Definition
Jus ex non scripto (Latin: "law from the unwritten") refers to law that derives its authority not from enacted legislation or formal written sources, but from long-standing custom and the tacit consent of the community. It stands in contrast to jus ex scripto — law arising from written enactments.
The concept rests on the principle that a practice observed consistently over time, and accepted as binding by those subject to it, acquires the force of law without any formal legislative act. The community's continued adherence to the custom is itself the evidence of consent. As Ulpian formulated it in the Digest: "Diuturna consuetudo pro jure et lege in his quæ non ex scripto descendunt, observari solet" — meaning, in substance, that long-standing custom is observed as law and rule in matters that do not descend from written sources.
In the common law tradition, jus ex non scripto encompasses the body of law developed through judicial decisions, usage, and immemorial practice — what English lawyers historically called the unwritten or common law — as distinguished from statute law.
Common Confusion
Jus ex non scripto is sometimes treated as synonymous with customary law, but the concepts are not identical in scope. Customary law typically refers to the practices of a particular community or locality that have hardened into legal obligation. Jus ex non scripto is the broader jurisprudential category: it names the entire domain of law that derives from sources other than written enactment, including both local custom and the general unwritten law of a jurisdiction. The common law itself — developed through judicial precedent and immemorial usage — falls within jus ex non scripto even though common law rules are eventually recorded in written opinions. The "unwritten" character refers to the source of authority, not the absence of any written record.
Why It Matters in Research
Researchers will encounter this term primarily in foundational jurisprudential texts, treatises on common law theory, and historical sources discussing the distinction between statute and common law. It appears with some frequency in Blackstone's Commentaries, where the division between lex scripta (statute) and lex non scripta (common law, custom, and usage) structures his entire account of English law's sources.
The critical research trap is anachronism. Modern legal systems have largely absorbed unwritten customary rules into codified or case-law form, making the practical distinction between written and unwritten law less sharp than it appeared to classical and early modern jurists. When reading 17th- or 18th-century sources that invoke jus ex non scripto, resist translating the concept into modern "common law" without accounting for the broader customary dimension the term carried.
In civilian and mixed legal systems, jus ex non scripto retains more distinct operational significance. Researchers working in comparative law, admiralty, or early American legal history — where civil and common law traditions intersected — should track which framework the source is operating within before inferring meaning.
The term also connects to validity debates in natural law and positivist theory. Some classical jurists treated long-observed custom as evidence of natural reason embedded in community practice; positivists reframed unwritten law as simply a category of social fact lacking formal pedigree. Sources invoking jus ex non scripto may carry one or the other theoretical commitment without making it explicit.
Historical Dictionary Support
Bouvier's Law Dictionary defines jus ex non scripto as "law constituted by custom or such usage as indicates the tacit consent of the community," grounding the definition directly in Ulpian's formulation from the Digest (D. 1, 3, 33). Bouvier's translation — "whatever has existed for a long period of time, and is in harmony with the moral judgment of the community is regarded [as law]" — is offered as free but serviceable.
The definition is reliable as far as it goes, but Bouvier's treatment is compressed. It does not address the distinction between general unwritten law (the common law of the realm) and purely local custom, nor does it engage the theoretical debates about whether the binding force of unwritten law rests on consent, reason, or immemorial usage. For fuller treatment, researchers should consult Blackstone's Commentaries Book I, which remains the most accessible extended account of lex non scripta in the English-language tradition, and Austin's Province of Jurisprudence Determined, which subjects the same concept to sustained critical analysis from a positivist perspective.
No significant divergence exists among historical dictionaries on the core definition. The term is stable in meaning; variation appears in the theoretical weight different authors assign to it.
Jurisdictional Note
The concept carries different practical weight across legal families. In English and American common law, jus ex non scripto is largely of historical and theoretical interest, as custom has been substantially absorbed into case law and statute. In mixed systems (Louisiana, Quebec, South Africa) and in international customary law, the category of unwritten law retains active doctrinal significance.
Encyclopedia Cross-Reference
Law Mind Encyclopedia — Customary Law
Law Mind Encyclopedia — Common Law Origins
Law Mind Encyclopedia — Sources of Law