This is not about whether you should buy a denim jacket; you already have one. Check the boot of the car. Or that overloaded coat hook by the back door. Told you! The only reason you wouldn’t have one is if you listened to misguided people who tell you to detox your wardrobe and get rid of all the useful stuff in favour of obscure capsule “pieces” that are then deemed over six months later.

The denim jacket is the opposite of a statement jacket. It is so far from being a “piece” that it’s almost invisible, in the same way that a pair of jeans almost disappears from view in a fashion context. It is functional and familiar and essential. You take for granted that it will be there when you need it, like ketchup for your fish and chips. The denim jacket is fundamentally unimprovable, so never really changes, which is brilliant, except that means it never feels terrifically exciting.

But there is every reason to rekindle your love for the denim jacket. It is the perfect weight for a summer jacket, sturdy enough to keep out a stiff breeze, cool enough not to overcook you. And it doesn’t crease or snag or even look obviously dirty.

But much more important than its practical qualities are its style attributes. A denim jacket is not smart, but neither is it silly. It is neither too masculine nor too feminine, but brings balance to whatever you wear it with. (See the tomboyishness it lends to a very feminine aesthetic: Nigella used to wear that look to great effect; see also Marilyn Monroe in The Misfits.) It is also pleasingly youthful without being overly teenage. A floral dress that could look stuffily grown-up with wedges loses a decade if you wear it with a denim jacket and flat white trainers.

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Denim on denim gets a bad press, but it’s easier to wear if you mix up the colours and weights. Dark denim with white has a summery, nautical vibe that feels less deliberately hipsterish than Spears-and-Timberlake blue-on-blue. The classic blue is the number one choice if you are after an ugly trainer/dad-core look, but I’m happy to pare things back to summer basics by teaming denim with gingham, broderie anglaise, white Converse. An indigo denim jacket is smarter than the traditional version, especially if the shape is neat. It’s also more all-weather, visually speaking: you can wear it with a black cotton turtleneck and black ankle-grazer trousers for an easing-into-autumn look. Perhaps you do need to buy one, after all.

• Jess wears jacket, £39, topshop.com. Top, £61, by Madewell, from net-a-porter.com. Jeans, £238, by Khaite, from matchesfashion.com. Heels, £120, dune.co.uk

Styling: Melanie Wilkinson. Hair and makeup: Johanni Nel at S Management.

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