Consanguinity, Affinity, and Adoption in Canon Law

Consanguinity joins persons descended from a common ancestor. In the direct line the number of degrees equals the number of generations between persons, while in the collateral line the degrees in both branches are counted together, excluding the common ancestor. Siblings are therefore related in the second collateral degree, an aunt and nephew in the third, and first cousins in the fourth. Popular expressions such as second cousin once removed must be converted carefully rather than guessed.

Affinity arises from a valid marriage, even if not consummated, between one spouse and the blood relatives of the other. It is counted so that a spouse is related by affinity in the same line and degree in which the other spouse is related by consanguinity. The spouses themselves are joined by marriage, not affinity, and the relatives of one spouse do not thereby become affines of the other spouse's relatives. Divorce does not supply a basis for pretending the valid marriage never existed.

Marriage is invalid between all ancestors and descendants in the direct line by consanguinity, whether legitimate or natural, and in the collateral line through the fourth degree inclusive. Affinity invalidates marriage in any degree of the direct line. A legal relationship arising from adoption invalidates marriage in the direct line or second degree of the collateral line. These are distinct impediments with distinct scopes; a broad civil category of incest does not supply the canonical calculation.^[1]

Divine-law limits cannot be dispensed, and the Code expressly forbids permission for marriage whenever doubt remains that parties are related in any degree of the direct line or in the second collateral degree. Other cases follow the Church's law on competent dispensation, just cause, documentation, and any reserved authority. A declaration of nullity examines the facts and law present when consent was exchanged; later discovery of kinship is evidence to investigate, not an automatic private sentence about validity.

Marriage preparation should ask about biological and adoptive relationships respectfully, especially in small communities, complex blended families, and places where civil records are incomplete. The purpose is not humiliation or ethnic stereotyping but protection of freedom, family order, and sacramental validity. Confidential facts are shared only with persons who need them for competent judgment. Genetic testing can sometimes clarify biological questions, but it raises consent, privacy, and family consequences beyond the canonical calculation itself.

Kinship language also appears in records, domicile rules for minors, guardianship, and institutional conflict-of-interest policies, but not every moral concern creates a universal canonical incapacity. Nepotism, financial dependence, coercion, and safeguarding may require action under other norms even when no marriage impediment exists. Accurate reference work therefore states the source of a relationship, the line and degree, the legal consequence, and the date of the governing law rather than treating family vocabulary as self-executing.^[2]