ius

Ius is a Latin noun meaning law, right, or obligation. In classical Roman usage it denotes both the body of law that governs social life and the set of rights recognized by a community. The term contrasts with lex, which refers to a concrete statute or written rule, though in practice the boundary between ius and lex could blur as statutes were integrated into the legal system. Ius civile refers to the law applicable to Roman citizens; ius gentium to what Romans regarded as the universal law applicable to foreigners and to natural interactions among peoples; and ius naturale to a body of principles that were supposed to be inherent in nature and discoverable by reason. The ius honorarium, a magistrate-generated body of rules, developed alongside the ius civile and was used to adapt and augment existing rules.

The concept of ius had a major influence on Western legal thought. In medieval and early modern Europe, scholars spoke of ius commune, the common law developed from a synthesis of Roman, canon, and local statutes. The Latin ius also gave rise to many modern terms such as jurisprudence (iurisprudentia), jurisdiction, and justiciary, all rooted in the idea of a system of right. In contemporary discussions, ius is often used as a historical or philological term rather than a contemporary statute, though phrases such as ius naturale and ius gentium continue to appear in legal theory. Plural iura denotes individual rights in contrast to the singular ius, or the general body of law.