Sorry if this is an ignorant question. But I was looking through a Lumen Christi Missal at a Church I visited and noted a couple things. In the initial sections which go through the whole year, an entrance, offertory and communion antiphon is provided for each Sunday and for each week for daily mass following that Sunday. They are pointed so the various tones at the very back of the missal can be use to chant them. Later there is a section called the "Simple Gradual" which also provides antiphons for entrance, offertory and communion. Focusing for now on Ordinary Time, I noticed that these antiphons in the different weeks were all listed as "seasonal" So for example for the 17th Sunday in Ordinary Time, there were a number of antiphons listed as seasonal (with suggested musical notation) which were different from the prescribed antiphon in the previous section of the missal. What is the point of the Simple Gradual section if the prescribed antiphon was provided in the previous section of the missal? Are they just acceptable "seasonal" substitutes for the prescribed antiphons?