Definition
Lineal consanguinity is the relationship by blood between persons standing in a direct line of descent from one another — that is, between an ancestor and a descendant. It connects individuals in a straight vertical line: grandparent to parent to child to grandchild, and so on in either direction. The line may ascend (from descendant toward ancestor) or descend (from ancestor toward descendant), but the defining characteristic is that one person is directly descended from the other.
Lineal consanguinity is distinguished from collateral consanguinity, which describes the blood relationship between persons who share a common ancestor but neither of whom is descended from the other — siblings, cousins, aunts, and uncles being the standard examples.
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Common Confusion
LINEAL CONSANGUINITY vs. COLLATERAL CONSANGUINITY vs. AFFINITY
These three terms operate as a system, and conflating them produces research errors. Lineal consanguinity runs vertically between ancestor and descendant. Collateral consanguinity runs horizontally between relatives who share a common progenitor but do not descend from each other. Affinity is not consanguinity at all — it is the legal relationship created by marriage, connecting a person to the blood relatives of their spouse. Historical sources sometimes use "consanguinity" alone to mean lineal consanguinity specifically, but in formal legal usage the word covers both lineal and collateral relationships. A researcher encountering a bare reference to "consanguinity" in a marriage prohibition statute or an intestacy provision must determine from context which category — or both — is intended.
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Why It Matters in Research
The distinction between lineal and collateral consanguinity appears most consequentially in two doctrinal areas: marriage prohibitions and intestate succession.
In marriage law, prohibitions on consanguineous marriages almost universally bar lineal relatives without exception or degree limit. A parent and child, or grandparent and grandchild, cannot marry regardless of remoteness in the line. Collateral prohibitions, by contrast, are degree-limited and vary widely by jurisdiction and era. When researching historical marriage validity or annulment grounds, confirming which category of consanguinity was at issue is the first analytical step.
In intestate succession, earlier common law schemes — and many statutory systems derived from them — allocated property differently depending on whether heirs were lineal descendants, lineal ancestors, or collateral relatives. The preference for lineal descendants over collateral kin, and the rules governing how the estate passed when the direct line failed, depended entirely on this classification. Nineteenth-century American statutes frequently used "lineal" and "collateral" as operative terms of art, and their meaning cannot be assumed to track modern statutory language.
A further research trap: degree-counting methods differ between the civil law and the canon law traditions, and historical sources do not always specify which method they apply. The civil law counts each generation as one degree; the canon law counts only to the common ancestor and then back down. This difference matters for collateral consanguinity more than lineal, but researchers working with ecclesiastical records, pre-Reformation English law, or jurisdictions with strong civilian influence should be alert to it.
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Historical Dictionary Support
Rapalje & Lawrence define lineal consanguinity as the relationship subsisting between persons of whom one is descended in a direct line from the other — giving the ascending series (son, father, grandfather, great-grandfather) and the descending series (father, son, grandson, great-grandson) as the standard illustrations. The entry draws directly on Blackstone's formulation, which structured consanguinity by these two axes — lineal and collateral — as a foundation for both the law of descent and the law of marriage. Rapalje & Lawrence treat the term as settled and uncontroversial, reflecting its status by the late nineteenth century as established taxonomy rather than contested doctrine.
The historical dictionaries are silent on jurisdictional variation in how lineal consanguinity bears on specific statutory schemes, which is precisely where modern research complexity arises. They also do not address the degree-counting divergence between civil and canon law traditions, an omission that can mislead researchers working with pre-nineteenth-century sources.
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Encyclopedia Cross-Reference
Marriage — Capacity to Marry (Age, Consanguinity, Affinity), The Law Mind Family Law Encyclopedia
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