Definition
Latin maxim meaning "do not harm another" or "do not injure another." One of three foundational principles of Roman law attributed to Ulpian and preserved in Justinian's Institutes, alongside *honeste vivere* (live honestly) and *suum cuique tribuere* (give to each his own). Together, these three maxims were framed as the philosophical bedrock upon which all rules of law rest.
In practical terms, *alterum non laedere* is understood as the moral and jurisprudential root of the law of tort and delict: the basic obligation each person owes to others not to cause unjustified harm. It does not create a standalone cause of action but functions as an organizing principle — a statement of the animating purpose behind liability rules across civil law systems and, by interpretive inheritance, the common law of torts.
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Common Confusion
The maxim is occasionally misspelled *alterum non lzedere* (an artifact of typographic corruption in older printed sources, where the ligature *æ* in *laedere* was misread or misset). Researchers encountering this variant in historical texts or digitized materials should treat it as identical to *alterum non laedere*. The corruption appears in some scanned editions and secondary indexes; do not treat it as a distinct term or alternate spelling.
*Alterum non laedere* is also sometimes loosely conflated with the neighbor principle articulated in Anglo-American negligence law. The maxim is an ancestor concept, not a direct legal rule; it does not import Roman law doctrine wholesale into common law analysis.
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Why It Matters in Research
This term appears almost exclusively in foundational and philosophical legal writing rather than in operative doctrine. Researchers will encounter it in:
**Roman and civil law sources.** The maxim's home is Justinian's *Institutes* (Book I, Title I, Section 3), where it is stated alongside the other two Ulpianic precepts. Any research into the philosophical foundations of civil law — continental European legal systems, Louisiana, Quebec, Scotland — should treat this as a primary organizing concept.
**Tort theory and comparative law scholarship.** Common law tort theorists frequently invoke *alterum non laedere* when tracing the doctrinal lineage of negligence and the duty of care. It appears in discussions of the theoretical underpinnings of Donoghue v. Stevenson and similar foundational tort cases, though the maxim itself is not cited as authority in those decisions.
**Historical legal dictionaries and encyclopedias.** Black's 2nd Edition entry is brief and primarily a translation vehicle. Researchers using 19th-century legal dictionaries should expect this maxim to appear as a cross-reference anchor rather than a substantive entry. Many later editions of Black's consolidate or expand the treatment; cross-checking editions is worthwhile.
**Trap for digitized text searches.** Because the *æ* ligature in *laedere* was frequently corrupted in early typesetting and OCR processing, full-text searches of digitized historical materials may miss occurrences of this maxim unless the researcher also searches variant spellings (*laedere*, *lzedere*, *lędere*). This is a practical indexing problem, not a doctrinal one.
Jurisdictional relevance is highest in civil law and mixed legal systems. In pure common law jurisdictions, the maxim functions as background philosophy rather than operative doctrine, but it remains a useful research bridge when tracing the historical roots of tort obligation.
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Historical Dictionary Support
Black's Law Dictionary (2nd Ed.) offers a spare but accurate entry: a translation, identification of the two companion maxims, and the citation to Justinian's *Institutes* I.1.3. This reflects the standard treatment of the period — the maxim is acknowledged as foundational but not elaborated upon, consistent with how 19th- and early 20th-century Anglo-American legal dictionaries handled Roman law principles: noted with deference, not engaged with depth.
What Black's does not address is the tension between the maxim's apparent universality and the significant body of law that permits harm under specified conditions — economic competition, privilege, necessity, consent. Modern tort scholarship has worked through this tension extensively. The maxim, read strictly, would seem to prohibit far more than any legal system actually forbids; its function is aspirational and directional, not definitional. Historical sources that present it as a literal rule rather than a guiding principle should be read with that limitation in mind.
No material divergence exists among historical dictionaries on the translation or attribution. The consistent citation to Justinian's *Institutes* I.1.3 provides a stable anchor for cross-referencing across legal traditions.
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Jurisdictional Note
The maxim carries operative weight in civil law systems, where it informs statutory interpretation of delict and extra-contractual liability. In common law jurisdictions it is background philosophy rather than binding principle. Mixed systems (Louisiana, Quebec, South Africa) occupy an intermediate position where the maxim may appear in judicial reasoning as substantive interpretive support.
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