Clerics and monks were originally chalk and cheese. The clergy were an increasingly complex system committed to highly structured hierarchy – but there were unresolved uncertainties about the precise form it should take. The chapter discusses for instance the clerical cursus honorum, reactions against fast-track promotion, and the bigamia rule against clerics in higher orders marrying more than once and the rule’s relation to pagan marriage. The apostolic see was called in to clarify problems arising from these systems and also from the awkward relation between clerics and monks. Monasticism was an unstructured movement, sometimes out of control, at one point banned from towns by imperial law. The interpenetration of the clerical and monastic systems only intensified the challenge of integrating them. The problem would recur in different forms throughout the history of the Latin Church, and the difficulty of coordinating the two overlapping systems had the unintended consequence of strengthening the papacy, constantly called in to integrate monks within the religious legal system and adjust the differences between the two religious elites. The process is already in evidence with the earliest papal jurisprudence.

The first and second decretal waves, c. 400 and c. 1200, both responded to unresolved complexities arising from the evolution of separate social systems. In the standard gloss on Gratian, ‘Gloss II’, decretals from the two ages are brought into conjunction. Innocent I’s ruling about pagan marriages was generating thoughtful discussion eight centuries after his death. The standard gloss discusses it together with a decretal of Innocent III. Between Innocent I and Innocent III, the ‘Pauline Privilege’ system emerges clearly into view, taken for granted by Innocent III after an evolution at which for want of evidence we can only guess. How to integrate the earlier Innocent’s ruling with the ‘Pauline Privilege’ system? This is an example of how the horizon of reflection about a text can be enlarged over time, without losing contact with the original meaning, as it is applied in new context and to complex scenarios not originally envisaged.

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.

The strange and interesting bigamia rule remained a constant from the fourth century on, but the social worlds to which it was applied were different. A high proportion of the (very numerous) thirteenth-century clerics in minor orders did not have much to do with the clerical world, whereas their late Antique counterparts were presumably more or less integrated into the tight community around the city’s bishop. In the thirteenth century, the bigamia rule enabled popes and kings to deny clerical privileges to phony clergymen who enjoyed fiscal and judicial immunities, even though those clerics were supported by bishops whose power and profits they enhanced.