and the dead. Indulgences granted to the living are granted per modum absolutionis. Every living member of the church is subject to its jurisdiction. Consequently when the Church grants an indulgence to one of the faithful, it exercises that power given to it by Christ. Hence, it is certain that the full affect of an indulgence is produced, provided all the requisite conditions are fulfilled. It is not to be presumed because of this that the Church allows the penitent to disavow the debt he owes to Almighty God. Rather, as St. Thomas says, "He who gains an indulgence is not thereby released outright from what he owes as a penalty, but is provided with the means of paying it." When the Church grants an indulgence applicable to the souls in Purgatory, She does so per modum suffragii, i.e. She offers to God a portion of this spiritual treasury entrusted to Her care, and asks Him to apply it to this or that particular soul, and thereby shorten its punishment in Purgatory. It should be noted here that all indulgences contained in the Raccolta are, by a decree of the Sacred Congregation of Indulgences, September 30, 1852, applicable to the souls in Purgatory. Moreover, according to Canon 930 of the Code, all indulgences granted by the Roman Pontiffs may be applied to the faithful departed.
The power of granting indulgences resides principally in the Pope, because as St. Thomas tells us, "the power of granting indulgences is given to him who presides over the Church." This teaching of the Angelic Doctor has been embodied in the Code where it is stated: "Besides the Roman Pontiff to whom the distribution of the entire spiritual treasury of the Church has been entrusted by Christ, the Lord, those only are able to grant indulgence to whom it has been expressly conceded by law." Those enumerated in the law as having this power are Cardinals who have the faculty of granting an indulgence of two hundred days toties quoties to persons in places or institutes under their jurisdiction. Should this indulgence be granted outside of their jurisdiction it may be gained only by those present. Metropolitans may grant an indulgence of one hundred days in their own and in the dioceses of their suffragans. Residential Bishops20 and Vicars and Prefects Apostolic even though these latter lack the episcopal character are empowered by law to grant an indulgence of fifty days within the confines of their respective territories. In order to prevent abuses which might arise, the Code" further states that inferiors of the Roman Pontiff are unable to grant to others the faculty of conceding indulgences they have received from the Holy See, without an express indult to that effect; they may not grant indulgences applicable to the souls in Purgatory; they cannot grant additional indulgences to an object, an act of piety or a confraternity to which the Holy See or someone else has attached indulgences, unless new conditions are prescribed. Although the Pope as head of the Church is the grantor of these indulgences, it has been customary for him to delegate this power to one of the Congregations. During the course of time this delegation has been transferred to various congregations. Due to changes of recent years, the faculty of granting indulgences was entrusted by Pope Pius X to the Sacred Penitentiary, while it remains the duty of the Holy Office to decide all questions concerning the doctrine of indulgences. In order to prevent the spread of apocryphal indulgences the Code decrees that all who have received concessions for all the faithful, are bound under pain of nullity of the favors received of sending an authentic copy to the Sacred Penitentiary..
Certain conditions have been laid down in the Code for the gaining of indulgences. Canon 925 No. 1 declares who are capable of gaining indulgences, while the second section of this same canon sets forth the necessary conditions for the actual gaining of them. Hence to be capable of gaining an indulgence for oneself one must be baptized, not excommunicated and in the state of grace for at least the last work prescribed and be a subject of the grantor. The second requirement of this section states that the person must be in the state of grace at the time the last work is performed. Thus, should a person fall into mortal sin while performing the necessary exercises, he would not lose the indulgences if before the exercises are completed, he again regained sanctifying grace either by Confession or making an act of perfect contrition. In connection with the last condition, it should be noted that unless stated otherwise, peregrini, vagi and those living in a territory may gain the indulgences granted for that territory, provided, these indulgences have not been restricted to a particular class of persons.
The second section of this canon treats of the requirements necessary for the actual gaining of indulgences. They are as follows; one must have at least a general intention, and the stated works must be fulfilled in the time and manner prescribed. It seems sufficient that this intention be at least habitual. Any notable change or omission of the works invalidates the gaining of the indulgences. These works must, with the exception of giving alms, be performed personally, and should also be of supererogation, unless he who concedes the indulgence decrees otherwise.
Often times certain particular works are accustomed to be prescribed for the gaining of an indulgence. Briefly they are Confession, Communion, Prayers for the intention of the Pope and visits to some church. The confession may be made within the eight days preceding the feast or within the octave. Communion may be received on the day before the feast or within the octave. For the intention of the Pope it is customary to recite five Paters and Aves for the fulfilment of this requirement. These prayers must be said orally however, as mental prayer does not suffice.