The invitation usually says more than it appears to. A card that names a garden, a terrace or a family house, a time in the late afternoon and a dress code of "cocktail" or "smart casual" describes almost every engagement party held in a warm climate, and it sets a clear level. This is a celebration of a promise rather than the wedding itself, and the right clothing for an engagement party sits one step below what the wedding will ask for. Most of the decisions that follow come from finding that step.

Engagement parties take many forms. In much of Europe they are drinks and dinner in a garden or a restaurant, hosted by one of the families; in the Gulf they can be large, separate gatherings for men and women with their own traditions; on the coast they often move outside, onto a terrace above the sea or a lawn beneath string lights. What they share is a mood. The couple is the centre, the families are meeting, sometimes for the first time, and the guests are there to be warm and present rather than to be noticed.

For men, a linen shirt with good trousers is right for nearly every warm-weather engagement party short of a formal hotel ballroom. The Bliss Linen Shirt in Dark Blue, buttoned to one below the collar, with PP Trousers 100% Linen in White, has the polish of evening dress without the stiffness. Where the invitation suggests something more formal, the Monte Carlo Blazer over a white linen shirt adds structure for the arrival and comes off once the dancing starts. Both shirts belong to the PP linen shirts collection. Leather or suede loafers suit the occasion better than canvas.

For women, the Amelia linen dress shirt is the natural first choice: worn as a dress with heeled sandals, it is elegant without competing with the bride-to-be. Violet suits an evening on a terrace, Coral Orange suits a garden in the afternoon, and Blue keeps the mood cool when the party is by the water. The PP linen blouse in Pink, with a long silk or linen skirt, is a second route for those who prefer a separate top and bottom. The full range is on the women's linen collection.

A few points of etiquette are worth keeping. White, or anything close to it, is usually left to the bride-to-be, and many guests avoid a dress in pure white even when the couple would not mind. Black is accepted in cities but can look severe on a summer lawn. Very bold prints draw the eye away from where the evening's attention belongs. For a Gulf celebration, the hosts' own customs decide the length of sleeve and hem, and guests follow them closely; a long-sleeved shirt and long trousers are correct for men in any case.

The couple themselves have more freedom, and more to think about. Many choose to wear coordinated rather than matching colours, so that they read as a pair in photographs without looking uniformed. The Monte-Carlo Male in Oyster and the Amelia linen dress shirt in Oyster share a tone and, unusually, the same detail: both are closed with walnut buttons. A couple dressed this way looks considered rather than staged, and the cloth is as comfortable at ten at night as it was at six.

Outdoor parties have one more practical demand. Linen moves with the body through a long evening of standing, sitting and dancing, and its natural texture photographs softly under string lights and candles. For the occasions that follow, the rehearsal dinner and the wedding itself, the same garments can be worn again in a different combination.

An engagement party is the first of several gatherings the couple will host over the following months. The guests who are remembered warmly are the ones who looked as though they understood the occasion, dressed with care for an evening outdoors and left the spotlight exactly where it belonged.

Read more: What to Wear to a Garden Party  ·  Can You Wear Linen to a Wedding?