MUNDANE MYSTERIES: Why Are Our Spouse’s Family Called “In-Laws”?

The other day, as I was trying to describe to someone the difference between my current & past mothers-in-law, I began to wonder: “why do we call our spouse’s relatives ‘in-laws’ in the first place?”

It’d be easy to assume that it’s because your spouse’s family members are related to you by law, not by blood. But, that law actually has nothing to do with the marriage license your officiant ships off to the county clerk. The Oxford English Dictionary says that the “in-law” title refers to canon law, a set of church rules & regulations that cover, among other things, which relatives you’re prohibited from marrying. The earliest known English mentioning of “in-laws” is “brother-in-law” from back in the 14th century, most likely a citation of the canon law of the Catholic Church.

At its inception, “in-law” was specifically used to describe any non-blood relative you were forbidden by the church from marrying if/when your spouse died; that included your spouse’s siblings, parents, and children, along with your own step-siblings, step-parents, and step-children. The term “father-in-law”, could either have meant your spouse’s father, or your mother’s new husband. But by the late 19th century, at which point the Church of England & other Protestant doctrines had established their own various canon laws & marriage rules, the colloquial definition had expanded to include all spousal relatives, at which point “in-laws” became its own standalone term. The earliest written mention of it comes from an article in Blackwood’s Edinburgh Magazine from 1894, which stated: “the position of the ‘in-laws’ (a happy phrase which is attributed with we know not what reason to her Majesty, than whom no one can be better acquainted with the article) is often not very apt to promote happiness.”

In other words, tension between people & their in-laws has been around for as long as the term itself. So, if you’ve got strife between yourself & your own in-laws, take heart in knowing you’re not the first & certainly won’t be the last.

Got a Mundane Mystery you’d like solved? Send me a message via social media (@AndyWebbRadioVoice), or shoot me an email at [email protected].