Next in line are memorials, which are classified as either obligatory or optional.  Memorials commemorate a saint or saints.  Obligatory memorials must be observed whereas optional memorials do not have to be observed.  For example, the memorial of St. John Bosco (January 31) is obligatory while the memorial of St. Blase (February 3) is optional.  Only the memorials of those saints who are of “universal significance” are observed by the whole Church and marked in the general liturgical calendar.

Particular churches, countries, or religious communities may also celebrate the memorials of other saints of “special significance” in accord with their special devotions.  For example, the memorial in honor of the patron saint of a diocese is raised to a “feast.”

The celebration of memorials is also governed by the liturgical season.  For instance, obligatory memorials occurring in Lent are only celebrated as optional memorials.  During “Privileged Seasons” (December 17-31 and Lent) the prayer of the Saint may be substituted for the regular collect (opening prayer) of the Mass.  During weekday Masses during Advent (prior to December 17), Christmas Season, Easter Season, and Ordinary Time, the priest may offer the Mass of the saint, or the Mass of any saint of the Roman Martyrology, or a Mass such as one for “Various Occasions” (e.g. Masses for the Spread of the Gospel or for Religious Vocations) or a Votive Mass (e.g. the Mass of St. Joseph or the Mass of the Angels).  Also on Saturdays, when there is no obligatory memorial, it is most appropriate to offer the Mass of the Blessed Mother.