Definition
In Roman and civil law, REI is the Latin plural of reus and carries two distinct senses depending on context:
1. In its special sense, rei refers specifically to defendants — the persons from whom something is demanded in an action, described in classical sources as ii unde petitur ("those from whom a thing is sought"). In this narrower usage, the term aligns with reus as the defending party in litigation.
2. In its general sense, rei refers more broadly to all parties to an action — both the plaintiff (actor) and the defendant (reus proper) — understood collectively as those whose matter is under dispute (ii quorum de re disceptatur). The term also extended to parties to a contract, capturing the sense of persons bound together by a legal relationship.
The term appears frequently in Latin maxims and civil law texts. The phrase favorabiliores rei, for example, reflects the principle that the law favors defendants in cases of doubt — a maxim relevant to the interpretation of ambiguous obligations.
Common Language
Modern common usage (Wiktionary): A Portuguese real — a unit of currency.
Historical common usage (Webster's 1913): A Portuguese money of account, worth approximately one tenth of a cent.
The common meaning of rei is purely monetary and Portuguese in origin, entirely unrelated to its Latin legal sense. Researchers encountering rei in legal texts should not confuse this currency term with the civil law usage; the contexts are distinct and the words share only orthographic identity across unrelated languages.
Common Confusion
REI (civil law parties) vs. RES (the thing or subject matter): These Latin terms are easily conflated at a glance. Res refers to the subject matter of a legal dispute or transaction — a thing or property interest. Rei, by contrast, refers to the persons involved. In possessory and property contexts, the two words appear in close proximity, and careless reading can produce misunderstanding. Additionally, rei is the genitive singular of res, meaning "of the thing" (as in rei vindicatio, "vindication of the thing"), adding a further layer of ambiguity: rei in one sentence may mean "of the thing" (genitive of res) and in another may mean "defendants" (plural of reus). Context and grammatical function must be assessed to determine which usage applies.
Why It Matters in Research
Researchers working in civil law materials, Roman law sources, or early common law texts that incorporate Latin terminology will encounter rei in both its senses. The genitive-of-res usage is especially pervasive: rei vindicatio, actio rei, and similar constructions appear throughout property and obligations doctrine and must be read carefully. A researcher who treats every instance of rei as referring to parties will misread foundational property law terminology; one who reads every instance as genitive of res will miss the procedural party-status discussions.
In historical dictionaries and commentaries, rei in the party sense often appears in discussions of procedural favoritism toward defendants — the maxim favorabiliores rei survives into civilian-influenced jurisdictions and has relevance to burden-of-proof and interpretive default rules. Burrill's entry points researchers toward this connection explicitly.
For Law Mind corpus users: when searching civil law treatises or early American legal works drawing on civilian tradition, query both reus and rei to capture the full range of party-status discussions. Entries treating defendants, obligors, and contracting parties in civilian sources may use either form depending on grammatical number and case.
Historical Dictionary Support
Burrill's Law Dictionary provides the primary entry, drawing on Heineccius's Elementa Juris Civilis (lib. 3, tit. 17, § 841) for both the special and general senses. Burrill is careful to distinguish the two meanings and to note that the general sense encompasses all litigating parties — not defendants only. This distinction matters because many summary treatments of rei collapse the two senses, leaving readers to assume the term always means defendant. Burrill's cross-reference to favorabiliores rei signals the doctrinal application most likely to surface in common law settings influenced by civilian thought. No other source dictionary is available for this entry; the term is underrepresented in English-language legal dictionaries, which typically address reus individually and leave rei to be inferred.
Jurisdictional Note
The term operates within Roman and civil law systems and in civilian-influenced American jurisdictions (Louisiana, historically). Common law jurisdictions do not use rei as a term of art in modern practice, though it appears in Latin maxims that retain doctrinal force in courts that consult such maxims during statutory or contractual interpretation.