Definition
Argumentum a divisione (Latin: "argument from division") is a maxim of legal reasoning holding that an argument constructed by systematically dividing a subject into its constituent parts and reasoning from those parts is among the most powerful forms of legal argument. The full maxim reads: Argumentum a divisione est fortissimum in jure — "An argument from division is of the greatest force in law."
The principle reflects the classical view that when a legal rule, right, or subject matter can be exhaustively partitioned into recognized categories, and the argument accounts for each part in sequence, the resulting conclusion carries exceptional persuasive and logical weight. By eliminating ambiguity through exhaustive classification, the argument leaves no analytical gaps for contradiction.
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Common Confusion
Black's 2nd Edition preserves this maxim in close proximity to two related but distinct maxims: Argumentum a simili (argument from analogy) and Argumentum a majori ad minus (argument from the greater to the lesser). Researchers encountering these entries together should treat them as separate principles. Argument from division is not the same as analogical reasoning, nor is it the same as the greater-to-lesser inference. Division proceeds by partition and exhaustion of categories; it does not rely on similarity or hierarchical implication.
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Why It Matters in Research
This term is encountered almost exclusively in older treatises, maxim collections, and common law opinions that openly cited Latin legal principles as stand-alone authority. Modern courts rarely invoke it by name, but the underlying reasoning pattern — exhaustive categorical analysis — appears constantly in statutory construction, constitutional interpretation, and pleading doctrine.
For corpus researchers, several navigational points apply:
First, the maxim appears in Coke's reports and commentary (Co. Litt. 213b; 6 Coke 60), which means it surfaces in English common law materials and early American cases drawing on those sources. Searching the Law Mind corpus for "a divisione" or the full Latin phrase will cluster results in treatise literature rather than case reporters.
Second, the maxim belongs to a family of argumentum maxims that 18th and 19th century legal writers organized together. Broom's Legal Maxims is the principal organizing source Black's cites for this cluster. Researchers following citations from Black's 2nd Edition entries in this family should go directly to Broom for the fuller analytical context.
Third, this principle connects directly to the canon of exhaustive enumeration in statutory construction — the idea that when a statute lists categories intended to cover a whole subject, the enumeration controls interpretation of each part. Researchers working on expressio unius or statutory completeness arguments may find the a divisione maxim cited in foundational treatise discussions of those doctrines.
Fourth, because this is a pure Latin maxim entry, its practical legal force today is indirect: it supports methodological arguments about how courts should structure analysis, not substantive claims about rights or duties. Treat it as a tool of legal rhetoric and argumentation theory rather than a rule of decision.
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Historical Dictionary Support
Black's 2nd Edition does not give this maxim its own standalone entry; it appears as part of a compressed series of argumentum maxims. The entry as printed reads: "Argumentum a divisione est fortissimum in jure. An argument from division [of the subject] is of the greatest force in law. Co. Litt. 213b; 6 Coke, 60."
This is consistent with how 19th century legal dictionaries handled Latin maxims generally — citation to Coke and the reporters as authority, no doctrinal elaboration. Bouvier's Law Dictionary similarly treats argumentum maxims as reference entries pointing researchers toward Coke and Broom rather than developing independent analysis.
What the historical dictionaries do not do is explain why this maxim was considered so significant. The underlying logic — that exhaustive partition forecloses interpretive dispute — was treated as self-evident by civilian and common law writers alike. Modern researchers should not read "fortissimum in jure" as a binding rule of procedure but as a classical rhetorical assessment of argumentative strength.
The adjacent maxim preserved in the same Black's passage — Argumentum a majori ad minus negative non valet; valet e converso ("an argument from the greater to the less is of no force negatively; affirmatively it is") — is frequently confused with a divisione in older treatises. The two are methodologically distinct and should be indexed separately in research notes.
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Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Legal Maxims; Statutory Construction; Rules of Legal Argument.
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