Liturgical Precedence and Order
Eucharistic celebrations, both those of the liturgical seasons and the sanctoral cycle, are governed by a precedence, established through the General Norms for the Liturgical Year and the Calendar. Often during any particular liturgical year, conflicts arise when a particular solemnity or feast falls either on a Sunday or during a period of specialized celebration, such as Holy Week or the octave of Easter. In such cases the General Norms provide guidance as to precedence (which celebration is to be followed) for feasts.
Besides precedence, the church year is also governed by certain norms, namely the use of specialized Biblical readings and liturgical colors for the celebration of the Eucharist. As described in Chapter 18, the readings for Mass, both on Sundays and daily, are programmed on a fixed cycle of three years and two years (odd and even), respectively. This pattern is generally continued through the various liturgical seasons, but there are some significant deviations from the general pattern of Ordinary Time during specialized seasons. During the Advent, Christmas, Lent, and Easter seasons, daily Mass readings, both the first reading and gospel, are the same each year. The readings are chosen to be consistent thematically and to highlight ideas relevant to the season. The general pattern for Sunday Mass of a first reading from the Hebrew Bible and a second from the New Testament is modified during the Easter season when the first reading is proclaimed from the Acts of the Apostles.