Getting to know the je ne sais quoi

Warm croissants, tar-black espresso, a Juliette Binoche lookalike at the next table. We can all imagine the perfect Paris cafe, but does it exist? To celebrate Bastille Day,

Cold beer, warm sun, espresso with a kick and a croque-monsieur, Gauloises in the air and a catwalk for a street. It's the perfect Paris moment in the perfect Paris cafe: that second when you're at the heart of something impossibly cool and elegant, when imperfections fade away and reality is an advert. Can that moment be achieved, and where? To find out, I spent a long, lost weekend on its trail. Well, someone had to do it.

Friday afternoon and I fell on my feet - or rather, slid on my seat - in the Petite Hostellerie de St Eustache, perched on the edge of the sprawl of Les Halles. Warm sun, cold beer, lunchtime in the city of light ... and a catwalk for a street. First up, a couple of ultra-cool Parisiennes - black clothes, black hair, pale faces accessorised with cigarettes and mobile phones: one pauses to make a call, strikes the keys and a pose. Leaning to the left, hand on hip, twirls a strand of hair round a finger as she laughs into the receiver. Flicks down the aerial, flicks back her hair.

Next there's the Ecstasy victim: loud turquoise T-shirt and fierce orange trousers, munching an apple the colour of her boots. Then a Reflecting Man: his bright new leather jacket catching the sun on its smooth surface, his bald head doing the same. It's a catwalk cameo, and in the front row seats on the terrasse, I want to applaud. It's not that the French are better-looking than us: they just think they are, act accordingly, and it works. But just in case preconceptions are too easily confirmed, the beer is English, though you wouldn't guess so by the taste. This is a world away from the warm stuff supped by old maids cycling to misty communion on county grounds, or however the Prime Minister's ridiculous whimsy had it. This is resolutely Europhile beer; it's called "John Martin" and I've never heard of it.

"C'est de chez vous!" says the waiter. "You must drink it all the time over there ..." I haven't the heart to tell him. If this is a perfect Paris cafe, he's the perfect Paris waiter. Briskly friendly, with that well-honed mix of service without deference, precision yet informality, which the English have either long lost or, more likely, never had. Either this guy loves his job or he's a very great pretender. He gets a big tip. Above me the bells of St Eustache clang a thundering 3pm.

To Cafe Beaubourg for more of the same. Crouched under the looming glass wall of the Pompidou Centre, figures sliding up the escalators, watching us, watching them. It's catwalk time again, but here the theme is the working world. In front of me, the human infrastructure of Paris is on parade. The firemen, the sapeurs pompiers, in their cute camion and their absurd helmets, all space age shine (they wear that to go to work?). Then a pair of gendarmes on official saunter - batons on one hip, guns on the other, and a sense of uniformed cool throughout.

A lawnmower-like hum brings on a small, squat robotic elephant, its hose nosing up choice morsels of crisp bags. It's a motorised vacuum cleaner of the Propriete de Paris. Dozens of them purr round the streets at dawn, giving central Paris that spring-cleaned air that's the envy of littery London. Some of the catwalk models are sitting practising their languid hand movements: cigarette to lips, then coffee cup, then hand through hair (and start again).

Clouds drift in across the sun; coats are pulled across chests; Beaubourg gets greyer, less beau. The elephant squeaks and rumbles past, worrying over some particularly sticky bit of litter. The cafe's shutter comes down, its leading edge complete with a couple of cut-outs for the two slender trees on the edge of the terrasse. It's hardly looking like rain, but maybe these guys have the weather sussed, and, like cows lying down in a field, are widely credited with climatic foresight. ("Eh bien, Raoul, they've lowered the shutters at the Beaubourg, take your mac, cheri...")

On the off-chance they're right, I duck inside the Pompidou Centre and ride the escalator (watching them watching us) to the roof. The Cafe Musee d'Art Moderne is about as imperfect as they come, at least by inflated Parisian norms. Packed with tourists, and without table service, it could be the Tate on a bad day. But step onto the flat roof outside and the view is ... well, to live for. Paris's wonderfully low-level smooth-slate roofs, roll out to the near horizon, cut only by church towers and the curve of the Louvre. The dips and rises are gentle on the eye, a soft grey parquet of slate spreading out to the slopes of Montmartre and the domes of the Sacre Coeur. And a thousand cafes, each holding the prospect of a perfect moment, nestle in the streets below.

Yet, in some ways, cafe society is dying on its seats. It's no longer de rigeur to call in for a shot of espresso en route to work, or a swift demi, or three, on return. It was a mainly male pastime, and revolutions in work and home life are rolling it away. In its place, though, comes the altogether more colourful cafe-as-theatre - a place to see, be seated, and be seen.

