Definition
Quasi affinity is a civil law concept describing the relationship that arises between two persons when one of them has been betrothed to a blood relative of the other, even though no marriage between those parties ever took place. It is a species of affinity — the legal relationship created by marriage between a spouse and the other spouse's kin — extended by analogy to cover formal betrothals that did not culminate in marriage.
In classical civil law systems, affinity was a recognized impediment to marriage: you could not marry certain relatives of your spouse (or former spouse). Quasi affinity extended that impediment one step further, treating a solemn betrothal as sufficient to generate a similar, if lesser, relational bond. The "quasi" prefix signals that the relationship mimics affinity without being identical to it — the full legal consequences of affinity attach only through marriage, but quasi affinity could independently bar or complicate certain unions under canon and civil law frameworks.
Common Confusion
Quasi affinity is easily conflated with ordinary affinity, but the distinction is precise. Affinity arises from a completed marriage; quasi affinity arises from betrothal alone, without consummation or solemnization of the marriage itself. Researchers should also be careful not to conflate quasi affinity with consanguinity, which describes blood relationships rather than relationships created by marriage or betrothal. A third potential confusion: the "quasi" construction here has nothing to do with quasi-contract or other quasi- terms of art in common law; this is a civil law doctrine with a self-contained meaning.
Why It Matters in Research
Quasi affinity is a historical doctrine with almost no operational significance in modern Anglo-American law. Researchers are most likely to encounter it in three contexts:
First, in civil law sources and canon law materials. The doctrine flourished in the Roman civil law tradition and was carried into canon law, where betrothal (sponsalia) was treated as a serious legal act with spiritual and social consequences. Impediments to marriage derived from quasi affinity appear in ecclesiastical court records, canonical treatises, and civil law commentaries through at least the nineteenth century.
Second, in historical marriage law research. Anyone tracing the history of marriage impediments — consanguinity tables, affinity prohibitions, dispensation records — will encounter quasi affinity as a recognized category. Its presence in sources signals that the author or jurisdiction was working within a civil or canon law framework, not a common law one.
Third, as a negative data point in common law jurisdictions. Quasi affinity as a formal legal category did not take root in English common law. English marriage law recognized affinity impediments but did not generally extend them to betrothals. A researcher finding the term in an English-language source is likely looking at a source with civil law influence, a treatise writer drawing on the continental tradition, or a historical comparative discussion.
The term's appearance in Black's Law Dictionary reflects the dictionary's traditional practice of cataloguing civil law and canon law vocabulary alongside common law terms — useful for identification, but not evidence that the doctrine was operative in American courts.
Historical Dictionary Support
Black's Law Dictionary provides the only dictionary treatment in the Law Mind corpus: "The affinity which exists between two persons, one of whom has been betrothed to a kinsman of the other, but who have never been married." This is a compact but accurate summary of the civilian doctrine. Black's does not elaborate on the legal consequences that attached to quasi affinity, the jurisdictions in which it was recognized, or its relationship to canon law marriage impediments — gaps a researcher should expect when working with this term beyond identification purposes.
No common-language dictionaries offer a relevant entry, as the term has no meaningful existence outside legal and canonical usage.
Jurisdictional Note
Quasi affinity as a legal impediment or recognized relational category is a civilian and canonical doctrine. It has no established footing in American common law or modern statutory marriage law. Researchers working in Louisiana or other mixed-jurisdiction contexts may find greater resonance with civil law sources, but even there, modern statutory codes have generally displaced the classical impediment structure.
Encyclopedia Cross-Reference
The Law Mind Family Law Encyclopedia — Marriage: Capacity to Marry (Age, Consanguinity, Affinity)