In the late Roman Empire, complexity and uncertainty created demand for responsa from the apostolic see. After the eleventh-century papal turn, new legislation and a different society generated new complexities and uncertainties. Decretals were not the only way to resolve them, but given the prominence of the tradition launched by Siricius and Innocent I, they were an obvious way. An unbroken chain of communication links the first and second decretal ages. Late Antiquity and the central Middle Ages need not be kept in separate compartments.

The book attempts a long-range history which is about expansion of meaning in the course of reception, and the kind of social soil in which papal jurisprudence flourished in periods widely separated in time.

In the fifth century bishops had brought problems to the apostolic see, which replied by laying down what was lawful and unlawful (leaving the bishops to do what they wanted with these responses). Shortly after the end of the empire in the West, the first decretal age comes to an end and a new phase begins: one of synthesis and compilation. This meant deciding what to leave out and what to include. Two collections, the Frisingensis prima and the Quesnelliana, include debate on the humanity and divinity of Christ, alongside the papal responses. The Dionysiana, however, leaves out these themes, which are in any case absent from the decretals of Siricius and Innocent I. Christological themes are absent also from letters of Leo I selected by Dionysius and from the ‘hold-all’ decretal Necessaria rerum dispositione of Gelasius I, which draws together in a quasi-synthesis the principal issues addressed in the first century of papal jurisprudence. Gelasius’s summative decretal and the Dionysiana anticipate the boundary that would separate canon law from what would be called theology, while the Frisingensis prima and Quesnelliana anticipate collections which recognize no such boundary.