Jeans and a nice top is a tried-and-tested formula when it comes to dressing for an evening out. It is the little black dress of real life. A local dinner, an outing to the theatre or cinema, a birthday gathering in the pub: these do not require a cocktail dress. Still, you want to look nice. So you wear jeans and a nice top.

If jeans and a nice top is the real life LBD, then jeans and a jacket is the normcore power suit. It is the no-nonsense, I’ve-got-this formula you need for daytime. It is an outfit that comes together in seconds and keeps on looking good and feeling comfortable for hours. It is grown up but not stiff, alpha but not snooty. It is – and this is important in our capricious climate, and when your commute can take you straight from overheated train carriage to chiller-cabinet level air conditioning – pitched neither too warm nor too cold, and offers flexibility. (You are wearing something under the jacket, you see. We will get to that.)

Jeans and a jacket works on the principle of yin and yang. Salt and pepper, the moon and the sun, Guinness and oysters. Jeans are the ultimate laid-back, easy-going, democratic piece. A jacket, whether it is a crisp tailored blazer, or a jazzy boucle tweed with shiny buttons, is giving a little shoulders-back, stand-up-straight polish. Jeans and a jumper is a snoozefest; a matching two-piece suit, on the other hand – whether androgynous and sleek, or Chanel-a-like and pretty – can be a lot.

You are probably familiar with one version of this, which is the longline blazer worn with high-waisted jeans. This formula has been around for a few years, and it still works. Maybe with a loafer, perhaps a kitten heel. It is slick and office appropriate and an excellent go-to for when you want to look presentable but in a low-key, faux-effortless kind of way.

But to fully update your jeans and jacket to fashion’s latest operating system, you need a shorter jacket. We don’t need to get into the fashion-week weeds of it all, but it is worth knowing that Jonathan Anderson and Matthieu Blazy, newish designers at Dior and Chanel respectively, are both doing a shorter jacket. Anderson has shrunk the classic Dior “bar” jacket, so that the peplum flares at the waist, not the hip, while the sharp-shouldered blazer cropped at the waist that opened Blazy’s Chanel catwalk debut has been worn by everyone from Jacob Elordi to Michelle Obama.

When you pair a short jacket with a slouchier jean, you may get a flash of your top visible between the two. Be cool with this, please. The slightly undone effect is part of the charm, and what makes this summer’s jeans-and-a-jacket a little more louche and exciting than the longline blazer version.

Ah yes, the top. Are you team T-shirt, or team shirt? Shirts have a useful ability to look expensive even when they are not. A collar and cuff implies effort in the way a T-shirt never quite can. However, if I wear a shirt under a jacket that has anything but the simplest neckline, I find the two collars end up scrapping and skirmishing, like two bored kids on a long car journey. Everyone ends up hot and bothered and a bit scruffy. So I am a big fan of a good T-shirt instead. Plain white always works, but I also enjoy the intrigue of a T-shirt with a slogan or a band name or a movie poster on it, just a slice glimpsed under a jacket.

But the choice is yours. Because that is the secret sauce of any good style formula: it allows you to bend fashion to your will. The jeans and a jacket combination is a recipe you can adjust to your taste. Perhaps with a shorter jacket than before, and a slouchier jean. That’s it; that’s the whole look. A look that took the industry’s brightest minds – and a Chanel catwalk and Michelle Obama – to arrive at. You probably have it hanging in your wardrobe already. For once, fashion makes perfect sense.

Styling: Melanie Wilkinson. Model: Maria Diaz at Milk. Hair and make up: Sophie Higginson using Davines and Dr Sam’s. Styling assistant: Charlotte Gornall. Jacket, £325, jeans, £175, and belt, £95, all ME+EM. Top, £30, Reiss. Shoes, £99, Dune. Earrings, £99, Daisy. Stool, £199.99, La Redoute