Perpendiculum: Presumptions and Legal Arguments in the 12th Century

David De Concilio, Ph.D. (2022, University of St Andrews/Università degli Studi Roma Tre), is research fellow at the Università degli Studi di Padova. He has published articles on medieval Roman and canon law, with a specific interest in the interaction between law, theology, and liberal arts.

"Overall, De Concilio has done legal historians a service by editing and translating this complex text in a clear and accessible manner and providing a lucid and concise discussion of its importance (though one should have copies of Gratian's Decretum and the Corpus Iuris Civilis at hand to make the most of it). The book offers a fascinating look into the twelfth-century legal classroom, especially the sorts of questions and problems that occupied canonists in this period and the methods they used to address them. It will be most useful to legal historians interested in the development of legal ideas and the ius commune at this critical moment in legal history, but those interested in scholasticism, the development of the universities, and, more generally, how ideas spread in the intellectual fervent of the twelfth century (especially outside the great schools of Paris and Bologna) will also find much to occupy them."Patrick R. Morgan, California Institute of Technology, in The Medieval Review, 8 October 2025

• AcknowledgementsPrefaceAbbreviationsIntroduction1 Eighty Years of Research: A Historiographical Account2 The Perpendiculum as a Source for the History of Presumptions3 The Reasons for a New Investigation4 Sources5 Map of the BookPart1 The Analysis of the Work1 The Work: The Perpendiculum and Its Text1 A European Text: The Manuscript Tradition of the Perpendiculum2 A Mosaic of Works: The Other Texts Inserted in the Perpendiculum3 Texts Appended to the Third Part of the Perpendiculum2 The Perpendiculum in Its Context1 The Importance of the Summula for the Development of Brocards2 The Importance of the Summula for the Glossators’ Theory on Presumptions3 Contemporary Works with Textual Links to the Perpendiculum4 Works Directly Influenced by the Perpendiculum5 Later Fortunes of the Summula’s Distinction on the praesumptio legis3 The Dating and the Author of the Perpendiculum1 The Dating of the Work2 The Problem of the Authorship4 Conclusions: The Perpendiculum between France and Italy1 Southern Ideas in Northern France2 Paris and Bologna: So Far and Yet So Close3 From Paris to Italy4 Rethinking Historiographical Boundaries: The Perpendiculum as a Case StudyPart2 The Texts1 Prolegomena to the Texts1 List of the Manuscripts2 Editorial Decisions3 Presentation of Text2 Manuscript Descriptions3 The Text of the PerpendiculumPartI (Summula de presumptionibus)‹I.› Incipit de presumptionibus‹II. Circa extrinseci facti essentiam›‹III. Circa extrinseci facti qualitatem›‹IV. Circa intrinseci facti substantiam›‹V. Circa intrinseci facti qualitatem›‹VI. Circa iuris vel scripture interpretationem›‹VII. De fide autem instrumentorum et attestationum›‹VIII. De re quam prelatus possedit›‹IX.› Quando presumptio non admittit probationem in contrarium‹X. Explicit›PartIIPartIII1 Critical Table of Contents2 Synoptic Table of the Brocards in PartIII3 List of Other Brocards that Occur Only in a Single Manuscript4 Appendix: Other Texts Inserted into the Perpendiculum1 Texts Inserted into Several Manuscripts2 Texts inserted into G and P1BibliographyIndex to Part1 (Chapters 1–4)Index to the Perpendiculum (PartsI–III) and the AppendixIndex to Legal SourcesIndex to Incipits of the Brocards (PartsII and III)Index to Manuscripts