I began reading “Secrets of the Rosary” and the author, of course, promotes praying the rosary on a daily basis. He mentions the 15 mysteries (book was written quite a number of years ago) and the inference is that the daily rosary should have all 15 decades (20 now, I guess). So my question is are the indulgences granted on the assumption that all of the mysteries are prayed, or are only 5 decades considered a complete rosary?
Only five decades of the rosary are necessary for gaining a partial or plenary indulgence. The Handbook of Indulgences (p.79-80) states:
“A plenary indulgence is granted when the rosary is recited in a church or oratory or when it is recited in a family, a religious community, or a pious association. A partial indulgence is granted for its recitation in all other circumstances.
“(The rosary is a prayer formula divided into fifteen decades of Hail Mary’s with the Lord’s Prayer separating each of these decades. During each of these decades we recall in devout meditation the mysteries or our redemption.)
“It has become customary to call but five such decades the “rosary” also. Concerning this customary usage then, the following norms are given regards a plenary indulgence.
"1. The recitation of a third of the rosary is sufficient for obtaining the plenary indulgence, but these five decades must be recited without interruption.
"2. Devout meditation on the mysteries is to be added to the vocal prayer.
"3. In its public recitation the mysteries must be announced in accord with approved local custom, but in its private recitation it is sufficient for the Christian faithful simply to join meditation on the mysteries to the vocal prayer.
"4. In the Eastern Churches where recitation of the Marian rosary as a devotional practice is not found, the patriarchs can establish other prayers in honor of the blessed Virgin Mary which will have the same indulgences as those attached to the rosary, (e.g., in the Byzantine churches, the Akathist hymn, or the office Paraclisis.)”
Keep in mind *Canon Law * (CIC) concerning gaining indulgences: “To be capable of gaining indulgences, a person must be baptized, not excommunicated, and in the state of grace at least at the end of the prescribed works. To gain indulgences, however, a capable subject must have at least the general intention of acquiring them and must fulfill the enjoined works in the established time and the proper method, according to the tenor of the grant” (CIC 996.1-2).
For additional information see Pope Paul VI’s Apostolic Constitution on Indulgences Indulgentiarum doctrina.