Definition
The Sextus Decretalium — commonly called the Sext, or Sixth Decretal — is the sixth book of the decretals of the Roman Catholic Church, forming part of the Corpus Juris Canonici, the foundational body of canon law. Published in 1298 under Pope Boniface VIII, it was appended to the five books of decretals compiled under Pope Gregory IX (the Decretales Gregorii IX, issued 1234), extending and supplementing that collection with additional papal constitutions and conciliar decisions accumulated in the intervening decades. The name derives from its position as the sixth book added to what had been a five-book corpus.
The Sextus is a primary source of medieval ecclesiastical law and was administered in the church courts — including the ecclesiastical tribunals that operated alongside English common law courts through much of the medieval and early modern periods.
Why It Matters in Research
Researchers working in ecclesiastical law, legal history, or the history of the common law's relationship to church jurisdiction will encounter references to the Sextus Decretalium in several contexts.
First, English legal sources through the seventeenth century — and occasionally later — treat canon law as operative law in matters of marriage, legitimacy, wills (for personal property), tithes, and clerical discipline. Understanding that the Sextus is one component of the Corpus Juris Canonici, not the whole, is essential to tracing specific rules to their source. A doctrine appearing in a church court case may originate in Gregory's Decretales, in the Sextus, or in later additions such as the Clementines (1317).
Second, the Sextus is referenced in classical common law commentary. Blackstone's Commentaries (1 Bl. Comm. 82) identifies it as part of the canon law foundation relevant to English legal history, making it a source that historical researchers using Blackstone as a guide will encounter by name.
Third, the overlap between canon law and early common law principles — particularly in areas of equity, testamentary law, and family law — means that a researcher tracing doctrinal origins may need to consult the Sextus as a primary historical source, not merely a bibliographic curiosity.
Fourth, citation conventions in older legal dictionaries are compressed. Black's first and second editions cite Butler's Horae Juridicae (Butl. Hor. Jur.) and Blackstone; Burrill adds Mackeldey's Civil Law with Kaufmann's notes. Researchers following these citations should be aware that Butler's pagination differs between editions, and that Mackeldey's Civil Law is an institutional treatise on Roman and canon law origins, not English law directly.
Historical Dictionary Support
The three source dictionaries agree closely on substance. All three identify the Sextus Decretalium as the sixth book of the decretals, situate it within the Corpus Juris Canonici, note its supplementary relationship to the five Gregorian books, and date its publication to 1298. The entries are essentially parallel, reflecting a stable and uncontested definition across the Black's editions and Burrill.
Burrill's entry is modestly more informative in two respects: it names the parent collection precisely (Decretales Gregorii IX) and cites Mackeldey's Civil Law alongside Butler and Blackstone, signaling that the Sextus is relevant to the civilian legal tradition as well as English ecclesiastical history. Burrill also supplies the English-language equivalents — "the Sext" and "Sixth Decretal" — which aids identification of the document in English-language sources that may not use the Latin form.
What the historical dictionaries do not provide: no account of the Sextus's content or structure, no discussion of its relationship to the Clementines or the Extravagantes (the other later additions to the Corpus Juris Canonici), and no guidance on how canon law sources were used in practice in English ecclesiastical courts. Researchers requiring that depth will need to consult specialized works in canon law history.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Canon Law; Corpus Juris Canonici; Ecclesiastical Courts