A place to talk, too, but not necessarily across a table, in some of the flashier quartiers, you're more likely to see Parisians mouthing sweet nothings into a mobile as into an ear. And they're probably on the phone to their broker, not lover. Money has swept through the centre of Paris like no other city, sweeping away old communities in a tide of yuppification which makes Islington look positively provincial. Rising prices have prised out the locals, transformed their boulangeries and blanchisseries into delis and designer clothes stores.

And yet, and yet: some at least of the cafes remain, and the waiters, too, primed to defend their honour. For example: midday, Au Petit Fer du Cheval, rue Tresor. Everything's fine: at least three impossibly cool locals are tucked into appropriate novels; the espresso has a kick like a .303; and the sun is soft on my face. Then two bull-necked Americans stop by and it goes like this:

"Messieurs...?"

"You got a Bud?"

"M'sieur?"

"Bud-weis-er." (He didn't quite add "asshole" but you could tell he would have liked to.)

"Non, M'sieur."

"OK, you got a Coke?"

"Non, M'sieur."

And with that, he turned away ...

Breakfast in the Place des Vosges: in Ma Bourgogne, tucked under the arches of this gorgeous slab of renaissance wedding cake. The salmon and grey facades are too spruced now, unlike a few years ago, when some were Bohemian-scruffy and you could entertain wistful dreams of moving in. There's still a busker, though. He's leant against a pillar like a long lost troubador, with his earring and his long grey hair and his keening, almost operatic voice. But this is PR Bohemia: there's a box of his CDs at his side, and they weren't recorded under any arches. But it's a sweet sound, all the same, and it follows me half way round the square to the cafe.

I'm poised for a perfect moment: I have the view, the morning and Le Monde, all unfolded before me. But it's not to be. The first sign something's wrong comes when the waiter opens negotiations in English (blithely ignoring my choice of paper). Then I open my ears and realise this is indeed the dominant tongue. It's tourist heaven, and it shouldn't matter, but it does, especially when two women sit down with that sort of crisp county accents designed to cut through the throng at a point-to-point, or a Harvey Nicks sale, maybe. "... And they've got a house in the next valley to ours, just outside Siena ...". Time to go-o.

There are, I suppose, two classes of cafes to be avoided. The over-hyped and the unspeakable. The former include such casualties of fame as Cafe Flore, once the haunt of Sartre and Beauvoir, now largely occupied by earnest American college boys in search of existential angoisse. The latter consists of the "McCafes", burger bars with beer, which, to the horror of those who would like their Paris frozen into mid-60s timewarp, are springing up relentlessly across the capital. Needless to say, they are populated almost entirely by Parisians, unfazed by cultural expectation and the ghosts of '68. The few tourists among them are shameless schoolkids or Big McAmericans, relieved at being able to munch their way out of homesickness beneath the golden arches of home. The rest of us look the other way.

It doesn't have to be like this, of course. There are havens of reality even in the heart of town. We stumbled over one such in the rue Montorgueuil, a stone's throw from Les Halles, but also a world away from its steel and glass shopping mall chic. Here is a cobbled street, garnished with market stalls and ordinary shops which seem extraordinary just for being there; dry cleaners, bakeries, hardware stores. It's packed with shoppers who've somehow materialised a real life (they eat! they get their shirts cleaned!) from the sterile beauty of the surrounding streets. They waft baguettes, not mobiles, and plonk heavy bags of shopping beside cafe tables.

We join them on a corner, opposite a stall overflowing with fruit, and a bellowing stallholder. "J'ai des fraises exceptionelles, j'ai des superbes avocats". (Imagine an English street trader, shouting out that he had "exceptional strawberries and superb avocados." That kind of claim doesn't really cross the Channel, somehow.)

Two immensely cool guys, with cropped hair and beards, kiss cheeks emphatically and take thei place side by side to get on with the very important business of sipping, only slightly camply, from tiny espressos and watching the world go by. The stallholder bellows on, sticking to the one refrain; you begin to wonder what's wrong with the other 20 species on display. Maybe he's running low on superlatives, or it's just that bananes extraordinaires wouldn't scan so well. Three more cafe boys appear; kiss both cheeks across the table, like a rather complex sort of cat's cradle, then rub their stubbly cheeks.

It's only on leaving that we see the plaque on the wall, recording that Balzac used it as a setting in his Comedie Humaine. So, no change there. And - hey! - no English, either. It's reeking of authenticity.

Try Cafe Marly instead. Try the bustle and the beautiful people, up among the old arcades in the Cour du Louvre. So it's pounds 3.50 for a beer, but it's also renting a table overlooking one of the finest views in all of Paris, across the vast square of the Louvre and over the Seine to a skyline pierced by the Eiffel Tower. Among these cool colonnades, even the tourists contrive to look elegant. And nobody asks for a Bud. !