I like to think that I have a sane, rational approach to fashion. This is probably a mistake, because when was sane rationalism ever cool or particularly interesting?

Ever since the trend for flinging your wolf skin over the right shoulder (or perhaps it was the left), fashion has been about passion and visceral insanity. In fact compared with Diana Vreeland's peerless advice to mothers to wash their children's blond hair in champagne, or make a bed quilt out of butterflies, sanity and rationalism are two of the dreariest qualities on the planet.

But there it is. Sanity and rationalism are my things. And since I am always preaching what a broad church fashion is, it's only right that it can accommodate someone as sensible as I am.

The real point of all this isn't the health or otherwise of my psychology, but the diseased state of the fashion mind. What other business deliberately cuts itself in the throat with a stiletto heel and then thwacks itself on the head with an outsized (and démodé) It bag?

This is what fashion does all the time these days. Point in case: the sales, which started earlier than ever this season. Once upon a time, sales began in July, just after you'd spent all your money on buying a full-priced selection of summer clothes. Frustrating, but you could see the logic (in the very olden days, when our mothers were in charge, some of the better-quality department stores held out until September as a point of pride).

Now they all engage in an undignified scrum to be first to mark their stock down - before many of us have begun buying our summer outfits. By mid-June this summer, the banners were up - and no dipping the toe in gently with 30 per cent mark-downs, either. Many went straight for 50 per cent.

This looks like such pathologically stupid behaviour to the layperson that I assumed that there must be some fiendishly sophisticated strategy behind it. But no. Off the record, retailers admit that their only rationale is to make sure they are not the only ones left selling at full price when all around them are screeching discounts.

“There is definitely a new mentality among customers which means that they're constantly on the lookout for a deal,” says Bridget Cosgrave, Creative Director of Matches. “In Germany there are laws to stop stores going on sale earlier... which seems quite a good idea. Except that here, we find a lot of the motivation for going on sale earlier and earlier and getting in new stock all the time is driven by the customer. They get bored.”

Whether this trend will continue remains to be seen. Many of the “dregs” in the sales this year are rather brilliant. And here's some more good news: some of next season's key pieces can actually be sourced from this season's sales.

Take the Marni's edge-to-edge, buttonless coat: this is classic Marni and dateless. It's also reduced from £830 to £580. Definitely a contender for the coming winter (from brownsfashion.com).

Or how about Roksanda Illincic's purple duchesse satin cocktail dress, in winter's “new” mid-calf length? It was produced exclusively for netaporter.com, so for £579 (reduced from £964) you're getting your hands on something pretty rare - and another classic that will do service for years.

The ruffled blouse will be one of winter's central pieces (worn with tuxedo trousers or slim skirts and leather jackets). Alexander Wang has one on netaporter.com reduced from £255 to a mere £127.50.

Roland Mouret's tulip skirt is the perfect combination of fashion statement and class act - it won't instantly go out of style because he keeps reproducing this shape in his collections, along with other designers. And at £369 (from netaporter.com) it becomes far more affordable than its original £615.

Accessories are still the key to updating any outfit. Tom Binns, the inspiration behind so many of the baroque jewellery designs that were on many winter catwalks, has a gold jewelled cuff reduced from £815 to £405 - still not cheap, but one of those items that you will find yourself wearing over and over again. As for bags - the demise of the It bag is excellent news for discerning shoppers. Chloe have a fabulous turquoise bag that is the the right shape and at £350, reduced from £504, the right price.

The only winter 2008 piece I couldn't find in the sales was the carrot-top trouser (also known as the banana trouser or tulip pant). All horrible names, but the shape, once you get used to it, is chic and flattering and a rapid way to modernise your jackets and knitwear. It's that very modernity that explains why they're not in the sales. You'll have to wait for the Whistles versions (they'll be all over the high street) or pay full whack for the YSL originals (Joanna Sykes does a great cut too, from Matches, 0870 0678838). But if you've shopped wisely in the sales, a little something at full price makes perfect sense.

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