According to the liturgical rubrics of the usus antiquior (the TLM), commemorations remain a humble but vital way of remembering saints – even if the great profusion of collects once familiar in earlier centuries has been greatly simplified or reduced. 

A commemoration is “an additional Collect, Secret and Post-Communion” at Mass (or analogous prayers in the Divine Office) for a feast which coincides with, or is overshadowed by, a more important celebration.

Thus, when two liturgical or feast days fall on the same calendar date – for example a Sunday or major feria together with a saint’s feast – the principal Mass propers follow the ruling day, and the lesser feast is not entirely omitted, but quietly commemorated.  The celebrant reads the second set of Collect, Secret, and Post-Communion proper to the commemorated feast, even in a Low Mass.

The current TLM rubrics classify commemorations into “privileged” and “ordinary.”  Privileged commemorations – such as ferial days, certain Ember days, Major Litanies, or days within the Octave of Christmas – are observed in all Masses (whether Low or Sung), and in the Office.  Ordinary commemorations, by contrast, are generally made only at Low Masses (and Lauds in the Divine Office).

On days of first class (major feasts), only one privileged commemoration may be added; on second class days, one commemoration (privileged or ordinary) is allowed; on third and fourth class days, up to two commemorations may be permitted.  (see here)

Thus the Missal preserves a living continuity with the older Roman Rite: minor feasts and saints’ days are not simply lost when a greater celebration occurs, but quietly folded into the liturgy so that their memory endures. 

For the faithful who assist at the traditional Mass, awareness of commemorations is a mark of attentiveness to the living tradition, and a way to honour saints and feast days which otherwise might pass uncelebrated.

May our devotion at every Mass, even when subtle, remain mindful of the full communion of saints – present and past – for whom the Church offers unceasing prayer.