Definition
A maxim of civil law meaning "a plaintiff ought not to be allowed what is not permitted to a defendant." The principle expresses a foundational rule of procedural symmetry: the rights and tools available in litigation should not be distributed so unevenly that one party enjoys a procedural advantage unavailable to the opposing party. In its broadest application, it stands for the proposition that the law's procedural apparatus should operate evenhandedly — what the defendant cannot do, the plaintiff should not be permitted to do either.
The maxim appears in the Digest of Justinian (Dig. 50, 17, 41) among the general rules of ancient law, placing it among the foundational axioms of the civil law tradition rather than as a specific rule of any particular cause of action.
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Common Confusion
Three distinct maxims share the "non debet" construction and appear in close proximity in historical dictionaries, creating easy conflation:
NON DEBET ACTORI LICERE: Procedural symmetry — the plaintiff cannot do what the defendant cannot.
NON DEBET ADDUCI EXCEPTIO EJUS REI CUJUS PETITUR DISSOLUTIO: A plea raising the same matter whose dissolution is sought by the action should not be brought forward. This is a rule about the improper use of pleadings, not about party symmetry.
NON DEBET ALII NOCERE QUOD INTER ALIOS ACTUM EST: That which is done between others ought not to harm one who was not a party. This is the ancestor of modern res inter alios acta principles — a rule of evidence and privity, not procedure.
Researchers working in historical sources should take care to read the full Latin phrase before relying on a "non debet" citation. Dictionary compilers, including Black's, frequently grouped these maxims together in a single block entry, making it easy to misread the scope of any one of them.
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Why It Matters in Research
This term will appear almost exclusively in sources rooted in the civil law tradition — Roman law commentaries, early equity treatises, and civil law jurisdictions — rather than in common law case reporters. Researchers encountering it in an English-language source are likely reading a treatise that draws on civilian authority to argue for procedural equality, or a court doing the same.
The maxim's practical significance in historical legal argument was as a check on asymmetric procedural rules. Advocates invoking it were typically arguing that a rule granting the plaintiff a power or immunity that the defendant did not share was fundamentally unjust and inconsistent with civilian principles. In equity practice, where courts had broader discretion over procedural fairness, arguments grounded in maxims of this kind carried rhetorical weight even when they lacked direct statutory or case authority.
Researchers should be aware that this maxim does not map cleanly onto any specific modern doctrine. Its legacy is diffuse — absorbed into contemporary principles of procedural due process, equal treatment of parties, and the general principle that courts should not favor one side in procedural matters without compelling justification. Do not search for it in modern case law expecting direct citation; it will rarely appear by name outside of comparative law scholarship or historical analysis.
The corpus context for this term is primarily maxim collections, civil law digests, and equity treatises. Black's 2nd edition treatment is compressed and partly obscured by typographical corruption in historical scans (note the "Hcere" rendering of "licere"), a common hazard when working with OCR'd versions of older dictionary editions. Always verify against a clean text when the Latin is critical to the argument.
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Historical Dictionary Support
Black's Law Dictionary (2nd Ed.) is the primary dictionary source for this entry, and its treatment is brief: it supplies the Latin text, the English translation, identifies the source as a rule of the civil law, and cites the Digest (Dig. 50, 17, 41). No elaboration on application is given, which is consistent with Black's treatment of purely maxim-based entries in the 2nd edition — these were recorded as reference points rather than analyzed doctrines.
The citation to Broom's Legal Maxims (Broom, Max. 166) in the adjacent entry (for Non debet adduci exceptio) suggests that Broom is a useful secondary source for the broader "non debet" family of maxims, and researchers who need deeper context should consult that work. Broom typically provides both the civilian origin and a discussion of how English courts had adopted, adapted, or declined to apply the maxim.
No modern law dictionary edition is known to carry this maxim as a standalone entry, reflecting the general trend of later editions of Black's to retire Latin maxims with limited active doctrinal life.
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Jurisdictional Note
This maxim originates in Roman civil law and retains greater vitality in civil law jurisdictions (including Louisiana, Quebec, and European systems) than in common law jurisdictions. In common law systems, its principles have been absorbed into general procedural fairness doctrine rather than cited as a named maxim.
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