Columbia subject headings:
Catholic Church--Liturgy--History.
Church music--Catholic Church--History.
Gregorian chants--History.
Harvard subject headings:
Catholic Church--Liturgy--History.
Church music--Catholic Church
Gregorian chants--500-1400--History and criticism.
Gregorian chants--History and criticism.
Princeton subject headings:
Catholic Church--Liturgy--History--Early church, ca. 30-600.
Catholic Church--Liturgy--History--Middle Ages, 600-1500.
Church music--Catholic Church.
Gregorian chants--History and criticism.