Definition
A Latin maxim from the civil law meaning "at the discretion of the judge." The phrase describes a matter left to the judge's sound judgment rather than governed by a fixed legal rule. Where a question falls ex arbitrio judicis, the court is not bound to a particular outcome by statute or rigid doctrine but instead exercises reasoned discretion in reaching a decision. The term captures the space between rule-bound adjudication and pure judicial will — it is discretion exercised within a legal framework, not arbitrary choice.
Common Language
The Latin components map cleanly to English: ex (from, at, upon), arbitrio (will, discretion, judgment), judicis (of the judge). No common English usage exists for the phrase as a unit. The nearest English counterpart — "at the judge's discretion" — carries the same meaning in modern usage. Because the term is pure legal Latin with no divergent common English meaning, no interpretive gap requires flagging.
Common Confusion
Ex arbitrio judicis is sometimes loosely equated with arbitrariness, but the civil law tradition from which it derives treated judicial discretion as structured and principled, not capricious. The phrase describes latitude within law, not freedom from it. Researchers encountering the term in historical sources should not conflate it with the pejorative sense of "arbitrary" that appears in constitutional due process analysis.
Why It Matters in Research
This is an infrequent but precise phrase encountered mainly in older legal writing, civilian-influenced treatises, and early common law scholarship that drew on Roman and canon law sources. Researchers are most likely to meet it when tracing the doctrinal history of judicial discretion — particularly in procedural and remedial contexts where courts historically possessed wide latitude, such as equity jurisdiction, sentencing, or the assessment of damages.
The cross-reference in both Black's editions to Blackstone's Commentaries (4 Bl. Comm. 394) and to Justinian's Institutes (4.6.31) is significant. The Institutes passage concerns actions in which the judge was empowered to assess the matter according to good faith and equity rather than a strict formula — the iudicia bonae fidei of Roman law. Researchers working on the historical foundations of equitable relief or good-faith damages will find this context valuable.
In Law Mind corpus searches, ex arbitrio judicis may appear as a signal phrase in treatises arguing either for or against expanded judicial discretion. When an author invokes the phrase approvingly, it typically supports flexible judicial power; when invoked critically, it often signals concern about unchecked judicial authority. The phrase can therefore function as an ideological marker in historical legal argument, not merely a neutral descriptor.
Because the term originates in civil law and was imported into English legal writing through civilian-trained scholars and equity jurists, it appears more frequently in treatises touching admiralty, ecclesiastical law, and early equity than in purely common law sources. Searching for it in common law pleading manuals will likely yield little.
Historical Dictionary Support
All three source dictionaries agree closely on meaning and attribution. Black's (1st ed.), Black's (2nd ed.), and Burrill's all define the phrase as "at, in, or upon the discretion of the judge" and identify it as a civil law term, citing the same two authorities: Blackstone's Commentaries at volume 4, page 394, and Justinian's Institutes at 4.6.31.
The entries are brief and do not analyze the phrase at length, reflecting its function as a reference point rather than a contested doctrine. Burrill's entry is the most spare; neither edition of Black's expands meaningfully beyond the definition. None of the historical dictionary entries explain the doctrinal context in Justinian's Institutes or engage with how the concept evolved from Roman law into English equity — a gap that limits their usefulness for substantive research without consulting the primary sources directly.
The appearance of "EX ASSENSU CURIÆ" immediately following the entry in Black's (1st ed.) is an artifact of alphabetical sequencing, not a related concept.
Jurisdictional Note
As a civil law maxim, ex arbitrio judicis has broader natural currency in mixed jurisdictions (Louisiana, Quebec, Scotland) and in legal systems descended from the Roman tradition. In common law jurisdictions, the concept it describes is fully operative, but the Latin phrase itself appears mainly in scholarly and historical writing rather than in judicial opinions or modern statutes.