A thorough and scholarly overview of the sources of the doctrine of Purgatory and the process of its distillation and solidification in the 12th and 13th centuries. In a nutshell, the scriptural basis of Purgatory is primarily 1 Corinthians 3:10-15, Matthew 12:31-32, and 2 Maccabees 12:4-46. A deeper and more cohesive picture emerged from the writings of St. Augustine, particularly his 'Enchiridion,' and Pope St. Gregory the Great, particularly his 'Dialogues.' All of these texts were then further synthesized and commented upon by a variety of theologians, most notably Peter Lombard (1155-57), whose 'Sententiae' became the core theology textbook for generations of Parisian academics. Because of this, Albertus Magnus, Bonaventure, Alexander of Hales, and Thomas Aquinas all produced commentaries on the 'Sententiae' which further fine-tuned and elaborated the doctrine. The 2nd Council of Lyons in 1274 first officially established Purgatory as Catholic dogma. A very worthwhile read, and even more interesting because the author is an agnostic, and so comes to the subject from more of an academic historical and sociological perspective, which seems helpful for a thorough understanding of this particular topic.