COMMEMORATION. — When the Office and Mass for one or more saints or for a feria, vigil, or octave cannot be celebrated on account of a feast of higher rank, a commemoration or memoria is often made in the Office and Mass of the day.
The cycles of the Temporal and the Sanctoral indeed run concurrently, and the Martyrology records many saints who on the same day are raised to heavenly glory. It is therefore not rare for a conflict to arise in the calendar between a feast, a Sunday, a feria, a vigil, or an octave. Liturgical rules aim to eliminate or mitigate such conflicts, either by suppressing less important feasts, or by transferring those of higher rank, or simply by commemorating some of them. This commemoration consists of an antiphon with its verse and collect at Vespers and Lauds, and of the collect in the Mass.