Definition
In civil and Scots law, cognates are relatives traced through female lines of descent — that is, persons related to one another through one or more female ancestors. The term derives from the Latin *cognati* (literally, those born together or sharing a common origin) and stands in contrast to *agnates*, who are relatives traced exclusively through male lines.
In Roman law, the distinction between cognates and agnates carried significant legal weight: agnatic relationship governed formal succession and family membership under the older civil law (*ius civile*), while cognatic relationship reflected the broader bonds of natural kinship. As Roman law developed toward the law of nations (*ius gentium*) and later under Justinian's reforms, cognatic ties gained increasing recognition for purposes of inheritance and guardianship. In Scots law, the term became a standard classification in the law of succession, used to identify a defined category of kindred for purposes of distributing moveable estate.
Common Language
Modern common usage (Wiktionary): "Cognates" is the plural of *cognate*, meaning words in different languages that share a common etymological origin (e.g., English "night" and German "Nacht").
Historical common usage (Webster's 1913): Webster defined "cognate" as "allied by birth; related; of the same family or kind," with application to persons, languages, and things of like nature.
The gap here is directional and technical. In ordinary and linguistic usage, "cognates" simply means things sharing a common origin, with no gendered implication. In civil and Scots law, "cognates" is a term of art specifically confined to kinship traced through females — a meaning that narrows and redirects the ordinary sense in a way that matters for reading historical legal documents.
Common Confusion
Cognates are frequently confused with *agnates* in historical sources, and the two terms are only meaningful in opposition to each other. Agnates are kin related through an unbroken chain of male descent; cognates are kin related through female descent at one or more points in the chain. A paternal uncle's children are agnates; a maternal aunt's children are cognates. Researchers encountering either term in a Roman law, civil law, or Scots law source should look immediately to the other, as the legal consequences — particularly for succession — depend on which category applies. The confusion is compounded because some sources use "cognate" loosely to mean simply "related by blood," which is the natural reading in English but legally imprecise in this context.
Why It Matters in Research
This term is a trap for researchers working from English common law backgrounds. In common law, cognates has no formal technical meaning — kinship rules do not historically sort relatives into agnatic and cognatic lines in the same formal way. When the term appears in Law Mind sources, it signals civil law or Scots law territory, and the researcher should shift interpretive frameworks accordingly.
Several practical research notes:
First, the term is most active in Scots law succession materials and Roman/civil law treatises. Encountering "cognates" in a 19th-century American legal dictionary entry on succession or inheritance almost certainly indicates the entry is drawing from civilian rather than common law sources.
Second, the Burrill entry is the most substantive of the historical dictionary sources here and contains a partial quotation suggesting a contrast between agnatic and cognatic kin — the cut-off text reinforces that the full significance of the term only emerges in comparative relief against agnates.
Third, the term becomes largely obsolete in operative legal contexts after Justinian's reforms in Roman law and after the gradual shift in Scots succession law toward statutory treatment of relatives without the agnate/cognate distinction. Researchers reading later sources should be alert to whether the term is being used descriptively (to classify historical law) or prescriptively (as an active legal category).
Historical Dictionary Support
The five historical dictionaries covered here converge on the same core definition: cognates are relations through females, with the term rooted in Roman law and recognized as a common term in Scots law. Black's (both editions) and Burrill cite Mackeldey's *Roman Law* for the definition, and Burrill and Black's (2nd ed.) additionally cite Erskine's *Institutes* — both standard civil and Scots law authorities of the period.
Bouvier is notably brief and adds only Bell's *Dictionary* as support, without elaborating on the Roman law background. Rapalje & Lawrence is equally spare.
Burrill offers the most useful entry: it preserves a fragment of explanatory text — apparently from Taylor or a similar source — that begins to articulate the contrast between agnatic and cognatic relationship. The truncated quotation in the source material suggests a longer passage in the original that would have fully developed the distinction. Researchers consulting Burrill directly should look at the surrounding material.
None of the historical dictionaries discuss the evolution of the cognate/agnate distinction under Justinian's reforms, which substantially narrowed the practical significance of the agnatic line in later Roman and civil law. That gap matters for researchers who need to understand not just what the term meant but when and under which legal system it was doing active legal work.
Jurisdictional Note
The term is operative in Roman law, Scots law, and civilian jurisdictions generally. It has no formal technical meaning in English common law. Louisiana, as a mixed jurisdiction with a civil law tradition, historically employed cognatic terminology in succession law, though modern Louisiana succession statutes use contemporary statutory language rather than the Roman classification system.