Definition
Diabolicum (Latin: "diabolical" or "of the devil") is a historical term applied to a specific English parliament convened at Coventry in the thirty-eighth year of the reign of Henry VI (c. 1459). The parliament earned this epithet on account of the severity and perceived injustice of its proceedings, most notably the attainder of Edward, Earl of March — later crowned King Edward IV — along with numerous leading noblemen of the Yorkist faction. The acts passed by this parliament were subsequently annulled by the parliament that followed, effectively repudiating its work as illegitimate.
The term functions as a proper historical designation rather than a general legal category. It does not describe a class of legislative acts or parliamentary procedures; it refers to one specific assembly, known in some sources as the Parliament of Devils or the Diabolical Parliament.
Common Confusion
Diabolicum is sometimes loosely grouped with other notorious or condemned English parliaments under the generic label "bad parliaments," but it is a distinct historical event with a specific name and a specific year. It should not be confused with the Parliamentum Indoctorum (the Unlearned Parliament of 1404, so called because lawyers were excluded) or the Merciles Parliament (1388), though all three have acquired pejorative designations for different reasons. The distinguishing feature of the Diabolicum is that its acts were formally annulled by a successor parliament — a relatively rare acknowledgment of legislative illegitimacy.
Why It Matters in Research
Researchers encounter Diabolicum almost exclusively in two contexts: histories of the Wars of the Roses and treatises on the law of attainder. Its primary legal significance lies not in doctrine but in the attainder proceedings themselves — the parliamentary condemnation of Edward, Earl of March and others without conventional judicial process. That the subsequent parliament annulled these attainders is significant for understanding how attainder and parliamentary reversal operated in fifteenth-century English constitutional practice.
When researching this term in historical sources, be alert to two navigational hazards. First, sources vary in translating or rendering the name: "Parliament of Devils," "Diabolical Parliament," and the Latin Diabolicum all circulate, and not all indexes cross-reference these variants. Second, the entry in Black's Law Dictionary cites Jacob — meaning Giles Jacob's Law Dictionary — as its authority, placing the chain of transmission through early modern English legal lexicography rather than primary parliamentary records. Researchers working from Black's alone are therefore one degree removed from the primary source.
The term has no modern doctrinal application. Its research value is entirely historical: it illuminates the use of parliamentary attainder as a weapon of factional politics, the constitutional mechanism by which a subsequent parliament could undo the legislative acts of a prior one, and the rhetorical tradition of assigning moral epithets to discredited assemblies.
Historical Dictionary Support
Black's Law Dictionary provides the foundational entry, drawing directly on Jacob's Law Dictionary. The entry is brief and consistent across sources: the parliament at Coventry, 38 Henry VI, so denominated because of its attainder of Edward, Earl of March and principal Yorkist nobles, with its acts annulled by the succeeding parliament.
Historical legal dictionaries are in agreement on the facts because there is effectively only one chain of authority — Jacob, transmitted through subsequent compilers. What the historical dictionaries do not provide is context: why the attainders were considered so extreme as to warrant the name, the specific noblemen affected beyond Edward of March, or the precise parliamentary mechanism of annulment. For that, researchers must move beyond the legal dictionary tradition to constitutional histories of the Lancastrian and Yorkist periods.
Jurisdictional Note
Diabolicum is specific to English parliamentary history and has no analogue in other common law jurisdictions. It carries no application in American, Canadian, or other derived legal systems.
Encyclopedia Cross-Reference
See ATTAINDER for the legal mechanism central to this parliament's infamy. See PARLIAMENT for the constitutional framework within which these proceedings occurred and were later annulled.