Before night falls; Autumn offers great options for formalwear: from short and sweet to a seriously tailored pantsuit.

Byline: Jane Herman

When Mary Quant introduced the mini in the sixties, it was not about new length, it was about freedom," says Alber Elbaz by way of explaining the flirtatious but strictly formal tuxedo-minis that he designed for Lanvin. A tuxedo-mini looks exactly like it sounds: It's a silk-satin jacket and a slim bow tie paired not with pants but with a matching skirt that hits a good five inches above the knee. It's undoubtedly very dressy, although it's also very short. Which brings up the question, Where should a woman wear it? "To a black-tie event," says Elbaz. "Definitely."

Just like Ms. Quant's shifty mod freedom-mini, the Lanvin tuxedo-mini is something really new. Think of it as a welcome break from the floor-sweeping ball and chain of a big gown. Appropriate and decorous, it meets all the requirements for black tie-except that it doesn't drag. "It's modern to have this short length," says Elbaz, "because it's about what works for women, not what's required or what designers are telling them to do. It's not about formula anymore."

The fall collections are delightfully leggy this year. This focus on legs started with the skinny jean, which gave way in 2005 to the legging . . . which then required a tunic . . . which then was translated into a minidress. Many designers, like Elbaz, have taken this progression further by applying the principles of eveningwear-volume, embroidery, beading, bow ties-to silhouettes with sky-high hemlines. Miuccia Prada's tapestry-print mini for Miu Miu, for example, has it all: the majestic fabric, the impeccably tailored bust, the regal color palette; it even drapes in such a way that it appears as if there's a long skirt there, like it's just been picked up and propped at the waist. Length notwithstanding, this Miu Miu look is curiously reminiscent of a formal dress, which makes it impossible to wear to, say, a garden party. What's stunning about the Miu Miu-its curt volumetric skirt and single bare shoulder-would only make it seem vulgar in the bright light of day.

"But cocktail's not that dressy, either," says New York tastemaker Amanda Brooks. "Today women wear shifts and pants to cocktail parties. Recently, I wore dressy short Chanel to an engagement party and felt completely overdressed. That's never fun."

"I'll only do a major dress if I know the event and the hostess well," says the social and stylish Anne Grauso. "You don't ever want to be the only gown in the room." Like many New York women, Grauso began planning her fall wardrobe during the fall/winter collections last February. At the top of her list: a fuchsia brocade Balenciaga jacket; another cropped Carolina Herrera chinchilla jacket to wear with a ruched Chanel blouse and long jersey skirt; and a black Dior tuxedo done in a sturdy men's fabric. She has one long serious dress, and it's Chanel, but what excites Grauso about it are the short, puffy sleeves that designer Karl Lagerfeld showed on the runway with gothic lace gloves. "I'm going to play with that idea a lot," says Grauso, hinting at what eveningwear might truly be about this season: the accessories.

"Ninety-nine percent of the time, something glamorous and short has the possibility of stretching from dinner to black tie," says Michael Kors, whose glittery, drop-waist Art Deco minis are incredibly dress code-ambiguous. "What turns a short dress from cocktail into something more formal can be as easy as switching a clutch to a jeweled minaudiere."