I found approaching canon law for the first time for historical research more than a little tricky, so I thought I would distill some of the most helpful ‘starter’ information I found on the way for anyone else embarking on it. (For more detail on what I was actually looking for, see my earlier post.)
James Brundage’s Medieval Canon Law is an excellent and very helpful introduction (particularly its appendices), but like most introductions to the subject, it focuses more on how canon law was developed and used in courts than on how one might go about actually using canon law commentaries to tease out ecclesiastical conceptions of a particular topic.
Very little of canon law has been translated into English. The Decretum and the collection of additional decretals issued by Gregory IX in 1234, known as the Liber Extra, are both only available in late 19th-century editions (although a current project at Yale will hopefully change things dramatically on both points). The situation for canon law commentaries is even more difficult, as few if any have a modern edition and they are therefore available only in either manuscript or early modern printed form (the latter of which are, however, sometimes helpfully available on Google Books, like this one).
Titles and Concordances. Because of the vastness of canon law, it’s helpful to have an idea of where to start looking. Ideally, footnotes from a related secondary source can help get you started, but you can also try the Wortkonkordanz zum Decretum Gratiani for the Decretum or looking under a relevant title within the collection.
Citations. A key part of any canon law commentary is its citations to both canon law (in the texts of my period, to both the Decretum and the Liber Extra) and to Roman law (Justinian’s Institutes, Digest, and Codex). Citation styles have understandably gone through a number of changes over the past 800-or-so years: Brundage groups them into the ‘obsolete’, ‘obsolescent’, and ‘modern’ styles.
Modern Citation Style
The modern style for the Decretum varies depending on the part of the work to which it is referring.
Part I – Referred to by its distinctions and chapters, e.g. D.23 c.7.
Part II – Referred to by its causa (case), question, and chapter, e.g. C.15 q.2 c.4.
Part III – As in Part I, with addition of abbreviation of its title (Tractatus de consecratione), e.g. D.2 de cons. c.82.
Liber Extra citations, indicated by an X (for Extra), are referred to by book, title, and chapter, e.g. X 3.10.4.
Modern Roman law citations refer to the work, book, title, law, and possibly section, e.g. Dig. (or D.) 18.104.22.168.
Medieval Citation Style
The now ‘obsolete’ style favoured by medieval canonists is also generally quite effective at marking out the relevant passage, but it requires a little more familiarity with the works or the use of a good index, as titles are more often referred to by their (highly) abbreviated names rather than their numbers, and canons or laws by their first word(s). Even in early printed editions, citations aren’t always italicized to distinguish them from the surrounding text, although they do usually begin with the word ut, ar[gumentum], infra or supra.
D.23 c.7 in a medieval text might be cited as xxiii. di. [or dist.] episcopus, i.e. within the twenty-third distinction, the canon beginning ‘Episcopus …’.
C.15 q.2 c.4 would be xv. q. ii. felix.
Liber Extra citations typically begin with an abbreviated title, followed by the title or number of the decretal. The following excerpt cites two decretals: de probat[ionibus]. c.3 (= X 2.19.3) and de test[ibus et attestationibus]. tam literis (= X 2.20.33).
In all these cases, the indispensable tool is Javier Ochoa Sanz’s Indices canonum, titulorum et capitulorum Corporis iuris canonici, which allows you to look up both Decretum and Liber Extra citations by the opening words of the canon.
Roman law citations typically begin ff. for the Digest (for reasons not entirely clear to me), C. for the Codex, and Inst. or some similar abbreviation for the Institutes. Again, the best tool for looking up cited Roman laws is Javier Ochoa Sanz’s Indices titulorum et legum Corporis iuris civilis.
Some Terminology on Law Collections, Apparatus and Commentaries.
[gleaned from J. A. Clarence-Smith’s Medieval Law Teachers and Writers: Civilian and Canonist (1975)]