Definition
Jus naturale (Latin: natural law) refers to the body of legal and moral principles understood to derive from nature, reason, or the universal moral order rather than from any enacted statute or sovereign command. In Roman and later Western jurisprudence, it designated law held to be binding upon all human beings by virtue of their rational nature, independent of the particular laws of any state or political community.
The concept carries two overlapping but distinct emphases found across historical sources:
(1) Law discoverable by reason. Principles accessible through abstract reasoning or the natural moral sense, universally applicable to all persons and nations. In this sense jus naturale stands above both jus civile (the particular law of a given city or state) and jus gentium (the law common to all peoples), though the three were frequently conflated or blended in Roman jurisprudential writing.
(2) Law derived from animal instinct. A narrower Roman usage, attributed to the jurist Ulpian and preserved in the Digest (1.1.1.4), treated jus naturale as the law common to humans and animals alike — the instincts governing reproduction, offspring-rearing, and self-preservation. This biological reading distinguished jus naturale from jus gentium, which applied only to humans capable of reason.
Common Language
Modern common usage (Wiktionary): "The law of nature; the common sense of justice."
Historical common usage: No distinct lay entry; the phrase remained a term of art borrowed directly into English legal and philosophical discourse from Latin.
Editorial note: The popular phrase "law of nature" in ordinary English suggests something like physical or scientific laws governing the natural world. In legal usage, jus naturale never referred to physical necessity but to normative principles — the "ought," not the "is." A researcher encountering the phrase in a legal or philosophical text should resist the modern scientific connotation entirely.
Common Confusion
Jus naturale, jus gentium, and jus civile form an interlocking triad that Roman jurists never fully stabilized. In some sources, jus naturale and jus gentium are treated as synonyms; in others, jus gentium is a subset of jus naturale, applying to rational beings; in still others, they are formally separated (jus naturale as instinctual, jus gentium as rational-universal). Black's (1st and 2nd) acknowledges the conflation explicitly, noting the terms were used interchangeably. Burrill distinguishes them more sharply, following Mackeldey's civil law taxonomy. A researcher should never assume a consistent distinction between these three terms across sources without checking the specific author's framework.
Jus naturale should also not be conflated with natural rights in the post-Enlightenment, constitutional sense. The Roman concept is a jurisprudential category about the source and validity of law; modern natural rights discourse concerns what individuals may claim against government. The lineage connects them, but they are not equivalent.
Why It Matters in Research
Structural pattern: historical evolution with deep cross-referencing. This term is less a rule of decision than a jurisprudential category that shaped centuries of legal argument — its significance lies in understanding where it appears and why.
Corpus researchers should watch for jus naturale doing different kinds of work depending on the era and context:
In Roman and civil law sources, the term anchors arguments about the foundation of property, slavery, family relations, and the obligations that exist prior to positive law. Bracton's use (cited in Burrill) carried jus naturale into English common law thinking, where it surfaced in equity reasoning and ecclesiastical courts.
In natural law theory (Grotius, Pufendorf, Vattel), jus naturale became the baseline for international law arguments. A treatise invoking jus naturale in an international law context is drawing on this tradition, not the Roman instinct-based definition.
In 19th-century American legal writing, jus naturale appears in constitutional argument — particularly in debates about the legitimacy of slavery, property rights, and the limits of legislative power. Courts and advocates used natural law language to challenge or defend positive enactments. Understanding which version of jus naturale the writer meant is essential to parsing the argument.
Trap for researchers: the Ulpianic definition (instinctual, shared with animals) was used by some pro-slavery writers to argue that slavery, though contrary to jus gentium's rational principles, was consistent with natural dominance hierarchies. Abolitionist writers inverted the argument, relying on the rational-universal reading. The same Latin phrase could fuel opposite conclusions depending on which Roman gloss was applied.
Bouvier's framing — jus naturale as opposed to positive law — reflects the dominant American usage of the 19th century. Black's and Burrill are closer to the Roman philological tradition. These represent different working vocabularies; a court opinion drawing on Bouvier is not necessarily making the same argument as a civil law treatise drawing on Mackeldey.
Historical Dictionary Support
All four source dictionaries agree on the basic identification: jus naturale means natural law, standing apart from enacted or state-made law. The divergence is in how they characterize its content and source.
Black's (both editions) offers the broadest gloss — law discoverable by reason or taught by nature to all nations — and notably calls this a "conceit" originating with Roman philosophical jurists, signaling a degree of editorial skepticism unusual in a law dictionary and reflecting the positivist current in late 19th-century Anglo-American jurisprudence.
Bouvier aligns jus naturale with universally binding rules sanctioned by right reason and contrasts it explicitly with positive law (jus civile, municipal law). This is the natural law theory framing most useful for understanding American legal argument in the 1800s. Bouvier references Ulpian's definition but treats it as a data point, not the controlling meaning.
Burrill is the most technically precise, following Mackeldey's civil law taxonomy and preserving the Ulpianic biological definition as the primary Roman meaning. Burrill also flags the overlap with jus gentium, citing the Institutes (1.2.11; 2.1.11) directly. This is the most useful entry for researchers working in Roman law or comparative civil law contexts.
What the historical dictionaries miss: none engages seriously with the 17th- and 18th-century natural law theorists (Grotius, Locke, Pufendorf) who transformed jus naturale from a Roman jurisprudential category into the philosophical foundation for international law and constitutional government. Researchers working in those traditions will need to supplement the dictionary definitions with the treatise literature.
Jurisdictional Note
Jus naturale has no operative jurisdiction in the technical sense — it is a jurisprudential concept, not a rule of decision in any modern court system. Its practical significance varies by legal tradition: civil law systems (especially those with Roman law heritage) retain more explicit natural law vocabulary in foundational texts; Anglo-American common law absorbed natural law reasoning primarily through equity and constitutional argument, where it surfaces without always being named.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Natural Law; Jus Gentium; Roman Law in American Jurisprudence