So basically, all three classes of feast are obligatory, and then for commemorations and feria the choice of Mass is optional?
The context that sparked my curiosity was that the professor claimed the Mass only contained an Old Testament reading (humorously, I think, still classed as the epistle) about 4 or 6 times a year. But I knew from my following of the feasts that MANY saints’ Masses and the commons use an Old Testament selection, including feasts and votives of Mary who often gets a reading about Wisdom. So he just seemed way off base - unless, of course, those third class feasts were not getting celebrated.
Usually, by custom, certain votives were assigned to weeks. Of course, most of the time, a priest could choose another votive within the rubrics.
Saturday: BVM
Monday: Holy Trinity
Tuesday:Holy Angels
Wednesday:St. Jospeh/ Ss. Peter and Paul/ Holy Apostles
Thurday: Blessed Sacrament/ Holy Spirit/ OLJC the High Priest
Friday: Passion of OLJC/ Holy Cross
Actually I think that in some ways your professor may have been somewhat right on saying that Masses for the Dead were common. Requiem Masses (of the semidouble rite meaning they were not on the day of death or the 3/7/30, etc day after the death) could be celebrated on any of the following days:
If sung: all non Double, non Sunday, non privileged vigils (Christmas, Epiphany, Pentecost), ferias (Ash Wednesday and Holy Week) and Octaves (see the 1962 changes thread)
If said (i.e. sine cantu): Semidouble or Simple Feast, a day within a common Octave, feria in Advent, Saturdays instead of S. Maria Sabbato, feria throughout the year. In Lent though, only on the first day of each week when a feria or semidouble/simple feast was said. They could not be celebrated on the days given above for sung Masses, and on the O Antiphon days (17-23 Dec) and Octave Days (eighth day of an Octave) and Rogation Monday.
These Masses could be said by priests who were not obliged to offer the day’s Mass for say, the people of a parish. If the priet’s were obliged to say the day’s Mass and could not celebrate anothe rMass they could always add a collect for the dead as when permitted by the rubrics. In cathedrals, for conventual Masses, two Masses could be said: one Requiem and one votive/ferial.
On the first day of the month (aside from November) a requiem was to be offered for all deceased priests, benefactors, family, etc. If a feast was celebrated then a commemoration was added using the collect ‘Fidelium’ (For all the faithful departed) in addition to other collects. Therefore, semidoubles would have 4 collects and Doubles 2, if there were no other commemorations
Prior to the changes of St. Pius X, priests were obliged to say a Mass of the Dead every Monday outside Advent and Lent, if there was no feast. This was reduced to an allowance of ferial or votive Mass for Monday (the Holy Trinity), however the collect Fidelium was required.
I think the Mass of the Dead and one of the votives of the BVM,
Salve Sancte Parens, were the best known. These were also the two that were permitted to blind priests. The Mass of the Dead was also quicker omitting several gestures in other Masses as well as the psalm Judica Me, and certain prayers.