In the highly ritualized world of orchestra-going, the rules have been set for decades — if not a century or more. The orchestra tunes to an “A.” Beethoven is heard at some point every season. And please, no clapping between movements.

And yet as the Philadelphia Orchestra begins its new season this week, it does so with a major trespass of tradition:

No more white tie and tails.

The ensemble has gone informal, at least relatively speaking. Men of the orchestra are now wearing a black suit, black shirt, and a long black tie, with women’s attire unchanged from the current full-length black dress, skirt, or pants policy long in place.

Even for special events like opening night Tuesday evening in Verizon Hall and the long-awaited reopening of Carnegie Hall on Wednesday, orchestra musicians will leave the white tie and tails in their lockers.

It marks a significant change for an institution that has often traded in the trappings of wealth and glamour.

“We’re well into the 21st century. It’s time to acknowledge that in many ways, and one of them is the way the orchestra looks on the stage,” says Philadelphia Orchestra president and CEO Matías Tarnopolsky.

Some hope that an alternative to white tie and tails will seem friendlier to audiences.

“If it makes people more comfortable to come to a concert, that’s a reason right there to do it,” says double-bass player David Fay, chairman of the orchestra’s members’ committee.

At a time when orchestras are working toward greater inclusion, white tie and tails is “redolent of exclusion and elitism, and it’s appropriate to cast that off,” says Simon Woods, president and CEO of the League of American Orchestras, the sector’s trade group. “I think more and more orchestras will do it.”

More are already. This season the New York Philharmonic, temporarily itinerant while its home undergoes renovation, is slipping into black collared shirts, jackets, and no tie for men, and a mid-calf or floor-length skirt, dress, or dress pants with formal black long-sleeved top for women. The San Francisco Symphony is also trying on a new all-black outfit, long black tie optional.

That white tie and tails might be dwindling is precisely the reason many want to keep it.

Longtime Philadelphia Orchestra violinist Boris Balter says he has heard calls for changes to orchestra customs for decades, including banishing white tie and tails. Still, he finds it “difficult to see how monochromatically casual attire would result in increased attendance and revenue. In my mind, this is another willful attempt to remove what is so unique in this distinctive art form,” he said.

“Completely ending white tie is a bad idea,” says orchestra patron Robin Mitchell-Boyask. “I don’t buy the idea that musicians should dress like everyone else, because going to a concert is supposed to be a departure from normal life.”

“I think it’s a positive move,” says Stanford Thompson, founder and executive director of after-school music program Play On Philly and a close orchestra follower. Thompson says he’d like to see white tie and tails kept for galas like opening night. But he feels that the look on stage gets translated by audiences into expectations about how they can dress, and that audiences should feel free to dress any way they want. “I think more and more the orchestra can just lighten up a little bit,” he says.

Realistic about the need for change but still wistful is how longtime orchestra volunteer May Belle Rauch characterizes her feelings about the end of white tie and tails. “There is something about the musicians being dressed that gives them great dignity and a sense of respect that you can appreciate,” she says. “But the music is so beautiful, and that obviously is the most important thing.”

Tarnopolsky says that while there is “some beautiful pageantry in white tie and tails, it also can set up a perception of a barrier between the audience and the musicians, and we want to make sure that that bond is stronger than ever. This new look is about strengthening the connection between the audience and the music and the musicians.”

An orchestra spokesperson said she did not know when the Philadelphians’ tradition of white-tie and tails began. It has been the standard for nighttime concerts for decades, with less formal attire long used for matinees.

The orchestra has rolled out its decision quietly while preparing to return to regular live performances this season with new pandemic-related protocols. An Inquirer article in May that mentioned the change produced no complaints, Tarnopolsky said.

And actually, white tie and tails went out and a more informal look came in more than a year ago with the online concerts the orchestra launched after the start of the pandemic.

But the possibility of new concert dress goes back years. It was floated during the tenure of Christoph Eschenbach, the music director from 2003 to 2008 whose trademark look was a Nehru collar top.

Current music director Yannick Nézet-Seguin — who conducted the orchestra’s free Sept. 18 Verizon Hall concert in a pair of red-soled black Louboutins and a black “Kimmel Cultural Campus” T-shirt — advocated for the banishing of white tie and tails, Tarnopolsky said.

The morning suit the men of the orchestra used for matinees, which included a stroller jacket and striped morning pants, went out of use in 2019.

What’s in an outfit anyway? After all, aren’t orchestra concerts all about the sound?

“A dress code or uniform provides visual cohesion,” says Clare Sauro, director and chief curator of the Robert and Penny Fox Historic Costume Collection at Drexel University. “If it’s busy with personal expression, that could be confusing or distracting to the audience.”

If it is a uniform, it’s a durable one. As a metaphor for upper-class ambition, it has had no equal.

The basic anatomy: patent leather laced shoes or opera pumps are the polished anchor, with black pants with a satin stripe up the sides. A black tailcoat hangs down long in back. In the front, a white vest, called a pique, juts down with two triangular points — but not too far. Studs and cuff links accent a stiff white evening shirt, and the package is topped in the satiny flourish of white bow tie. (Splash of No. 4711 Eau de Cologne optional.)

The origins of the costume date to the early 19th century, when “menswear was really getting its standard of elegance from London’s Savile Row,” says Sauro. “To be improperly dressed at a social occasion, you could be ostracized for wearing a morning suit in the evening,” she said. “This was social gatekeeping.”

White tie became codified by the end of the 19th century and endured well into the 20th, she said.

Social gatekeeping is about the last thing of which orchestras today want to be accused, and the Philadelphia Orchestra has, especially in the last several seasons, brought social change and the outside world into the art itself. Since the #MeToo movement, it has engaged more female conductors and composers. New works have broadly mirrored the message of Black Lives Matter. This month the orchestra premieres Robin Holcomb’s Paradise, a musical response to the 2018 Camp Fire that devastated Paradise, Calif. (on a program with two Beethoven symphonies).

The orchestra could decide to restore white tie and tails, but a reversal is unlikely, the orchestra’s spokesperson said. Even if there is a return of a reformatted Academy of Music Anniversary Concert and Ball, the society event at which both orchestra and audience have worn white tie, Tarnopolsky expects it will be without a white tie and tails dress code.

Of course, maybe there are ways for the orchestra to retain the specialness of white tie and tails while relieving the outfit of its ultra-rich connotations. Drexel’s Sauro suggests a redesigned, modified white tie and tails uniform — and that it be adopted by the women of the orchestra as well.

“It would be a nod to the heritage, a nod to the past, but it would be starting fresh. They become equals because they are all wearing the same thing,” she says. “It would be so beautiful. It would take out all of that angst about what [white tie and tails] means.”

“It’s a costume that has almost entirely fallen out of use almost everywhere else in society, so it begs the question, why do we do it?” says Woods. “To people outside of the orchestra world, it’s incredibly puzzling.”

It even puzzles some within the orchestra world. A couple of seasons back, one patron at his first Academy of Music Anniversary Concert and Ball stood in the Academy lobby in wonder of the costume he had donned for the night.

“I’ve never worn white tie and tails before,” he said.

The newbie in question was Tarnopolsky.