Disputa del Santissimo Sacramento (detail)
Raffaello Sanzio, ca. 1510

Fathers of the Church: The Fathers of the whole Church are especially the earlier teachers, who instructed her in the teaching of the Apostles, during her infancy and first growth.

Doctors of the Church: Certain ecclesiastical writers have received this title on account of the great advantage the whole Church has derived from their doctrine. In the Western church four eminent Fathers of the Church attained this honour in the early Middle Ages: St. Gregory the Great, St. Ambrose, St. Augustine, and St. Jerome. In the Eastern Church three Doctors were pre-eminent: St. John Chrysostom, St. Basil, and St. Gregory Nazianzen. To these great names others have subsequently been added, bringing the current total to 33.

Saints: The Catholic Church canonizes or beatifies only those whose lives have been marked by the exercise of heroic virtue, and only after this has been proved by common repute for sanctity and by conclusive arguments. Though their writings are not infallible, nor do they have any special authority (other than that accorded them by the Church as Fathers or Doctors), the great majority of the writings of the Saints are founts of holiness that can be of great advantage to their readers.

Secular Clergy: From the humble history of their Parish to great works of Theology, those men who have been ordained into Holy Orders have produced many great works.

Laity: The great majority of the Church, the faithful laity are called not to religious or priestly life, but to live out the Evangelical Counsels in the world. Though laymen (even Emperors) were rarely allowed to write or teach matters pertaining to the Faith during much of the Church's existence, a great plethora of works has sprung up in the last few Centuries.