• Aelred of Rievaulx. De spirituali amicitia. 12th c.
• Aelred of Rievaulx. On Spiritual Friendship. 12th c. trans. Lawrence C. Braceland. 2010.
• St. Athanasius of Alexandria. De incarnatione verbi. 4th c..
• Umberto Eco. The Name of the Rose. 1980.
• Hermann Hesse. The Glass Bead Game. 1943.
• St. Irenaeus of Lyons. Adversus haereses. 2nd c..
• St. Jerome. Letters of St. Jerome. 4th c. trans. W. H. Fremantle et al.. 1893.
• Catechism of the Catholic Church. 1970.