What are in-laws — really?


Why do I call my wife’s sister my sister-in-law?  Likewise for other relatives by marriage?  And, could I marry an in-law if I wanted to?

Prohibitions against incest

All societies have strict rules against incest; that is, sexual relations with relatives. Our Judeo-Christian tradition looks back to the Hebrew Scriptures.  Leviticus Chapter 18: 6-18 identifies women with whom a man may not have intercourse, and similarly for a woman.  Relationships that are clearly incestuous include parents, aunts and uncles, siblings, children, and grandchildren.  It also identifies step-siblings and half-siblings, because they are also blood relations.

But it also includes people of no blood relation.  These include parents-in-law, brothers- and sisters-in law, and sons- and daughters-in-law.  The reason is that a marriage joins the two families together. The bride’s or bridegroom’s relatives become part of his or her family.  It is just as if they were blood relations.  The marriage ceremony of the Anglican Church of Canada retains this language.  “In marriage, husband and wife … are linked to each other’s families …” (Book of Alternative Services page 541).

If it would be improper to have sex with someone, it would be improper to allow them to marry.  Leviticus 20: 11-21 banned marriage to an in-law relative, if it forbade marriage to the corresponding blood relative. This prohibition continued to apply, even when the original spouse died.  For example, a man could not marry his dead wife’s sister.  It would be like marrying his blood sister.

The Sadducees and the question about resurrection

The previous example raises an interesting issue.  In Mark 12: 18-27 some Sadducees asked Jesus a question about the resurrection of the dead.  Suppose a man dies without children and his widow then marries his brother.  Then he dies and the widow, marries a third, fourth, fifth, sixth and seventh brother.  Whose wife would she be after resurrection, since she had married all seven brothers?  

This scenario seems to flout the Leviticus laws.  But there was a special dispensation for women who became widowed while childless (Deuteronomy 25: 5-10).  This was because a childless widow could not inherit.  That made it the brother-in-law’s duty to marry her, so that she would not be left destitute. 

Christianity incorporated the prohibitions from Leviticus, except for the special dispensation.  In England, the position of the Church of England as an ‘established” (state-sponsored) church made this church requirement the law of the land.  Hence the term “in-law”.  A brother-in-law meant exactly that.  A man married to one’s sister was legally the same as your brother. 

The legal position in Canada

What does this mean for Canadian civil law?  The Statute of Westminster (1931) made Canada self-governing.  As a starting point, it carried the U.K. Parliament’s laws over into Canadian law.  By that time, U.K law had changed to allow marriage between an unmarried woman and her late sister’s widower (1907).  This was the Deceased Wife’s Sister’s Marriage Act   The corresponding law involving an unmarried man and his brother’s widow became law in 1921.  Its name was the Deceased Husband’s Brother’s Marriage Act Interestingly, it thereby made legal the “special dispensation 

Today, the Canadian Marriage (Prohibited Degrees) Act, of 2004,sets out which marriages are not allowed.  The term “lineally by consanguinity” means blood relations in the line of grandparent through grandchild. “Half-blood” means step-parents, -siblings, and children.

The Act prohibits the following marriages between people who are related lineally by consanguinity or adoption.  Brothers and sisters may not marry, whether by the whole blood or the half-blood, or even if they were adopted.  

The Church position

The Church of England authorities had strongly resisted both the changes that became law in 1907 and 1921.  And in Canada, as recently as 1962, the Anglican Church of Canada continued to publish a Table of Kindred and Affinity in the Book of Common Prayer.  Kindred means blood relations. Affinity means “in-laws” in common language.  The prohibited types of marriage remained essentially according to Leviticus 20.  More recently, this has changed.  The Anglican Church of Canada now has rules that align closely with civil law.  As far as I could determine, the Roman Catholic Church adheres to the traditional position. 

The Anglican Church of Canada’s Marriage Canon, Section 17, aligns church law with civil law.  It removes all references to affinity but adds certain restrictions.  These recognize that the concept of “family” has broadened in recent years.  It also permits marriages involving divorced persons.  

  • The Marriage Canon, Section 17

Here is the relevant extract (slightly amended for clarity). 

“The parties to a marriage may not marry each other if either of them is under the age of 16 years, or they are related to each other:

  1. a) lineally by consanguinity or adoption;
  2. b) as brother and sister by consanguinity, whether by the whole blood or the half-blood, or
  3. c) as brother and sister by adoption;

 Or if they both live, or have previously lived, in the same household and one of them is or has been treated by the other as a child or parent

Or if either of them has gone through a ceremony of marriage with a person who is living at the time of the application, unless the previous ceremony of marriage has been found to have been invalid, or has been dissolved or terminated according to the civil law.”

To sum up

So there you have it.  The term in-law now has no legal meaning, even though we continue to use it informally.  Legally, the Anglican Church of Canada permits you to marry anyone you wish. However, you must be 16 or over, and unmarried at the time.  You must also not be closely related, nor have lived with the proposed spouse in a family situation.