These works complement one another, and can be consulted individually or used together. Translations of papal decretals—responses to questions posed by bishops—make up the bulk of Papal Jurisprudence, c. 400 and the appendices of Papal Jurisprudence, 385–1234. The texts and their contents lay the foundation for Papal Jurisprudence, 385–1234, which explores the social circumstances of their issuance and their continued use in the twelfth- and thirteenth-century canonical tradition. Together these works seek to understand the legal uncertainties that drove bishops to consult the papacy for assistance.

Papal Jurisprudence c.400 secures a critical base for and provides translations of decretals from the pontificates of Siricius (384–399) to Celestine I (422–432), a period during which the Roman Empire waned in the west. Minus free will, grace, and predestination, theological concerns were not at the foreground but rather themes such as: ritual and liturgy; clerical celibacy and “bigamy” (the ban on twice-married men or widowers becoming clerics); relations between monks and the secular clergy; heretics returning to the faith; and marriage as it related divorce, polygamy, and adultery came to the foreground. The decretals are then traced in three early canonical collections: the Frisingensis Prima, the Dionysiana, and the Quesnelliana. The Latin text, however, is not provided for every decretal. This is the case for chapter 4, in particular, where only the English translation is provided along with a reference to the critical edition (Zechiel-Eckes, Die erste Dekretale or Cabié, La lettre). The omission is unfortunate, as there is no framework for the list of significant variants. D'Avray then provides key stages in the reception of the decretals by listing whether they appear in Cresconius's Concordantia canonum, the Vetus Gallica, the Hispana, the Pseudo-Isidorian Decretals, Burchard of Worms's Decretum, the Collection in 74 Titles, and in Gratian's Decretum.

Aside from the translations, there are a number of pedagogical features to appreciate in this work. The introduction provides a helpful guide on how to use the Clavis canonum, a database that allows researchers to look up the transmission of a particular canon in canonical collections compiled before 1140 (Gratian's Decretum). In chapter 3 on texts and manuscripts, d'Avray introduces key terminology and explains his working method for creating the critical transcription of the texts translated as well as for his apparatus. I also appreciated d'Avray's modelling of the type of information to consider when working with manuscripts: why a manuscript was chosen, date (with sources provided on how that date was ascertained), contents by folio, number of leaves, material, dimensions, layout and ruling, quiring, script, punctuation, decoration, hands, and provenance.

Using the papal decretals and the themes of ritual, penance culminating with Easter, and the quality of the clerical cursus found in Papal Jurisprudence c.400 as a foundation, Papal Jurisprudence, 385–1234 focuses on the social factors that connect ca. 400, which d'Avray dubs the first decretal age, with ca. 1200, which he dubs the second decretal age. Both decretal ages were framed by demand-driven responses to social complexities and uncertainties. Furthermore, glosses from the second decretal age show that the meanings of papal responses from the first decretal age were still being expanded. Diversity marked the period ca. 400. Popes were consulted regarding uncertainties about the Trinity and the nature of Christ, and regarding the range of rituals and practices resulting from a growth in the number of Christian converts and the extent of geographic mobility. In the second decretal age, the standard gloss of Gratian's Decretum, first compiled by Johannes Teutonicus and then updated by Bartholomaeus Brixiensis, and the Liber Extra demonstrate the adaption of early papal jurisprudence to respond to social changes and their accompanying complexities. Without losing sight of the decretals’ original meaning, the glosses used these texts to reframe: the concept of the “Pauline Privilege” whereby non-Christian marriages were valid but dissoluble if one partner was baptized but the other refused; the application of the “bigamia” rule to deny clerical exemptions from taxation and secular justice to those falsely claiming to be in the minor orders; and the emergence of the system for the election of bishops by the maior et sanior pars of the cathedral chapter.

Both decretal ages had a conception of canon law as separate from theological concerns. d'Avray does so by noting three systems for canonical collections found in Late Antiquity and the early Middle Ages. The “inclusive” type of collection, such as Vetus Gallica and Hibernensis and Burchard of Worms's Decretum, included a wide swath of religious writing, such as that from the Church Fathers and penitential material, but omitted a lot of the early papal jurisprudence studied in Papal Jurisprudence c.400. The Pseudo-Isidorian Decretals, representing a second system, comprises a combination of conciliar canons and papal decretals but did not include other genres of religious writings. It was a mixed collection in that it did include theological material about the Trinity and nature(s) of Christ. The third system, represented by collections such as Dionysiana, Dacheriana and Dionysio-Hadriana, included early papal jurisprudence and conciliar canons but did not include theological material. In this category, d'Avray included Charlemagne's Admonitio generalis, a secular capitulary that also addressed ecclesiastical affairs. It is this last system that would eventually take hold in the twelfth and thirteenth century and led d'Avray to place particular emphasis on the Dionysiana, the Admonitio generalis, and the Pseudo-Isidore Decretals as vital vehicles for the transmission of papal jurisprudence. The thirteenth-century schools of Paris contributed further to the separation of law and theology, as it was there that questions of speculative theology were worked out. As a result, the papacy was not called upon as often to resolve theological differences. Contributing further were changes in intellectual leadership in Paris, which saw the collaborative relationship between law and theology fall by the wayside.

The connections between the first and second decretal ages led d'Avray to reassess the eleventh-century reform movement, commonly referred to as the Gregorian Reform, Investiture Controversy, or “papal turn.” He maintains that the root of reform lay in the disconnect between the contents of the papal jurisprudence of Late Antiquity—a jurisprudence that was alive but static in its structures and had been issued to address the complexities of an urban church and clergy (180)—and eleventh-century social practice, a time in which the clergy had been ruralized and no longer intimately connected to the bishop. D'Avray's reassessment offers tremendous food for thought. Conflict arises when old law cannot be applied easily to new realities. Late Antiquity, for example, conceived of clerical celibacy as celibacy within a marriage, while reformers conceived of celibacy as life without a wife. Laws were thus needed to address the reality on the ground: that sons of priests wanted to follow in their fathers’ footsteps.

D'Avray's works serve as models for future research. They model how to work with manuscripts. They model how to navigate a dense historiographical tradition. Finally, they model how to consider the relationship between law and society. We must consider the time, place, and context of law and, if it is used later, the extent to which these were still applicable. During points of conflict, we must consider the responsiveness of the law available, that is, how those engaged in the legal process work through the challenges posed by the law they have and the realities they face.