Definition
A Latin term from Roman and civil law meaning a person related by blood — specifically, one descended from the same common stock as another. In classical usage, *consanguineus* denotes blood relationship as distinct from relationship by marriage (*affinitas*). The term carried operative legal weight in civil law systems governing inheritance, intestate succession, and the degrees of kinship used to determine heirs.
In its narrower application, particularly in feudal and civil law contexts, *consanguineus frater* (or *frater consanguineus*) designated a half-brother on the father's side — a paternal half-sibling — as distinguished from *frater uterinus*, a half-brother on the mother's side. This distinction mattered significantly in succession schemes that privileged agnatic (paternal-line) descent.
Common Language
Modern common usage (Wiktionary): "Of the same blood; related by birth; descended from the same parent or ancestor."
Historical common usage (Webster's 1913): "Of the same blood; related by birth; descended from the same parent or ancestor."
The common and legal meanings align closely in general sense, but the legal term carries precise technical weight that ordinary usage does not. In law, *consanguineus* is not merely a description of family feeling or general relatedness — it triggers specific rules about degrees of kinship, inheritance priority, and the distinction between agnatic and cognatic descent. The half-sibling distinction embedded in *consanguineus frater* has no equivalent in ordinary usage and would be invisible to a reader approaching the term without civil law background.
Common Confusion
*Consanguineus* is frequently read as a simple synonym for "relative" or "family member," but the term operates in strict contrast to *affinis* (one related by marriage) and to *uterinus* (one related through the mother's line). Collapsing these distinctions in a historical source can produce serious misreading of inheritance and succession passages. A person described as *consanguineus* in a Roman law or early English equity text is being identified by a specific legal category, not merely acknowledged as a family member.
Why It Matters in Research
Researchers encounter *consanguineus* most often in three contexts: Roman and civil law texts on succession, early English common law and equity materials dealing with inheritance and next of kin, and canon law sources governing prohibited degrees of marriage.
In succession materials, the term does real classificatory work. Civil law inheritance schemes organized potential heirs into ranked classes, and *consanguinei* as a class had specific priority positions. Misreading the term as a generic reference to relatives — rather than a defined category — can distort analysis of who inherited and why.
The *consanguineus frater* / *frater uterinus* distinction is a particular research trap. In feudal land law and early common law, half-siblings on the paternal side were treated more favorably in inheritance than half-siblings on the maternal side, reflecting the preference for agnatic descent. Burrill's entry correctly flags this and cites Bracton, which is the right place to trace the distinction in English legal history. Researchers working in medieval property records or early equity cases should not assume half-siblings were treated symmetrically.
In canon law materials, *consanguineus* (and the related noun *consanguinitas*) governs prohibited degrees — the degrees of blood relationship within which marriage was forbidden. The computational methods for calculating degrees differed between Roman law and canon law, and this divergence has generated substantial secondary literature. A source using *consanguineus* in a marriage prohibition context may be working from either system, and the researcher should identify which before drawing conclusions.
Law Mind's corpus includes materials spanning all three of these contexts. When moving between Roman law sources, Bracton-era English materials, and later equity texts, watch for shifting usage: the term is consistent in its core meaning but the legal consequences it triggers vary substantially by system and era.
Historical Dictionary Support
Black's (1st and 2nd editions) and Burrill's are in agreement on the core definition: a person related by blood, descended from the same common stock, distinguished from *affinis*. All three sources cite Coke on Littleton 157 for the maxim *consanguineus est quasi eodem sanguine natus* ("a person related by consanguinity is, as it were, sprung from the same blood"), which is appropriate — Coke's treatment is the standard English authority for the proposition.
Burrill's is the more useful entry for research purposes. It flags the contrast with *affinis*, cites the Digest (38.16.1.10) for the Roman law foundation, cites Bracton for the English reception, and notes the general sense of "cousin" or blood relation. Black's 2nd edition adds the *consanguineus frater* sub-entry, which is the most practically significant distinction for inheritance research.
What none of the historical dictionaries address adequately is the canon law computational divergence, or the specific inheritance-class significance of *consanguinei* in civil law succession schemes. Researchers needing that level of depth will need to move beyond dictionary sources to treatises on Roman succession or canon law.
Jurisdictional Note
The term is native to civil law and Roman law systems. In American law, it appears primarily in historical sources, equity opinions drawing on civil law reasoning, and statutory definitions of consanguinity for purposes of prohibited marriages or intestate succession. Common law jurisdictions developed their own vocabulary for degrees of kinship, but courts and treatise writers in the eighteenth and nineteenth centuries regularly imported civil law terminology, including *consanguineus*, when addressing succession and marriage questions.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia: Consanguinity and Affinity; Intestate Succession; Degrees of Kinship; Half-Blood.