An indulgence that may be gained in any part of the world is universal, while one that can be gained only in a specified place (Rome, Jerusalem, etc.) is local. A further distinction is that between perpetual indulgences, which may be gained at any time, and temporary, which are available on certain days only, or within certain periods. Real indulgences are attached to the use of certain objects (crucifix, rosary, medal); personal are those which do not require the use of any such material thing, or which are granted only to a certain class of individuals, e.g. members of an order or confraternity. The most important distinction, however, is that between plenary indulgences and partial.
By a plenary indulgence is meant the remission of the entire temporal punishment due to sin so that no further expiation is required in Purgatory. A partial indulgence commutes only a certain portion of the penalty; and this portion is determined in accordance with the penitential discipline of the early Church. To say that an indulgence of so many days or years is granted means that it cancels an amount of purgatorial punishment equivalent to that which would have been remitted, in the sight of God, by the performance of so many days or years of the ancient canonical penance. Here, evidently, the reckoning makes no claim to absolute exactness; it has only a relative value.
God alone knows what penalty remains to be paid and what its precise amount is in severity and duration. Finally, some indulgences are granted in behalf of the living only, while others may be applied in behalf of the souls departed. It should be noted, however, that the application has not the same significance in both cases. The Church in granting an indulgence to the living exercises her jurisdiction; over the dead she has no jurisdiction and therefore makes the indulgence available for them by way of suffrage (per modum suffragii), i.e. she petitions God to accept these works of satisfaction and in consideration thereof to mitigate or shorten the sufferings of the souls in Purgatory.