Definition
A Latin term from the civil law meaning affinity — the legal relationship created by marriage between one spouse and the blood relatives of the other. Affinitas is not a relationship of blood (consanguinitas) but one arising from the marriage bond itself.
Two related forms appear in historical sources:
1. Affinitas: The basic tie of affinity — the connection between a husband and his wife's blood relations, and between a wife and her husband's blood relations. The blood relatives of one spouse bear no affinitas to the blood relatives of the other spouse; the relationship runs only through the married pair.
2. Affinitas affinitatis: A more remote or extended relationship — the connection between a party and the kindred of their spouse's kin. Sometimes described as affinity of affinity. This concept was debated in canon and civil law contexts, particularly when courts assessed whether degrees of relationship were close enough to create impediments to marriage or to bar inheritance.
Common Confusion
Affinitas is frequently encountered alongside consanguinitas in historical legal texts, and the two are easily conflated. Consanguinitas denotes blood relationship — lineage traced through shared ancestry. Affinitas is entirely distinct: it arises from the act of marriage, not from birth, and it dissolves in some legal frameworks upon dissolution of the marriage that created it. A researcher reading a canon law or civil law text that references degrees of kinship must determine which relationship is being measured; conflating the two produces fundamentally different conclusions about who is prohibited from marrying, who may inherit, or who is disqualified from serving as a witness.
Why It Matters in Research
Researchers encounter affinitas most heavily in three contexts: marriage impediment analysis, inheritance and intestacy disputes, and witness disqualification rules — all areas where relationship proximity controlled legal outcomes.
In canon law sources especially, the computation of degrees of affinitas was technically demanding and shifted across different counting systems (the Roman civil law method versus the canon law method). Historical documents using this term may be applying different computational rules depending on era and jurisdiction, producing different conclusions about whether a prohibited degree existed.
The distinction between affinitas and affinitas affinitatis matters most in marriage law contexts. Many early authorities recognized affinitas affinitatis as a potential impediment to marriage, but this doctrine was contested and eventually narrowed or eliminated in many secular legal systems. A source asserting that affinitas affinitatis bars a marriage may reflect a strictly canonical position not adopted in the common law or in later civil codes.
Researchers should also note that affinity rules varied on whether the death of the spouse who created the tie extinguished affinitas. In some civil law traditions, the relationship persisted; in others, it did not. This affects the reading of historical wills, intestacy proceedings, and disqualification disputes.
The Rapalje & Lawrence entry in the source corpus does not appear to contain a substantive treatment of affinitas, suggesting researchers relying on that dictionary alone will find no guidance here and should cross-reference Burrill or Anderson.
Historical Dictionary Support
The source dictionaries are in agreement on the core meaning: affinitas denotes relationship by marriage in the civil law, with all sources tracing the concept to Justinian's Institutes (Inst. 1, 10, 6). Burrill adds the Latin root — affinis — and cross-references affinity and ad fines, providing useful entry points into the broader conceptual family.
Anderson's Dictionary of Law offers the most substantive treatment among the sources. It correctly articulates the asymmetry of affinitas: the relationship runs between each spouse and the other's blood kindred, but not between the two sets of blood kindred themselves. Anderson also separately defines affines (relations by marriage) and affinitas affinitatis (the tie between respective kindreds of a married couple), treating these as distinct, which is the more precise formulation.
Black's (2nd Ed.) adds the definition of affinitas affinitatis as "remote relationship by marriage," consistent with its function as an extended or secondary tier of affinity.
What the historical dictionaries collectively underemphasize is the degree-computation problem — the fact that the legal consequences of affinitas depended entirely on counting degrees of relationship, and that different legal systems counted differently. A researcher using these dictionary entries as a complete guide to the term will understand what affinitas means but will still need a canon law or civil law treatise to understand how it operated procedurally.
Jurisdictional Note
Affinitas is a civil law and canon law term with no direct common law equivalent, though English courts recognized affinity as a legal concept and applied similar rules in ecclesiastical and later statutory contexts. American state law on affinity-based marriage prohibitions and inheritance disqualifications varies significantly, and the term itself rarely appears in American statutory text; researchers finding affinitas in a U.S. legal document are almost certainly reading a source with civil law or ecclesiastical law lineage.