Columbia subject headings:
Catholic Church--Clergy.
Celibacy--History.
Church history--11th century.
Harvard subject headings:
Catholic Church--Clergy.
Celibacy--Christianity--History of doctrines--Middle Ages, 600-1500.
Celibacy--History.
Church history--11th century.
Princeton subject headings:
Catholic Church--Clergy.
Celibacy--History.
Church history--11th century.