There's a reason so many women you know have the middle name 'Louise'.

“Is it just me or does literally every girl have the middle name Louise? Trying to figure this out.”

This was the title of a post written by The Tab‘s Roisin Lanigan last weekend, which has already been shared thousands of times.

“There is one constant in life and it’s that every girl you know has the middle name Louise,” she wrote.

“The middle name Louise transcends all differences which divide us as women.”

Okay, so Lanigan is talking about the UK, and she is exaggerating slightly. But there’s some truth to what she’s saying. Louise is a ridiculously common middle name in Australia too. Why is that? What’s so special about Louise?

Well, I’m a former names researcher and I can answer that question for you.

Back in the 1980s, Louise was the third most popular middle name for girls born in Australia, behind Anne and Jane. By the 1990s, it had crept up to second spot.

It’s not like Louise was ever a really popular first name in Australia. So what was going on?

Well, it’s all about the rhythm. Most popular ‘80s and ‘90s girls’ names had two or three syllables, with the accent on the first syllable: Jessica, Sarah, Amy, Emma, Katherine, Rachel, Hannah, Georgia, Caitlin. To make a pretty-sounding combination, most parents would – subconsciously – choose a middle name with one syllable (Anne, Jane, Lee, Kate), or else two syllables, with the accent on the second syllable (Louise, Marie, Renee, Nicole).

Sarah Louise just sounds better than Sarah Lucy or Sarah Lisa, doesn’t it? In fact, almost every name sounds good followed by Louise: Emma Louise, Hannah Louise, Lucy Louise, Lisa Louise. It’s light and almost musical. Louise is a winner.

For parents in the ‘80s and ‘90s, naming children was less about commemorating family members than it once had been. They simply wanted to give their daughters the gift of a beautiful name.

(Interestingly, there’s no real boy equivalent to Louise. Matthew James, Michael John, Christopher David, Daniel William – solid and steady has always been the way to go.)

Listen: Pregnancy announcements are big business in 2017. (Post continues after audio.)

Of course, not every girl has Louise as a middle name. Even Lanigan admits this.

“There is but one exception to the Twilight Zone-esque Louise phenomenon, and that is Rose,” she wrote in her post.

“If you are a woman, in the UK especially, born in the early to mid-90s, probably white, and your middle-and-or-Facebook name isn’t Louise, then the reason why – get ready for some near-clairvoyant skills of deduction here – is that your middle name is Rose.”

Something similar was happening in Australia. By the mid-1990s, Rose had risen to become the third most popular middle name for girls.

It’s not hard to see why. Vintage names were really taking off at that point, and Rose worked with almost all of them: Emily Rose, Madeleine Rose, Amelia Rose, Isabella Rose, Molly Rose…

(If Australian parents didn’t go for Rose as their one-syllable vintage middle name, it was usually Grace.)

Lanigan acknowledges she’s not the first person to notice the “Louise Rose phenomenon”, as she dubs it. She says people on the internet have decided girls with these middle names are “basic”. But she says those people are wrong.

“It’s funny,” she writes. “It’s fodder for small talk when you’re in a room full of girls you don’t know without any alcohol to make you brave enough to make friends. Here’s a thing you have in common: you’ve all got the middle name Rose or Louise.”