What's in a name? When you're the prime minister's wife, plenty.

The Prime Minister's Office has let it be known that Sophie Grégoire prefers to be referred to as Sophie Grégoire-Trudeau, marking the first time a prime ministerial spouse has opted for a hyphenated surname. Perhaps it's another sign of generational change in Ottawa – every prime minister's wife has taken her husband's name while he is in office except Maureen McTeer, who insisted on keeping her maiden name and caused a scandal.

To some, the tandem surname is an expression of modern partnership. But the choice happens to put Ms. Grégoire-Trudeau at odds with the couple's home province of Quebec, where adopting your husband's name is neither customary nor legal.

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Under Quebec's Civil Code, women are not allowed to formally change their name at marriage and they can't tether their husband's names to their own either. "In marriage, both spouses retain their respective names, and exercise their respective civil rights under those names," the law states.

The 1981 reform was seen as significant gain for equality between men and women in Quebec, where Sophie's choice is getting some critical commentary.

"She should be called by her own family name. Didn't her husband say 'It's 2015?'" said Louise Langevin, a specialist in women's law at Laval University in Quebec City. "To take the name of your husband is a patriarchal tradition. From a legal standpoint, you can't do it in Quebec, and symbolically, it's a step backward. This is a real anachronism."

Other Quebec observers believe the double-barrelled surname is a concession to conservative voters who might balk at the prime minister's spouse keeping her maiden name.

In fact, the adoption of the dual surname coincided with Justin Trudeau's rise in politics. Ms. Grégoire-Trudeau was referred to in news stories as Sophie Grégoire for years after marrying Mr. Trudeau in 2005. The hyphenated name first appeared on occasion when Mr. Trudeau announced he was seeking the Liberal nomination in the Montreal riding of Papineau in 2007. This year, it gained traction in the lead-up to the federal vote, and the PMO says when asked that the double name is preferred.

"I don't believe this is a decision she took alone," said sociologist Denyse Côté, director of an observatory on gender studies at the University of Quebec in Gatineau. "It's a strategy. The wife of the prime minister is a political position." Prof. Côté said that while she respects the 40-year-old Ms. Grégoire-Trudeau's personal choice, the use of the double surname "sets her apart from Quebec customs."

"It's a nod to English Canada," Prof. Côté said. "My view is that if a woman adds her husband's name, then a man should add his wife's name. It's not because a woman marries someone that she has to lose the identity she's had since childhood, and take the identity of the other person."

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Under Quebec's rules, a woman is free to adopt her spouse's name in social situations, but her maiden name remains on legal documents and it's up to her to clear up any confusion. While a person can ask for a legal name change, the rules are very strict. The Registrar of Civil Status will only consider changes based on "serious" motives such as having a name that invites ridicule, or becomes infamous (murderer Karla Homolka tried to change her name to Emily Chiara Tremblay when she lived in Quebec, and was turned down).

Ms. Grégoire-Trudeau, who gained her own profile as a TV host and activist as Sophie Grégoire, would not be the first person to recognize the political weight of surnames.

Hillary Clinton was Hillary Rodham until husband Bill Clinton lost his re-election bid for Arkansas governor in 1980. Polls suggested her use of her maiden name cost him support and she switched to Hillary Rodham Clinton. In her current presidential bid, she is Hillary Clinton.

Closer to home, Laureen Teskey kept her maiden name until her husband was elected prime minister in 2006, when she became Laureen Harper. But the wife of former Bloc Québécois leader Gilles Duceppe, who often campaigned with him in this year's election, is known by her own name, Yolande Brunelle.

To some, Ms. Grégoire-Trudeau's choice is a sign of personal freedom. Nancy Peckford, spokesperson for Equal Voice, a national group dedicated to the participation of women in politics, says the way Ms. Grégoire-Trudeau wants to self-identify is up to her. "I think she's a very strong and independent woman and I can't imagine this was anything other than personal choice," she says.

Either way, Ms. Grégoire-Trudeau has decided to make a name for herself. As for what lay behind the decision, the PMO declined to comment.