Definition
Canonum (also rendered in the fuller phrase Concordia Discordantium Canonum, meaning "the harmony of the discordant canons") is the name applied to the foundational compilation of canon law assembled by the Italian monk Gratian around A.D. 1151. The work organized and reconciled the accumulated, often contradictory ecclesiastical constitutions, conciliar decrees, and papal pronouncements that had developed over the preceding centuries of Christian legal tradition. Though popularly known as the Decretum Gratiani, the formal title Concordia Discordantium Canonum reflects Gratian's core method: systematic reconciliation of conflicting canonical authorities into a coherent body of law. The Decretum became the foundational text of medieval canon law and the starting point for all subsequent canonical study in the Western church.
Common Confusion
Canonum is frequently encountered in legal dictionaries as a shorthand reference to the full phrase Concordia Discordantium Canonum, and researchers sometimes mistake it for a standalone term with an independent legal meaning. It is not. Canonum is a genitive plural Latin form meaning "of the canons," and it carries legal significance only as part of the compilation title or in derivative references. Researchers should also take care not to conflate the Decretum Gratiani with later collections in the Corpus Juris Canonici — particularly the Decretals of Gregory IX (Liber Extra, 1234) — which supplemented and in some respects superseded Gratian's work. The Decretum was never formally promulgated by papal authority, making its legal standing in ecclesiastical courts technically different from later official collections.
Why It Matters in Research
Researchers encountering canonum in historical legal sources are almost certainly looking at a reference to the Decretum Gratiani and the medieval canon law tradition that flowed from it. Several research traps are worth flagging.
First, the Decretum was the foundation of the Corpus Juris Canonici, the body of law that governed ecclesiastical courts across Western Europe for centuries. Any research touching on probate, matrimonial causes, tithes, defamation, or moral offenses in English legal history before and after the Reformation will encounter the shadow of Gratian's compilation, even when sources do not name it directly.
Second, the relationship between canon law and English common law is a recurring tension in primary sources. Blackstone (1 Bl. Com. 82, cited by Burrill) engages directly with the canon law tradition as part of the background of English law, and Coke's Institutes (4 Inst. 74, cited across all source dictionaries here) provide the standard common law jurist's attitude toward ecclesiastical jurisdiction. Researchers working in these sources need to understand that canonum references situate a discussion within this contested boundary.
Third, the inclusion of the maxim Concordia parvæ res crescunt et opulentia lites — "small means increase by concord and litigations by opulence" — in multiple dictionary entries alongside the Canonum definition is not incidental. The maxim appears to have been appended by compilers to illustrate the spirit of reconciliation animating Gratian's method, but it is a distinct legal maxim with its own application in argument. Researchers should not treat the maxim as part of the definition of canonum itself.
Fourth, post-Reformation English sources will treat canon law references with hostility or significant qualification. Ecclesiastical law surviving in the Church of England after the Reformation was heavily circumscribed, and a 17th-century common lawyer citing canonum may be doing so to dismiss canonical authority rather than invoke it.
Historical Dictionary Support
All four source dictionaries agree on the core identification: canonum refers to Gratian's Concordia Discordantium Canonum of A.D. 1151, more commonly called the Decretum Gratiani. Burrill adds the Blackstone citation (1 Bl. Com. 82), which is the most useful pointer for English legal researchers, and explicitly redirects to "Canon law" as the broader entry. Rapalje & Lawrence redirects entirely to Decretum Gratiani, treating canonum as a mere cross-reference term rather than a substantive entry in its own right — a reasonable editorial judgment.
What the historical dictionaries do not supply is any account of the Decretum's internal structure (it is divided into three parts: the Distinctiones, the Causae, and the De Consecratione), nor do they situate it within the larger Corpus Juris Canonici that developed after Gratian. Researchers needing that fuller picture must move beyond these dictionary entries to canonist scholarship and Blackstone's own treatment of the ecclesiastical law tradition.
The consistent attachment of the maxim Concordia parvæ res crescunt et opulentia lites across multiple dictionary editions, without explanation of the connection, is an editorial quirk that may mislead. It appears to have migrated from entry to entry through dictionary compilation tradition rather than reflecting a legally significant relationship between the maxim and the term.
Jurisdictional Note
The Decretum Gratiani operated across the Western Catholic church as a whole. In English legal history, canon law administered through ecclesiastical courts had recognized authority in specific subject-matter areas (matrimony, testaments, tithes) until those jurisdictions were progressively transferred to common law courts. Scottish ecclesiastical law followed its own post-Reformation trajectory. For U.S. researchers, canonum and the Decretum are historical background rather than operative authority.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Canon Law; Corpus Juris Canonici; Ecclesiastical Courts.