Practically speaking, how does one sing the Mass? Does the priest sing everything; the homily, too? How do we know which parts of the Mass to sing? Fortunately, the second Vatican Council provided us with instructions on how to sing the Mass. Published in 1967, Musicam sacram provided clarification regarding the council fathers’ intentions for music. The document claims that singing the Mass will assist people as they strive to participate more fully. The Mass texts to be sung are organized into three degrees, or groups, which help to highlight the solemnity of the liturgical celebration. Therefore, at a weekday Mass the priest might sing only the parts from the first degree, whereas, at the Easter Vigil, the priest might sing all three degrees (which means everything being sung, except the homily). Here is an outline of progressive solemnity as presented in Musicam sacram. What is especially interesting is how the document groups the sung parts. The first degree texts (which should be sung most often, if not always, and before singing those parts from the second and third degree) include the dialogues, greetings and prayers.
In 2008, the United States Council of Catholic Bishops published Sing to the Lord: Music in Divine Worship, which also commends the practice of singing the Mass. In chapter 4, the authors give their own version of progressive solemnity and it differs only slightly from the degrees given by Pope Paul VI in Musicam sacram.