Prohibited Marriages

During the holidays my partner and I got to spend some time on the road and we ended up having a conversation about work, as we do, but this time we weren’t talking about divorce law – we were talking about marriage. I was telling him the different types of illegal marriages, some of which he found rather interesting and said I should share it with you.

Below I set out the two types of illegal marriages, one through blood and the other through marriage;

Relationships by blood

  • If the parties intending to marry are related to one another within certain degrees of blood this may be an obstacle.
  • The first group of blood relationship which are prohibited is if the parties are related to one another through one common parent, it does not matter if the parties are related by full or half blood. Thus, marriage between a father and daughter, a mother and son, a grandfather and granddaughter, a grandmother and grandson is illegal.
  • The second group of blood relationships which are prohibited is if the parties are related to one another through a common ancestor and if one of them is related in the first degree to that common ancestor. Thus, marriage is forbidden between brother and sister, uncle and niece, aunt and nephew, it extends to great uncles and great aunts related in the first degree to the common ancestor.
  • Adoption does not remove the obstacle and it is illegal for adopted parties to marry persons related to them in the prohibited degrees of blood, even though there is no blood connection.
  • Marriage between cousins is not forbidden.

Relationships by marriage

  • The reasoning of this law is from the Christian faith that husband and wife became one flesh, and that a spouse was disqualified from marrying the blood relations of his spouse if they were related to that spouse within the prohibitions outlined in point 1 above.
  • However, modern society has changed, and the rule is now only limited to relatives in law in the direct line. i.e. a man may not marry the daughter or granddaughter or mother or grandmother of his wife and that the woman may not marry the son or grandson or father or grandfather of her husband, whether the marriage is dissolved by death or divorce is irrelevant.
  • Section 28 of the Marriage Act sets out the lawful marriages between a person and relatives of his/her deceased/ divorced spouse.


A Man May Not Marry A Woman May Not Marry
Mother Father
Daughter Son
Father’s mother Father’s father
Mother’s mother Mother’s father
Son’s daughter Son’s son
Daughter’s daughter Daughter’s son
Sister Brother
Wife’s mother Husband’s father
Wife’s daughter Husband’s son
Father’s wife Mother’s husband
Son’s wife Daughter’s husband
Father’s father’s wife Father’s mother’s husband
Mother’s father’s wife Mother’s mother’s husband
Wife’s father’s mother Husband’s father’s father
Wife’s mother’s mother Husband’s mother’s father
Wife’s son’s daughter Husband’s son’s son
Wife’s daughter’s daughter Husband’s daughter’s son
Son’s son’s wife Son’s daughter’s husband
Daughter’s son’s wife Daughter’s daughter’s husband
Father’s sister Father’s brother
Mother’s sister Mother’s brother
Brother’s daughter Brother’s son
Brother’s daughter’s daughter Brother’s son’s son
Sister’s daughter Sister’s son
Sister’s daughter’s daughter Sister’s son’s son
Sister’s son’s daughter Sister’s daughter’s son