Why Do We Call Our Spouse's Relatives 'In-Laws'?

There's no law requiring you to spend every other holiday with your in-laws.
There's no law requiring you to spend every other holiday with your in-laws.
monkeybusinessimages/iStock via Getty Images

While we’re all busy trying to remember that the plural of mother-in-law is mothers-in-law, not mother-in-laws, we often forget to ask a far more interesting question: Why do we call them in-laws in the first place?

You might assume it’s because your spouse’s family members are related to you by law, not by blood—but the law in question has nothing to do with the marriage license your officiant ships off to the county clerk. According to the Oxford English Dictionary, in-law refers to canon law, a church’s set of rules and regulations that covers, among many other things, which relatives you’re prohibited from marrying. Since the earliest known mention of the term in English is brother-in-law from the 14th century, it was most likely citing the canon law of the Catholic Church (as the Church of England wasn’t founded until the 16th century).

At its inception, in-law was specifically used to describe any non-blood relative that the church forbade you from marrying if your spouse died: your spouse’s siblings, parents, and children, and even your own stepsiblings, stepparents, and stepchildren. So father-in-law, as The Word Detective explains, could’ve either meant your spouse’s father, or your mother’s new husband. But by the late 19th century—at which point the Church of England and other Protestant faiths had established their own canon laws with varying marriage rules—the colloquial definition had expanded to include all spousal relatives, and in-laws became a standalone phrase. The earliest written mention of it comes from an 1894 article in Blackwood’s Edinburgh Magazine, which states that “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 and their in-laws has been around for as long as the phrase itself. If that's part of what brought you here in the first place, here are 12 pieces of 19th-century advice for dealing with them.

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Why Do We Celebrate Christmas on December 25?

If Jesus wasn't born on December 25, does this rule still apply?
If Jesus wasn't born on December 25, does this rule still apply?
Jon Tyson, Unsplash

Each December, Christians throw a collective birthday bash to celebrate the anniversary of Jesus’s arrival on Earth. But without a birth certificate—or any other official record of his actual birthdate—in existence, December 25 seems like an arbitrary day for all our Christmas traditions. So how did early observers choose it?

When Was Jesus Really Born?

Since the Bible doesn’t name a month or even a season for Jesus’s birth, historians have relied on other context clues to estimate when it occurred. Shepherds tend sheep in the Nativity story, which people often cite as evidence that Jesus was more likely born during the spring. Others argue that Israel’s mild winter temperatures allow sheep to graze even in December. According to Slate, it’s also possible that sheep set aside for religious sacrifices may have been given free rein, frigid night or not.

The Adoration of the Shepherds by Sebastiano Conca, 1720.J. Paul Getty Museum // Public Domain

One clue pointing specifically to December 25 comes from the story of Mary’s cousin Elizabeth, who approached old age without having given birth to any children. One day, her husband, a priest named Zacharias, was burning incense in the temple when the angel Gabriel appeared to him with good news: Elizabeth would bear a son. Early Christians guessed that Zacharias was probably in the temple for Yom Kippur, which they believed always took place on September 24 (it actually shifts year to year based on the Jewish lunisolar calendar). Nine months after September 24 is June 24, so they chose that as the birthdate—and feast day—of Elizabeth and Zacharias’s son, John the Baptist. When Gabriel later visited Mary to let her know that she’d bear a son, too, he mentioned that Elizabeth was in her sixth month of pregnancy. That means Jesus would’ve been conceived in late March, and born in late December—the night of December 24, to be exact, or the early hours of December 25.

Another theory suggests that Christians arrived at December 25 based on an ancient Jewish idea that prophets die on their birthday. During the 3rd century CE, theologists like Tertullian and Hippolytus dated Jesus’s crucifixion to March 25, since it happened around Passover. But to Sextus Julius Africanus, it was less about when Jesus was born and more about when he first came to Earth; in other words, he believed Jesus’s death and conception coincided on March 25, and thus his birth occurred on December 25 [PDF].

The Early History of Christmas

Even if Zacharias was in the temple on September 24, Gabriel did visit Mary exactly six months later, and Jesus was born right on his due date, it’s still possible that we celebrate Christmas on December 25 for a different reason altogether.

While 3rd-century Christians were busy worshiping the Son of God, some of their pagan counterparts were busy worshiping the Sun God. In the 270s, Roman emperor Aurelian popularized the cult of Sol Invictus, or “The Unconquered Sun,” whose feast day was celebrated on December 25. According to John Carroll University history professor Joseph F. Kelly, other Romans revered a Persian god, Mithra, whose feast day also may have fallen on December 25. There was also Saturnalia, an annual Roman festival that ran from December 17 to December 23. In short, many ancient Romans were well-accustomed to celebrating something in late December by the time Christianity entered the mainstream.

A painting of Saturnalia festivities by Antoine Callet, 1783.Themadchopper, Wikimedia Commons // Public Domain

That happened during Constantine’s rule over Rome in the early 4th century. In 313, Constantine and his fellow ruler Licinius issued the Edict of Milan, which basically legalized Christianity and condemned the ongoing persecution of anyone who practiced it. Constantine was a devout Christian himself, and he spent the rest of his reign spreading the religion throughout the empire. The first known record of December 25 as Jesus’s official birthday is from 336, the year before Constantine died. Because it’s mentioned in a volume containing other important religious dates, some have assumed that a celebration probably occurred on that day, and 336 is often cited as the first known “Christmas.”

Whether Christians celebrated Christmas on December 25 before 336 may forever be unknown, but we do know that the custom quickly caught on (spending the holiday watching A Christmas Story marathon wouldn't come until much later). By the end of the 4th century, Christian bishops were holding Christmas Mass all over Rome, and pagan festivals soon fell out of fashion. The fact that Christmas essentially replaced those earlier December traditions could be a coincidence, but some believe it was by design: Since Romans were already primed for parties on December 25, the Church could’ve been trying to co-opt a built-in subscriber base.

In summary, the origins of Christmas are just as subject to interpretation as Jesus’s actual birthdate—so feel free to play Christmas music whenever you want.

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