Can Seventh Avenue ditch its delusions and learn to serve a cohort of customers who want to shop Saks and Wal-Mart and the Salvation Army and eBay to put together an outfit as individual as a fingerprint?

The latest thing is guerrilla fashion putting together bits and pieces from Neiman?s, Target, Lands? End, eBay, the local Goodwill, and your grandmother?s closet to create a spur-of-the-moment, one-of-a-kind look.

Not that this is exactly new: Art students and other Bohemians have been doing it forever. What?s new is that now, even society ladies, company presidents and suburban soccer moms want to dress that way or look as if they do.

Mainstream fashion has been drifting in this direction for a while.

It?s why, for years, you?ve been seeing stories about the importance of the item stories reporting, always with apparent surprise, that this season, instead of buying whole outfits the way the designers showed them on the runway, women have been shopping for the one or two or three new things a leather jacket, a mohair shawl, a pair of high boots that would update all the stuff already in their closets.

People in the fashion business dutifully learned to locate and sell items but it?s as if they always thought it was temporary, and assumed that, when times improved and people had more money to spend, shoppers would once again be shopping for whole new pre-assembled outfits.

In retrospect, it?s not unlike the way, ever since the 1960s, milliners have been awaiting ?the return of the hat?.

Also in retrospect, it?s clear that for decades, the fashion business has been chasing a fantasy. It?s been organised around an imaginary customer for a pre-assembled total look.

This is why auteur designers first demanded real estate in department stores, so they could organise their merch to project the look they?d orchestrated for the season instead of leaving it to some apprentice department assistant manager. (?No, no, no! Don?t put the navy blazer with the navy pants! It?s too, too matchy-matchy!?)

But no store bought everything in a designer?s collection, so even when they tried to showcase the designer?s look, they were only partially successful.

How were shoppers to know exactly what the designer had in mind when the store wasn?t playing with a full deck? It?s why designers started opening shops of their own, which would get things just right, and thus provide an authoritative reading of the season?s look.

It?s why designers organised their collections into groups of garments in complementary shapes and colours that could be matched up dozens of different ways and still have a consistent feeling. The customer could wear these pants with the tweed jacket or the cashmere jacket or the velvet blazer or the patchwork vest or the beaded twinset, and the combination would work perfectly. She?d still have the look.

It?s why stores that used to have blouse departments started organising their selling floors by label instead, so customers could find the blouse that the designer intended to go with the blazer that had been designed to go over the skirt.

Some labels even promised to keep their colours consistent from season to season, so that this year?s chocolate brown flannel skirt would work with next year?s brown checked jacket.

It?s as if they all shared this sustaining fantasy of the perfect customer, who would understand the designer?s look and embrace it, and buy a hundred pieces from the fall line, and mix them back and forth to create a million outfits, just the way the designer had intended.

You can see a strong element of wishful thinking at work here. The delusion was organised around this Cinderella customer who had left her cinder-scorched rags at the wicked stepmother?s house and needed a whole new wardrobe, and was going to buy it all from a single label and be faithful to that label ?til death parted her from it.

As if shopping could be monogamous!

Much as shoppers may complain about the difficulty of finding a shirt to go with the skirt they?ve just bought, very few are willing to stick to one brand or one designer.

There?s always the temptation to, say, spring for the expensive Ellen Tracy jacket, but make up for it by wearing it with a $15 Isaac Mizrahi top from Target and last year?s black pants.

And now, apparently, shoppers not only refuse to be limited to a single designer, they won?t even be limited to a single era. Why buy a knock-off of a 1982 Chanel tweed jacket when you can track down the real thing at a charity sale for peanuts or at a vintage shop for considerably more?

As Teri Agins noticed in The Wall Street Journal, the ascendancy of mixmaster fashion has affected the fashion industry in a way ?similar to what?s happening wherever technology has zapped the authority of cultural arbiters.

?Consumers? newfound freedom to customise their lives from burning their own music CDs to publishing political commentary online is throwing basic business models of many businesses into disarray.?

It used to be that just about any designer or retail executive could tell you with a fair degree of confidence who his customer was.

Now they?re having to recognise that they share that customer with lots of other stores and lots of other labels.

One likely effect will be more specialisation. Twenty or 30 years ago, you could walk into a big department store and find almost anything you could want evening dresses, layettes, furniture, books, lunch, thread, corsets, cookies, pots and pans, televisions, sewing machines, beauty salons, etc. Since then, stores have been cutting back to the things they?re best at (to be optimistic) or, anyway, the things that return the highest profit.

Mixmaster chic should accelerate that trend: If your customers don?t want to buy everything from the same place anyway, why knock yourself out to sell it to them?

Similarly, many designers who used to feel obliged to dress ?their? customer for every occasion now feel freer to specialise in sportswear or evening dresses or whatever. The trickier challenge: How do you renovate a business model based on selling ensembles pieces designed to look as if they belong together now that ?your? customer wants to wear pieces that look as if they weren?t meant to be worn together, but nonetheless happen to combine to piquant effect?

And how do you satisfy a customer who wants to look as if she put her outfit together from a dozen sources according to her own slightly eccentric taste, but doesn?t have time to surf eBay and scour thrift shops and find the one perfect skirt at Wal-Mart to wear with last year?s Chanel?

Don?t say it can?t be done.

It?s already happening. The collection Y and Kei showed for spring 2005 a few weeks ago started off with ensembles that looked as if the pieces hadn?t been designed for each other but, once tossed together by some fascinating young woman, just happened to look quietly fabulous.

For instance: a bed-jacket-y linen jacket, a camisole, a pair of loose satin Capri pants with rolled-up cuffs. Or a long, concierge-ish cardigan in avocado green over a purple lace camisole and an off-white linen skirt.

Later they also showed things e.g., a long, heavily embroidered linen coatdress, worn open over pants that looked as if they?d been unearthed in Edith Wharton?s attic, but just happened to be the one thing you?d grab if you saw it on a rack at a vintage shop and then, unlike so many of those vintage purchases, actually wear with clothes you already have.

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