liturgy as different prayers (_e.g., Accendamur exemplis; instruamur
exemplis_, Feast of St. Philip and St. James, Feasts of several
martyrs). So, too, prayers which have the same form of petition (e.g.,
the prayers on feast of St. Joseph and on feast of St. Mathew), are not
considered as different and must not be repeated in the same hour. But
where the petition is different, even though all the remainder of the
prayers are similar in wording, they may be repeated in the same hour.

But what is to be done in offices where a commemoration prayer and the
prayer of the office is from the common? What must be done where the
feast is the feast of a Doctor and a commemoration of a Doctor is to be
made? What is to be done when the office of the feast is of a virgin not
a martyr, and a commemoration of a virgin not a martyr is to be made? In
the first case the prayer from the office of a confessor or Pontiff
should be said, adding to it the title of Doctor. In the other case, the
prayer _Indulgentiam_, omitting the word _martyr_, is to be said.

The origin of these commemorations was, that the Popes in removing the
solemn celebrations of certain feasts of Apostles and Martyrs, which
were formerly of precept, provided that their _cultus_ should not be
forgotten, and that their commemoration in the office should remind
priests and the faithful of those servants of God, whom the Church
wishes ever to honour. I have said the order given for commemoration in
the _Ordo_ should be followed; but not to follow this order does not
exceed a venial sin. Even the deliberate omission of a commemoration in
Lauds or Vespers is not a violation of a grave precept.