kinship created as a result of someone's marriage with blood relatives of the other spouse

In law, affinity is the kinship relationship that exists between two or more people as a result of somebody's marriage.[1] It is different from consanguinity (blood relationship).[1] Affinity is the relationship which each party to a marriage has to the relatives of the other partner to the marriage. But affinity does not cover the marital relationship of the parties to the marriage themselves.

Affinity laws


Under the law, such relatives by marriage are known as affines.[2] More commonly, they are known as "in-laws", as affinity is usually signified by adding "-in-law" to a degree of kinship.[n 1]

In law, affinity may be used to prohibit incestuous sexual relations. It may also be relevant in preventing some couples from marrying. Which relationships are prohibited varys from country to country, and from time to time. In some countries, especially in the past, the prohibited relationships were based on religious laws. In earlier laws, affinity was used in the same degrees as consanguinity in prohibiting marriages.[3]

Though laws vary considerably, affinity does not always cease with the death of one of the marriage partners through whom affinity is traced. It does not always end with the divorce of the marriage partners. In addition to kinship by marriage, "affinity" can sometimes also include kinship by adoption and step relationship.

  1. This is standard for the closest degrees of kinship—father-in-law, daughter-in-law, &c.—but is frequently omitted in the case of more extended relations. As uncle and aunt are frequently used to refer to friends of the family. The terms may be used without specifying whether the person is a cognate (blood relative) or affine (related by marriage). A spouse of a cousin may not be called a relation at all or may be called a "cousin by marriage".


  1. 1.0 1.1 Saint Raymond of Peñafort; Pierre J. Payer, Summa on Marriage (Toronto: Pontifical Institute of Mediaeval Studies, 2005), p. 61
  2. "What is AFFINES?". My Law Dictionary. Archived from the original on 5 October 2019. Retrieved 27 August 2016.
  3. American Family Laws, Volume I (Stanford, CA: Stanford University Press, 1931), p. 183

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